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Re: [PATCH v3 2/2] xfs: Don't keep silent if sunit/swidth can not be cha

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH v3 2/2] xfs: Don't keep silent if sunit/swidth can not be changed via mount
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Thu, 02 May 2013 10:28:36 -0500
Cc: "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <51824DB9.6090401@xxxxxxxxxx>
References: <51824DB9.6090401@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 05/02/13 06:27, 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 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, e.g.
# 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
XFS (sdb1): cannot change alignment: superblock does not support data

Signed-off-by: Jie Liu<jeff.liu@xxxxxxxxxx>

Looks good.

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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