Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma

Pull rdma updates from Jason Gunthorpe:
 "A more active cycle than most of the recent past, with a few large,
  long discussed works this time.

  The RNBD block driver has been posted for nearly two years now, and
  flowing through RDMA due to it also introducing a new ULP.

  The removal of FMR has been a recurring discussion theme for a long
  time.

  And the usual smattering of features and bug fixes.

  Summary:

   - Various small driver bugs fixes in rxe, mlx5, hfi1, and efa

   - Continuing driver cleanups in bnxt_re, hns

   - Big cleanup of mlx5 QP creation flows

   - More consistent use of src port and flow label when LAG is used and
     a mlx5 implementation

   - Additional set of cleanups for IB CM

   - 'RNBD' network block driver and target. This is a network block
     RDMA device specific to ionos's cloud environment. It brings strong
     multipath and resiliency capabilities.

   - Accelerated IPoIB for HFI1

   - QP/WQ/SRQ ioctl migration for uverbs, and support for multiple
     async fds

   - Support for exchanging the new IBTA defiend ECE data during RDMA CM
     exchanges

   - Removal of the very old and insecure FMR interface from all ULPs
     and drivers. FRWR should be preferred for at least a decade now"

* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma: (247 commits)
  RDMA/cm: Spurious WARNING triggered in cm_destroy_id()
  RDMA/mlx5: Return ECE DC support
  RDMA/mlx5: Don't rely on FW to set zeros in ECE response
  RDMA/mlx5: Return an error if copy_to_user fails
  IB/hfi1: Use free_netdev() in hfi1_netdev_free()
  RDMA/hns: Uninitialized variable in modify_qp_init_to_rtr()
  RDMA/core: Move and rename trace_cm_id_create()
  IB/hfi1: Fix hfi1_netdev_rx_init() error handling
  RDMA: Remove 'max_map_per_fmr'
  RDMA: Remove 'max_fmr'
  RDMA/core: Remove FMR device ops
  RDMA/rdmavt: Remove FMR memory registration
  RDMA/mthca: Remove FMR support for memory registration
  RDMA/mlx4: Remove FMR support for memory registration
  RDMA/i40iw: Remove FMR leftovers
  RDMA/bnxt_re: Remove FMR leftovers
  RDMA/mlx5: Remove FMR leftovers
  RDMA/core: Remove FMR pool API
  RDMA/rds: Remove FMR support for memory registration
  RDMA/srp: Remove support for FMR memory registration
  ...

16 files changed, 4392 insertions, 0 deletions

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 025b1b77b11a..084b9efcefca 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -458,4 +458,6 @@ config BLK_DEV_RSXX
 	  To compile this driver as a module, choose M here: the
 	  module will be called rsxx.
 
+source "drivers/block/rnbd/Kconfig"
+
 endif # BLK_DEV
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index 795facd8cf19..e1f63117ee94 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -39,6 +39,7 @@ obj-$(CONFIG_BLK_DEV_PCIESSD_MTIP32XX)	+= mtip32xx/
 
 obj-$(CONFIG_BLK_DEV_RSXX) += rsxx/
 obj-$(CONFIG_ZRAM) += zram/
+obj-$(CONFIG_BLK_DEV_RNBD)	+= rnbd/
 
