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Re: [PATCH] xfs: Don't keep silent if sunit/swidth can not be changed vi

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: Don't keep silent if sunit/swidth can not be changed via mount
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 30 Apr 2013 17:36:59 +1000
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <517E5D12.5010809@xxxxxxxxxx>
References: <517E5D12.5010809@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Apr 29, 2013 at 07:44:18PM +0800, Jeff Liu wrote:
> From: Jie Liu <jeff.liu@xxxxxxxxxx>
> 
> 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 will be silently ignored, so it's better to tell user
> that the alignment-changing can not take affect in one way or another.
> 
> With this fix, the attempt to mount a storage without strip alignment
> setup on super block will failed if XFS_MOUNT_RETERR is enabled, or
> just ignore the given alignment and drop a warning to indicate the
> cause in syslog.
> 
> # 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: no data alignment on superblock
> 
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
> 
> ---
>  fs/xfs/xfs_mount.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 3806088..bc7fdd4 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -924,6 +924,13 @@ xfs_update_alignment(xfs_mount_t *mp)
>                               sbp->sb_width = mp->m_swidth;
>                               mp->m_update_flags |= XFS_SB_WIDTH;
>                       }
> +             } else {
> +                     xfs_warn(mp, "can not change alignment: "
> +                             "no data alignment on superblock");
> +                     if (mp->m_flags & XFS_MOUNT_RETERR)
> +                             return XFS_ERROR(EINVAL);
> +                     mp->m_dalign = 0;
> +                     mp->m_swidth = 0;

Can someone tell me why the XFS_MOUNT_RETERR flag exists?

It looks like dead code to me as the only time mp->m_dalign is set
prior to calling xfs_update_alignment() is the same code that sets
XFS_MOUNT_RETERR in xfs_parseargs().

IOWs, any time we enter this "if (mp->m_dalign)" branch in
xfs_update_alignment(), XFS_MOUNT_RETERR is going to be set and so
we should always be emitting a warning and returning an error.

If this is correct, Jeff, can you remove the XFS_MOUNT_RETERR flag
and get rid of all the dead code in xfs_update_alignment() at the
same time, please?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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