linux-kernel - Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems

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Message-ID: <20140515221624.GY26353@dastard>
Date:	Fri, 16 May 2014 08:16:24 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Mateusz Guzik <mguzik@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Josef Bacik <jbacik@...com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Eric Sandeen <esandeen@...hat.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing
 filesystems

On Thu, May 15, 2014 at 12:13:56PM +0200, Jan Kara wrote:
> On Thu 15-05-14 08:37:45, Dave Chinner wrote:
> > On Thu, May 15, 2014 at 08:00:52AM +1000, Dave Chinner wrote:
> > > On Wed, May 14, 2014 at 01:39:45PM +0200, Jan Kara wrote:
> > > > On Wed 14-05-14 13:26:21, Mateusz Guzik wrote:
> > > > > On Wed, May 14, 2014 at 01:14:49PM +0200, Jan Kara wrote:
> > > > > > On Wed 14-05-14 00:04:43, Mateusz Guzik wrote:
> > > > > > > This helps hang troubleshooting efforts when only dmesg is available.
> > > > > > > 
> > > > > > > While here remove code duplication with MS_RDONLY case and fix a
> > > > > > > whitespace nit.
> > > > > >   I'm somewhat undecided here I have to say. On one hand I don't like
> > > > > > printing to kernel log when everything is fine and kernel is operating
> > > > > > normally. On the other hand I've seen quite a few cases where people have
> > > > > > shot themselves in the foot with filesystem freezing so having some trace
> > > > > > of this in the log doesn't seem like a completely bad thing either. What do
> > > > > > other people think?
> > > > > > 
> > > > > 
> > > > > I would like to note that the kernel already prints messages when e.g.
> > > > > filesystems get mounted.
> > > >   Yeah, that's a fair point.
> > > 
> > > But filesystems choose to output that info, not the VFS. When you do
> > > a remount,ro there is no output in syslog, because filesystems don't
> > > need to dump any output - the state change is reflected in
> > > /proc/self/mounts. IMO frozen should state should be communicated
> > > the same way so that it is silent when it just works, and the state
> > > can easily be determined when something goes wrong.
> > 
> > Say, like this:
> > 
> > $ grep /mnt/test /proc/mounts
> > /dev/vda /mnt/test xfs rw,relatime,attr2,inode64,noquota 0 0
> > $ sudo xfs_freeze -f /mnt/test
> > $ grep /mnt/test /proc/mounts
> > /dev/vda /mnt/test xfs rw,frozen,relatime,attr2,inode64,noquota 0 0
> > $ sudo xfs_freeze -u /mnt/test
> > $ grep /mnt/test /proc/mounts
> > /dev/vda /mnt/test xfs rw,relatime,attr2,inode64,noquota 0 0
> > $
> > 
> > Patch below does this.
>   Hum, same as Eric I'm not very enthusiastic about a fake mount option in
> /proc/mounts. Maybe we could stuff some extra field in /proc/self/mountinfo?

sure - I'd forgotten about /proc/self/mountinfo, but the way i wrote
the patch will also dump the information into it. It's just a case
of moving the code to show_mountinfo() rather than show_sb_opts().

If that's acceptible for everyone, then I'll update the patch to do
that....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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