 obj-$(CONFIG_BLK_DEV_NULL_BLK)	+= null_blk.o
 null_blk-objs	:= null_blk_main.o
diff --git a/drivers/block/rnbd/Kconfig b/drivers/block/rnbd/Kconfig
new file mode 100644
index 000000000000..4b6d3d816d1f
--- /dev/null
+++ b/drivers/block/rnbd/Kconfig
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+config BLK_DEV_RNBD
+	bool
+
+config BLK_DEV_RNBD_CLIENT
+	tristate "RDMA Network Block Device driver client"
+	depends on INFINIBAND_RTRS_CLIENT
+	select BLK_DEV_RNBD
+	help
+	  RNBD client is a network block device driver using rdma transport.
+
+	  RNBD client allows for mapping of a remote block devices over
+	  RTRS protocol from a target system where RNBD server is running.
+
+	  If unsure, say N.
+
+config BLK_DEV_RNBD_SERVER
+	tristate "RDMA Network Block Device driver server"
+	depends on INFINIBAND_RTRS_SERVER
+	select BLK_DEV_RNBD
+	help
+	  RNBD server is the server side of RNBD using rdma transport.
+
+	  RNBD server allows for exporting local block devices to a remote client
+	  over RTRS protocol.
+
+	  If unsure, say N.
diff --git a/drivers/block/rnbd/Makefile b/drivers/block/rnbd/Makefile
new file mode 100644
index 000000000000..5bb1a7ad1ada
--- /dev/null
+++ b/drivers/block/rnbd/Makefile
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+ccflags-y := -I$(srctree)/drivers/infiniband/ulp/rtrs
+
+rnbd-client-y := rnbd-clt.o \
+		  rnbd-clt-sysfs.o \
+		  rnbd-common.o
+
+rnbd-server-y := rnbd-common.o \
+		  rnbd-srv.o \
+		  rnbd-srv-dev.o \
+		  rnbd-srv-sysfs.o
+
+obj-$(CONFIG_BLK_DEV_RNBD_CLIENT) += rnbd-client.o
+obj-$(CONFIG_BLK_DEV_RNBD_SERVER) += rnbd-server.o
diff --git a/drivers/block/rnbd/README b/drivers/block/rnbd/README
new file mode 100644
index 000000000000..1773c0aa0bd4
--- /dev/null
+++ b/drivers/block/rnbd/README
@@ -0,0 +1,92 @@
+********************************
+RDMA Network Block Device (RNBD)
+********************************
+
+Introduction
+------------
+
+RNBD (RDMA Network Block Device) is a pair of kernel modules
+(client and server) that allow for remote access of a block device on
+the server over RTRS protocol using the RDMA (InfiniBand, RoCE, iWARP)
+transport. After being mapped, the remote block devices can be accessed
+on the client side as local block devices.
+
+I/O is transferred between client and server by the RTRS transport
+modules. The administration of RNBD and RTRS modules is done via
+sysfs entries.
+
+Requirements
+------------
+
+  RTRS kernel modules
+
+Quick Start
+-----------
+
+Server side:
+  # modprobe rnbd_server
+
+Client side:
+  # modprobe rnbd_client
+  # echo "sessname=blya path=ip:10.50.100.66 device_path=/dev/ram0" > \
+            /sys/devices/virtual/rnbd-client/ctl/map_device
+
+  Where "sessname=" is a session name, a string to identify the session
+  on client and on server sides; "path=" is a destination IP address or
+  a pair of a source and a destination IPs, separated by comma.  Multiple
+  "path=" options can be specified in order to use multipath  (see RTRS
+  description for details); "device_path=" is the block device to be
+  mapped from the server side. After the session to the server machine is
+  established, the mapped device will appear on the client side under
+  /dev/rnbd<N>.
+
+
+RNBD-Server Module Parameters
+=============================
+
+dev_search_path
+---------------
+
+When a device is mapped from the client, the server generates the path
+to the block device on the server side by concatenating dev_search_path
+and the "device_path" that was specified in the map_device operation.
+
+The default dev_search_path is: "/".
+
+dev_search_path option can also contain %SESSNAME% in order to provide
+different device namespaces for different sessions.  See "device_path"
+option for details.
+
+============================
+Protocol (rnbd/rnbd-proto.h)
+============================
+
+1. Before mapping first device from a given server, client sends an
+RNBD_MSG_SESS_INFO to the server. Server responds with
+RNBD_MSG_SESS_INFO_RSP. Currently the messages only contain the protocol
+version for backward compatibility.
+
+2. Client requests to open a device by sending RNBD_MSG_OPEN message. This
+contains the path to the device and access mode (read-only or writable).
+Server responds to the message with RNBD_MSG_OPEN_RSP. This contains
+a 32 bit device id to be used for  IOs and device "geometry" related
+information: side, max_hw_sectors, etc.
+
+3. Client attaches RNBD_MSG_IO to each IO message send to a device. This
+message contains device id, provided by server in his rnbd_msg_open_rsp,
+sector to be accessed, read-write flags and bi_size.
+
+4. Client closes a device by sending RNBD_MSG_CLOSE which contains only the
+device id provided by the server.
+
+=========================================
+Contributors List(in alphabetical order)
+=========================================
+Danil Kipnis <danil.kipnis@profitbricks.com>
+Fabian Holler <mail@fholler.de>
+Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
+Jack Wang <jinpu.wang@profitbricks.com>
+Kleber Souza <kleber.souza@profitbricks.com>
+Lutz Pogrell <lutz.pogrell@cloud.ionos.com>
+Milind Dumbare <Milind.dumbare@gmail.com>
+Roman Penyaev <roman.penyaev@profitbricks.com>
diff --git a/drivers/block/rnbd/rnbd-clt-sysfs.c b/drivers/block/rnbd/rnbd-clt-sysfs.c
new file mode 100644
index 000000000000..4f4474eecadb
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-clt-sysfs.c
@@ -0,0 +1,639 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+
+#undef pr_fmt
+#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
+
+#include <linux/types.h>
+#include <linux/ctype.h>
+#include <linux/parser.h>
+#include <linux/module.h>
+#include <linux/in6.h>
+#include <linux/fs.h>
+#include <linux/uaccess.h>
+#include <linux/device.h>
+#include <rdma/ib.h>
+#include <rdma/rdma_cm.h>
+
+#include "rnbd-clt.h"
+
+static struct device *rnbd_dev;
+static struct class *rnbd_dev_class;
+static struct kobject *rnbd_devs_kobj;
+
+enum {
+	RNBD_OPT_ERR		= 0,
+	RNBD_OPT_DEST_PORT	= 1 << 0,
+	RNBD_OPT_PATH		= 1 << 1,
+	RNBD_OPT_DEV_PATH	= 1 << 2,
+	RNBD_OPT_ACCESS_MODE	= 1 << 3,
+	RNBD_OPT_SESSNAME	= 1 << 6,
+};
+
+static const unsigned int rnbd_opt_mandatory[] = {
+	RNBD_OPT_PATH,
+	RNBD_OPT_DEV_PATH,
+	RNBD_OPT_SESSNAME,
+};
+
+static const match_table_t rnbd_opt_tokens = {
+	{RNBD_OPT_PATH,		"path=%s"	},
+	{RNBD_OPT_DEV_PATH,	"device_path=%s"},
+	{RNBD_OPT_DEST_PORT,	"dest_port=%d"  },
+	{RNBD_OPT_ACCESS_MODE,	"access_mode=%s"},
+	{RNBD_OPT_SESSNAME,	"sessname=%s"	},
+	{RNBD_OPT_ERR,		NULL		},
+};
+
+struct rnbd_map_options {
+	char *sessname;
+	struct rtrs_addr *paths;
+	size_t *path_cnt;
+	char *pathname;
+	u16 *dest_port;
+	enum rnbd_access_mode *access_mode;
+};
+
+static int rnbd_clt_parse_map_options(const char *buf, size_t max_path_cnt,
+				       struct rnbd_map_options *opt)
+{
+	char *options, *sep_opt;
+	char *p;
+	substring_t args[MAX_OPT_ARGS];
+	int opt_mask = 0;
+	int token;
+	int ret = -EINVAL;
+	int i, dest_port;
+	int p_cnt = 0;
+
+	options = kstrdup(buf, GFP_KERNEL);
+	if (!options)
+		return -ENOMEM;
+
+	sep_opt = strstrip(options);
+	while ((p = strsep(&sep_opt, " ")) != NULL) {
+		if (!*p)
+			continue;
+
+		token = match_token(p, rnbd_opt_tokens, args);
+		opt_mask |= token;
+
+		switch (token) {
+		case RNBD_OPT_SESSNAME:
+			p = match_strdup(args);
+			if (!p) {
+				ret = -ENOMEM;
+				goto out;
+			}
+			if (strlen(p) > NAME_MAX) {
+				pr_err("map_device: sessname too long\n");
+				ret = -EINVAL;
+				kfree(p);
+				goto out;
+			}
+			strlcpy(opt->sessname, p, NAME_MAX);
+			kfree(p);
+			break;
+
+		case RNBD_OPT_PATH:
+			if (p_cnt >= max_path_cnt) {
+				pr_err("map_device: too many (> %zu) paths provided\n",
+				       max_path_cnt);
+				ret = -ENOMEM;
+				goto out;
+			}
+			p = match_strdup(args);
+			if (!p) {
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			ret = rtrs_addr_to_sockaddr(p, strlen(p),
+						    *opt->dest_port,
+						    &opt->paths[p_cnt]);
+			if (ret) {
+				pr_err("Can't parse path %s: %d\n", p, ret);
+				kfree(p);
+				goto out;
+			}
+
+			p_cnt++;
+
+			kfree(p);
+			break;
+
+		case RNBD_OPT_DEV_PATH:
+			p = match_strdup(args);
+			if (!p) {
+				ret = -ENOMEM;
+				goto out;
+			}
+			if (strlen(p) > NAME_MAX) {
+				pr_err("map_device: Device path too long\n");
+				ret = -EINVAL;
+				kfree(p);
+				goto out;
+			}
+			strlcpy(opt->pathname, p, NAME_MAX);
+			kfree(p);
+			break;
+
+		case RNBD_OPT_DEST_PORT:
+			if (match_int(args, &dest_port) || dest_port < 0 ||
+			    dest_port > 65535) {
+				pr_err("bad destination port number parameter '%d'\n",
+				       dest_port);
+				ret = -EINVAL;
+				goto out;
+			}
+			*opt->dest_port = dest_port;
+			break;
+
+		case RNBD_OPT_ACCESS_MODE:
+			p = match_strdup(args);
+			if (!p) {
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			if (!strcmp(p, "ro")) {
+				*opt->access_mode = RNBD_ACCESS_RO;
+			} else if (!strcmp(p, "rw")) {
+				*opt->access_mode = RNBD_ACCESS_RW;
+			} else if (!strcmp(p, "migration")) {
+				*opt->access_mode = RNBD_ACCESS_MIGRATION;
+			} else {
+				pr_err("map_device: Invalid access_mode: '%s'\n",
+				       p);
+				ret = -EINVAL;
+				kfree(p);
+				goto out;
+			}
+
+			kfree(p);
+			break;
+
+		default:
+			pr_err("map_device: Unknown parameter or missing value '%s'\n",
+			       p);
+			ret = -EINVAL;
+			goto out;
+		}
+	}
+
+	for (i = 0; i < ARRAY_SIZE(rnbd_opt_mandatory); i++) {
+		if ((opt_mask & rnbd_opt_mandatory[i])) {
+			ret = 0;
+		} else {
+			pr_err("map_device: Parameters missing\n");
+			ret = -EINVAL;
+			break;
+		}
+	}
+
+out:
+	*opt->path_cnt = p_cnt;
+	kfree(options);
+	return ret;
+}
+
+static ssize_t state_show(struct kobject *kobj,
+			  struct kobj_attribute *attr, char *page)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	switch (dev->dev_state) {
+	case DEV_STATE_INIT:
+		return snprintf(page, PAGE_SIZE, "init\n");
+	case DEV_STATE_MAPPED:
+		/* TODO fix cli tool before changing to proper state */
+		return snprintf(page, PAGE_SIZE, "open\n");
+	case DEV_STATE_MAPPED_DISCONNECTED:
+		/* TODO fix cli tool before changing to proper state */
+		return snprintf(page, PAGE_SIZE, "closed\n");
+	case DEV_STATE_UNMAPPED:
+		return snprintf(page, PAGE_SIZE, "unmapped\n");
+	default:
+		return snprintf(page, PAGE_SIZE, "unknown\n");
+	}
+}
+
+static struct kobj_attribute rnbd_clt_state_attr = __ATTR_RO(state);
+
+static ssize_t mapping_path_show(struct kobject *kobj,
+				 struct kobj_attribute *attr, char *page)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	return scnprintf(page, PAGE_SIZE, "%s\n", dev->pathname);
+}
+
+static struct kobj_attribute rnbd_clt_mapping_path_attr =
+	__ATTR_RO(mapping_path);
+
+static ssize_t access_mode_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *page)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	return snprintf(page, PAGE_SIZE, "%s\n",
+			rnbd_access_mode_str(dev->access_mode));
+}
+
+static struct kobj_attribute rnbd_clt_access_mode =
+	__ATTR_RO(access_mode);
+
+static ssize_t rnbd_clt_unmap_dev_show(struct kobject *kobj,
+					struct kobj_attribute *attr, char *page)
+{
+	return scnprintf(page, PAGE_SIZE, "Usage: echo <normal|force> > %s\n",
+			 attr->attr.name);
+}
+
+static ssize_t rnbd_clt_unmap_dev_store(struct kobject *kobj,
+					 struct kobj_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct rnbd_clt_dev *dev;
+	char *opt, *options;
+	bool force;
+	int err;
+
+	opt = kstrdup(buf, GFP_KERNEL);
+	if (!opt)
+		return -ENOMEM;
+
+	options = strstrip(opt);
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+	if (sysfs_streq(options, "normal")) {
+		force = false;
+	} else if (sysfs_streq(options, "force")) {
+		force = true;
+	} else {
+		rnbd_clt_err(dev,
+			      "unmap_device: Invalid value: %s\n",
+			      options);
+		err = -EINVAL;
+		goto out;
+	}
+
+	rnbd_clt_info(dev, "Unmapping device, option: %s.\n",
+		       force ? "force" : "normal");
+
+	/*
+	 * We take explicit module reference only for one reason: do not
+	 * race with lockless rnbd_destroy_sessions().
+	 */
+	if (!try_module_get(THIS_MODULE)) {
+		err = -ENODEV;
+		goto out;
+	}
+	err = rnbd_clt_unmap_device(dev, force, &attr->attr);
+	if (err) {
+		if (err != -EALREADY)
+			rnbd_clt_err(dev, "unmap_device: %d\n",  err);
+		goto module_put;
+	}
+
+	/*
+	 * Here device can be vanished!
+	 */
+
+	err = count;
+
+module_put:
+	module_put(THIS_MODULE);
+out:
+	kfree(opt);
+
+	return err;
+}
+
+static struct kobj_attribute rnbd_clt_unmap_device_attr =
+	__ATTR(unmap_device, 0644, rnbd_clt_unmap_dev_show,
+	       rnbd_clt_unmap_dev_store);
+
+static ssize_t rnbd_clt_resize_dev_show(struct kobject *kobj,
+					 struct kobj_attribute *attr,
+					 char *page)
+{
+	return scnprintf(page, PAGE_SIZE,
+			 "Usage: echo <new size in sectors> > %s\n",
+			 attr->attr.name);
+}
+
+static ssize_t rnbd_clt_resize_dev_store(struct kobject *kobj,
+					  struct kobj_attribute *attr,
+					  const char *buf, size_t count)
+{
+	int ret;
+	unsigned long sectors;
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	ret = kstrtoul(buf, 0, &sectors);
+	if (ret)
+		return ret;
+
+	ret = rnbd_clt_resize_disk(dev, (size_t)sectors);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
+static struct kobj_attribute rnbd_clt_resize_dev_attr =
+	__ATTR(resize, 0644, rnbd_clt_resize_dev_show,
+	       rnbd_clt_resize_dev_store);
+
+static ssize_t rnbd_clt_remap_dev_show(struct kobject *kobj,
+					struct kobj_attribute *attr, char *page)
+{
+	return scnprintf(page, PAGE_SIZE, "Usage: echo <1> > %s\n",
+			 attr->attr.name);
+}
+
+static ssize_t rnbd_clt_remap_dev_store(struct kobject *kobj,
+					 struct kobj_attribute *attr,
+					 const char *buf, size_t count)
+{
+	struct rnbd_clt_dev *dev;
+	char *opt, *options;
+	int err;
+
+	opt = kstrdup(buf, GFP_KERNEL);
+	if (!opt)
+		return -ENOMEM;
+
+	options = strstrip(opt);
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+	if (!sysfs_streq(options, "1")) {
+		rnbd_clt_err(dev,
+			      "remap_device: Invalid value: %s\n",
+			      options);
+		err = -EINVAL;
+		goto out;
+	}
+	err = rnbd_clt_remap_device(dev);
+	if (likely(!err))
+		err = count;
+
+out:
+	kfree(opt);
+
+	return err;
+}
+
+static struct kobj_attribute rnbd_clt_remap_device_attr =
+	__ATTR(remap_device, 0644, rnbd_clt_remap_dev_show,
+	       rnbd_clt_remap_dev_store);
+
+static ssize_t session_show(struct kobject *kobj, struct kobj_attribute *attr,
+			    char *page)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_clt_dev, kobj);
+
+	return scnprintf(page, PAGE_SIZE, "%s\n", dev->sess->sessname);
+}
+
+static struct kobj_attribute rnbd_clt_session_attr =
+	__ATTR_RO(session);
+
+static struct attribute *rnbd_dev_attrs[] = {
+	&rnbd_clt_unmap_device_attr.attr,
+	&rnbd_clt_resize_dev_attr.attr,
+	&rnbd_clt_remap_device_attr.attr,
+	&rnbd_clt_mapping_path_attr.attr,
+	&rnbd_clt_state_attr.attr,
+	&rnbd_clt_session_attr.attr,
+	&rnbd_clt_access_mode.attr,
+	NULL,
+};
+
+void rnbd_clt_remove_dev_symlink(struct rnbd_clt_dev *dev)
+{
+	/*
+	 * The module unload rnbd_client_exit path is racing with unmapping of
+	 * the last single device from the sysfs manually
+	 * i.e. rnbd_clt_unmap_dev_store() leading to a sysfs warning because
+	 * of sysfs link already was removed already.
+	 */
+	if (strlen(dev->blk_symlink_name) && try_module_get(THIS_MODULE)) {
+		sysfs_remove_link(rnbd_devs_kobj, dev->blk_symlink_name);
+		module_put(THIS_MODULE);
+	}
+}
+
+static struct kobj_type rnbd_dev_ktype = {
+	.sysfs_ops      = &kobj_sysfs_ops,
+	.default_attrs  = rnbd_dev_attrs,
+};
+
+static int rnbd_clt_add_dev_kobj(struct rnbd_clt_dev *dev)
+{
+	int ret;
+	struct kobject *gd_kobj = &disk_to_dev(dev->gd)->kobj;
+
+	ret = kobject_init_and_add(&dev->kobj, &rnbd_dev_ktype, gd_kobj, "%s",
+				   "rnbd");
+	if (ret)
+		rnbd_clt_err(dev, "Failed to create device sysfs dir, err: %d\n",
+			      ret);
+
+	return ret;
+}
+
+static ssize_t rnbd_clt_map_device_show(struct kobject *kobj,
+					 struct kobj_attribute *attr,
+					 char *page)
+{
+	return scnprintf(page, PAGE_SIZE,
+			 "Usage: echo \"[dest_port=server port number] sessname=<name of the rtrs session> path=<[srcaddr@]dstaddr> [path=<[srcaddr@]dstaddr>] device_path=<full path on remote side> [access_mode=<ro|rw|migration>]\" > %s\n\naddr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]\n",
+			 attr->attr.name);
+}
+
+static int rnbd_clt_get_path_name(struct rnbd_clt_dev *dev, char *buf,
+				   size_t len)
+{
+	int ret;
