dax: Kill DEV_DAX_PMEM_COMPAT

The /sys/class/dax compatibility option has shipped in the kernel for 4
years now which should be sufficient time for tools to abandon the old
ABI in favor of the /sys/bus/dax device-model. Delete it now and see if
anyone screams.

Since this compatibility option shipped there has been more reports of
users being surprised by the compat ABI than surprised by the "new", so
the compat infrastructure has outlived its usefulness. Recall that
/sys/bus/dax device-model is required for the dax kmem driver which
allows PMEM to be used as "System RAM".

The following projects were known to have a dependency on /sys/class/dax
and have dropped their dependency as of the listed version:

- ndctl (including libndctl, daxctl, and libdaxctl): v64+
- fio: v3.13+
- pmdk: v1.5.2+

As further evidence this option is no longer needed some distributions
have already stopped enabling CONFIG_DEV_DAX_PMEM_COMPAT.

Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Reported-by: Vishal Verma <vishal.l.verma@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Link: https://lore.kernel.org/r/163701116195.3784476.726128179293466337.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 103 insertions, 0 deletions

diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
new file mode 100644
index 000000000000..f050ea78bb83
--- /dev/null
+++ b/drivers/dax/pmem.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2016 - 2018 Intel Corporation. All rights reserved. */
+#include <linux/memremap.h>
+#include <linux/module.h>
+#include <linux/pfn_t.h>
+#include "../nvdimm/pfn.h"
+#include "../nvdimm/nd.h"
+#include "bus.h"
+
+static struct dev_dax *__dax_pmem_probe(struct device *dev)
+{
+	struct range range;
+	int rc, id, region_id;
+	resource_size_t offset;
+	struct nd_pfn_sb *pfn_sb;
+	struct dev_dax *dev_dax;
+	struct dev_dax_data data;
+	struct nd_namespace_io *nsio;
+	struct dax_region *dax_region;
+	struct dev_pagemap pgmap = { };
+	struct nd_namespace_common *ndns;
+	struct nd_dax *nd_dax = to_nd_dax(dev);
+	struct nd_pfn *nd_pfn = &nd_dax->nd_pfn;
+	struct nd_region *nd_region = to_nd_region(dev->parent);
+
+	ndns = nvdimm_namespace_common_probe(dev);
+	if (IS_ERR(ndns))
+		return ERR_CAST(ndns);
+
+	/* parse the 'pfn' info block via ->rw_bytes */
+	rc = devm_namespace_enable(dev, ndns, nd_info_block_reserve());
+	if (rc)
+		return ERR_PTR(rc);
+	rc = nvdimm_setup_pfn(nd_pfn, &pgmap);
+	if (rc)
+		return ERR_PTR(rc);
+	devm_namespace_disable(dev, ndns);
+
+	/* reserve the metadata area, device-dax will reserve the data */
+	pfn_sb = nd_pfn->pfn_sb;
+	offset = le64_to_cpu(pfn_sb->dataoff);
+	nsio = to_nd_namespace_io(&ndns->dev);
+	if (!devm_request_mem_region(dev, nsio->res.start, offset,
+				dev_name(&ndns->dev))) {
+		dev_warn(dev, "could not reserve metadata\n");
+		return ERR_PTR(-EBUSY);
+	}
+
+	rc = sscanf(dev_name(&ndns->dev), "namespace%d.%d", &region_id, &id);
+	if (rc != 2)
+		return ERR_PTR(-EINVAL);
+
+	/* adjust the dax_region range to the start of data */
+	range = pgmap.range;
+	range.start += offset;
+	dax_region = alloc_dax_region(dev, region_id, &range,
+			nd_region->target_node, le32_to_cpu(pfn_sb->align),
+			IORESOURCE_DAX_STATIC);
+	if (!dax_region)
+		return ERR_PTR(-ENOMEM);
+
+	data = (struct dev_dax_data) {
+		.dax_region = dax_region,
+		.id = id,
+		.pgmap = &pgmap,
+		.size = range_len(&range),
+	};
+	dev_dax = devm_create_dev_dax(&data);
+
+	/* child dev_dax instances now own the lifetime of the dax_region */
+	dax_region_put(dax_region);
+
+	return dev_dax;
+}
+
+static int dax_pmem_probe(struct device *dev)
+{
+	return PTR_ERR_OR_ZERO(__dax_pmem_probe(dev));
+}
+
+static struct nd_device_driver dax_pmem_driver = {
+	.probe = dax_pmem_probe,
+	.drv = {
+		.name = "dax_pmem",
+	},
+	.type = ND_DRIVER_DAX_PMEM,
+};
+
+static int __init dax_pmem_init(void)
+{
+	return nd_driver_register(&dax_pmem_driver);
+}
+module_init(dax_pmem_init);
+
+static void __exit dax_pmem_exit(void)
+{
+	driver_unregister(&dax_pmem_driver.drv);
+}
+module_exit(dax_pmem_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Intel Corporation");
+MODULE_ALIAS_ND_DEVICE(ND_DEVICE_DAX_PMEM);