[PATCH v3 3/3] dm: prevent DAX mounts if not supported

[Ross Zwisler]

Currently device_supports_dax() just checks to see if the QUEUE_FLAG_DAX
flag is set on the device's request queue to decide whether or not the
device supports filesystem DAX.  Really we should be using
bdev_dax_supported() like filesystems do at mount time.  This performs
other tests like checking to make sure the dax_direct_access() path works.

Conditionally set QUEUE_FLAG_DAX on the DM device's request queue based on
whether all underlying devices support DAX.  Now that bdev_dax_supported()
explicitly checks for this flag, this will ensure that filesystems built
upon DM devices will only be able to mount with DAX if all underlying
devices also support DAX.

Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Fixes: commit 545ed20e6df6 ("dm: add infrastructure for DAX support")
Cc: stable@xxxxxxxxxxxxxxx
---
 drivers/md/dm-ioctl.c         | 5 +++++
 drivers/md/dm-table.c         | 7 +++----
 drivers/md/dm.c               | 3 +--
 include/linux/device-mapper.h | 5 +++++
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index b810ea77e6b1..0055bdbee5b1 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1350,6 +1350,11 @@ static int table_load(struct file *filp, struct dm_ioctl *param, size_t param_si
 		goto err_unlock_md_type;
 	}
 
+	if (dm_table_supports_dax(t))
+		blk_queue_flag_set(QUEUE_FLAG_DAX, md->queue);
+	else
+		blk_queue_flag_clear(QUEUE_FLAG_DAX, md->queue);
+
 	dm_unlock_md_type(md);
 
 	/* stage inactive table */
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 938766794c2e..c673b4a51fb2 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -885,12 +885,10 @@ EXPORT_SYMBOL_GPL(dm_table_set_type);
 static int device_supports_dax(struct dm_target *ti, struct dm_dev *dev,
 			       sector_t start, sector_t len, void *data)
 {
-	struct request_queue *q = bdev_get_queue(dev->bdev);
-
-	return q && blk_queue_dax(q);
+	return bdev_dax_supported(dev->bdev, PAGE_SIZE);
 }
 
-static bool dm_table_supports_dax(struct dm_table *t)
+bool dm_table_supports_dax(struct dm_table *t)
 {
 	struct dm_target *ti;
 	unsigned i;
@@ -909,6 +907,7 @@ static bool dm_table_supports_dax(struct dm_table *t)
 
 	return true;
 }
+EXPORT_SYMBOL_GPL(dm_table_supports_dax);
 
 static bool dm_table_does_not_support_partial_completion(struct dm_table *t);
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e65429a29c06..bef5a3f243ed 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1056,8 +1056,7 @@ static long dm_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
 	if (len < 1)
 		goto out;
 	nr_pages = min(len, nr_pages);
-	if (ti->type->direct_access)
-		ret = ti->type->direct_access(ti, pgoff, nr_pages, kaddr, pfn);
+	ret = ti->type->direct_access(ti, pgoff, nr_pages, kaddr, pfn);
 
  out:
 	dm_put_live_table(md, srcu_idx);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 6fb0808e87c8..45ea9e1f9af9 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -461,6 +461,11 @@ void dm_table_add_target_callbacks(struct dm_table *t, struct dm_target_callback
  */
 void dm_table_set_type(struct dm_table *t, enum dm_queue_mode type);
 
+/*
+ * Check to see if this target type and all table devices support DAX.
+ */
+bool dm_table_supports_dax(struct dm_table *t);
+
 /*
  * Finally call this to make the table ready for use.
  */
-- 
2.14.4