+	char pathname[NAME_MAX], *s;
+
+	strlcpy(pathname, dev->pathname, sizeof(pathname));
+	while ((s = strchr(pathname, '/')))
+		s[0] = '!';
+
+	ret = snprintf(buf, len, "%s", pathname);
+	if (ret >= len)
+		return -ENAMETOOLONG;
+
+	return 0;
+}
+
+static int rnbd_clt_add_dev_symlink(struct rnbd_clt_dev *dev)
+{
+	struct kobject *gd_kobj = &disk_to_dev(dev->gd)->kobj;
+	int ret;
+
+	ret = rnbd_clt_get_path_name(dev, dev->blk_symlink_name,
+				      sizeof(dev->blk_symlink_name));
+	if (ret) {
+		rnbd_clt_err(dev, "Failed to get /sys/block symlink path, err: %d\n",
+			      ret);
+		goto out_err;
+	}
+
+	ret = sysfs_create_link(rnbd_devs_kobj, gd_kobj,
+				dev->blk_symlink_name);
+	if (ret) {
+		rnbd_clt_err(dev, "Creating /sys/block symlink failed, err: %d\n",
+			      ret);
+		goto out_err;
+	}
+
+	return 0;
+
+out_err:
+	dev->blk_symlink_name[0] = '\0';
+	return ret;
+}
+
+static ssize_t rnbd_clt_map_device_store(struct kobject *kobj,
+					  struct kobj_attribute *attr,
+					  const char *buf, size_t count)
+{
+	struct rnbd_clt_dev *dev;
+	struct rnbd_map_options opt;
+	int ret;
+	char pathname[NAME_MAX];
+	char sessname[NAME_MAX];
+	enum rnbd_access_mode access_mode = RNBD_ACCESS_RW;
+	u16 port_nr = RTRS_PORT;
+
+	struct sockaddr_storage *addrs;
+	struct rtrs_addr paths[6];
+	size_t path_cnt;
+
+	opt.sessname = sessname;
+	opt.paths = paths;
+	opt.path_cnt = &path_cnt;
+	opt.pathname = pathname;
+	opt.dest_port = &port_nr;
+	opt.access_mode = &access_mode;
+	addrs = kcalloc(ARRAY_SIZE(paths) * 2, sizeof(*addrs), GFP_KERNEL);
+	if (!addrs)
+		return -ENOMEM;
+
+	for (path_cnt = 0; path_cnt < ARRAY_SIZE(paths); path_cnt++) {
+		paths[path_cnt].src = &addrs[path_cnt * 2];
+		paths[path_cnt].dst = &addrs[path_cnt * 2 + 1];
+	}
+
+	ret = rnbd_clt_parse_map_options(buf, ARRAY_SIZE(paths), &opt);
+	if (ret)
+		goto out;
+
+	pr_info("Mapping device %s on session %s, (access_mode: %s)\n",
+		pathname, sessname,
+		rnbd_access_mode_str(access_mode));
+
+	dev = rnbd_clt_map_device(sessname, paths, path_cnt, port_nr, pathname,
+				  access_mode);
+	if (IS_ERR(dev)) {
+		ret = PTR_ERR(dev);
+		goto out;
+	}
+
+	ret = rnbd_clt_add_dev_kobj(dev);
+	if (ret)
+		goto unmap_dev;
+
+	ret = rnbd_clt_add_dev_symlink(dev);
+	if (ret)
+		goto unmap_dev;
+
+	kfree(addrs);
+	return count;
+
+unmap_dev:
+	rnbd_clt_unmap_device(dev, true, NULL);
+out:
+	kfree(addrs);
+	return ret;
+}
+
+static struct kobj_attribute rnbd_clt_map_device_attr =
+	__ATTR(map_device, 0644,
+	       rnbd_clt_map_device_show, rnbd_clt_map_device_store);
+
+static struct attribute *default_attrs[] = {
+	&rnbd_clt_map_device_attr.attr,
+	NULL,
+};
+
+static struct attribute_group default_attr_group = {
+	.attrs = default_attrs,
+};
+
+static const struct attribute_group *default_attr_groups[] = {
+	&default_attr_group,
+	NULL,
+};
+
+int rnbd_clt_create_sysfs_files(void)
+{
+	int err;
+
+	rnbd_dev_class = class_create(THIS_MODULE, "rnbd-client");
+	if (IS_ERR(rnbd_dev_class))
+		return PTR_ERR(rnbd_dev_class);
+
+	rnbd_dev = device_create_with_groups(rnbd_dev_class, NULL,
+					      MKDEV(0, 0), NULL,
+					      default_attr_groups, "ctl");
+	if (IS_ERR(rnbd_dev)) {
+		err = PTR_ERR(rnbd_dev);
+		goto cls_destroy;
+	}
+	rnbd_devs_kobj = kobject_create_and_add("devices", &rnbd_dev->kobj);
+	if (!rnbd_devs_kobj) {
+		err = -ENOMEM;
+		goto dev_destroy;
+	}
+
+	return 0;
+
+dev_destroy:
+	device_destroy(rnbd_dev_class, MKDEV(0, 0));
+cls_destroy:
+	class_destroy(rnbd_dev_class);
+
+	return err;
+}
+
+void rnbd_clt_destroy_default_group(void)
+{
+	sysfs_remove_group(&rnbd_dev->kobj, &default_attr_group);
+}
+
+void rnbd_clt_destroy_sysfs_files(void)
+{
+	kobject_del(rnbd_devs_kobj);
+	kobject_put(rnbd_devs_kobj);
+	device_destroy(rnbd_dev_class, MKDEV(0, 0));
+	class_destroy(rnbd_dev_class);
+}
diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
new file mode 100644
index 000000000000..cc6a4e2587ae
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-clt.c
@@ -0,0 +1,1729 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+
+#undef pr_fmt
+#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
+
+#include <linux/module.h>
+#include <linux/blkdev.h>
+#include <linux/hdreg.h>
+#include <linux/scatterlist.h>
+#include <linux/idr.h>
+
+#include "rnbd-clt.h"
+
+MODULE_DESCRIPTION("RDMA Network Block Device Client");
+MODULE_LICENSE("GPL");
+
+static int rnbd_client_major;
+static DEFINE_IDA(index_ida);
+static DEFINE_MUTEX(ida_lock);
+static DEFINE_MUTEX(sess_lock);
+static LIST_HEAD(sess_list);
+
+/*
+ * Maximum number of partitions an instance can have.
+ * 6 bits = 64 minors = 63 partitions (one minor is used for the device itself)
+ */
+#define RNBD_PART_BITS		6
+
+static inline bool rnbd_clt_get_sess(struct rnbd_clt_session *sess)
+{
+	return refcount_inc_not_zero(&sess->refcount);
+}
+
+static void free_sess(struct rnbd_clt_session *sess);
+
+static void rnbd_clt_put_sess(struct rnbd_clt_session *sess)
+{
+	might_sleep();
+
+	if (refcount_dec_and_test(&sess->refcount))
+		free_sess(sess);
+}
+
+static void rnbd_clt_put_dev(struct rnbd_clt_dev *dev)
+{
+	might_sleep();
+
+	if (!refcount_dec_and_test(&dev->refcount))
+		return;
+
+	mutex_lock(&ida_lock);
+	ida_simple_remove(&index_ida, dev->clt_device_id);
+	mutex_unlock(&ida_lock);
+	kfree(dev->hw_queues);
+	rnbd_clt_put_sess(dev->sess);
+	mutex_destroy(&dev->lock);
+	kfree(dev);
+}
+
+static inline bool rnbd_clt_get_dev(struct rnbd_clt_dev *dev)
+{
+	return refcount_inc_not_zero(&dev->refcount);
+}
+
+static int rnbd_clt_set_dev_attr(struct rnbd_clt_dev *dev,
+				 const struct rnbd_msg_open_rsp *rsp)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+
+	if (!rsp->logical_block_size)
+		return -EINVAL;
+
+	dev->device_id		    = le32_to_cpu(rsp->device_id);
+	dev->nsectors		    = le64_to_cpu(rsp->nsectors);
+	dev->logical_block_size	    = le16_to_cpu(rsp->logical_block_size);
+	dev->physical_block_size    = le16_to_cpu(rsp->physical_block_size);
+	dev->max_write_same_sectors = le32_to_cpu(rsp->max_write_same_sectors);
+	dev->max_discard_sectors    = le32_to_cpu(rsp->max_discard_sectors);
+	dev->discard_granularity    = le32_to_cpu(rsp->discard_granularity);
+	dev->discard_alignment	    = le32_to_cpu(rsp->discard_alignment);
+	dev->secure_discard	    = le16_to_cpu(rsp->secure_discard);
+	dev->rotational		    = rsp->rotational;
+
+	dev->max_hw_sectors = sess->max_io_size / SECTOR_SIZE;
+	dev->max_segments = BMAX_SEGMENTS;
+
+	dev->max_hw_sectors = min_t(u32, dev->max_hw_sectors,
+				    le32_to_cpu(rsp->max_hw_sectors));
+	dev->max_segments = min_t(u16, dev->max_segments,
+				  le16_to_cpu(rsp->max_segments));
+
+	return 0;
+}
+
+static int rnbd_clt_change_capacity(struct rnbd_clt_dev *dev,
+				    size_t new_nsectors)
+{
+	int err = 0;
+
+	rnbd_clt_info(dev, "Device size changed from %zu to %zu sectors\n",
+		       dev->nsectors, new_nsectors);
+	dev->nsectors = new_nsectors;
+	set_capacity(dev->gd, dev->nsectors);
+	err = revalidate_disk(dev->gd);
+	if (err)
+		rnbd_clt_err(dev,
+			      "Failed to change device size from %zu to %zu, err: %d\n",
+			      dev->nsectors, new_nsectors, err);
+	return err;
+}
+
+static int process_msg_open_rsp(struct rnbd_clt_dev *dev,
+				struct rnbd_msg_open_rsp *rsp)
+{
+	int err = 0;
+
+	mutex_lock(&dev->lock);
+	if (dev->dev_state == DEV_STATE_UNMAPPED) {
+		rnbd_clt_info(dev,
+			       "Ignoring Open-Response message from server for  unmapped device\n");
+		err = -ENOENT;
+		goto out;
+	}
+	if (dev->dev_state == DEV_STATE_MAPPED_DISCONNECTED) {
+		u64 nsectors = le64_to_cpu(rsp->nsectors);
+
+		/*
+		 * If the device was remapped and the size changed in the
+		 * meantime we need to revalidate it
+		 */
+		if (dev->nsectors != nsectors)
+			rnbd_clt_change_capacity(dev, nsectors);
+		rnbd_clt_info(dev, "Device online, device remapped successfully\n");
+	}
+	err = rnbd_clt_set_dev_attr(dev, rsp);
+	if (err)
+		goto out;
+	dev->dev_state = DEV_STATE_MAPPED;
+
+out:
+	mutex_unlock(&dev->lock);
+
+	return err;
+}
+
+int rnbd_clt_resize_disk(struct rnbd_clt_dev *dev, size_t newsize)
+{
+	int ret = 0;
+
+	mutex_lock(&dev->lock);
+	if (dev->dev_state != DEV_STATE_MAPPED) {
+		pr_err("Failed to set new size of the device, device is not opened\n");
+		ret = -ENOENT;
+		goto out;
+	}
+	ret = rnbd_clt_change_capacity(dev, newsize);
+
+out:
+	mutex_unlock(&dev->lock);
+
+	return ret;
+}
+
+static inline void rnbd_clt_dev_requeue(struct rnbd_queue *q)
+{
+	if (WARN_ON(!q->hctx))
+		return;
+
+	/* We can come here from interrupt, thus async=true */
+	blk_mq_run_hw_queue(q->hctx, true);
+}
+
+enum {
+	RNBD_DELAY_IFBUSY = -1,
+};
+
+/**
+ * rnbd_get_cpu_qlist() - finds a list with HW queues to be rerun
+ * @sess:	Session to find a queue for
+ * @cpu:	Cpu to start the search from
+ *
+ * Description:
+ *     Each CPU has a list of HW queues, which needs to be rerun.  If a list
+ *     is not empty - it is marked with a bit.  This function finds first
+ *     set bit in a bitmap and returns corresponding CPU list.
+ */
+static struct rnbd_cpu_qlist *
+rnbd_get_cpu_qlist(struct rnbd_clt_session *sess, int cpu)
+{
+	int bit;
+
+	/* Search from cpu to nr_cpu_ids */
+	bit = find_next_bit(sess->cpu_queues_bm, nr_cpu_ids, cpu);
+	if (bit < nr_cpu_ids) {
+		return per_cpu_ptr(sess->cpu_queues, bit);
+	} else if (cpu != 0) {
+		/* Search from 0 to cpu */
+		bit = find_next_bit(sess->cpu_queues_bm, cpu, 0);
+		if (bit < cpu)
+			return per_cpu_ptr(sess->cpu_queues, bit);
+	}
+
+	return NULL;
+}
+
+static inline int nxt_cpu(int cpu)
+{
+	return (cpu + 1) % nr_cpu_ids;
+}
+
+/**
+ * rnbd_rerun_if_needed() - rerun next queue marked as stopped
+ * @sess:	Session to rerun a queue on
+ *
+ * Description:
+ *     Each CPU has it's own list of HW queues, which should be rerun.
+ *     Function finds such list with HW queues, takes a list lock, picks up
+ *     the first HW queue out of the list and requeues it.
+ *
+ * Return:
+ *     True if the queue was requeued, false otherwise.
+ *
+ * Context:
+ *     Does not matter.
+ */
+static bool rnbd_rerun_if_needed(struct rnbd_clt_session *sess)
+{
+	struct rnbd_queue *q = NULL;
+	struct rnbd_cpu_qlist *cpu_q;
+	unsigned long flags;
+	int *cpup;
+
+	/*
+	 * To keep fairness and not to let other queues starve we always
+	 * try to wake up someone else in round-robin manner.  That of course
+	 * increases latency but queues always have a chance to be executed.
+	 */
+	cpup = get_cpu_ptr(sess->cpu_rr);
+	for (cpu_q = rnbd_get_cpu_qlist(sess, nxt_cpu(*cpup)); cpu_q;
+	     cpu_q = rnbd_get_cpu_qlist(sess, nxt_cpu(cpu_q->cpu))) {
+		if (!spin_trylock_irqsave(&cpu_q->requeue_lock, flags))
+			continue;
+		if (unlikely(!test_bit(cpu_q->cpu, sess->cpu_queues_bm)))
+			goto unlock;
+		q = list_first_entry_or_null(&cpu_q->requeue_list,
+					     typeof(*q), requeue_list);
+		if (WARN_ON(!q))
+			goto clear_bit;
+		list_del_init(&q->requeue_list);
+		clear_bit_unlock(0, &q->in_list);
+
+		if (list_empty(&cpu_q->requeue_list)) {
+			/* Clear bit if nothing is left */
+clear_bit:
+			clear_bit(cpu_q->cpu, sess->cpu_queues_bm);
+		}
+unlock:
+		spin_unlock_irqrestore(&cpu_q->requeue_lock, flags);
+
+		if (q)
+			break;
+	}
+
+	/**
+	 * Saves the CPU that is going to be requeued on the per-cpu var. Just
+	 * incrementing it doesn't work because rnbd_get_cpu_qlist() will
+	 * always return the first CPU with something on the queue list when the
+	 * value stored on the var is greater than the last CPU with something
+	 * on the list.
+	 */
+	if (cpu_q)
+		*cpup = cpu_q->cpu;
+	put_cpu_var(sess->cpu_rr);
+
+	if (q)
+		rnbd_clt_dev_requeue(q);
+
+	return q;
+}
+
+/**
+ * rnbd_rerun_all_if_idle() - rerun all queues left in the list if
+ *				 session is idling (there are no requests
+ *				 in-flight).
+ * @sess:	Session to rerun the queues on
+ *
+ * Description:
+ *     This function tries to rerun all stopped queues if there are no
+ *     requests in-flight anymore.  This function tries to solve an obvious
+ *     problem, when number of tags < than number of queues (hctx), which
+ *     are stopped and put to sleep.  If last permit, which has been just put,
+ *     does not wake up all left queues (hctxs), IO requests hang forever.
+ *
+ *     That can happen when all number of permits, say N, have been exhausted
+ *     from one CPU, and we have many block devices per session, say M.
+ *     Each block device has it's own queue (hctx) for each CPU, so eventually
+ *     we can put that number of queues (hctxs) to sleep: M x nr_cpu_ids.
+ *     If number of permits N < M x nr_cpu_ids finally we will get an IO hang.
+ *
+ *     To avoid this hang last caller of rnbd_put_permit() (last caller is the
+ *     one who observes sess->busy == 0) must wake up all remaining queues.
+ *
+ * Context:
+ *     Does not matter.
+ */
+static void rnbd_rerun_all_if_idle(struct rnbd_clt_session *sess)
+{
+	bool requeued;
+
+	do {
+		requeued = rnbd_rerun_if_needed(sess);
+	} while (atomic_read(&sess->busy) == 0 && requeued);
+}
+
+static struct rtrs_permit *rnbd_get_permit(struct rnbd_clt_session *sess,
+					     enum rtrs_clt_con_type con_type,
+					     int wait)
+{
+	struct rtrs_permit *permit;
+
+	permit = rtrs_clt_get_permit(sess->rtrs, con_type,
+				      wait ? RTRS_PERMIT_WAIT :
+				      RTRS_PERMIT_NOWAIT);
+	if (likely(permit))
+		/* We have a subtle rare case here, when all permits can be
+		 * consumed before busy counter increased.  This is safe,
+		 * because loser will get NULL as a permit, observe 0 busy
+		 * counter and immediately restart the queue himself.
+		 */
+		atomic_inc(&sess->busy);
+
+	return permit;
+}
+
+static void rnbd_put_permit(struct rnbd_clt_session *sess,
+			     struct rtrs_permit *permit)
+{
+	rtrs_clt_put_permit(sess->rtrs, permit);
+	atomic_dec(&sess->busy);
+	/* Paired with rnbd_clt_dev_add_to_requeue().  Decrement first
+	 * and then check queue bits.
+	 */
+	smp_mb__after_atomic();
+	rnbd_rerun_all_if_idle(sess);
+}
+
+static struct rnbd_iu *rnbd_get_iu(struct rnbd_clt_session *sess,
+				     enum rtrs_clt_con_type con_type,
+				     int wait)
+{
+	struct rnbd_iu *iu;
+	struct rtrs_permit *permit;
+
+	permit = rnbd_get_permit(sess, con_type,
+				  wait ? RTRS_PERMIT_WAIT :
+				  RTRS_PERMIT_NOWAIT);
+	if (unlikely(!permit))
+		return NULL;
+	iu = rtrs_permit_to_pdu(permit);
+	iu->permit = permit;
+	/*
+	 * 1st reference is dropped after finishing sending a "user" message,
+	 * 2nd reference is dropped after confirmation with the response is
+	 * returned.
+	 * 1st and 2nd can happen in any order, so the rnbd_iu should be
+	 * released (rtrs_permit returned to ibbtrs) only leased after both
+	 * are finished.
+	 */
+	atomic_set(&iu->refcount, 2);
+	init_waitqueue_head(&iu->comp.wait);
+	iu->comp.errno = INT_MAX;
+
+	return iu;
+}
+
+static void rnbd_put_iu(struct rnbd_clt_session *sess, struct rnbd_iu *iu)
+{
+	if (atomic_dec_and_test(&iu->refcount))
+		rnbd_put_permit(sess, iu->permit);
+}
+
+static void rnbd_softirq_done_fn(struct request *rq)
+{
+	struct rnbd_clt_dev *dev	= rq->rq_disk->private_data;
+	struct rnbd_clt_session *sess	= dev->sess;
+	struct rnbd_iu *iu;
+
+	iu = blk_mq_rq_to_pdu(rq);
+	rnbd_put_permit(sess, iu->permit);
+	blk_mq_end_request(rq, errno_to_blk_status(iu->errno));
+}
+
+static void msg_io_conf(void *priv, int errno)
+{
+	struct rnbd_iu *iu = priv;
+	struct rnbd_clt_dev *dev = iu->dev;
+	struct request *rq = iu->rq;
+	int rw = rq_data_dir(rq);
+
+	iu->errno = errno;
+
+	blk_mq_complete_request(rq);
+
+	if (errno)
+		rnbd_clt_info_rl(dev, "%s I/O failed with err: %d\n",
+				 rw == READ ? "read" : "write", errno);
+}
+
+static void wake_up_iu_comp(struct rnbd_iu *iu, int errno)
+{
+	iu->comp.errno = errno;
+	wake_up(&iu->comp.wait);
+}
+
+static void msg_conf(void *priv, int errno)
+{
+	struct rnbd_iu *iu = priv;
+
+	iu->errno = errno;
+	schedule_work(&iu->work);
+}
+
+enum wait_type {
+	NO_WAIT = 0,
+	WAIT    = 1
+};
+
+static int send_usr_msg(struct rtrs_clt *rtrs, int dir,
+			struct rnbd_iu *iu, struct kvec *vec, size_t nr,
+			size_t len, struct scatterlist *sg, unsigned int sg_len,
+			void (*conf)(struct work_struct *work),
+			int *errno, enum wait_type wait)
+{
+	int err;
+	struct rtrs_clt_req_ops req_ops;
+
+	INIT_WORK(&iu->work, conf);
+	req_ops = (struct rtrs_clt_req_ops) {
+		.priv = iu,
+		.conf_fn = msg_conf,
+	};
+	err = rtrs_clt_request(dir, &req_ops, rtrs, iu->permit,
+				vec, nr, len, sg, sg_len);
+	if (!err && wait) {
+		wait_event(iu->comp.wait, iu->comp.errno != INT_MAX);
