[PATCH v2 2/3] ext2: 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_direct_access to check the alignment when -o dax is
specified.

Signed-off-by: Toshi Kani <toshi.k...@hpe.com>
Cc: Jan Kara <j...@suse.cz>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
Cc: Christoph Hellwig <h...@infradead.org>
Cc: Boaz Harrosh <b...@plexistor.com>
---
 fs/ext2/super.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index b78caf2..e636b56 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -922,14 +922,31 @@ static int ext2_fill_super(struct super_block *sb, void 
*data, int silent)
        blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
 
        if (sbi->s_mount_opt & EXT2_MOUNT_DAX) {
+               struct blk_dax_ctl dax = {
+                       .sector = 0,
+                       .size = PAGE_SIZE,
+               };
                if (blocksize != PAGE_SIZE) {
                        ext2_msg(sb, KERN_ERR,
                                        "error: unsupported blocksize for dax");
                        goto failed_mount;
                }
-               if (!sb->s_bdev->bd_disk->fops->direct_access) {
-                       ext2_msg(sb, KERN_ERR,
+               err = bdev_direct_access(sb->s_bdev, &dax);
+               if (err < 0) {
+                       switch (err) {
+                       case -EOPNOTSUPP:
+                               ext2_msg(sb, KERN_ERR,
                                        "error: device does not support dax");
+                               break;
+                       case -EINVAL:
+                               ext2_msg(sb, KERN_ERR,
+                                       "error: unaligned partition for dax");
+                               break;
+                       default:
+                               ext2_msg(sb, KERN_ERR,
+                                       "error: dax access failed (%d)", err);
+                               break;
+                       }
                        goto failed_mount;
                }
        }