dax: Arrange for dax_supported check to span multiple devices

Pankaj reports that starting with commit ad428cdb525a "dax: Check the
end of the block-device capacity with dax_direct_access()" device-mapper
no longer allows dax operation. This results from the stricter checks in
__bdev_dax_supported() that validate that the start and end of a
block-device map to the same 'pagemap' instance.

Teach the dax-core and device-mapper to validate the 'pagemap' on a
per-target basis. This is accomplished by refactoring the
bdev_dax_supported() internals into generic_fsdax_supported() which
takes a sector range to validate. Consequently generic_fsdax_supported()
is suitable to be used in a device-mapper ->iterate_devices() callback.
A new ->dax_supported() operation is added to allow composite devices to
split and route upper-level bdev_dax_supported() requests.

Fixes: ad428cdb525a ("dax: Check the end of the block-device...")
Cc: <stable@vger.kernel.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reported-by: Pankaj Gupta <pagupta@redhat.com>
Reviewed-by: Pankaj Gupta <pagupta@redhat.com>
Tested-by: Pankaj Gupta <pagupta@redhat.com>
Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 2d539b82ec08..17e3db54404c 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -72,6 +72,7 @@ bool dm_table_bio_based(struct dm_table *t);
 bool dm_table_request_based(struct dm_table *t);
 void dm_table_free_md_mempools(struct dm_table *t);
 struct dm_md_mempools *dm_table_get_md_mempools(struct dm_table *t);
+bool dm_table_supports_dax(struct dm_table *t, int blocksize);
 
 void dm_lock_md_type(struct mapped_device *md);
 void dm_unlock_md_type(struct mapped_device *md);