+		*errno = iu->comp.errno;
+	} else {
+		*errno = 0;
+	}
+
+	return err;
+}
+
+static void msg_close_conf(struct work_struct *work)
+{
+	struct rnbd_iu *iu = container_of(work, struct rnbd_iu, work);
+	struct rnbd_clt_dev *dev = iu->dev;
+
+	wake_up_iu_comp(iu, iu->errno);
+	rnbd_put_iu(dev->sess, iu);
+	rnbd_clt_put_dev(dev);
+}
+
+static int send_msg_close(struct rnbd_clt_dev *dev, u32 device_id, bool wait)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+	struct rnbd_msg_close msg;
+	struct rnbd_iu *iu;
+	struct kvec vec = {
+		.iov_base = &msg,
+		.iov_len  = sizeof(msg)
+	};
+	int err, errno;
+
+	iu = rnbd_get_iu(sess, RTRS_ADMIN_CON, RTRS_PERMIT_WAIT);
+	if (!iu)
+		return -ENOMEM;
+
+	iu->buf = NULL;
+	iu->dev = dev;
+
+	sg_mark_end(&iu->sglist[0]);
+
+	msg.hdr.type	= cpu_to_le16(RNBD_MSG_CLOSE);
+	msg.device_id	= cpu_to_le32(device_id);
+
+	WARN_ON(!rnbd_clt_get_dev(dev));
+	err = send_usr_msg(sess->rtrs, WRITE, iu, &vec, 1, 0, NULL, 0,
+			   msg_close_conf, &errno, wait);
+	if (err) {
+		rnbd_clt_put_dev(dev);
+		rnbd_put_iu(sess, iu);
+	} else {
+		err = errno;
+	}
+
+	rnbd_put_iu(sess, iu);
+	return err;
+}
+
+static void msg_open_conf(struct work_struct *work)
+{
+	struct rnbd_iu *iu = container_of(work, struct rnbd_iu, work);
+	struct rnbd_msg_open_rsp *rsp = iu->buf;
+	struct rnbd_clt_dev *dev = iu->dev;
+	int errno = iu->errno;
+
+	if (errno) {
+		rnbd_clt_err(dev,
+			      "Opening failed, server responded: %d\n",
+			      errno);
+	} else {
+		errno = process_msg_open_rsp(dev, rsp);
+		if (errno) {
+			u32 device_id = le32_to_cpu(rsp->device_id);
+			/*
+			 * If server thinks its fine, but we fail to process
+			 * then be nice and send a close to server.
+			 */
+			(void)send_msg_close(dev, device_id, NO_WAIT);
+		}
+	}
+	kfree(rsp);
+	wake_up_iu_comp(iu, errno);
+	rnbd_put_iu(dev->sess, iu);
+	rnbd_clt_put_dev(dev);
+}
+
+static void msg_sess_info_conf(struct work_struct *work)
+{
+	struct rnbd_iu *iu = container_of(work, struct rnbd_iu, work);
+	struct rnbd_msg_sess_info_rsp *rsp = iu->buf;
+	struct rnbd_clt_session *sess = iu->sess;
+
+	if (!iu->errno)
+		sess->ver = min_t(u8, rsp->ver, RNBD_PROTO_VER_MAJOR);
+
+	kfree(rsp);
+	wake_up_iu_comp(iu, iu->errno);
+	rnbd_put_iu(sess, iu);
+	rnbd_clt_put_sess(sess);
+}
+
+static int send_msg_open(struct rnbd_clt_dev *dev, bool wait)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+	struct rnbd_msg_open_rsp *rsp;
+	struct rnbd_msg_open msg;
+	struct rnbd_iu *iu;
+	struct kvec vec = {
+		.iov_base = &msg,
+		.iov_len  = sizeof(msg)
+	};
+	int err, errno;
+
+	rsp = kzalloc(sizeof(*rsp), GFP_KERNEL);
+	if (!rsp)
+		return -ENOMEM;
+
+	iu = rnbd_get_iu(sess, RTRS_ADMIN_CON, RTRS_PERMIT_WAIT);
+	if (!iu) {
+		kfree(rsp);
+		return -ENOMEM;
+	}
+
+	iu->buf = rsp;
+	iu->dev = dev;
+
+	sg_init_one(iu->sglist, rsp, sizeof(*rsp));
+
+	msg.hdr.type	= cpu_to_le16(RNBD_MSG_OPEN);
+	msg.access_mode	= dev->access_mode;
+	strlcpy(msg.dev_name, dev->pathname, sizeof(msg.dev_name));
+
+	WARN_ON(!rnbd_clt_get_dev(dev));
+	err = send_usr_msg(sess->rtrs, READ, iu,
+			   &vec, 1, sizeof(*rsp), iu->sglist, 1,
+			   msg_open_conf, &errno, wait);
+	if (err) {
+		rnbd_clt_put_dev(dev);
+		rnbd_put_iu(sess, iu);
+		kfree(rsp);
+	} else {
+		err = errno;
+	}
+
+	rnbd_put_iu(sess, iu);
+	return err;
+}
+
+static int send_msg_sess_info(struct rnbd_clt_session *sess, bool wait)
+{
+	struct rnbd_msg_sess_info_rsp *rsp;
+	struct rnbd_msg_sess_info msg;
+	struct rnbd_iu *iu;
+	struct kvec vec = {
+		.iov_base = &msg,
+		.iov_len  = sizeof(msg)
+	};
+	int err, errno;
+
+	rsp = kzalloc(sizeof(*rsp), GFP_KERNEL);
+	if (!rsp)
+		return -ENOMEM;
+
+	iu = rnbd_get_iu(sess, RTRS_ADMIN_CON, RTRS_PERMIT_WAIT);
+	if (!iu) {
+		kfree(rsp);
+		return -ENOMEM;
+	}
+
+	iu->buf = rsp;
+	iu->sess = sess;
+
+	sg_init_one(iu->sglist, rsp, sizeof(*rsp));
+
+	msg.hdr.type = cpu_to_le16(RNBD_MSG_SESS_INFO);
+	msg.ver      = RNBD_PROTO_VER_MAJOR;
+
+	if (!rnbd_clt_get_sess(sess)) {
+		/*
+		 * That can happen only in one case, when RTRS has restablished
+		 * the connection and link_ev() is called, but session is almost
+		 * dead, last reference on session is put and caller is waiting
+		 * for RTRS to close everything.
+		 */
+		err = -ENODEV;
+		goto put_iu;
+	}
+	err = send_usr_msg(sess->rtrs, READ, iu,
+			   &vec, 1, sizeof(*rsp), iu->sglist, 1,
+			   msg_sess_info_conf, &errno, wait);
+	if (err) {
+		rnbd_clt_put_sess(sess);
+put_iu:
+		rnbd_put_iu(sess, iu);
+		kfree(rsp);
+	} else {
+		err = errno;
+	}
+
+	rnbd_put_iu(sess, iu);
+	return err;
+}
+
+static void set_dev_states_to_disconnected(struct rnbd_clt_session *sess)
+{
+	struct rnbd_clt_dev *dev;
+
+	mutex_lock(&sess->lock);
+	list_for_each_entry(dev, &sess->devs_list, list) {
+		rnbd_clt_err(dev, "Device disconnected.\n");
+
+		mutex_lock(&dev->lock);
+		if (dev->dev_state == DEV_STATE_MAPPED)
+			dev->dev_state = DEV_STATE_MAPPED_DISCONNECTED;
+		mutex_unlock(&dev->lock);
+	}
+	mutex_unlock(&sess->lock);
+}
+
+static void remap_devs(struct rnbd_clt_session *sess)
+{
+	struct rnbd_clt_dev *dev;
+	struct rtrs_attrs attrs;
+	int err;
+
+	/*
+	 * Careful here: we are called from RTRS link event directly,
+	 * thus we can't send any RTRS request and wait for response
+	 * or RTRS will not be able to complete request with failure
+	 * if something goes wrong (failing of outstanding requests
+	 * happens exactly from the context where we are blocking now).
+	 *
+	 * So to avoid deadlocks each usr message sent from here must
+	 * be asynchronous.
+	 */
+
+	err = send_msg_sess_info(sess, NO_WAIT);
+	if (err) {
+		pr_err("send_msg_sess_info(\"%s\"): %d\n", sess->sessname, err);
+		return;
+	}
+
+	rtrs_clt_query(sess->rtrs, &attrs);
+	mutex_lock(&sess->lock);
+	sess->max_io_size = attrs.max_io_size;
+
+	list_for_each_entry(dev, &sess->devs_list, list) {
+		bool skip;
+
+		mutex_lock(&dev->lock);
+		skip = (dev->dev_state == DEV_STATE_INIT);
+		mutex_unlock(&dev->lock);
+		if (skip)
+			/*
+			 * When device is establishing connection for the first
+			 * time - do not remap, it will be closed soon.
+			 */
+			continue;
+
+		rnbd_clt_info(dev, "session reconnected, remapping device\n");
+		err = send_msg_open(dev, NO_WAIT);
+		if (err) {
+			rnbd_clt_err(dev, "send_msg_open(): %d\n", err);
+			break;
+		}
+	}
+	mutex_unlock(&sess->lock);
+}
+
+static void rnbd_clt_link_ev(void *priv, enum rtrs_clt_link_ev ev)
+{
+	struct rnbd_clt_session *sess = priv;
+
+	switch (ev) {
+	case RTRS_CLT_LINK_EV_DISCONNECTED:
+		set_dev_states_to_disconnected(sess);
+		break;
+	case RTRS_CLT_LINK_EV_RECONNECTED:
+		remap_devs(sess);
+		break;
+	default:
+		pr_err("Unknown session event received (%d), session: %s\n",
+		       ev, sess->sessname);
+	}
+}
+
+static void rnbd_init_cpu_qlists(struct rnbd_cpu_qlist __percpu *cpu_queues)
+{
+	unsigned int cpu;
+	struct rnbd_cpu_qlist *cpu_q;
+
+	for_each_possible_cpu(cpu) {
+		cpu_q = per_cpu_ptr(cpu_queues, cpu);
+
+		cpu_q->cpu = cpu;
+		INIT_LIST_HEAD(&cpu_q->requeue_list);
+		spin_lock_init(&cpu_q->requeue_lock);
+	}
+}
+
+static void destroy_mq_tags(struct rnbd_clt_session *sess)
+{
+	if (sess->tag_set.tags)
+		blk_mq_free_tag_set(&sess->tag_set);
+}
+
+static inline void wake_up_rtrs_waiters(struct rnbd_clt_session *sess)
+{
+	sess->rtrs_ready = true;
+	wake_up_all(&sess->rtrs_waitq);
+}
+
+static void close_rtrs(struct rnbd_clt_session *sess)
+{
+	might_sleep();
+
+	if (!IS_ERR_OR_NULL(sess->rtrs)) {
+		rtrs_clt_close(sess->rtrs);
+		sess->rtrs = NULL;
+		wake_up_rtrs_waiters(sess);
+	}
+}
+
+static void free_sess(struct rnbd_clt_session *sess)
+{
+	WARN_ON(!list_empty(&sess->devs_list));
+
+	might_sleep();
+
+	close_rtrs(sess);
+	destroy_mq_tags(sess);
+	if (!list_empty(&sess->list)) {
+		mutex_lock(&sess_lock);
+		list_del(&sess->list);
+		mutex_unlock(&sess_lock);
+	}
+	free_percpu(sess->cpu_queues);
+	free_percpu(sess->cpu_rr);
+	mutex_destroy(&sess->lock);
+	kfree(sess);
+}
+
+static struct rnbd_clt_session *alloc_sess(const char *sessname)
+{
+	struct rnbd_clt_session *sess;
+	int err, cpu;
+
+	sess = kzalloc_node(sizeof(*sess), GFP_KERNEL, NUMA_NO_NODE);
+	if (!sess)
+		return ERR_PTR(-ENOMEM);
+	strlcpy(sess->sessname, sessname, sizeof(sess->sessname));
+	atomic_set(&sess->busy, 0);
+	mutex_init(&sess->lock);
+	INIT_LIST_HEAD(&sess->devs_list);
+	INIT_LIST_HEAD(&sess->list);
+	bitmap_zero(sess->cpu_queues_bm, NR_CPUS);
+	init_waitqueue_head(&sess->rtrs_waitq);
+	refcount_set(&sess->refcount, 1);
+
+	sess->cpu_queues = alloc_percpu(struct rnbd_cpu_qlist);
+	if (!sess->cpu_queues) {
+		err = -ENOMEM;
+		goto err;
+	}
+	rnbd_init_cpu_qlists(sess->cpu_queues);
+
+	/*
+	 * That is simple percpu variable which stores cpu indeces, which are
+	 * incremented on each access.  We need that for the sake of fairness
+	 * to wake up queues in a round-robin manner.
+	 */
+	sess->cpu_rr = alloc_percpu(int);
+	if (!sess->cpu_rr) {
+		err = -ENOMEM;
+		goto err;
+	}
+	for_each_possible_cpu(cpu)
+		* per_cpu_ptr(sess->cpu_rr, cpu) = cpu;
+
+	return sess;
+
+err:
+	free_sess(sess);
+
+	return ERR_PTR(err);
+}
+
+static int wait_for_rtrs_connection(struct rnbd_clt_session *sess)
+{
+	wait_event(sess->rtrs_waitq, sess->rtrs_ready);
+	if (IS_ERR_OR_NULL(sess->rtrs))
+		return -ECONNRESET;
+
+	return 0;
+}
+
+static void wait_for_rtrs_disconnection(struct rnbd_clt_session *sess)
+	__releases(&sess_lock)
+	__acquires(&sess_lock)
+{
+	DEFINE_WAIT(wait);
+
+	prepare_to_wait(&sess->rtrs_waitq, &wait, TASK_UNINTERRUPTIBLE);
+	if (IS_ERR_OR_NULL(sess->rtrs)) {
+		finish_wait(&sess->rtrs_waitq, &wait);
+		return;
+	}
+	mutex_unlock(&sess_lock);
+	/* loop in caller, see __find_and_get_sess().
+	 * You can't leave mutex locked and call schedule(), you will catch a
+	 * deadlock with a caller of free_sess(), which has just put the last
+	 * reference and is about to take the sess_lock in order to delete
+	 * the session from the list.
+	 */
+	schedule();
+	mutex_lock(&sess_lock);
+}
+
+static struct rnbd_clt_session *__find_and_get_sess(const char *sessname)
+	__releases(&sess_lock)
+	__acquires(&sess_lock)
+{
+	struct rnbd_clt_session *sess, *sn;
+	int err;
+
+again:
+	list_for_each_entry_safe(sess, sn, &sess_list, list) {
+		if (strcmp(sessname, sess->sessname))
+			continue;
+
+		if (sess->rtrs_ready && IS_ERR_OR_NULL(sess->rtrs))
+			/*
+			 * No RTRS connection, session is dying.
+			 */
+			continue;
+
+		if (rnbd_clt_get_sess(sess)) {
+			/*
+			 * Alive session is found, wait for RTRS connection.
+			 */
+			mutex_unlock(&sess_lock);
+			err = wait_for_rtrs_connection(sess);
+			if (err)
+				rnbd_clt_put_sess(sess);
+			mutex_lock(&sess_lock);
+
+			if (err)
+				/* Session is dying, repeat the loop */
+				goto again;
+
+			return sess;
+		}
+		/*
+		 * Ref is 0, session is dying, wait for RTRS disconnect
+		 * in order to avoid session names clashes.
+		 */
+		wait_for_rtrs_disconnection(sess);
+		/*
+		 * RTRS is disconnected and soon session will be freed,
+		 * so repeat a loop.
+		 */
+		goto again;
+	}
+
+	return NULL;
+}
+
+static struct
+rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
+{
+	struct rnbd_clt_session *sess = NULL;
+
+	mutex_lock(&sess_lock);
+	sess = __find_and_get_sess(sessname);
+	if (!sess) {
+		sess = alloc_sess(sessname);
+		if (IS_ERR(sess)) {
+			mutex_unlock(&sess_lock);
+			return sess;
+		}
+		list_add(&sess->list, &sess_list);
+		*first = true;
+	} else
+		*first = false;
+	mutex_unlock(&sess_lock);
+
+	return sess;
+}
+
+static int rnbd_client_open(struct block_device *block_device, fmode_t mode)
+{
+	struct rnbd_clt_dev *dev = block_device->bd_disk->private_data;
+
+	if (dev->read_only && (mode & FMODE_WRITE))
+		return -EPERM;
+
+	if (dev->dev_state == DEV_STATE_UNMAPPED ||
+	    !rnbd_clt_get_dev(dev))
+		return -EIO;
+
+	return 0;
+}
+
+static void rnbd_client_release(struct gendisk *gen, fmode_t mode)
+{
+	struct rnbd_clt_dev *dev = gen->private_data;
+
+	rnbd_clt_put_dev(dev);
+}
+
+static int rnbd_client_getgeo(struct block_device *block_device,
+			      struct hd_geometry *geo)
+{
+	u64 size;
+	struct rnbd_clt_dev *dev;
+
+	dev = block_device->bd_disk->private_data;
+	size = dev->size * (dev->logical_block_size / SECTOR_SIZE);
+	geo->cylinders	= size >> 6;	/* size/64 */
+	geo->heads	= 4;
+	geo->sectors	= 16;
+	geo->start	= 0;
+
+	return 0;
+}
+
+static const struct block_device_operations rnbd_client_ops = {
+	.owner		= THIS_MODULE,
+	.open		= rnbd_client_open,
+	.release	= rnbd_client_release,
+	.getgeo		= rnbd_client_getgeo
+};
+
+/* The amount of data that belongs to an I/O and the amount of data that
+ * should be read or written to the disk (bi_size) can differ.
+ *
+ * E.g. When WRITE_SAME is used, only a small amount of data is
+ * transferred that is then written repeatedly over a lot of sectors.
+ *
+ * Get the size of data to be transferred via RTRS by summing up the size
+ * of the scather-gather list entries.
+ */
+static size_t rnbd_clt_get_sg_size(struct scatterlist *sglist, u32 len)
+{
+	struct scatterlist *sg;
+	size_t tsize = 0;
+	int i;
+
+	for_each_sg(sglist, sg, len, i)
+		tsize += sg->length;
+	return tsize;
+}
+
+static int rnbd_client_xfer_request(struct rnbd_clt_dev *dev,
+				     struct request *rq,
+				     struct rnbd_iu *iu)
+{
+	struct rtrs_clt *rtrs = dev->sess->rtrs;
+	struct rtrs_permit *permit = iu->permit;
+	struct rnbd_msg_io msg;
+	struct rtrs_clt_req_ops req_ops;
+	unsigned int sg_cnt = 0;
+	struct kvec vec;
+	size_t size;
+	int err;
+
+	iu->rq		= rq;
+	iu->dev		= dev;
+	msg.sector	= cpu_to_le64(blk_rq_pos(rq));
+	msg.bi_size	= cpu_to_le32(blk_rq_bytes(rq));
+	msg.rw		= cpu_to_le32(rq_to_rnbd_flags(rq));
+	msg.prio	= cpu_to_le16(req_get_ioprio(rq));
+
+	/*
+	 * We only support discards with single segment for now.
+	 * See queue limits.
+	 */
+	if (req_op(rq) != REQ_OP_DISCARD)
+		sg_cnt = blk_rq_map_sg(dev->queue, rq, iu->sglist);
+
+	if (sg_cnt == 0)
+		/* Do not forget to mark the end */
+		sg_mark_end(&iu->sglist[0]);
+
+	msg.hdr.type	= cpu_to_le16(RNBD_MSG_IO);
+	msg.device_id	= cpu_to_le32(dev->device_id);
+
+	vec = (struct kvec) {
+		.iov_base = &msg,
+		.iov_len  = sizeof(msg)
+	};
+	size = rnbd_clt_get_sg_size(iu->sglist, sg_cnt);
+	req_ops = (struct rtrs_clt_req_ops) {
+		.priv = iu,
+		.conf_fn = msg_io_conf,
+	};
+	err = rtrs_clt_request(rq_data_dir(rq), &req_ops, rtrs, permit,
+			       &vec, 1, size, iu->sglist, sg_cnt);
+	if (unlikely(err)) {
+		rnbd_clt_err_rl(dev, "RTRS failed to transfer IO, err: %d\n",
+				 err);
+		return err;
+	}
+
+	return 0;
+}
+
+/**
+ * rnbd_clt_dev_add_to_requeue() - add device to requeue if session is busy
+ * @dev:	Device to be checked
+ * @q:		Queue to be added to the requeue list if required
+ *
+ * Description:
+ *     If session is busy, that means someone will requeue us when resources
+ *     are freed.  If session is not doing anything - device is not added to
+ *     the list and @false is returned.
+ */
+static bool rnbd_clt_dev_add_to_requeue(struct rnbd_clt_dev *dev,
+						struct rnbd_queue *q)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+	struct rnbd_cpu_qlist *cpu_q;
+	unsigned long flags;
+	bool added = true;
+	bool need_set;
+
+	cpu_q = get_cpu_ptr(sess->cpu_queues);
+	spin_lock_irqsave(&cpu_q->requeue_lock, flags);
+
+	if (likely(!test_and_set_bit_lock(0, &q->in_list))) {
+		if (WARN_ON(!list_empty(&q->requeue_list)))
+			goto unlock;
+
+		need_set = !test_bit(cpu_q->cpu, sess->cpu_queues_bm);
+		if (need_set) {
+			set_bit(cpu_q->cpu, sess->cpu_queues_bm);
+			/* Paired with rnbd_put_permit(). Set a bit first
+			 * and then observe the busy counter.
+			 */
+			smp_mb__before_atomic();
+		}
+		if (likely(atomic_read(&sess->busy))) {
+			list_add_tail(&q->requeue_list, &cpu_q->requeue_list);
+		} else {
+			/* Very unlikely, but possible: busy counter was
+			 * observed as zero.  Drop all bits and return
+			 * false to restart the queue by ourselves.
+			 */
+			if (need_set)
+				clear_bit(cpu_q->cpu, sess->cpu_queues_bm);
+			clear_bit_unlock(0, &q->in_list);
+			added = false;
+		}
+	}
+unlock:
+	spin_unlock_irqrestore(&cpu_q->requeue_lock, flags);
+	put_cpu_ptr(sess->cpu_queues);
+
+	return added;
+}
+
+static void rnbd_clt_dev_kick_mq_queue(struct rnbd_clt_dev *dev,
+					struct blk_mq_hw_ctx *hctx,
+					int delay)
+{
+	struct rnbd_queue *q = hctx->driver_data;
+
+	if (delay != RNBD_DELAY_IFBUSY)
+		blk_mq_delay_run_hw_queue(hctx, delay);
+	else if (unlikely(!rnbd_clt_dev_add_to_requeue(dev, q)))
+		/*
+		 * If session is not busy we have to restart
+		 * the queue ourselves.
