[PATCH v3 3/5] ext4: Add alignment check for DAX mount

[Toshi Kani]

When a partition is not aligned by 4KB, mount -o dax succeeds,
but any read/write access to the filesystem fails, except for
metadata update.

Call bdev_supports_dax() to perform proper precondition checks
which includes this partition alignment check.

Reported-by: Micah Parrish <micah.parrish@xxxxxxx>
Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
---
 fs/ext4/super.c |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 304c712..e7ca71c 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3416,16 +3416,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
-		if (blocksize != PAGE_SIZE) {
-			ext4_msg(sb, KERN_ERR,
-					"error: unsupported blocksize for dax");
-			goto failed_mount;
-		}
-		if (!sb->s_bdev->bd_disk->fops->direct_access) {
-			ext4_msg(sb, KERN_ERR,
-					"error: device does not support dax");
+		err = bdev_supports_dax(sb, blocksize);
+		if (err)
 			goto failed_mount;
-		}
 	}
 
 	if (ext4_has_feature_encrypt(sb) && es->s_encryption_level) {