xfs: Don't keep silent if sunit/swidth can not be changed via mount

From: Jie Liu <[email protected]>

As per the mount man page, sunit and swidth can be changed via mount options. For XFS, on the face of it, those options seems works if the specified alignments is properly, e.g.

# mount -o sunit=4096,swidth=8192 /dev/sdb1 /mnt
# mount | grep sdb1
/dev/sdb1 on /mnt type xfs (rw,sunit=4096,swidth=8192)

However, neither sunit nor swidth is shown from the xfs_info output.

# xfs_info /mnt
meta-data=/dev/sdb1    isize=256    agcount=4, agsize=262144 blks
         =             sectsz=512   attr=2
data     =             bsize=4096   blocks=1048576, imaxpct=25
         =             sunit=0      swidth=0 blks
		       ^^^^^^^^^^^^^^^^^^^^^^^^^^
naming   =version 2    bsize=4096   ascii-ci=0
log      =internal     bsize=4096   blocks=2560, version=2
         =             sectsz=512   sunit=0 blks, lazy-count=1
realtime =none         extsz=4096   blocks=0, rtextents=0

The reason is that the alignment can only be changed if the relevant super block is already configured with alignments, otherwise, the given value is silently ignored.

With this fix, the attempt to mount a storage without strip alignment setup on a super block will get an error with a warning in syslog to indicate the true cause.

# mount -o sunit=4096,swidth=8192 /dev/sdb1 /mnt
mount: wrong fs type, bad option, bad superblock on /dev/sdb1,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
	dmesg | tail  or so
# dmesg|tail
.......
XFS (sdb1): can not change alignment: superblock does not support data
alignment

Signed-off-by Jie Liu <[email protected]>

Cc Mark Tinguely <[email protected]>

Cc Dave Chinner <[email protected]>

---
 fs/xfs/xfs_mount.c |    4 ++++
 1 file changed, 4 insertions(+)

fs/xfs/xfs_mount.c +0 -0

index 29e8de8..2836ef6 100644

Quoted 46 lines · Jeff Liu

From: Jie Liu <[email protected]>

As per the mount man page, sunit and swidth can be changed via mount options. For XFS, on the face of it, those options seems works if the specified alignments is properly, e.g.

# mount -o sunit=4096,swidth=8192 /dev/sdb1 /mnt
# mount | grep sdb1
/dev/sdb1 on /mnt type xfs (rw,sunit=4096,swidth=8192)

However, neither sunit nor swidth is shown from the xfs_info output.

# xfs_info /mnt
meta-data=/dev/sdb1    isize=256    agcount=4, agsize=262144 blks
         =             sectsz=512   attr=2
data     =             bsize=4096   blocks=1048576, imaxpct=25
         =             sunit=0      swidth=0 blks
		       ^^^^^^^^^^^^^^^^^^^^^^^^^^
naming   =version 2    bsize=4096   ascii-ci=0
log      =internal     bsize=4096   blocks=2560, version=2
         =             sectsz=512   sunit=0 blks, lazy-count=1
realtime =none         extsz=4096   blocks=0, rtextents=0

The reason is that the alignment can only be changed if the relevant super block is already configured with alignments, otherwise, the given value is silently ignored.

With this fix, the attempt to mount a storage without strip alignment setup on a super block will get an error with a warning in syslog to indicate the true cause.

# mount -o sunit=4096,swidth=8192 /dev/sdb1 /mnt
mount: wrong fs type, bad option, bad superblock on /dev/sdb1,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
	dmesg | tail  or so
# dmesg|tail
.......
XFS (sdb1): can not change alignment: superblock does not support data
alignment

Signed-off-by Jie Liu <[email protected]>

Cc Mark Tinguely <[email protected]>

Cc Dave Chinner <[email protected]>

---
 fs/xfs/xfs_mount.c |    4 ++++
 1 file changed, 4 insertions(+)

fs/xfs/xfs_mount.c xfs_update_alignment(xfs_mount_t *mp) · line 914

Quoted 11 lines

fs/xfs/xfs_mount.c +3 -0

index 29e8de8..2836ef6 100644
@@ -909,6 +909,10 @@ xfs_update_alignment(xfs_mount_t *mp)
 				sbp->sb_width = mp->m_swidth;
 				mp->m_update_flags |= XFS_SB_WIDTH;
 			}
+		} else {
+			xfs_warn(mp, "cannot change alignment: "
+				 "superblock does not support data alignment");

Same comment again about single line format strings. Otherwise it's ok.

Quoted 15 lines · Dave Chinner

fs/xfs/xfs_mount.c xfs_update_alignment(xfs_mount_t *mp) · line 914

Quoted 11 lines · Jeff Liu

fs/xfs/xfs_mount.c +3 -0

index 29e8de8..2836ef6 100644
@@ -909,6 +909,10 @@ xfs_update_alignment(xfs_mount_t *mp)
 				sbp->sb_width = mp->m_swidth;
 				mp->m_update_flags |= XFS_SB_WIDTH;
 			}
+		} else {
+			xfs_warn(mp, "cannot change alignment: "
+				 "superblock does not support data alignment");

Same comment again about single line format strings. Otherwise it's ok.

Ah, sorry! I misunderstood the comments of Mark before. I was bluffed into believing that I should cut the length of log string as short as possible. :(

Quoted 16 lines · Jeff Liu

Quoted 15 lines · Dave Chinner

fs/xfs/xfs_mount.c xfs_update_alignment(xfs_mount_t *mp) · line 914

Quoted 11 lines · Jeff Liu

fs/xfs/xfs_mount.c +3 -0

index 29e8de8..2836ef6 100644
@@ -909,6 +909,10 @@ xfs_update_alignment(xfs_mount_t *mp)
 				sbp->sb_width = mp->m_swidth;
 				mp->m_update_flags |= XFS_SB_WIDTH;
 			}
+		} else {
+			xfs_warn(mp, "cannot change alignment: "
+				 "superblock does not support data alignment");

Same comment again about single line format strings. Otherwise it's ok.

Quoted 3 lines

Ah, sorry! I misunderstood the comments of Mark before. I was bluffed into believing that I should cut the length of log string as short as possible. :(

Thing of being able cut-n-paste the error message out of the log and then being able to grep the source tree for it. i.e.

$ git grep "cannot change alignment: superblock does not support data alignment"

Will fail to find anything in the former case, but in the single line case it will identify the file the error lies in immediately. So the question I always ask myself is "is that format string easy to find with grep?" :)