From: Fernando Luis Vazquez Cao <fernando_b1@lab.ntt.co.jp>
To: Eric Sandeen <sandeen@redhat.com>
Cc: Josef Bacik <jbacik@fusionio.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Dave Chinner <dchinner@redhat.com>,
Christoph Hellwig <hch@infradead.org>, Jan Kara <jack@suse.cz>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC 6/9] fsfreeze: move emergency thaw code to fs/super.c
Date: Fri, 14 Sep 2012 11:11:16 +0900 [thread overview]
Message-ID: <50529244.3010201@lab.ntt.co.jp> (raw)
In-Reply-To: <50524BCB.8090500@redhat.com>
On 2012/09/14 06:10, Eric Sandeen wrote:
> The stupid emergency sysrq thing was my fault (at someone else's suggestion) ;)
>
> It's caused a lot of woe, and hasn't worked for two years. Should we keep it?
It turns out that emergency thaw is useful in virtuazalition
environments where a guest's filesystem can be frozen
by a hypervisor controlled guest agent without the guest's
users and administrator being aware of it. In such scenarios
if the guest agent dies leaving a filesystem frozen we are
in trouble. The guest's administrator or root user will eventually
notice that writes to the filesystem that was frozen behind its back
block but it has no way to figure out what is going on since
we do not have check ioctls. In such cases emergency thaw
is very useful. Please notice that even if we managed to restart
the guest agent, in many cases it is stateless so it will not
remember that a froze the filesystem.
next prev parent reply other threads:[~2012-09-14 2:11 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-13 10:57 [RFC 0/9 v3] fsfreeze: miscellaneous fixes and cleanups Fernando Luis Vázquez Cao
2012-09-13 11:00 ` [PATCH 1/9] vfs: add __iterate_supers() helper Fernando Luis Vázquez Cao
2012-09-14 2:36 ` Eric Sandeen
2012-09-14 2:40 ` Fernando Luis Vazquez Cao
2012-09-13 11:01 ` [RFC 2/9] fsfreeze: add unlocked version of thaw_super Fernando Luis Vázquez Cao
2012-09-13 18:13 ` Eric Sandeen
2012-09-13 11:03 ` [RFC 3/9] fsfreeze: Prevent emergency thaw from looping infinitely Fernando Luis Vázquez Cao
2012-09-13 16:40 ` Eric Sandeen
2012-09-13 11:04 ` [RFC 4/9] fsfreeze: emergency thaw will deadlock on s_umount Fernando Luis Vázquez Cao
2012-09-13 11:07 ` [RFC 5/9] xfs: switch to using super methods for fsfreeze Fernando Luis Vázquez Cao
2012-09-13 11:08 ` [RFC 6/9] fsfreeze: move emergency thaw code to fs/super.c Fernando Luis Vázquez Cao
2012-09-13 19:00 ` Josef Bacik
2012-09-13 21:10 ` Eric Sandeen
2012-09-14 2:11 ` Fernando Luis Vazquez Cao [this message]
2012-09-14 1:59 ` Fernando Luis Vazquez Cao
2012-09-13 11:10 ` [PATCH 7/9] fsfreeze: freeze_super and thaw_bdev don't play well together Fernando Luis Vázquez Cao
2012-09-13 11:11 ` [PATCH 8/9] fsfreeze: add vfs ioctl to check freeze state Fernando Luis Vázquez Cao
2012-09-13 11:13 ` [PATCH 9/9] fsfreeze: add block device " Fernando Luis Vázquez Cao
2012-09-14 0:57 ` [RFC 0/9 v3] fsfreeze: miscellaneous fixes and cleanups Dave Chinner
2012-09-14 2:20 ` Fernando Luis Vazquez Cao
2012-09-14 2:33 ` Eric Sandeen
2012-09-14 2:48 ` Fernando Luis Vazquez Cao
2012-09-14 6:22 ` Fernando Luis Vazquez Cao
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