Merge tag 'libnvdimm-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm

Pull libnvdimm updates from Dan Williams:

 - Fix a race condition in the teardown path of raw mode pmem
   namespaces.

 - Cleanup the code that filesystems use to detect filesystem-dax
   capabilities of their underlying block device.

* tag 'libnvdimm-for-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm:
  dax: remove bdev_dax_supported
  xfs: factor out a xfs_buftarg_is_dax helper
  dax: stub out dax_supported for !CONFIG_FS_DAX
  dax: remove __generic_fsdax_supported
  dax: move the dax_read_lock() locking into dax_supported
  dax: mark dax_get_by_host static
  dm: use fs_dax_get_by_bdev instead of dax_get_by_host
  dax: stop using bdevname
  fsdax: improve the FS_DAX Kconfig description and help text
  libnvdimm/pmem: Fix crash triggered when I/O in-flight during unbind

1 files changed, 18 insertions, 3 deletions

diff --git a/fs/Kconfig b/fs/Kconfig
index d8207a1b8c44..c854725db417 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -43,7 +43,7 @@ source "fs/f2fs/Kconfig"
 source "fs/zonefs/Kconfig"
 
 config FS_DAX
-	bool "Direct Access (DAX) support"
+	bool "File system based Direct Access (DAX) support"
 	depends on MMU
 	depends on !(ARM || MIPS || SPARC)
 	select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED)
@@ -53,8 +53,23 @@ config FS_DAX
 	  Direct Access (DAX) can be used on memory-backed block devices.
 	  If the block device supports DAX and the filesystem supports DAX,
 	  then you can avoid using the pagecache to buffer I/Os.  Turning
-	  on this option will compile in support for DAX; you will need to
-	  mount the filesystem using the -o dax option.
+	  on this option will compile in support for DAX.
+
+	  For a DAX device to support file system access it needs to have
+	  struct pages.  For the nfit based NVDIMMs this can be enabled
+	  using the ndctl utility:
+
+		# ndctl create-namespace --force --reconfig=namespace0.0 \
+			--mode=fsdax --map=mem
+
+	  See the 'create-namespace' man page for details on the overhead of
+	  --map=mem:
+	  https://docs.pmem.io/ndctl-user-guide/ndctl-man-pages/ndctl-create-namespace
+
+          For ndctl to work CONFIG_DEV_DAX needs to be enabled as well. For most
+	  file systems DAX support needs to be manually enabled globally or
+	  per-inode using a mount option as well.  See the file documentation in
+	  Documentation/filesystems/dax.rst for details.
 
 	  If you do not have a block device that is capable of using this,
 	  or if unsure, say N.  Saying Y will increase the size of the kernel