+		 */
+		blk_mq_delay_run_hw_queue(hctx, 10/*ms*/);
+}
+
+static blk_status_t rnbd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				   const struct blk_mq_queue_data *bd)
+{
+	struct request *rq = bd->rq;
+	struct rnbd_clt_dev *dev = rq->rq_disk->private_data;
+	struct rnbd_iu *iu = blk_mq_rq_to_pdu(rq);
+	int err;
+
+	if (unlikely(dev->dev_state != DEV_STATE_MAPPED))
+		return BLK_STS_IOERR;
+
+	iu->permit = rnbd_get_permit(dev->sess, RTRS_IO_CON,
+				      RTRS_PERMIT_NOWAIT);
+	if (unlikely(!iu->permit)) {
+		rnbd_clt_dev_kick_mq_queue(dev, hctx, RNBD_DELAY_IFBUSY);
+		return BLK_STS_RESOURCE;
+	}
+
+	blk_mq_start_request(rq);
+	err = rnbd_client_xfer_request(dev, rq, iu);
+	if (likely(err == 0))
+		return BLK_STS_OK;
+	if (unlikely(err == -EAGAIN || err == -ENOMEM)) {
+		rnbd_clt_dev_kick_mq_queue(dev, hctx, 10/*ms*/);
+		rnbd_put_permit(dev->sess, iu->permit);
+		return BLK_STS_RESOURCE;
+	}
+
+	rnbd_put_permit(dev->sess, iu->permit);
+	return BLK_STS_IOERR;
+}
+
+static int rnbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
+			      unsigned int hctx_idx, unsigned int numa_node)
+{
+	struct rnbd_iu *iu = blk_mq_rq_to_pdu(rq);
+
+	sg_init_table(iu->sglist, BMAX_SEGMENTS);
+	return 0;
+}
+
+static struct blk_mq_ops rnbd_mq_ops = {
+	.queue_rq	= rnbd_queue_rq,
+	.init_request	= rnbd_init_request,
+	.complete	= rnbd_softirq_done_fn,
+};
+
+static int setup_mq_tags(struct rnbd_clt_session *sess)
+{
+	struct blk_mq_tag_set *tag_set = &sess->tag_set;
+
+	memset(tag_set, 0, sizeof(*tag_set));
+	tag_set->ops		= &rnbd_mq_ops;
+	tag_set->queue_depth	= sess->queue_depth;
+	tag_set->numa_node		= NUMA_NO_NODE;
+	tag_set->flags		= BLK_MQ_F_SHOULD_MERGE |
+				  BLK_MQ_F_TAG_SHARED;
+	tag_set->cmd_size		= sizeof(struct rnbd_iu);
+	tag_set->nr_hw_queues	= num_online_cpus();
+
+	return blk_mq_alloc_tag_set(tag_set);
+}
+
+static struct rnbd_clt_session *
+find_and_get_or_create_sess(const char *sessname,
+			    const struct rtrs_addr *paths,
+			    size_t path_cnt, u16 port_nr)
+{
+	struct rnbd_clt_session *sess;
+	struct rtrs_attrs attrs;
+	int err;
+	bool first;
+	struct rtrs_clt_ops rtrs_ops;
+
+	sess = find_or_create_sess(sessname, &first);
+	if (sess == ERR_PTR(-ENOMEM))
+		return ERR_PTR(-ENOMEM);
+	else if (!first)
+		return sess;
+
+	rtrs_ops = (struct rtrs_clt_ops) {
+		.priv = sess,
+		.link_ev = rnbd_clt_link_ev,
+	};
+	/*
+	 * Nothing was found, establish rtrs connection and proceed further.
+	 */
+	sess->rtrs = rtrs_clt_open(&rtrs_ops, sessname,
+				   paths, path_cnt, port_nr,
+				   sizeof(struct rnbd_iu),
+				   RECONNECT_DELAY, BMAX_SEGMENTS,
+				   BLK_MAX_SEGMENT_SIZE,
+				   MAX_RECONNECTS);
+	if (IS_ERR(sess->rtrs)) {
+		err = PTR_ERR(sess->rtrs);
+		goto wake_up_and_put;
+	}
+	rtrs_clt_query(sess->rtrs, &attrs);
+	sess->max_io_size = attrs.max_io_size;
+	sess->queue_depth = attrs.queue_depth;
+
+	err = setup_mq_tags(sess);
+	if (err)
+		goto close_rtrs;
+
+	err = send_msg_sess_info(sess, WAIT);
+	if (err)
+		goto close_rtrs;
+
+	wake_up_rtrs_waiters(sess);
+
+	return sess;
+
+close_rtrs:
+	close_rtrs(sess);
+put_sess:
+	rnbd_clt_put_sess(sess);
+
+	return ERR_PTR(err);
+
+wake_up_and_put:
+	wake_up_rtrs_waiters(sess);
+	goto put_sess;
+}
+
+static inline void rnbd_init_hw_queue(struct rnbd_clt_dev *dev,
+				       struct rnbd_queue *q,
+				       struct blk_mq_hw_ctx *hctx)
+{
+	INIT_LIST_HEAD(&q->requeue_list);
+	q->dev  = dev;
+	q->hctx = hctx;
+}
+
+static void rnbd_init_mq_hw_queues(struct rnbd_clt_dev *dev)
+{
+	int i;
+	struct blk_mq_hw_ctx *hctx;
+	struct rnbd_queue *q;
+
+	queue_for_each_hw_ctx(dev->queue, hctx, i) {
+		q = &dev->hw_queues[i];
+		rnbd_init_hw_queue(dev, q, hctx);
+		hctx->driver_data = q;
+	}
+}
+
+static int setup_mq_dev(struct rnbd_clt_dev *dev)
+{
+	dev->queue = blk_mq_init_queue(&dev->sess->tag_set);
+	if (IS_ERR(dev->queue)) {
+		rnbd_clt_err(dev, "Initializing multiqueue queue failed, err: %ld\n",
+			      PTR_ERR(dev->queue));
+		return PTR_ERR(dev->queue);
+	}
+	rnbd_init_mq_hw_queues(dev);
+	return 0;
+}
+
+static void setup_request_queue(struct rnbd_clt_dev *dev)
+{
+	blk_queue_logical_block_size(dev->queue, dev->logical_block_size);
+	blk_queue_physical_block_size(dev->queue, dev->physical_block_size);
+	blk_queue_max_hw_sectors(dev->queue, dev->max_hw_sectors);
+	blk_queue_max_write_same_sectors(dev->queue,
+					 dev->max_write_same_sectors);
+
+	/*
+	 * we don't support discards to "discontiguous" segments
+	 * in on request
+	 */
+	blk_queue_max_discard_segments(dev->queue, 1);
+
+	blk_queue_max_discard_sectors(dev->queue, dev->max_discard_sectors);
+	dev->queue->limits.discard_granularity	= dev->discard_granularity;
+	dev->queue->limits.discard_alignment	= dev->discard_alignment;
+	if (dev->max_discard_sectors)
+		blk_queue_flag_set(QUEUE_FLAG_DISCARD, dev->queue);
+	if (dev->secure_discard)
+		blk_queue_flag_set(QUEUE_FLAG_SECERASE, dev->queue);
+
+	blk_queue_flag_set(QUEUE_FLAG_SAME_COMP, dev->queue);
+	blk_queue_flag_set(QUEUE_FLAG_SAME_FORCE, dev->queue);
+	blk_queue_max_segments(dev->queue, dev->max_segments);
+	blk_queue_io_opt(dev->queue, dev->sess->max_io_size);
+	blk_queue_virt_boundary(dev->queue, SZ_4K - 1);
+	blk_queue_write_cache(dev->queue, true, true);
+	dev->queue->queuedata = dev;
+}
+
+static void rnbd_clt_setup_gen_disk(struct rnbd_clt_dev *dev, int idx)
+{
+	dev->gd->major		= rnbd_client_major;
+	dev->gd->first_minor	= idx << RNBD_PART_BITS;
+	dev->gd->fops		= &rnbd_client_ops;
+	dev->gd->queue		= dev->queue;
+	dev->gd->private_data	= dev;
+	snprintf(dev->gd->disk_name, sizeof(dev->gd->disk_name), "rnbd%d",
+		 idx);
+	pr_debug("disk_name=%s, capacity=%zu\n",
+		 dev->gd->disk_name,
+		 dev->nsectors * (dev->logical_block_size / SECTOR_SIZE)
+		 );
+
+	set_capacity(dev->gd, dev->nsectors);
+
+	if (dev->access_mode == RNBD_ACCESS_RO) {
+		dev->read_only = true;
+		set_disk_ro(dev->gd, true);
+	} else {
+		dev->read_only = false;
+	}
+
+	if (!dev->rotational)
+		blk_queue_flag_set(QUEUE_FLAG_NONROT, dev->queue);
+}
+
+static int rnbd_client_setup_device(struct rnbd_clt_session *sess,
+				     struct rnbd_clt_dev *dev, int idx)
+{
+	int err;
+
+	dev->size = dev->nsectors * dev->logical_block_size;
+
+	err = setup_mq_dev(dev);
+	if (err)
+		return err;
+
+	setup_request_queue(dev);
+
+	dev->gd = alloc_disk_node(1 << RNBD_PART_BITS,	NUMA_NO_NODE);
+	if (!dev->gd) {
+		blk_cleanup_queue(dev->queue);
+		return -ENOMEM;
+	}
+
+	rnbd_clt_setup_gen_disk(dev, idx);
+
+	return 0;
+}
+
+static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
+				      enum rnbd_access_mode access_mode,
+				      const char *pathname)
+{
+	struct rnbd_clt_dev *dev;
+	int ret;
+
+	dev = kzalloc_node(sizeof(*dev), GFP_KERNEL, NUMA_NO_NODE);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	dev->hw_queues = kcalloc(nr_cpu_ids, sizeof(*dev->hw_queues),
+				 GFP_KERNEL);
+	if (!dev->hw_queues) {
+		ret = -ENOMEM;
+		goto out_alloc;
+	}
+
+	mutex_lock(&ida_lock);
+	ret = ida_simple_get(&index_ida, 0, 1 << (MINORBITS - RNBD_PART_BITS),
+			     GFP_KERNEL);
+	mutex_unlock(&ida_lock);
+	if (ret < 0) {
+		pr_err("Failed to initialize device '%s' from session %s, allocating idr failed, err: %d\n",
+		       pathname, sess->sessname, ret);
+		goto out_queues;
+	}
+	dev->clt_device_id	= ret;
+	dev->sess		= sess;
+	dev->access_mode	= access_mode;
+	strlcpy(dev->pathname, pathname, sizeof(dev->pathname));
+	mutex_init(&dev->lock);
+	refcount_set(&dev->refcount, 1);
+	dev->dev_state = DEV_STATE_INIT;
+
+	/*
+	 * Here we called from sysfs entry, thus clt-sysfs is
+	 * responsible that session will not disappear.
+	 */
+	WARN_ON(!rnbd_clt_get_sess(sess));
+
+	return dev;
+
+out_queues:
+	kfree(dev->hw_queues);
+out_alloc:
+	kfree(dev);
+	return ERR_PTR(ret);
+}
+
+static bool __exists_dev(const char *pathname)
+{
+	struct rnbd_clt_session *sess;
+	struct rnbd_clt_dev *dev;
+	bool found = false;
+
+	list_for_each_entry(sess, &sess_list, list) {
+		mutex_lock(&sess->lock);
+		list_for_each_entry(dev, &sess->devs_list, list) {
+			if (!strncmp(dev->pathname, pathname,
+				     sizeof(dev->pathname))) {
+				found = true;
+				break;
+			}
+		}
+		mutex_unlock(&sess->lock);
+		if (found)
+			break;
+	}
+
+	return found;
+}
+
+static bool exists_devpath(const char *pathname)
+{
+	bool found;
+
+	mutex_lock(&sess_lock);
+	found = __exists_dev(pathname);
+	mutex_unlock(&sess_lock);
+
+	return found;
+}
+
+static bool insert_dev_if_not_exists_devpath(const char *pathname,
+					     struct rnbd_clt_session *sess,
+					     struct rnbd_clt_dev *dev)
+{
+	bool found;
+
+	mutex_lock(&sess_lock);
+	found = __exists_dev(pathname);
+	if (!found) {
+		mutex_lock(&sess->lock);
+		list_add_tail(&dev->list, &sess->devs_list);
+		mutex_unlock(&sess->lock);
+	}
+	mutex_unlock(&sess_lock);
+
+	return found;
+}
+
+static void delete_dev(struct rnbd_clt_dev *dev)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+
+	mutex_lock(&sess->lock);
+	list_del(&dev->list);
+	mutex_unlock(&sess->lock);
+}
+
+struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
+					   struct rtrs_addr *paths,
+					   size_t path_cnt, u16 port_nr,
+					   const char *pathname,
+					   enum rnbd_access_mode access_mode)
+{
+	struct rnbd_clt_session *sess;
+	struct rnbd_clt_dev *dev;
+	int ret;
+
+	if (exists_devpath(pathname))
+		return ERR_PTR(-EEXIST);
+
+	sess = find_and_get_or_create_sess(sessname, paths, path_cnt, port_nr);
+	if (IS_ERR(sess))
+		return ERR_CAST(sess);
+
+	dev = init_dev(sess, access_mode, pathname);
+	if (IS_ERR(dev)) {
+		pr_err("map_device: failed to map device '%s' from session %s, can't initialize device, err: %ld\n",
+		       pathname, sess->sessname, PTR_ERR(dev));
+		ret = PTR_ERR(dev);
+		goto put_sess;
+	}
+	if (insert_dev_if_not_exists_devpath(pathname, sess, dev)) {
+		ret = -EEXIST;
+		goto put_dev;
+	}
+	ret = send_msg_open(dev, WAIT);
+	if (ret) {
+		rnbd_clt_err(dev,
+			      "map_device: failed, can't open remote device, err: %d\n",
+			      ret);
+		goto del_dev;
+	}
+	mutex_lock(&dev->lock);
+	pr_debug("Opened remote device: session=%s, path='%s'\n",
+		 sess->sessname, pathname);
+	ret = rnbd_client_setup_device(sess, dev, dev->clt_device_id);
+	if (ret) {
+		rnbd_clt_err(dev,
+			      "map_device: Failed to configure device, err: %d\n",
+			      ret);
+		mutex_unlock(&dev->lock);
+		goto del_dev;
+	}
+
+	rnbd_clt_info(dev,
+		       "map_device: Device mapped as %s (nsectors: %zu, logical_block_size: %d, physical_block_size: %d, max_write_same_sectors: %d, max_discard_sectors: %d, discard_granularity: %d, discard_alignment: %d, secure_discard: %d, max_segments: %d, max_hw_sectors: %d, rotational: %d)\n",
+		       dev->gd->disk_name, dev->nsectors,
+		       dev->logical_block_size, dev->physical_block_size,
+		       dev->max_write_same_sectors, dev->max_discard_sectors,
+		       dev->discard_granularity, dev->discard_alignment,
+		       dev->secure_discard, dev->max_segments,
+		       dev->max_hw_sectors, dev->rotational);
+
+	mutex_unlock(&dev->lock);
+
+	add_disk(dev->gd);
+	rnbd_clt_put_sess(sess);
+
+	return dev;
+
+del_dev:
+	delete_dev(dev);
+put_dev:
+	rnbd_clt_put_dev(dev);
+put_sess:
+	rnbd_clt_put_sess(sess);
+
+	return ERR_PTR(ret);
+}
+
+static void destroy_gen_disk(struct rnbd_clt_dev *dev)
+{
+	del_gendisk(dev->gd);
+	blk_cleanup_queue(dev->queue);
+	put_disk(dev->gd);
+}
+
+static void destroy_sysfs(struct rnbd_clt_dev *dev,
+			  const struct attribute *sysfs_self)
+{
+	rnbd_clt_remove_dev_symlink(dev);
+	if (dev->kobj.state_initialized) {
+		if (sysfs_self)
+			/* To avoid deadlock firstly remove itself */
+			sysfs_remove_file_self(&dev->kobj, sysfs_self);
+		kobject_del(&dev->kobj);
+		kobject_put(&dev->kobj);
+	}
+}
+
+int rnbd_clt_unmap_device(struct rnbd_clt_dev *dev, bool force,
+			   const struct attribute *sysfs_self)
+{
+	struct rnbd_clt_session *sess = dev->sess;
+	int refcount, ret = 0;
+	bool was_mapped;
+
+	mutex_lock(&dev->lock);
+	if (dev->dev_state == DEV_STATE_UNMAPPED) {
+		rnbd_clt_info(dev, "Device is already being unmapped\n");
+		ret = -EALREADY;
+		goto err;
+	}
+	refcount = refcount_read(&dev->refcount);
+	if (!force && refcount > 1) {
+		rnbd_clt_err(dev,
+			      "Closing device failed, device is in use, (%d device users)\n",
+			      refcount - 1);
+		ret = -EBUSY;
+		goto err;
+	}
+	was_mapped = (dev->dev_state == DEV_STATE_MAPPED);
+	dev->dev_state = DEV_STATE_UNMAPPED;
+	mutex_unlock(&dev->lock);
+
+	delete_dev(dev);
+	destroy_sysfs(dev, sysfs_self);
+	destroy_gen_disk(dev);
+	if (was_mapped && sess->rtrs)
+		send_msg_close(dev, dev->device_id, WAIT);
+
+	rnbd_clt_info(dev, "Device is unmapped\n");
+
+	/* Likely last reference put */
+	rnbd_clt_put_dev(dev);
+
+	/*
+	 * Here device and session can be vanished!
+	 */
+
+	return 0;
+err:
+	mutex_unlock(&dev->lock);
+
+	return ret;
+}
+
+int rnbd_clt_remap_device(struct rnbd_clt_dev *dev)
+{
+	int err;
+
+	mutex_lock(&dev->lock);
+	if (dev->dev_state == DEV_STATE_MAPPED_DISCONNECTED)
+		err = 0;
+	else if (dev->dev_state == DEV_STATE_UNMAPPED)
+		err = -ENODEV;
+	else if (dev->dev_state == DEV_STATE_MAPPED)
+		err = -EALREADY;
+	else
+		err = -EBUSY;
+	mutex_unlock(&dev->lock);
+	if (!err) {
+		rnbd_clt_info(dev, "Remapping device.\n");
+		err = send_msg_open(dev, WAIT);
+		if (err)
+			rnbd_clt_err(dev, "remap_device: %d\n", err);
+	}
+
+	return err;
+}
+
+static void unmap_device_work(struct work_struct *work)
+{
+	struct rnbd_clt_dev *dev;
+
+	dev = container_of(work, typeof(*dev), unmap_on_rmmod_work);
+	rnbd_clt_unmap_device(dev, true, NULL);
+}
+
+static void rnbd_destroy_sessions(void)
+{
+	struct rnbd_clt_session *sess, *sn;
+	struct rnbd_clt_dev *dev, *tn;
+
+	/* Firstly forbid access through sysfs interface */
+	rnbd_clt_destroy_default_group();
+	rnbd_clt_destroy_sysfs_files();
+
+	/*
+	 * Here at this point there is no any concurrent access to sessions
+	 * list and devices list:
+	 *   1. New session or device can'be be created - session sysfs files
+	 *      are removed.
+	 *   2. Device or session can't be removed - module reference is taken
+	 *      into account in unmap device sysfs callback.
+	 *   3. No IO requests inflight - each file open of block_dev increases
+	 *      module reference in get_disk().
+	 *
+	 * But still there can be user requests inflights, which are sent by
+	 * asynchronous send_msg_*() functions, thus before unmapping devices
+	 * RTRS session must be explicitly closed.
+	 */
+
+	list_for_each_entry_safe(sess, sn, &sess_list, list) {
+		WARN_ON(!rnbd_clt_get_sess(sess));
+		close_rtrs(sess);
+		list_for_each_entry_safe(dev, tn, &sess->devs_list, list) {
+			/*
+			 * Here unmap happens in parallel for only one reason:
+			 * blk_cleanup_queue() takes around half a second, so
+			 * on huge amount of devices the whole module unload
+			 * procedure takes minutes.
+			 */
+			INIT_WORK(&dev->unmap_on_rmmod_work, unmap_device_work);
+			queue_work(system_long_wq, &dev->unmap_on_rmmod_work);
+		}
+		rnbd_clt_put_sess(sess);
+	}
+	/* Wait for all scheduled unmap works */
+	flush_workqueue(system_long_wq);
+	WARN_ON(!list_empty(&sess_list));
+}
+
+static int __init rnbd_client_init(void)
+{
+	int err = 0;
+
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_hdr) != 4);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info) != 36);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info_rsp) != 36);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_open) != 264);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_close) != 8);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_open_rsp) != 56);
+	rnbd_client_major = register_blkdev(rnbd_client_major, "rnbd");
+	if (rnbd_client_major <= 0) {
+		pr_err("Failed to load module, block device registration failed\n");
+		return -EBUSY;
+	}
+
+	err = rnbd_clt_create_sysfs_files();
+	if (err) {
+		pr_err("Failed to load module, creating sysfs device files failed, err: %d\n",
+		       err);
+		unregister_blkdev(rnbd_client_major, "rnbd");
+	}
+
+	return err;
+}
+
+static void __exit rnbd_client_exit(void)
+{
+	rnbd_destroy_sessions();
+	unregister_blkdev(rnbd_client_major, "rnbd");
+	ida_destroy(&index_ida);
+}
+
+module_init(rnbd_client_init);
+module_exit(rnbd_client_exit);
diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h
new file mode 100644
index 000000000000..ed33654aa486
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-clt.h
@@ -0,0 +1,156 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+
+#ifndef RNBD_CLT_H
+#define RNBD_CLT_H
+
