linux-kernel - Re: linux-next: build failure after merge of the vfs tree

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Message-ID: <20120104222649.GF28907@quack.suse.cz>
Date:	Wed, 4 Jan 2012 23:26:49 +0100
From:	Jan Kara <jack@...e.cz>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, Dave Chinner <david@...morbit.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mikulas Patocka <mpatocka@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: linux-next: build failure after merge of the vfs tree

On Wed 04-01-12 13:47:46, Christoph Hellwig wrote:
> On Wed, Jan 04, 2012 at 07:00:33PM +0100, Jan Kara wrote:
> > On Wed 04-01-12 13:50:20, Dave Chinner wrote:
> > > On Wed, Jan 04, 2012 at 02:17:54AM +0000, Al Viro wrote:
> > > > I'm still not
> > > > sure about ->statfs(), BTW - any input on that would be welcome.  Can
> > > > it end up blocked on a frozen fs until said fs is thawed?
> > > 
> > > I don't see why this should ever happen - ->statfs has to work on
> > > read-only filesystems so shoul dnot be modifying state, and hence
> > > should never need to care about the frozen state of the superblock.
> >   Well, I'm also not aware of a filesystem where ->statfs would wait on
> > frozen filesystem. Just note that e.g. for stat(2) frozen filesystem and
> > RO filesystem *are* different because of atime updates. So stat(2) can
> > block on frozen fs because of atime update while on RO filesystem it is
> > just fine.
> 
> Neither of those should cause atime updates.
  Sorry, I'm not sure why I thought stat(2) would touch atime. But still my
claim is correct in the sence that operations that do touch atime
(follow_link, readdir, ...) behave differently on frozen filesystem and on
read-only filesystem. So rDave's argument that read-only access to frozen
filesystem is OK is not correct in general.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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