block/rnbd: a bit of documentation

README with description of major sysfs entries, sysfs documentation
are moved to ABI dir as Bart suggested.

Link: https://lore.kernel.org/r/20200511135131.27580-25-danil.kipnis@cloud.ionos.com
Signed-off-by: Danil Kipnis <danil.kipnis@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

3 files changed, 207 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-block-rnbd b/Documentation/ABI/testing/sysfs-block-rnbd
new file mode 100644
index 000000000000..8f070b47f361
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-block-rnbd
@@ -0,0 +1,46 @@
+What:		/sys/block/rnbd<N>/rnbd/unmap_device
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	To unmap a volume, "normal" or "force" has to be written to:
+		/sys/block/rnbd<N>/rnbd/unmap_device
+
+		When "normal" is used, the operation will fail with EBUSY if any process
+		is using the device.  When "force" is used, the device is also unmapped
+		when device is in use.  All I/Os that are in progress will fail.
+
+		Example:
+
+		# echo "normal" > /sys/block/rnbd0/rnbd/unmap_device
+
+What:		/sys/block/rnbd<N>/rnbd/state
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	The file contains the current state of the block device. The state file
+		returns "open" when the device is successfully mapped from the server
+		and accepting I/O requests. When the connection to the server gets
+		disconnected in case of an error (e.g. link failure), the state file
+		returns "closed" and all I/O requests submitted to it will fail with -EIO.
+
+What:		/sys/block/rnbd<N>/rnbd/session
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	RNBD uses RTRS session to transport the data between client and
+		server.  The entry "session" contains the name of the session, that
+		was used to establish the RTRS session.  It's the same name that
+		was passed as server parameter to the map_device entry.
+
+What:		/sys/block/rnbd<N>/rnbd/mapping_path
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the path that was passed as "device_path" to the map_device
+		operation.
+
+What:		/sys/block/rnbd<N>/rnbd/access_mode
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the device access mode: ro, rw or migration.
diff --git a/Documentation/ABI/testing/sysfs-class-rnbd-client b/Documentation/ABI/testing/sysfs-class-rnbd-client
new file mode 100644
index 000000000000..c084f203b41e
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rnbd-client
@@ -0,0 +1,111 @@
+What:		/sys/class/rnbd-client
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Provide information about RNBD-client.
+		All sysfs files that are not read-only provide the usage information on read:
+
+		Example:
+		# cat /sys/class/rnbd-client/ctl/map_device
+
+		> Usage: echo "sessname=<name of the rtrs session> path=<[srcaddr,]dstaddr>
+		> [path=<[srcaddr,]dstaddr>] device_path=<full path on remote side>
+		> [access_mode=<ro|rw|migration>] > map_device
+		>
+		> addr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]
+
+What:		/sys/class/rnbd-client/ctl/map_device
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Expected format is the following:
+
+		sessname=<name of the rtrs session>
+		path=<[srcaddr,]dstaddr> [path=<[srcaddr,]dstaddr> ...]
+		device_path=<full path on remote side>
+		[access_mode=<ro|rw|migration>]
+
+		Where:
+
+		sessname: accepts a string not bigger than 256 chars, which identifies
+		a given session on the client and on the server.
+		I.e. "clt_hostname-srv_hostname" could be a natural choice.
+
+		path:     describes a connection between the client and the server by
+		specifying destination and, when required, the source address.
+		The addresses are to be provided in the following format:
+
+		ip:<IPv6>
+		ip:<IPv4>
+		gid:<GID>
+
+		for example:
+
+		path=ip:10.0.0.66
+		The single addr is treated as the destination.
+		The connection will be established to this server from any client IP address.
+
+		path=ip:10.0.0.66,ip:10.0.1.66
+		First addr is the source address and the second is the destination.
+
+		If multiple "path=" options are specified multiple connection
+		will be established and data will be sent according to
+		the selected multipath policy (see RTRS mp_policy sysfs entry description).
+
+		device_path: Path to the block device on the server side. Path is specified
+		relative to the directory on server side configured in the
+		'dev_search_path' module parameter of the rnbd_server.
+		The rnbd_server prepends the <device_path> received from client
+		with <dev_search_path> and tries to open the
+		<dev_search_path>/<device_path> block device.  On success,
+		a /dev/rnbd<N> device file, a /sys/block/rnbd_client/rnbd<N>/
+		directory and an entry in /sys/class/rnbd-client/ctl/devices
+		will be created.
+
+		If 'dev_search_path' contains '%SESSNAME%', then each session can
+		have different devices namespace, e.g. server was configured with
+		the following parameter "dev_search_path=/run/rnbd-devs/%SESSNAME%",
+		client has this string "sessname=blya device_path=sda", then server
+		will try to open: /run/rnbd-devs/blya/sda.
+
+		access_mode: the access_mode parameter specifies if the device is to be
+		mapped as "ro" read-only or "rw" read-write. The server allows
+		a device to be exported in rw mode only once. The "migration"
+		access mode has to be specified if a second mapping in read-write
+		mode is desired.
+
+		By default "rw" is used.
+
+		Exit Codes:
+
+		If the device is already mapped it will fail with EEXIST. If the input
+		has an invalid format it will return EINVAL. If the device path cannot
+		be found on the server, it will fail with ENOENT.
+
+		Finding device file after mapping
+		---------------------------------
+
+		After mapping, the device file can be found by:
+		o  The symlink /sys/class/rnbd-client/ctl/devices/<device_id>
+		points to /sys/block/<dev-name>. The last part of the symlink destination
+		is the same as the device name.  By extracting the last part of the
+		path the path to the device /dev/<dev-name> can be build.
+
+		o /dev/block/$(cat /sys/class/rnbd-client/ctl/devices/<device_id>/dev)
+
+		How to find the <device_id> of the device is described on the next
+		section.
+
+What:		/sys/class/rnbd-client/ctl/devices/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	For each device mapped on the client a new symbolic link is created as
+		/sys/class/rnbd-client/ctl/devices/<device_id>, which points
+		to the block device created by rnbd (/sys/block/rnbd<N>/).
+		The <device_id> of each device is created as follows:
+
+		- If the 'device_path' provided during mapping contains slashes ("/"),
+		they are replaced by exclamation mark ("!") and used as as the
+		<device_id>. Otherwise, the <device_id> will be the same as the
+		"device_path" provided.
diff --git a/Documentation/ABI/testing/sysfs-class-rnbd-server b/Documentation/ABI/testing/sysfs-class-rnbd-server
new file mode 100644
index 000000000000..ba60a90c0e45
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rnbd-server
@@ -0,0 +1,50 @@
+What:		/sys/class/rnbd-server
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	provide information about RNBD-server.
+
+What:		/sys/class/rnbd-server/ctl/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	When a client maps a device, a directory entry with the name of the
+		block device is created under /sys/class/rnbd-server/ctl/devices/.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/block_dev
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Is a symlink to the sysfs entry of the exported device.
+
+		Example:
+		block_dev -> ../../../../class/block/ram0
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	For each client a particular device is exported to, following directory will be
+		created:
+
+		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/
+
+		When the device is unmapped by that client, the directory will be removed.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/read_only
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains '1' if device is mapped read-only, otherwise '0'.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/mapping_path
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the relative device path provided by the user during mapping.
+
+What:		/sys/class/rnbd-server/ctl/devices/<device_name>/sessions/<session-name>/access_mode
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the device access mode: ro, rw or migration.