+#include <linux/wait.h>
+#include <linux/in.h>
+#include <linux/inet.h>
+#include <linux/blk-mq.h>
+#include <linux/refcount.h>
+
+#include <rtrs.h>
+#include "rnbd-proto.h"
+#include "rnbd-log.h"
+
+/* Max. number of segments per IO request, Mellanox Connect X ~ Connect X5,
+ * choose minimial 30 for all, minus 1 for internal protocol, so 29.
+ */
+#define BMAX_SEGMENTS 29
+/*  time in seconds between reconnect tries, default to 30 s */
+#define RECONNECT_DELAY 30
+/*
+ * Number of times to reconnect on error before giving up, 0 for * disabled,
+ * -1 for forever
+ */
+#define MAX_RECONNECTS -1
+
+enum rnbd_clt_dev_state {
+	DEV_STATE_INIT,
+	DEV_STATE_MAPPED,
+	DEV_STATE_MAPPED_DISCONNECTED,
+	DEV_STATE_UNMAPPED,
+};
+
+struct rnbd_iu_comp {
+	wait_queue_head_t wait;
+	int errno;
+};
+
+struct rnbd_iu {
+	union {
+		struct request *rq; /* for block io */
+		void *buf; /* for user messages */
+	};
+	struct rtrs_permit	*permit;
+	union {
+		/* use to send msg associated with a dev */
+		struct rnbd_clt_dev *dev;
+		/* use to send msg associated with a sess */
+		struct rnbd_clt_session *sess;
+	};
+	struct scatterlist	sglist[BMAX_SEGMENTS];
+	struct work_struct	work;
+	int			errno;
+	struct rnbd_iu_comp	comp;
+	atomic_t		refcount;
+};
+
+struct rnbd_cpu_qlist {
+	struct list_head	requeue_list;
+	spinlock_t		requeue_lock;
+	unsigned int		cpu;
+};
+
+struct rnbd_clt_session {
+	struct list_head        list;
+	struct rtrs_clt        *rtrs;
+	wait_queue_head_t       rtrs_waitq;
+	bool                    rtrs_ready;
+	struct rnbd_cpu_qlist	__percpu
+				*cpu_queues;
+	DECLARE_BITMAP(cpu_queues_bm, NR_CPUS);
+	int	__percpu	*cpu_rr; /* per-cpu var for CPU round-robin */
+	atomic_t		busy;
+	int			queue_depth;
+	u32			max_io_size;
+	struct blk_mq_tag_set	tag_set;
+	struct mutex		lock; /* protects state and devs_list */
+	struct list_head        devs_list; /* list of struct rnbd_clt_dev */
+	refcount_t		refcount;
+	char			sessname[NAME_MAX];
+	u8			ver; /* protocol version */
+};
+
+/**
+ * Submission queues.
+ */
+struct rnbd_queue {
+	struct list_head	requeue_list;
+	unsigned long		in_list;
+	struct rnbd_clt_dev	*dev;
+	struct blk_mq_hw_ctx	*hctx;
+};
+
+struct rnbd_clt_dev {
+	struct rnbd_clt_session	*sess;
+	struct request_queue	*queue;
+	struct rnbd_queue	*hw_queues;
+	u32			device_id;
+	/* local Idr index - used to track minor number allocations. */
+	u32			clt_device_id;
+	struct mutex		lock;
+	enum rnbd_clt_dev_state	dev_state;
+	char			pathname[NAME_MAX];
+	enum rnbd_access_mode	access_mode;
+	bool			read_only;
+	bool			rotational;
+	u32			max_hw_sectors;
+	u32			max_write_same_sectors;
+	u32			max_discard_sectors;
+	u32			discard_granularity;
+	u32			discard_alignment;
+	u16			secure_discard;
+	u16			physical_block_size;
+	u16			logical_block_size;
+	u16			max_segments;
+	size_t			nsectors;
+	u64			size;		/* device size in bytes */
+	struct list_head        list;
+	struct gendisk		*gd;
+	struct kobject		kobj;
+	char			blk_symlink_name[NAME_MAX];
+	refcount_t		refcount;
+	struct work_struct	unmap_on_rmmod_work;
+};
+
+/* rnbd-clt.c */
+
+struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
+					   struct rtrs_addr *paths,
+					   size_t path_cnt, u16 port_nr,
+					   const char *pathname,
+					   enum rnbd_access_mode access_mode);
+int rnbd_clt_unmap_device(struct rnbd_clt_dev *dev, bool force,
+			   const struct attribute *sysfs_self);
+
+int rnbd_clt_remap_device(struct rnbd_clt_dev *dev);
+int rnbd_clt_resize_disk(struct rnbd_clt_dev *dev, size_t newsize);
+
+/* rnbd-clt-sysfs.c */
+
+int rnbd_clt_create_sysfs_files(void);
+
+void rnbd_clt_destroy_sysfs_files(void);
+void rnbd_clt_destroy_default_group(void);
+
+void rnbd_clt_remove_dev_symlink(struct rnbd_clt_dev *dev);
+
+#endif /* RNBD_CLT_H */
diff --git a/drivers/block/rnbd/rnbd-common.c b/drivers/block/rnbd/rnbd-common.c
new file mode 100644
index 000000000000..596c3f732403
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-common.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#include "rnbd-proto.h"
+
+const char *rnbd_access_mode_str(enum rnbd_access_mode mode)
+{
+	switch (mode) {
+	case RNBD_ACCESS_RO:
+		return "ro";
+	case RNBD_ACCESS_RW:
+		return "rw";
+	case RNBD_ACCESS_MIGRATION:
+		return "migration";
+	default:
+		return "unknown";
+	}
+}
diff --git a/drivers/block/rnbd/rnbd-log.h b/drivers/block/rnbd/rnbd-log.h
new file mode 100644
index 000000000000..136e7d6c3451
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-log.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#ifndef RNBD_LOG_H
+#define RNBD_LOG_H
+
+#include "rnbd-clt.h"
+#include "rnbd-srv.h"
+
+#define rnbd_clt_log(fn, dev, fmt, ...) (				\
+		fn("<%s@%s> " fmt, (dev)->pathname,			\
+		(dev)->sess->sessname,					\
+		   ##__VA_ARGS__))
+#define rnbd_srv_log(fn, dev, fmt, ...) (				\
+			fn("<%s@%s>: " fmt, (dev)->pathname,		\
+			   (dev)->sess->sessname, ##__VA_ARGS__))
+
+#define rnbd_clt_err(dev, fmt, ...)	\
+	rnbd_clt_log(pr_err, dev, fmt, ##__VA_ARGS__)
+#define rnbd_clt_err_rl(dev, fmt, ...)	\
+	rnbd_clt_log(pr_err_ratelimited, dev, fmt, ##__VA_ARGS__)
+#define rnbd_clt_info(dev, fmt, ...) \
+	rnbd_clt_log(pr_info, dev, fmt, ##__VA_ARGS__)
+#define rnbd_clt_info_rl(dev, fmt, ...) \
+	rnbd_clt_log(pr_info_ratelimited, dev, fmt, ##__VA_ARGS__)
+
+#define rnbd_srv_err(dev, fmt, ...)	\
+	rnbd_srv_log(pr_err, dev, fmt, ##__VA_ARGS__)
+#define rnbd_srv_err_rl(dev, fmt, ...)	\
+	rnbd_srv_log(pr_err_ratelimited, dev, fmt, ##__VA_ARGS__)
+#define rnbd_srv_info(dev, fmt, ...) \
+	rnbd_srv_log(pr_info, dev, fmt, ##__VA_ARGS__)
+#define rnbd_srv_info_rl(dev, fmt, ...) \
+	rnbd_srv_log(pr_info_ratelimited, dev, fmt, ##__VA_ARGS__)
+
+#endif /* RNBD_LOG_H */
diff --git a/drivers/block/rnbd/rnbd-proto.h b/drivers/block/rnbd/rnbd-proto.h
new file mode 100644
index 000000000000..ca166241452c
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-proto.h
@@ -0,0 +1,303 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#ifndef RNBD_PROTO_H
+#define RNBD_PROTO_H
+
+#include <linux/types.h>
+#include <linux/blkdev.h>
+#include <linux/limits.h>
+#include <linux/inet.h>
+#include <linux/in.h>
+#include <linux/in6.h>
+#include <rdma/ib.h>
+
+#define RNBD_PROTO_VER_MAJOR 2
+#define RNBD_PROTO_VER_MINOR 0
+
+/* The default port number the RTRS server is listening on. */
+#define RTRS_PORT 1234
+
+/**
+ * enum rnbd_msg_types - RNBD message types
+ * @RNBD_MSG_SESS_INFO:	initial session info from client to server
+ * @RNBD_MSG_SESS_INFO_RSP:	initial session info from server to client
+ * @RNBD_MSG_OPEN:		open (map) device request
+ * @RNBD_MSG_OPEN_RSP:		response to an @RNBD_MSG_OPEN
+ * @RNBD_MSG_IO:		block IO request operation
+ * @RNBD_MSG_CLOSE:		close (unmap) device request
+ */
+enum rnbd_msg_type {
+	RNBD_MSG_SESS_INFO,
+	RNBD_MSG_SESS_INFO_RSP,
+	RNBD_MSG_OPEN,
+	RNBD_MSG_OPEN_RSP,
+	RNBD_MSG_IO,
+	RNBD_MSG_CLOSE,
+};
+
+/**
+ * struct rnbd_msg_hdr - header of RNBD messages
+ * @type:	Message type, valid values see: enum rnbd_msg_types
+ */
+struct rnbd_msg_hdr {
+	__le16		type;
+	__le16		__padding;
+};
+
+/**
+ * We allow to map RO many times and RW only once. We allow to map yet another
+ * time RW, if MIGRATION is provided (second RW export can be required for
+ * example for VM migration)
+ */
+enum rnbd_access_mode {
+	RNBD_ACCESS_RO,
+	RNBD_ACCESS_RW,
+	RNBD_ACCESS_MIGRATION,
+};
+
+/**
+ * struct rnbd_msg_sess_info - initial session info from client to server
+ * @hdr:		message header
+ * @ver:		RNBD protocol version
+ */
+struct rnbd_msg_sess_info {
+	struct rnbd_msg_hdr hdr;
+	u8		ver;
+	u8		reserved[31];
+};
+
+/**
+ * struct rnbd_msg_sess_info_rsp - initial session info from server to client
+ * @hdr:		message header
+ * @ver:		RNBD protocol version
+ */
+struct rnbd_msg_sess_info_rsp {
+	struct rnbd_msg_hdr hdr;
+	u8		ver;
+	u8		reserved[31];
+};
+
+/**
+ * struct rnbd_msg_open - request to open a remote device.
+ * @hdr:		message header
+ * @access_mode:	the mode to open remote device, valid values see:
+ *			enum rnbd_access_mode
+ * @device_name:	device path on remote side
+ */
+struct rnbd_msg_open {
+	struct rnbd_msg_hdr hdr;
+	u8		access_mode;
+	u8		resv1;
+	s8		dev_name[NAME_MAX];
+	u8		reserved[3];
+};
+
+/**
+ * struct rnbd_msg_close - request to close a remote device.
+ * @hdr:	message header
+ * @device_id:	device_id on server side to identify the device
+ */
+struct rnbd_msg_close {
+	struct rnbd_msg_hdr hdr;
+	__le32		device_id;
+};
+
+/**
+ * struct rnbd_msg_open_rsp - response message to RNBD_MSG_OPEN
+ * @hdr:		message header
+ * @device_id:		device_id on server side to identify the device
+ * @nsectors:		number of sectors in the usual 512b unit
+ * @max_hw_sectors:	max hardware sectors in the usual 512b unit
+ * @max_write_same_sectors: max sectors for WRITE SAME in the 512b unit
+ * @max_discard_sectors: max. sectors that can be discarded at once in 512b
+ * unit.
+ * @discard_granularity: size of the internal discard allocation unit in bytes
+ * @discard_alignment: offset from internal allocation assignment in bytes
+ * @physical_block_size: physical block size device supports in bytes
+ * @logical_block_size: logical block size device supports in bytes
+ * @max_segments:	max segments hardware support in one transfer
+ * @secure_discard:	supports secure discard
+ * @rotation:		is a rotational disc?
+ */
+struct rnbd_msg_open_rsp {
+	struct rnbd_msg_hdr	hdr;
+	__le32			device_id;
+	__le64			nsectors;
+	__le32			max_hw_sectors;
+	__le32			max_write_same_sectors;
+	__le32			max_discard_sectors;
+	__le32			discard_granularity;
+	__le32			discard_alignment;
+	__le16			physical_block_size;
+	__le16			logical_block_size;
+	__le16			max_segments;
+	__le16			secure_discard;
+	u8			rotational;
+	u8			reserved[11];
+};
+
+/**
+ * struct rnbd_msg_io - message for I/O read/write
+ * @hdr:	message header
+ * @device_id:	device_id on server side to find the right device
+ * @sector:	bi_sector attribute from struct bio
+ * @rw:		valid values are defined in enum rnbd_io_flags
+ * @bi_size:    number of bytes for I/O read/write
+ * @prio:       priority
+ */
+struct rnbd_msg_io {
+	struct rnbd_msg_hdr hdr;
+	__le32		device_id;
+	__le64		sector;
+	__le32		rw;
+	__le32		bi_size;
+	__le16		prio;
+};
+
+#define RNBD_OP_BITS  8
+#define RNBD_OP_MASK  ((1 << RNBD_OP_BITS) - 1)
+
+/**
+ * enum rnbd_io_flags - RNBD request types from rq_flag_bits
+ * @RNBD_OP_READ:	     read sectors from the device
+ * @RNBD_OP_WRITE:	     write sectors to the device
+ * @RNBD_OP_FLUSH:	     flush the volatile write cache
+ * @RNBD_OP_DISCARD:        discard sectors
+ * @RNBD_OP_SECURE_ERASE:   securely erase sectors
+ * @RNBD_OP_WRITE_SAME:     write the same sectors many times
+
+ * @RNBD_F_SYNC:	     request is sync (sync write or read)
+ * @RNBD_F_FUA:             forced unit access
+ */
+enum rnbd_io_flags {
+
+	/* Operations */
+
+	RNBD_OP_READ		= 0,
+	RNBD_OP_WRITE		= 1,
+	RNBD_OP_FLUSH		= 2,
+	RNBD_OP_DISCARD	= 3,
+	RNBD_OP_SECURE_ERASE	= 4,
+	RNBD_OP_WRITE_SAME	= 5,
+
+	RNBD_OP_LAST,
+
+	/* Flags */
+
+	RNBD_F_SYNC  = 1<<(RNBD_OP_BITS + 0),
+	RNBD_F_FUA   = 1<<(RNBD_OP_BITS + 1),
+
+	RNBD_F_ALL   = (RNBD_F_SYNC | RNBD_F_FUA)
+
+};
+
+static inline u32 rnbd_op(u32 flags)
+{
+	return flags & RNBD_OP_MASK;
+}
+
+static inline u32 rnbd_flags(u32 flags)
+{
+	return flags & ~RNBD_OP_MASK;
+}
+
+static inline bool rnbd_flags_supported(u32 flags)
+{
+	u32 op;
+
+	op = rnbd_op(flags);
+	flags = rnbd_flags(flags);
+
+	if (op >= RNBD_OP_LAST)
+		return false;
+	if (flags & ~RNBD_F_ALL)
+		return false;
+
+	return true;
+}
+
+static inline u32 rnbd_to_bio_flags(u32 rnbd_opf)
+{
+	u32 bio_opf;
+
+	switch (rnbd_op(rnbd_opf)) {
+	case RNBD_OP_READ:
+		bio_opf = REQ_OP_READ;
+		break;
+	case RNBD_OP_WRITE:
+		bio_opf = REQ_OP_WRITE;
+		break;
+	case RNBD_OP_FLUSH:
+		bio_opf = REQ_OP_FLUSH | REQ_PREFLUSH;
+		break;
+	case RNBD_OP_DISCARD:
+		bio_opf = REQ_OP_DISCARD;
+		break;
+	case RNBD_OP_SECURE_ERASE:
+		bio_opf = REQ_OP_SECURE_ERASE;
+		break;
+	case RNBD_OP_WRITE_SAME:
+		bio_opf = REQ_OP_WRITE_SAME;
+		break;
+	default:
+		WARN(1, "Unknown RNBD type: %d (flags %d)\n",
+		     rnbd_op(rnbd_opf), rnbd_opf);
+		bio_opf = 0;
+	}
+
+	if (rnbd_opf & RNBD_F_SYNC)
+		bio_opf |= REQ_SYNC;
+
+	if (rnbd_opf & RNBD_F_FUA)
+		bio_opf |= REQ_FUA;
+
+	return bio_opf;
+}
+
+static inline u32 rq_to_rnbd_flags(struct request *rq)
+{
+	u32 rnbd_opf;
+
+	switch (req_op(rq)) {
+	case REQ_OP_READ:
+		rnbd_opf = RNBD_OP_READ;
+		break;
+	case REQ_OP_WRITE:
+		rnbd_opf = RNBD_OP_WRITE;
+		break;
+	case REQ_OP_DISCARD:
+		rnbd_opf = RNBD_OP_DISCARD;
+		break;
+	case REQ_OP_SECURE_ERASE:
+		rnbd_opf = RNBD_OP_SECURE_ERASE;
+		break;
+	case REQ_OP_WRITE_SAME:
+		rnbd_opf = RNBD_OP_WRITE_SAME;
+		break;
+	case REQ_OP_FLUSH:
+		rnbd_opf = RNBD_OP_FLUSH;
+		break;
+	default:
+		WARN(1, "Unknown request type %d (flags %llu)\n",
+		     req_op(rq), (unsigned long long)rq->cmd_flags);
+		rnbd_opf = 0;
+	}
+
+	if (op_is_sync(rq->cmd_flags))
+		rnbd_opf |= RNBD_F_SYNC;
+
+	if (op_is_flush(rq->cmd_flags))
+		rnbd_opf |= RNBD_F_FUA;
+
+	return rnbd_opf;
+}
+
+const char *rnbd_access_mode_str(enum rnbd_access_mode mode);
+
+#endif /* RNBD_PROTO_H */
diff --git a/drivers/block/rnbd/rnbd-srv-dev.c b/drivers/block/rnbd/rnbd-srv-dev.c
new file mode 100644
index 000000000000..5eddfd29ab64
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-srv-dev.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#undef pr_fmt
+#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
+
+#include "rnbd-srv-dev.h"
+#include "rnbd-log.h"
+
+struct rnbd_dev *rnbd_dev_open(const char *path, fmode_t flags,
+			       struct bio_set *bs)
+{
+	struct rnbd_dev *dev;
+	int ret;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	dev->blk_open_flags = flags;
+	dev->bdev = blkdev_get_by_path(path, flags, THIS_MODULE);
+	ret = PTR_ERR_OR_ZERO(dev->bdev);
+	if (ret)
+		goto err;
+
+	dev->blk_open_flags = flags;
+	bdevname(dev->bdev, dev->name);
+	dev->ibd_bio_set = bs;
+
+	return dev;
+
+err:
+	kfree(dev);
+	return ERR_PTR(ret);
+}
+
+void rnbd_dev_close(struct rnbd_dev *dev)
+{
+	blkdev_put(dev->bdev, dev->blk_open_flags);
+	kfree(dev);
+}
+
+static void rnbd_dev_bi_end_io(struct bio *bio)
+{
+	struct rnbd_dev_blk_io *io = bio->bi_private;
+
+	rnbd_endio(io->priv, blk_status_to_errno(bio->bi_status));
+	bio_put(bio);
+}
+
+/**
+ *	rnbd_bio_map_kern	-	map kernel address into bio
+ *	@data: pointer to buffer to map
+ *	@bs: bio_set to use.
+ *	@len: length in bytes
+ *	@gfp_mask: allocation flags for bio allocation
+ *
+ *	Map the kernel address into a bio suitable for io to a block
+ *	device. Returns an error pointer in case of error.
+ */
+static struct bio *rnbd_bio_map_kern(void *data, struct bio_set *bs,
+				     unsigned int len, gfp_t gfp_mask)
+{
+	unsigned long kaddr = (unsigned long)data;
+	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	unsigned long start = kaddr >> PAGE_SHIFT;
+	const int nr_pages = end - start;
+	int offset, i;
+	struct bio *bio;
+
+	bio = bio_alloc_bioset(gfp_mask, nr_pages, bs);
+	if (!bio)
+		return ERR_PTR(-ENOMEM);
+
+	offset = offset_in_page(kaddr);
+	for (i = 0; i < nr_pages; i++) {
+		unsigned int bytes = PAGE_SIZE - offset;
+
+		if (len <= 0)
+			break;
+
+		if (bytes > len)
+			bytes = len;
+
+		if (bio_add_page(bio, virt_to_page(data), bytes,
+				    offset) < bytes) {
+			/* we don't support partial mappings */
+			bio_put(bio);
+			return ERR_PTR(-EINVAL);
+		}
+
+		data += bytes;
+		len -= bytes;
+		offset = 0;
+	}
+
+	bio->bi_end_io = bio_put;
+	return bio;
+}
+
+int rnbd_dev_submit_io(struct rnbd_dev *dev, sector_t sector, void *data,
+		       size_t len, u32 bi_size, enum rnbd_io_flags flags,
+		       short prio, void *priv)
+{
+	struct rnbd_dev_blk_io *io;
+	struct bio *bio;
+
+	/* Generate bio with pages pointing to the rdma buffer */
+	bio = rnbd_bio_map_kern(data, dev->ibd_bio_set, len, GFP_KERNEL);
+	if (IS_ERR(bio))
+		return PTR_ERR(bio);
+
+	io = container_of(bio, struct rnbd_dev_blk_io, bio);
+
+	io->dev	= dev;
+	io->priv = priv;
+
+	bio->bi_end_io = rnbd_dev_bi_end_io;
+	bio->bi_private	= io;
+	bio->bi_opf = rnbd_to_bio_flags(flags);
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_iter.bi_size = bi_size;
+	bio_set_prio(bio, prio);
+	bio_set_dev(bio, dev->bdev);
+
+	submit_bio(bio);
+
+	return 0;
+}
diff --git a/drivers/block/rnbd/rnbd-srv-dev.h b/drivers/block/rnbd/rnbd-srv-dev.h
new file mode 100644
index 000000000000..0f65b09a270e
