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

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Message-ID: <5373F0D6.4090600@redhat.com>
Date:	Wed, 14 May 2014 17:40:22 -0500
From:	Eric Sandeen <esandeen@...hat.com>
To:	Dave Chinner <david@...morbit.com>, 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>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems

On 5/14/14, 5:37 PM, 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
> $

I'm not totally convinced that including a non-mount option in what
has always (?) been a list of mount options is a great idea.

(Granted, some options there are defaults, and weren't actually specified
as a mount option, but if they had been, they'd have been accepted).

Maybe add a "mount -o remount,frozen" handler ?  ;)

-Eric
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