[RFC PATCH v4 03/12] dm: Treat alloc_dax() -EOPNOTSUPP failure as non-fatal

[Mathieu Desnoyers]

In preparation for checking whether the architecture has data cache
aliasing within alloc_dax(), modify the error handling of dm alloc_dev()
to treat alloc_dax() -EOPNOTSUPP failure as non-fatal.

For the transition, consider that alloc_dax() returning NULL is the
same as returning -EOPNOTSUPP.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing 
caches")
Suggested-by: Dan Williams <dan.j.willi...@intel.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
Cc: Alasdair Kergon <a...@redhat.com>
Cc: Mike Snitzer <snit...@kernel.org>
Cc: Mikulas Patocka <mpato...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Vishal Verma <vishal.l.ve...@intel.com>
Cc: Dave Jiang <dave.ji...@intel.com>
Cc: Matthew Wilcox <wi...@infradead.org>
Cc: Arnd Bergmann <a...@arndb.de>
Cc: Russell King <li...@armlinux.org.uk>
Cc: linux-a...@vger.kernel.org
Cc: linux-...@vger.kernel.org
Cc: linux-fsde...@vger.kernel.org
Cc: linux...@kvack.org
Cc: linux-...@vger.kernel.org
Cc: dm-devel@lists.linux.dev
Cc: nvd...@lists.linux.dev
---
 drivers/md/dm.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 23c32cd1f1d8..2fc22cae9089 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2054,6 +2054,7 @@ static void cleanup_mapped_device(struct mapped_device 
*md)
 static struct mapped_device *alloc_dev(int minor)
 {
        int r, numa_node_id = dm_get_numa_node();
+       struct dax_device *dax_dev;
        struct mapped_device *md;
        void *old_md;
 
@@ -2122,15 +2123,15 @@ static struct mapped_device *alloc_dev(int minor)
        md->disk->private_data = md;
        sprintf(md->disk->disk_name, "dm-%d", minor);
 
-       if (IS_ENABLED(CONFIG_FS_DAX)) {
-               md->dax_dev = alloc_dax(md, &dm_dax_ops);
-               if (IS_ERR(md->dax_dev)) {
-                       md->dax_dev = NULL;
+       dax_dev = alloc_dax(md, &dm_dax_ops);
+       if (IS_ERR_OR_NULL(dax_dev)) {
+               if (IS_ERR(dax_dev) && PTR_ERR(dax_dev) != -EOPNOTSUPP)
                        goto bad;
-               }
-               set_dax_nocache(md->dax_dev);
-               set_dax_nomc(md->dax_dev);
-               if (dax_add_host(md->dax_dev, md->disk))
+       } else {
+               set_dax_nocache(dax_dev);
+               set_dax_nomc(dax_dev);
+               md->dax_dev = dax_dev;
+               if (dax_add_host(dax_dev, md->disk))
                        goto bad;
        }
 
-- 
2.39.2