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Re: [PATCH] xfsprogs: skip over "rootfs" entry if mtab links to /proc/mo

To: Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH] xfsprogs: skip over "rootfs" entry if mtab links to /proc/mounts
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Wed, 3 Aug 2011 15:02:16 -0400
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <4E399677.1010508@xxxxxxxxxx>
References: <4E399677.1010508@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, Aug 03, 2011 at 01:41:59PM -0500, Eric Sandeen wrote:
> This is for RH bug 727938, xfs_fsr regression for root file system
> 
> Fedora has made /etc/mtab a symlink to /proc/mounts, but when
> we issue "xfs_fsr /" and fsr's getmntany() goes looking for
> the "/" entry, the first one it finds is
> 
> rootfs / rootfs rw 0 0
> 
> it says no way, that's a rootfs filesystem type, not xfs!
> And it never finds this later:
> 
> /dev/sda2 / xfs rw,relatime,attr2,noquota 0 0
> 
> This patch to skip over the rootfs entry seems to fix it.

I don't like this.  rootfs is the symptom, but the underlying problem
is that in Linux we're perfectly fine to have multiple filesystems
mounted on a single mountpoint, and the getmntany can't deal with it.

I think the right fix is to simply remove the break from the loop,
and thus let a second match for our fs override the first.  This relies
on getmntent returning entries in the order they were mounted, but
without that I can't think of a reliable way for getmntent to work
with the multiple mounts in Linux.

It would also be nice to have a testcase for this behaviour in xfstests,
creating two loop devices with different backing files and mounting them
at the same mount point.

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