linux-kernel - Re: [PATCH -v5 2/2] Updating ctime and mtime at syncing

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Message-ID: <20080117132429.GB14692@bitwizard.nl>
Date:	Thu, 17 Jan 2008 14:24:29 +0100
From:	Rogier Wolff <R.E.Wolff@...Wizard.nl>
To:	Anton Salikhmetov <salikhmetov@...il.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-mm@...ck.org,
	jakob@...hought.net, linux-kernel@...r.kernel.org,
	valdis.kletnieks@...edu, riel@...hat.com, ksm@...dk,
	staubach@...hat.com, jesper.juhl@...il.com,
	torvalds@...ux-foundation.org, a.p.zijlstra@...llo.nl,
	akpm@...ux-foundation.org, protasnb@...il.com,
	r.e.wolff@...wizard.nl, hidave.darkstar@...il.com,
	hch@...radead.org
Subject: Re: [PATCH -v5 2/2] Updating ctime and mtime at syncing

On Thu, Jan 17, 2008 at 04:16:47PM +0300, Anton Salikhmetov wrote:
> 2008/1/17, Miklos Szeredi <miklos@...redi.hu>:
> > > > 4. Recording the time was the file data changed
> > > >
> > > > Finally, I noticed yet another issue with the previous version of my patch.
> > > > Specifically, the time stamps were set to the current time of the moment
> > > > when syncing but not the write reference was being done. This led to the
> > > > following adverse effect on my development system:
> > > >
> > > > 1) a text file A was updated by process B;
> > > > 2) process B exits without calling any of the *sync() functions;
> > > > 3) vi editor opens the file A;
> > > > 4) file data synced, file times updated;
> > > > 5) vi is confused by "thinking" that the file was changed after 3).
> >
> > Updating the time in remove_vma() would fix this, no?
> 
> We need to save modification time. Otherwise, updating time stamps
> will be confusing the vi editor.

If process B exits before vi opens the file, the timestamp should at
the latest be the time that process B exits. There is no excuse for
setting the timestamp later than the time that B exits.

If process B no longer modifies the file, but still keeps it mapped
until after vi starts, then the system can't help the
situation. Wether or not B acesses those pages is unknown to the
system. So you get what you deserve.

	Roger. 

-- 
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