ext4: Add alignment check for DAX mount

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

Reported-by: Micah Parrish <[email protected]>
Signed-off-by: Toshi Kani <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Boaz Harrosh <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>

Author: toshikani

fs/ext4/super.c

@@ -3417,16 +3417,9 @@ 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_dax_supported(sb, blocksize);
+		if (err)
 			goto failed_mount;
-		}
 	}
 
 	if (ext4_has_feature_encrypt(sb) && es->s_encryption_level) {