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-srv-dev.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#ifndef RNBD_SRV_DEV_H
+#define RNBD_SRV_DEV_H
+
+#include <linux/fs.h>
+#include "rnbd-proto.h"
+
+struct rnbd_dev {
+	struct block_device	*bdev;
+	struct bio_set		*ibd_bio_set;
+	fmode_t			blk_open_flags;
+	char			name[BDEVNAME_SIZE];
+};
+
+struct rnbd_dev_blk_io {
+	struct rnbd_dev *dev;
+	void		 *priv;
+	/* have to be last member for front_pad usage of bioset_init */
+	struct bio	bio;
+};
+
+/**
+ * rnbd_dev_open() - Open a device
+ * @flags:	open flags
+ * @bs:		bio_set to use during block io,
+ */
+struct rnbd_dev *rnbd_dev_open(const char *path, fmode_t flags,
+			       struct bio_set *bs);
+
+/**
+ * rnbd_dev_close() - Close a device
+ */
+void rnbd_dev_close(struct rnbd_dev *dev);
+
+void rnbd_endio(void *priv, int error);
+
+static inline int rnbd_dev_get_max_segs(const struct rnbd_dev *dev)
+{
+	return queue_max_segments(bdev_get_queue(dev->bdev));
+}
+
+static inline int rnbd_dev_get_max_hw_sects(const struct rnbd_dev *dev)
+{
+	return queue_max_hw_sectors(bdev_get_queue(dev->bdev));
+}
+
+static inline int rnbd_dev_get_secure_discard(const struct rnbd_dev *dev)
+{
+	return blk_queue_secure_erase(bdev_get_queue(dev->bdev));
+}
+
+static inline int rnbd_dev_get_max_discard_sects(const struct rnbd_dev *dev)
+{
+	if (!blk_queue_discard(bdev_get_queue(dev->bdev)))
+		return 0;
+
+	return blk_queue_get_max_sectors(bdev_get_queue(dev->bdev),
+					 REQ_OP_DISCARD);
+}
+
+static inline int rnbd_dev_get_discard_granularity(const struct rnbd_dev *dev)
+{
+	return bdev_get_queue(dev->bdev)->limits.discard_granularity;
+}
+
+static inline int rnbd_dev_get_discard_alignment(const struct rnbd_dev *dev)
+{
+	return bdev_get_queue(dev->bdev)->limits.discard_alignment;
+}
+
+/**
+ * rnbd_dev_submit_io() - Submit an I/O to the disk
+ * @dev:	device to that the I/O is submitted
+ * @sector:	address to read/write data to
+ * @data:	I/O data to write or buffer to read I/O date into
+ * @len:	length of @data
+ * @bi_size:	Amount of data that will be read/written
+ * @prio:       IO priority
+ * @priv:	private data passed to @io_fn
+ */
+int rnbd_dev_submit_io(struct rnbd_dev *dev, sector_t sector, void *data,
+			size_t len, u32 bi_size, enum rnbd_io_flags flags,
+			short prio, void *priv);
+
+#endif /* RNBD_SRV_DEV_H */
diff --git a/drivers/block/rnbd/rnbd-srv-sysfs.c b/drivers/block/rnbd/rnbd-srv-sysfs.c
new file mode 100644
index 000000000000..106775c074d1
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-srv-sysfs.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#undef pr_fmt
+#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
+
+#include <uapi/linux/limits.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
+#include <linux/stat.h>
+#include <linux/genhd.h>
+#include <linux/list.h>
+#include <linux/moduleparam.h>
+#include <linux/device.h>
+
+#include "rnbd-srv.h"
+
+static struct device *rnbd_dev;
+static struct class *rnbd_dev_class;
+static struct kobject *rnbd_devs_kobj;
+
+static void rnbd_srv_dev_release(struct kobject *kobj)
+{
+	struct rnbd_srv_dev *dev;
+
+	dev = container_of(kobj, struct rnbd_srv_dev, dev_kobj);
+
+	kfree(dev);
+}
+
+static struct kobj_type dev_ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
+	.release = rnbd_srv_dev_release
+};
+
+int rnbd_srv_create_dev_sysfs(struct rnbd_srv_dev *dev,
+			       struct block_device *bdev,
+			       const char *dev_name)
+{
+	struct kobject *bdev_kobj;
+	int ret;
+
+	ret = kobject_init_and_add(&dev->dev_kobj, &dev_ktype,
+				   rnbd_devs_kobj, dev_name);
+	if (ret)
+		return ret;
+
+	dev->dev_sessions_kobj = kobject_create_and_add("sessions",
+							&dev->dev_kobj);
+	if (!dev->dev_sessions_kobj)
+		goto put_dev_kobj;
+
+	bdev_kobj = &disk_to_dev(bdev->bd_disk)->kobj;
+	ret = sysfs_create_link(&dev->dev_kobj, bdev_kobj, "block_dev");
+	if (ret)
+		goto put_sess_kobj;
+
+	return 0;
+
+put_sess_kobj:
+	kobject_put(dev->dev_sessions_kobj);
+put_dev_kobj:
+	kobject_put(&dev->dev_kobj);
+	return ret;
+}
+
+void rnbd_srv_destroy_dev_sysfs(struct rnbd_srv_dev *dev)
+{
+	sysfs_remove_link(&dev->dev_kobj, "block_dev");
+	kobject_del(dev->dev_sessions_kobj);
+	kobject_put(dev->dev_sessions_kobj);
+	kobject_del(&dev->dev_kobj);
+	kobject_put(&dev->dev_kobj);
+}
+
+static ssize_t read_only_show(struct kobject *kobj, struct kobj_attribute *attr,
+			      char *page)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
+
+	return scnprintf(page, PAGE_SIZE, "%d\n",
+			 !(sess_dev->open_flags & FMODE_WRITE));
+}
+
+static struct kobj_attribute rnbd_srv_dev_session_ro_attr =
+	__ATTR_RO(read_only);
+
+static ssize_t access_mode_show(struct kobject *kobj,
+				struct kobj_attribute *attr,
+				char *page)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
+
+	return scnprintf(page, PAGE_SIZE, "%s\n",
+			 rnbd_access_mode_str(sess_dev->access_mode));
+}
+
+static struct kobj_attribute rnbd_srv_dev_session_access_mode_attr =
+	__ATTR_RO(access_mode);
+
+static ssize_t mapping_path_show(struct kobject *kobj,
+				 struct kobj_attribute *attr, char *page)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
+
+	return scnprintf(page, PAGE_SIZE, "%s\n", sess_dev->pathname);
+}
+
+static struct kobj_attribute rnbd_srv_dev_session_mapping_path_attr =
+	__ATTR_RO(mapping_path);
+
+static struct attribute *rnbd_srv_default_dev_sessions_attrs[] = {
+	&rnbd_srv_dev_session_access_mode_attr.attr,
+	&rnbd_srv_dev_session_ro_attr.attr,
+	&rnbd_srv_dev_session_mapping_path_attr.attr,
+	NULL,
+};
+
+static struct attribute_group rnbd_srv_default_dev_session_attr_group = {
+	.attrs = rnbd_srv_default_dev_sessions_attrs,
+};
+
+void rnbd_srv_destroy_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev)
+{
+	sysfs_remove_group(&sess_dev->kobj,
+			   &rnbd_srv_default_dev_session_attr_group);
+
+	kobject_del(&sess_dev->kobj);
+	kobject_put(&sess_dev->kobj);
+}
+
+static void rnbd_srv_sess_dev_release(struct kobject *kobj)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = container_of(kobj, struct rnbd_srv_sess_dev, kobj);
+	rnbd_destroy_sess_dev(sess_dev);
+}
+
+static struct kobj_type rnbd_srv_sess_dev_ktype = {
+	.sysfs_ops	= &kobj_sysfs_ops,
+	.release	= rnbd_srv_sess_dev_release,
+};
+
+int rnbd_srv_create_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev)
+{
+	int ret;
+
+	ret = kobject_init_and_add(&sess_dev->kobj, &rnbd_srv_sess_dev_ktype,
+				   sess_dev->dev->dev_sessions_kobj, "%s",
+				   sess_dev->sess->sessname);
+	if (ret)
+		return ret;
+
+	ret = sysfs_create_group(&sess_dev->kobj,
+				 &rnbd_srv_default_dev_session_attr_group);
+	if (ret)
+		goto err;
+
+	return 0;
+
+err:
+	kobject_put(&sess_dev->kobj);
+
+	return ret;
+}
+
+int rnbd_srv_create_sysfs_files(void)
+{
+	int err;
+
+	rnbd_dev_class = class_create(THIS_MODULE, "rnbd-server");
+	if (IS_ERR(rnbd_dev_class))
+		return PTR_ERR(rnbd_dev_class);
+
+	rnbd_dev = device_create(rnbd_dev_class, NULL,
+				  MKDEV(0, 0), NULL, "ctl");
+	if (IS_ERR(rnbd_dev)) {
+		err = PTR_ERR(rnbd_dev);
+		goto cls_destroy;
+	}
+	rnbd_devs_kobj = kobject_create_and_add("devices", &rnbd_dev->kobj);
+	if (!rnbd_devs_kobj) {
+		err = -ENOMEM;
+		goto dev_destroy;
+	}
+
+	return 0;
+
+dev_destroy:
+	device_destroy(rnbd_dev_class, MKDEV(0, 0));
+cls_destroy:
+	class_destroy(rnbd_dev_class);
+
+	return err;
+}
+
+void rnbd_srv_destroy_sysfs_files(void)
+{
+	kobject_del(rnbd_devs_kobj);
+	kobject_put(rnbd_devs_kobj);
+	device_destroy(rnbd_dev_class, MKDEV(0, 0));
+	class_destroy(rnbd_dev_class);
+}
diff --git a/drivers/block/rnbd/rnbd-srv.c b/drivers/block/rnbd/rnbd-srv.c
new file mode 100644
index 000000000000..86e61523907b
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-srv.c
@@ -0,0 +1,844 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#undef pr_fmt
+#define pr_fmt(fmt) KBUILD_MODNAME " L" __stringify(__LINE__) ": " fmt
+
+#include <linux/module.h>
+#include <linux/blkdev.h>
+
+#include "rnbd-srv.h"
+#include "rnbd-srv-dev.h"
+
+MODULE_DESCRIPTION("RDMA Network Block Device Server");
+MODULE_LICENSE("GPL");
+
+static u16 port_nr = RTRS_PORT;
+
+module_param_named(port_nr, port_nr, ushort, 0444);
+MODULE_PARM_DESC(port_nr,
+		 "The port number the server is listening on (default: "
+		 __stringify(RTRS_PORT)")");
+
+#define DEFAULT_DEV_SEARCH_PATH "/"
+
+static char dev_search_path[PATH_MAX] = DEFAULT_DEV_SEARCH_PATH;
+
+static int dev_search_path_set(const char *val, const struct kernel_param *kp)
+{
+	const char *p = strrchr(val, '\n') ? : val + strlen(val);
+
+	if (strlen(val) >= sizeof(dev_search_path))
+		return -EINVAL;
+
+	snprintf(dev_search_path, sizeof(dev_search_path), "%.*s",
+		 (int)(p - val), val);
+
+	pr_info("dev_search_path changed to '%s'\n", dev_search_path);
+
+	return 0;
+}
+
+static struct kparam_string dev_search_path_kparam_str = {
+	.maxlen	= sizeof(dev_search_path),
+	.string	= dev_search_path
+};
+
+static const struct kernel_param_ops dev_search_path_ops = {
+	.set	= dev_search_path_set,
+	.get	= param_get_string,
+};
+
+module_param_cb(dev_search_path, &dev_search_path_ops,
+		&dev_search_path_kparam_str, 0444);
+MODULE_PARM_DESC(dev_search_path,
+		 "Sets the dev_search_path. When a device is mapped this path is prepended to the device path from the map device operation.  If %SESSNAME% is specified in a path, then device will be searched in a session namespace. (default: "
+		 DEFAULT_DEV_SEARCH_PATH ")");
+
+static DEFINE_MUTEX(sess_lock);
+static DEFINE_SPINLOCK(dev_lock);
+
+static LIST_HEAD(sess_list);
+static LIST_HEAD(dev_list);
+
+struct rnbd_io_private {
+	struct rtrs_srv_op		*id;
+	struct rnbd_srv_sess_dev	*sess_dev;
+};
+
+static void rnbd_sess_dev_release(struct kref *kref)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = container_of(kref, struct rnbd_srv_sess_dev, kref);
+	complete(sess_dev->destroy_comp);
+}
+
+static inline void rnbd_put_sess_dev(struct rnbd_srv_sess_dev *sess_dev)
+{
+	kref_put(&sess_dev->kref, rnbd_sess_dev_release);
+}
+
+void rnbd_endio(void *priv, int error)
+{
+	struct rnbd_io_private *rnbd_priv = priv;
+	struct rnbd_srv_sess_dev *sess_dev = rnbd_priv->sess_dev;
+
+	rnbd_put_sess_dev(sess_dev);
+
+	rtrs_srv_resp_rdma(rnbd_priv->id, error);
+
+	kfree(priv);
+}
+
+static struct rnbd_srv_sess_dev *
+rnbd_get_sess_dev(int dev_id, struct rnbd_srv_session *srv_sess)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+	int ret = 0;
+
+	rcu_read_lock();
+	sess_dev = xa_load(&srv_sess->index_idr, dev_id);
+	if (likely(sess_dev))
+		ret = kref_get_unless_zero(&sess_dev->kref);
+	rcu_read_unlock();
+
+	if (!sess_dev || !ret)
+		return ERR_PTR(-ENXIO);
+
+	return sess_dev;
+}
+
+static int process_rdma(struct rtrs_srv *sess,
+			struct rnbd_srv_session *srv_sess,
+			struct rtrs_srv_op *id, void *data, u32 datalen,
+			const void *usr, size_t usrlen)
+{
+	const struct rnbd_msg_io *msg = usr;
+	struct rnbd_io_private *priv;
+	struct rnbd_srv_sess_dev *sess_dev;
+	u32 dev_id;
+	int err;
+
+	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	dev_id = le32_to_cpu(msg->device_id);
+
+	sess_dev = rnbd_get_sess_dev(dev_id, srv_sess);
+	if (IS_ERR(sess_dev)) {
+		pr_err_ratelimited("Got I/O request on session %s for unknown device id %d\n",
+				   srv_sess->sessname, dev_id);
+		err = -ENOTCONN;
+		goto err;
+	}
+
+	priv->sess_dev = sess_dev;
+	priv->id = id;
+
+	err = rnbd_dev_submit_io(sess_dev->rnbd_dev, le64_to_cpu(msg->sector),
+				  data, datalen, le32_to_cpu(msg->bi_size),
+				  le32_to_cpu(msg->rw),
+				  srv_sess->ver < RNBD_PROTO_VER_MAJOR ||
+				  usrlen < sizeof(*msg) ?
+				  0 : le16_to_cpu(msg->prio), priv);
+	if (unlikely(err)) {
+		rnbd_srv_err(sess_dev, "Submitting I/O to device failed, err: %d\n",
+			      err);
+		goto sess_dev_put;
+	}
+
+	return 0;
+
+sess_dev_put:
+	rnbd_put_sess_dev(sess_dev);
+err:
+	kfree(priv);
+	return err;
+}
+
+static void destroy_device(struct rnbd_srv_dev *dev)
+{
+	WARN_ONCE(!list_empty(&dev->sess_dev_list),
+		  "Device %s is being destroyed but still in use!\n",
+		  dev->id);
+
+	spin_lock(&dev_lock);
+	list_del(&dev->list);
+	spin_unlock(&dev_lock);
+
+	mutex_destroy(&dev->lock);
+	if (dev->dev_kobj.state_in_sysfs)
+		/*
+		 * Destroy kobj only if it was really created.
+		 */
+		rnbd_srv_destroy_dev_sysfs(dev);
+	else
+		kfree(dev);
+}
+
+static void destroy_device_cb(struct kref *kref)
+{
+	struct rnbd_srv_dev *dev;
+
+	dev = container_of(kref, struct rnbd_srv_dev, kref);
+
+	destroy_device(dev);
+}
+
+static void rnbd_put_srv_dev(struct rnbd_srv_dev *dev)
+{
+	kref_put(&dev->kref, destroy_device_cb);
+}
+
+void rnbd_destroy_sess_dev(struct rnbd_srv_sess_dev *sess_dev)
+{
+	DECLARE_COMPLETION_ONSTACK(dc);
+
+	xa_erase(&sess_dev->sess->index_idr, sess_dev->device_id);
+	synchronize_rcu();
+	sess_dev->destroy_comp = &dc;
+	rnbd_put_sess_dev(sess_dev);
+	wait_for_completion(&dc); /* wait for inflights to drop to zero */
+
+	rnbd_dev_close(sess_dev->rnbd_dev);
+	list_del(&sess_dev->sess_list);
+	mutex_lock(&sess_dev->dev->lock);
+	list_del(&sess_dev->dev_list);
+	if (sess_dev->open_flags & FMODE_WRITE)
+		sess_dev->dev->open_write_cnt--;
+	mutex_unlock(&sess_dev->dev->lock);
+
+	rnbd_put_srv_dev(sess_dev->dev);
+
+	rnbd_srv_info(sess_dev, "Device closed\n");
+	kfree(sess_dev);
+}
+
+static void destroy_sess(struct rnbd_srv_session *srv_sess)
+{
+	struct rnbd_srv_sess_dev *sess_dev, *tmp;
+
+	if (list_empty(&srv_sess->sess_dev_list))
+		goto out;
+
+	mutex_lock(&srv_sess->lock);
+	list_for_each_entry_safe(sess_dev, tmp, &srv_sess->sess_dev_list,
+				 sess_list)
+		rnbd_srv_destroy_dev_session_sysfs(sess_dev);
+	mutex_unlock(&srv_sess->lock);
+
+out:
+	xa_destroy(&srv_sess->index_idr);
+	bioset_exit(&srv_sess->sess_bio_set);
+
+	pr_info("RTRS Session %s disconnected\n", srv_sess->sessname);
+
+	mutex_lock(&sess_lock);
+	list_del(&srv_sess->list);
+	mutex_unlock(&sess_lock);
+
+	mutex_destroy(&srv_sess->lock);
+	kfree(srv_sess);
+}
+
+static int create_sess(struct rtrs_srv *rtrs)
+{
+	struct rnbd_srv_session *srv_sess;
+	char sessname[NAME_MAX];
+	int err;
+
+	err = rtrs_srv_get_sess_name(rtrs, sessname, sizeof(sessname));
+	if (err) {
+		pr_err("rtrs_srv_get_sess_name(%s): %d\n", sessname, err);
+
+		return err;
+	}
+	srv_sess = kzalloc(sizeof(*srv_sess), GFP_KERNEL);
+	if (!srv_sess)
+		return -ENOMEM;
+
+	srv_sess->queue_depth = rtrs_srv_get_queue_depth(rtrs);
+	err = bioset_init(&srv_sess->sess_bio_set, srv_sess->queue_depth,
+			  offsetof(struct rnbd_dev_blk_io, bio),
+			  BIOSET_NEED_BVECS);
+	if (err) {
+		pr_err("Allocating srv_session for session %s failed\n",
+		       sessname);
+		kfree(srv_sess);
+		return err;
+	}
+
+	xa_init_flags(&srv_sess->index_idr, XA_FLAGS_ALLOC);
+	INIT_LIST_HEAD(&srv_sess->sess_dev_list);
+	mutex_init(&srv_sess->lock);
+	mutex_lock(&sess_lock);
+	list_add(&srv_sess->list, &sess_list);
+	mutex_unlock(&sess_lock);
+
+	srv_sess->rtrs = rtrs;
+	strlcpy(srv_sess->sessname, sessname, sizeof(srv_sess->sessname));
+
+	rtrs_srv_set_sess_priv(rtrs, srv_sess);
+
+	return 0;
+}
+
+static int rnbd_srv_link_ev(struct rtrs_srv *rtrs,
+			     enum rtrs_srv_link_ev ev, void *priv)
+{
+	struct rnbd_srv_session *srv_sess = priv;
+
+	switch (ev) {
+	case RTRS_SRV_LINK_EV_CONNECTED:
+		return create_sess(rtrs);
+
+	case RTRS_SRV_LINK_EV_DISCONNECTED:
+		if (WARN_ON_ONCE(!srv_sess))
+			return -EINVAL;
+
+		destroy_sess(srv_sess);
+		return 0;
+
+	default:
+		pr_warn("Received unknown RTRS session event %d from session %s\n",
+			ev, srv_sess->sessname);
+		return -EINVAL;
+	}
+}
+
+static int process_msg_close(struct rtrs_srv *rtrs,
+			     struct rnbd_srv_session *srv_sess,
+			     void *data, size_t datalen, const void *usr,
+			     size_t usrlen)
+{
+	const struct rnbd_msg_close *close_msg = usr;
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	sess_dev = rnbd_get_sess_dev(le32_to_cpu(close_msg->device_id),
+				      srv_sess);
+	if (IS_ERR(sess_dev))
+		return 0;
+
+	rnbd_put_sess_dev(sess_dev);
+	mutex_lock(&srv_sess->lock);
+	rnbd_srv_destroy_dev_session_sysfs(sess_dev);
+	mutex_unlock(&srv_sess->lock);
+	return 0;
+}
+
+static int process_msg_open(struct rtrs_srv *rtrs,
+			    struct rnbd_srv_session *srv_sess,
+			    const void *msg, size_t len,
+			    void *data, size_t datalen);
+
+static int process_msg_sess_info(struct rtrs_srv *rtrs,
+				 struct rnbd_srv_session *srv_sess,
+				 const void *msg, size_t len,
+				 void *data, size_t datalen);
+
+static int rnbd_srv_rdma_ev(struct rtrs_srv *rtrs, void *priv,
+			     struct rtrs_srv_op *id, int dir,
+			     void *data, size_t datalen, const void *usr,
