From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mateusz Guzik Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfreezing filesystems Date: Thu, 15 May 2014 12:47:48 +0200 Message-ID: <20140515104746.GF10637@mguzik.redhat.com> References: <1400018683-5565-1-git-send-email-mguzik@redhat.com> <1400018683-5565-2-git-send-email-mguzik@redhat.com> <20140514111449.GB5824@quack.suse.cz> <20140514112619.GA10637@mguzik.redhat.com> <20140514113945.GC5824@quack.suse.cz> <20140514220052.GD5421@dastard> <20140514223745.GF5421@dastard> <5373F0D6.4090600@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: sandeen@redhat.com, Dave Chinner , Jan Kara , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Josef Bacik , Al Viro , Joe Perches To: =?utf-8?B?THVrw6HFoQ==?= Czerner Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 15, 2014 at 12:40:19PM +0200, Luk=C3=A1=C5=A1 Czerner wrote= : > On Wed, 14 May 2014, Eric Sandeen wrote: >=20 > > Date: Wed, 14 May 2014 17:40:22 -0500 > > From: Eric Sandeen > > Reply-To: sandeen@redhat.com > > To: Dave Chinner , Jan Kara > > Cc: Mateusz Guzik , linux-kernel@vger.kernel.org= , > > linux-fsdevel@vger.kernel.org, Josef Bacik , > > Al Viro , Joe Perches > > Subject: Re: [PATCH V2 2/2] fs: print a message when freezing/unfre= ezing > > filesystems > >=20 > > 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 a= vailable. > > >>>>>> > > >>>>>> While here remove code duplication with MS_RDONLY case and f= ix a > > >>>>>> whitespace nit. > > >>>>> I'm somewhat undecided here I have to say. On one hand I do= n'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 havin= g some trace > > >>>>> of this in the log doesn't seem like a completely bad thing e= ither. What do > > >>>>> other people think? > > >>>>> > > >>>> > > >>>> I would like to note that the kernel already prints messages w= hen e.g. > > >>>> filesystems get mounted. > > >>> Yeah, that's a fair point. > > >> > > >> But filesystems choose to output that info, not the VFS. When yo= u do > > >> a remount,ro there is no output in syslog, because filesystems d= on't > > >> need to dump any output - the state change is reflected in > > >> /proc/self/mounts. IMO frozen should state should be communicate= d > > >> the same way so that it is silent when it just works, and the st= ate > > >> can easily be determined when something goes wrong. > > >=20 > > > Say, like this: > > >=20 > > > $ 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 > > > $ > >=20 > > 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. >=20 > I do not like it either. Mixing this together with other mount > options does not seem like a great idea, however we really need a > way to report this and I guess we can not just change the > /proc/self/mounts, or /proc/self/mountinfo format. >=20 > So what about crating a new file /proc/self/frozen with the list of > frozen file systems in the same format what mounts, or mountinfo has > ? >=20 As the time goes on there will be more data to present about given mountpoint. So either mountinfo should be extendable to support this (can't see why not) or new generic file with that property should be provided. I vote for the former. IOW, a new column in mountinfo. For frozen filesystems it would contain 'frozen_by=3D[%s]:[%d]' (escaped comm, pid). --=20 Mateusz Guzik