+			     size_t usrlen)
+{
+	struct rnbd_srv_session *srv_sess = priv;
+	const struct rnbd_msg_hdr *hdr = usr;
+	int ret = 0;
+	u16 type;
+
+	if (WARN_ON_ONCE(!srv_sess))
+		return -ENODEV;
+
+	type = le16_to_cpu(hdr->type);
+
+	switch (type) {
+	case RNBD_MSG_IO:
+		return process_rdma(rtrs, srv_sess, id, data, datalen, usr,
+				    usrlen);
+	case RNBD_MSG_CLOSE:
+		ret = process_msg_close(rtrs, srv_sess, data, datalen,
+					usr, usrlen);
+		break;
+	case RNBD_MSG_OPEN:
+		ret = process_msg_open(rtrs, srv_sess, usr, usrlen,
+				       data, datalen);
+		break;
+	case RNBD_MSG_SESS_INFO:
+		ret = process_msg_sess_info(rtrs, srv_sess, usr, usrlen,
+					    data, datalen);
+		break;
+	default:
+		pr_warn("Received unexpected message type %d with dir %d from session %s\n",
+			type, dir, srv_sess->sessname);
+		return -EINVAL;
+	}
+
+	rtrs_srv_resp_rdma(id, ret);
+	return 0;
+}
+
+static struct rnbd_srv_sess_dev
+*rnbd_sess_dev_alloc(struct rnbd_srv_session *srv_sess)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+	int error;
+
+	sess_dev = kzalloc(sizeof(*sess_dev), GFP_KERNEL);
+	if (!sess_dev)
+		return ERR_PTR(-ENOMEM);
+
+	error = xa_alloc(&srv_sess->index_idr, &sess_dev->device_id, sess_dev,
+			 xa_limit_32b, GFP_NOWAIT);
+	if (error < 0) {
+		pr_warn("Allocating idr failed, err: %d\n", error);
+		kfree(sess_dev);
+		return ERR_PTR(error);
+	}
+
+	return sess_dev;
+}
+
+static struct rnbd_srv_dev *rnbd_srv_init_srv_dev(const char *id)
+{
+	struct rnbd_srv_dev *dev;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	strlcpy(dev->id, id, sizeof(dev->id));
+	kref_init(&dev->kref);
+	INIT_LIST_HEAD(&dev->sess_dev_list);
+	mutex_init(&dev->lock);
+
+	return dev;
+}
+
+static struct rnbd_srv_dev *
+rnbd_srv_find_or_add_srv_dev(struct rnbd_srv_dev *new_dev)
+{
+	struct rnbd_srv_dev *dev;
+
+	spin_lock(&dev_lock);
+	list_for_each_entry(dev, &dev_list, list) {
+		if (!strncmp(dev->id, new_dev->id, sizeof(dev->id))) {
+			if (!kref_get_unless_zero(&dev->kref))
+				/*
+				 * We lost the race, device is almost dead.
+				 *  Continue traversing to find a valid one.
+				 */
+				continue;
+			spin_unlock(&dev_lock);
+			return dev;
+		}
+	}
+	list_add(&new_dev->list, &dev_list);
+	spin_unlock(&dev_lock);
+
+	return new_dev;
+}
+
+static int rnbd_srv_check_update_open_perm(struct rnbd_srv_dev *srv_dev,
+					    struct rnbd_srv_session *srv_sess,
+					    enum rnbd_access_mode access_mode)
+{
+	int ret = -EPERM;
+
+	mutex_lock(&srv_dev->lock);
+
+	switch (access_mode) {
+	case RNBD_ACCESS_RO:
+		ret = 0;
+		break;
+	case RNBD_ACCESS_RW:
+		if (srv_dev->open_write_cnt == 0)  {
+			srv_dev->open_write_cnt++;
+			ret = 0;
+		} else {
+			pr_err("Mapping device '%s' for session %s with RW permissions failed. Device already opened as 'RW' by %d client(s), access mode %s.\n",
+			       srv_dev->id, srv_sess->sessname,
+			       srv_dev->open_write_cnt,
+			       rnbd_access_mode_str(access_mode));
+		}
+		break;
+	case RNBD_ACCESS_MIGRATION:
+		if (srv_dev->open_write_cnt < 2) {
+			srv_dev->open_write_cnt++;
+			ret = 0;
+		} else {
+			pr_err("Mapping device '%s' for session %s with migration permissions failed. Device already opened as 'RW' by %d client(s), access mode %s.\n",
+			       srv_dev->id, srv_sess->sessname,
+			       srv_dev->open_write_cnt,
+			       rnbd_access_mode_str(access_mode));
+		}
+		break;
+	default:
+		pr_err("Received mapping request for device '%s' on session %s with invalid access mode: %d\n",
+		       srv_dev->id, srv_sess->sessname, access_mode);
+		ret = -EINVAL;
+	}
+
+	mutex_unlock(&srv_dev->lock);
+
+	return ret;
+}
+
+static struct rnbd_srv_dev *
+rnbd_srv_get_or_create_srv_dev(struct rnbd_dev *rnbd_dev,
+				struct rnbd_srv_session *srv_sess,
+				enum rnbd_access_mode access_mode)
+{
+	int ret;
+	struct rnbd_srv_dev *new_dev, *dev;
+
+	new_dev = rnbd_srv_init_srv_dev(rnbd_dev->name);
+	if (IS_ERR(new_dev))
+		return new_dev;
+
+	dev = rnbd_srv_find_or_add_srv_dev(new_dev);
+	if (dev != new_dev)
+		kfree(new_dev);
+
+	ret = rnbd_srv_check_update_open_perm(dev, srv_sess, access_mode);
+	if (ret) {
+		rnbd_put_srv_dev(dev);
+		return ERR_PTR(ret);
+	}
+
+	return dev;
+}
+
+static void rnbd_srv_fill_msg_open_rsp(struct rnbd_msg_open_rsp *rsp,
+					struct rnbd_srv_sess_dev *sess_dev)
+{
+	struct rnbd_dev *rnbd_dev = sess_dev->rnbd_dev;
+
+	rsp->hdr.type = cpu_to_le16(RNBD_MSG_OPEN_RSP);
+	rsp->device_id =
+		cpu_to_le32(sess_dev->device_id);
+	rsp->nsectors =
+		cpu_to_le64(get_capacity(rnbd_dev->bdev->bd_disk));
+	rsp->logical_block_size	=
+		cpu_to_le16(bdev_logical_block_size(rnbd_dev->bdev));
+	rsp->physical_block_size =
+		cpu_to_le16(bdev_physical_block_size(rnbd_dev->bdev));
+	rsp->max_segments =
+		cpu_to_le16(rnbd_dev_get_max_segs(rnbd_dev));
+	rsp->max_hw_sectors =
+		cpu_to_le32(rnbd_dev_get_max_hw_sects(rnbd_dev));
+	rsp->max_write_same_sectors =
+		cpu_to_le32(bdev_write_same(rnbd_dev->bdev));
+	rsp->max_discard_sectors =
+		cpu_to_le32(rnbd_dev_get_max_discard_sects(rnbd_dev));
+	rsp->discard_granularity =
+		cpu_to_le32(rnbd_dev_get_discard_granularity(rnbd_dev));
+	rsp->discard_alignment =
+		cpu_to_le32(rnbd_dev_get_discard_alignment(rnbd_dev));
+	rsp->secure_discard =
+		cpu_to_le16(rnbd_dev_get_secure_discard(rnbd_dev));
+	rsp->rotational =
+		!blk_queue_nonrot(bdev_get_queue(rnbd_dev->bdev));
+}
+
+static struct rnbd_srv_sess_dev *
+rnbd_srv_create_set_sess_dev(struct rnbd_srv_session *srv_sess,
+			      const struct rnbd_msg_open *open_msg,
+			      struct rnbd_dev *rnbd_dev, fmode_t open_flags,
+			      struct rnbd_srv_dev *srv_dev)
+{
+	struct rnbd_srv_sess_dev *sdev = rnbd_sess_dev_alloc(srv_sess);
+
+	if (IS_ERR(sdev))
+		return sdev;
+
+	kref_init(&sdev->kref);
+
+	strlcpy(sdev->pathname, open_msg->dev_name, sizeof(sdev->pathname));
+
+	sdev->rnbd_dev		= rnbd_dev;
+	sdev->sess		= srv_sess;
+	sdev->dev		= srv_dev;
+	sdev->open_flags	= open_flags;
+	sdev->access_mode	= open_msg->access_mode;
+
+	return sdev;
+}
+
+static char *rnbd_srv_get_full_path(struct rnbd_srv_session *srv_sess,
+				     const char *dev_name)
+{
+	char *full_path;
+	char *a, *b;
+
+	full_path = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!full_path)
+		return ERR_PTR(-ENOMEM);
+
+	/*
+	 * Replace %SESSNAME% with a real session name in order to
+	 * create device namespace.
+	 */
+	a = strnstr(dev_search_path, "%SESSNAME%", sizeof(dev_search_path));
+	if (a) {
+		int len = a - dev_search_path;
+
+		len = snprintf(full_path, PATH_MAX, "%.*s/%s/%s", len,
+			       dev_search_path, srv_sess->sessname, dev_name);
+		if (len >= PATH_MAX) {
+			pr_err("Too long path: %s, %s, %s\n",
+			       dev_search_path, srv_sess->sessname, dev_name);
+			kfree(full_path);
+			return ERR_PTR(-EINVAL);
+		}
+	} else {
+		snprintf(full_path, PATH_MAX, "%s/%s",
+			 dev_search_path, dev_name);
+	}
+
+	/* eliminitate duplicated slashes */
+	a = strchr(full_path, '/');
+	b = a;
+	while (*b != '\0') {
+		if (*b == '/' && *a == '/') {
+			b++;
+		} else {
+			a++;
+			*a = *b;
+			b++;
+		}
+	}
+	a++;
+	*a = '\0';
+
+	return full_path;
+}
+
+static int process_msg_sess_info(struct rtrs_srv *rtrs,
+				 struct rnbd_srv_session *srv_sess,
+				 const void *msg, size_t len,
+				 void *data, size_t datalen)
+{
+	const struct rnbd_msg_sess_info *sess_info_msg = msg;
+	struct rnbd_msg_sess_info_rsp *rsp = data;
+
+	srv_sess->ver = min_t(u8, sess_info_msg->ver, RNBD_PROTO_VER_MAJOR);
+	pr_debug("Session %s using protocol version %d (client version: %d, server version: %d)\n",
+		 srv_sess->sessname, srv_sess->ver,
+		 sess_info_msg->ver, RNBD_PROTO_VER_MAJOR);
+
+	rsp->hdr.type = cpu_to_le16(RNBD_MSG_SESS_INFO_RSP);
+	rsp->ver = srv_sess->ver;
+
+	return 0;
+}
+
+/**
+ * find_srv_sess_dev() - a dev is already opened by this name
+ * @srv_sess:	the session to search.
+ * @dev_name:	string containing the name of the device.
+ *
+ * Return struct rnbd_srv_sess_dev if srv_sess already opened the dev_name
+ * NULL if the session didn't open the device yet.
+ */
+static struct rnbd_srv_sess_dev *
+find_srv_sess_dev(struct rnbd_srv_session *srv_sess, const char *dev_name)
+{
+	struct rnbd_srv_sess_dev *sess_dev;
+
+	if (list_empty(&srv_sess->sess_dev_list))
+		return NULL;
+
+	list_for_each_entry(sess_dev, &srv_sess->sess_dev_list, sess_list)
+		if (!strcmp(sess_dev->pathname, dev_name))
+			return sess_dev;
+
+	return NULL;
+}
+
+static int process_msg_open(struct rtrs_srv *rtrs,
+			    struct rnbd_srv_session *srv_sess,
+			    const void *msg, size_t len,
+			    void *data, size_t datalen)
+{
+	int ret;
+	struct rnbd_srv_dev *srv_dev;
+	struct rnbd_srv_sess_dev *srv_sess_dev;
+	const struct rnbd_msg_open *open_msg = msg;
+	fmode_t open_flags;
+	char *full_path;
+	struct rnbd_dev *rnbd_dev;
+	struct rnbd_msg_open_rsp *rsp = data;
+
+	pr_debug("Open message received: session='%s' path='%s' access_mode=%d\n",
+		 srv_sess->sessname, open_msg->dev_name,
+		 open_msg->access_mode);
+	open_flags = FMODE_READ;
+	if (open_msg->access_mode != RNBD_ACCESS_RO)
+		open_flags |= FMODE_WRITE;
+
+	mutex_lock(&srv_sess->lock);
+
+	srv_sess_dev = find_srv_sess_dev(srv_sess, open_msg->dev_name);
+	if (srv_sess_dev)
+		goto fill_response;
+
+	if ((strlen(dev_search_path) + strlen(open_msg->dev_name))
+	    >= PATH_MAX) {
+		pr_err("Opening device for session %s failed, device path too long. '%s/%s' is longer than PATH_MAX (%d)\n",
+		       srv_sess->sessname, dev_search_path, open_msg->dev_name,
+		       PATH_MAX);
+		ret = -EINVAL;
+		goto reject;
+	}
+	if (strstr(open_msg->dev_name, "..")) {
+		pr_err("Opening device for session %s failed, device path %s contains relative path ..\n",
+		       srv_sess->sessname, open_msg->dev_name);
+		ret = -EINVAL;
+		goto reject;
+	}
+	full_path = rnbd_srv_get_full_path(srv_sess, open_msg->dev_name);
+	if (IS_ERR(full_path)) {
+		ret = PTR_ERR(full_path);
+		pr_err("Opening device '%s' for client %s failed, failed to get device full path, err: %d\n",
+		       open_msg->dev_name, srv_sess->sessname, ret);
+		goto reject;
+	}
+
+	rnbd_dev = rnbd_dev_open(full_path, open_flags,
+				 &srv_sess->sess_bio_set);
+	if (IS_ERR(rnbd_dev)) {
+		pr_err("Opening device '%s' on session %s failed, failed to open the block device, err: %ld\n",
+		       full_path, srv_sess->sessname, PTR_ERR(rnbd_dev));
+		ret = PTR_ERR(rnbd_dev);
+		goto free_path;
+	}
+
+	srv_dev = rnbd_srv_get_or_create_srv_dev(rnbd_dev, srv_sess,
+						  open_msg->access_mode);
+	if (IS_ERR(srv_dev)) {
+		pr_err("Opening device '%s' on session %s failed, creating srv_dev failed, err: %ld\n",
+		       full_path, srv_sess->sessname, PTR_ERR(srv_dev));
+		ret = PTR_ERR(srv_dev);
+		goto rnbd_dev_close;
+	}
+
+	srv_sess_dev = rnbd_srv_create_set_sess_dev(srv_sess, open_msg,
+						     rnbd_dev, open_flags,
+						     srv_dev);
+	if (IS_ERR(srv_sess_dev)) {
+		pr_err("Opening device '%s' on session %s failed, creating sess_dev failed, err: %ld\n",
+		       full_path, srv_sess->sessname, PTR_ERR(srv_sess_dev));
+		ret = PTR_ERR(srv_sess_dev);
+		goto srv_dev_put;
+	}
+
+	/* Create the srv_dev sysfs files if they haven't been created yet. The
+	 * reason to delay the creation is not to create the sysfs files before
+	 * we are sure the device can be opened.
+	 */
+	mutex_lock(&srv_dev->lock);
+	if (!srv_dev->dev_kobj.state_in_sysfs) {
+		ret = rnbd_srv_create_dev_sysfs(srv_dev, rnbd_dev->bdev,
+						 rnbd_dev->name);
+		if (ret) {
+			mutex_unlock(&srv_dev->lock);
+			rnbd_srv_err(srv_sess_dev,
+				      "Opening device failed, failed to create device sysfs files, err: %d\n",
+				      ret);
+			goto free_srv_sess_dev;
+		}
+	}
+
+	ret = rnbd_srv_create_dev_session_sysfs(srv_sess_dev);
+	if (ret) {
+		mutex_unlock(&srv_dev->lock);
+		rnbd_srv_err(srv_sess_dev,
+			      "Opening device failed, failed to create dev client sysfs files, err: %d\n",
+			      ret);
+		goto free_srv_sess_dev;
+	}
+
+	list_add(&srv_sess_dev->dev_list, &srv_dev->sess_dev_list);
+	mutex_unlock(&srv_dev->lock);
+
+	list_add(&srv_sess_dev->sess_list, &srv_sess->sess_dev_list);
+
+	rnbd_srv_info(srv_sess_dev, "Opened device '%s'\n", srv_dev->id);
+
+	kfree(full_path);
+
+fill_response:
+	rnbd_srv_fill_msg_open_rsp(rsp, srv_sess_dev);
+	mutex_unlock(&srv_sess->lock);
+	return 0;
+
+free_srv_sess_dev:
+	xa_erase(&srv_sess->index_idr, srv_sess_dev->device_id);
+	synchronize_rcu();
+	kfree(srv_sess_dev);
+srv_dev_put:
+	if (open_msg->access_mode != RNBD_ACCESS_RO) {
+		mutex_lock(&srv_dev->lock);
+		srv_dev->open_write_cnt--;
+		mutex_unlock(&srv_dev->lock);
+	}
+	rnbd_put_srv_dev(srv_dev);
+rnbd_dev_close:
+	rnbd_dev_close(rnbd_dev);
+free_path:
+	kfree(full_path);
+reject:
+	mutex_unlock(&srv_sess->lock);
+	return ret;
+}
+
+static struct rtrs_srv_ctx *rtrs_ctx;
+
+static struct rtrs_srv_ops rtrs_ops;
+static int __init rnbd_srv_init_module(void)
+{
+	int err;
+
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_hdr) != 4);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info) != 36);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_sess_info_rsp) != 36);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_open) != 264);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_close) != 8);
+	BUILD_BUG_ON(sizeof(struct rnbd_msg_open_rsp) != 56);
+	rtrs_ops = (struct rtrs_srv_ops) {
+		.rdma_ev = rnbd_srv_rdma_ev,
+		.link_ev = rnbd_srv_link_ev,
+	};
+	rtrs_ctx = rtrs_srv_open(&rtrs_ops, port_nr);
+	if (IS_ERR(rtrs_ctx)) {
+		err = PTR_ERR(rtrs_ctx);
+		pr_err("rtrs_srv_open(), err: %d\n", err);
+		return err;
+	}
+
+	err = rnbd_srv_create_sysfs_files();
+	if (err) {
+		pr_err("rnbd_srv_create_sysfs_files(), err: %d\n", err);
+		rtrs_srv_close(rtrs_ctx);
+		return err;
+	}
+
+	return 0;
+}
+
+static void __exit rnbd_srv_cleanup_module(void)
+{
+	rtrs_srv_close(rtrs_ctx);
+	WARN_ON(!list_empty(&sess_list));
+	rnbd_srv_destroy_sysfs_files();
+}
+
+module_init(rnbd_srv_init_module);
+module_exit(rnbd_srv_cleanup_module);
diff --git a/drivers/block/rnbd/rnbd-srv.h b/drivers/block/rnbd/rnbd-srv.h
new file mode 100644
index 000000000000..5a8544b5e74f
--- /dev/null
+++ b/drivers/block/rnbd/rnbd-srv.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * RDMA Network Block Driver
+ *
+ * Copyright (c) 2014 - 2018 ProfitBricks GmbH. All rights reserved.
+ * Copyright (c) 2018 - 2019 1&1 IONOS Cloud GmbH. All rights reserved.
+ * Copyright (c) 2019 - 2020 1&1 IONOS SE. All rights reserved.
+ */
+#ifndef RNBD_SRV_H
+#define RNBD_SRV_H
+
+#include <linux/types.h>
+#include <linux/idr.h>
+#include <linux/kref.h>
+
+#include <rtrs.h>
+#include "rnbd-proto.h"
+#include "rnbd-log.h"
+
+struct rnbd_srv_session {
+	/* Entry inside global sess_list */
+	struct list_head        list;
+	struct rtrs_srv		*rtrs;
+	char			sessname[NAME_MAX];
+	int			queue_depth;
+	struct bio_set		sess_bio_set;
+
+	struct xarray		index_idr;
+	/* List of struct rnbd_srv_sess_dev */
+	struct list_head        sess_dev_list;
+	struct mutex		lock;
+	u8			ver;
+};
+
+struct rnbd_srv_dev {
+	/* Entry inside global dev_list */
+	struct list_head                list;
+	struct kobject                  dev_kobj;
+	struct kobject                  *dev_sessions_kobj;
+	struct kref                     kref;
+	char				id[NAME_MAX];
+	/* List of rnbd_srv_sess_dev structs */
+	struct list_head		sess_dev_list;
+	struct mutex			lock;
+	int				open_write_cnt;
+};
+
+/* Structure which binds N devices and N sessions */
+struct rnbd_srv_sess_dev {
+	/* Entry inside rnbd_srv_dev struct */
+	struct list_head		dev_list;
+	/* Entry inside rnbd_srv_session struct */
+	struct list_head		sess_list;
+	struct rnbd_dev			*rnbd_dev;
+	struct rnbd_srv_session		*sess;
+	struct rnbd_srv_dev		*dev;
+	struct kobject                  kobj;
+	u32                             device_id;
+	fmode_t                         open_flags;
+	struct kref			kref;
+	struct completion               *destroy_comp;
+	char				pathname[NAME_MAX];
+	enum rnbd_access_mode		access_mode;
+};
+
+/* rnbd-srv-sysfs.c */
+
+int rnbd_srv_create_dev_sysfs(struct rnbd_srv_dev *dev,
+			      struct block_device *bdev,
+			      const char *dir_name);
+void rnbd_srv_destroy_dev_sysfs(struct rnbd_srv_dev *dev);
+int rnbd_srv_create_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev);
+void rnbd_srv_destroy_dev_session_sysfs(struct rnbd_srv_sess_dev *sess_dev);
+int rnbd_srv_create_sysfs_files(void);
+void rnbd_srv_destroy_sysfs_files(void);
+void rnbd_destroy_sess_dev(struct rnbd_srv_sess_dev *sess_dev);
+
+#endif /* RNBD_SRV_H */