linux-ext4 - Re: [PATCH 1/5][TAKE3] fallocate() implementation on i86, x86

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Message-ID: <20070516234036.GQ85884050@sgi.com>
Date:	Thu, 17 May 2007 09:40:36 +1000
From:	David Chinner <dgc@....com>
To:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
Cc:	David Chinner <dgc@....com>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>, torvalds@...l.org,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, suparna@...ibm.com, cmm@...ibm.com
Subject: Re: [PATCH 1/5][TAKE3] fallocate() implementation on i86, x86_64 and powerpc

On Wed, May 16, 2007 at 07:21:16AM -0500, Dave Kleikamp wrote:
> On Wed, 2007-05-16 at 13:16 +1000, David Chinner wrote:
> > On Wed, May 16, 2007 at 01:33:59AM +0530, Amit K. Arora wrote:
> 
> > > Following changes were made to the previous version:
> > >  1) Added description before sys_fallocate() definition.
> > >  2) Return EINVAL for len<=0 (With new draft that Ulrich pointed to,
> > >     posix_fallocate should return EINVAL for len <= 0.
> > >  3) Return EOPNOTSUPP if mode is not one of FA_ALLOCATE or FA_DEALLOCATE
> > >  4) Do not return ENODEV for dirs (let individual file systems decide if
> > >     they want to support preallocation to directories or not.
> > >  5) Check for wrap through zero.
> > >  6) Update c/mtime if fallocate() succeeds.
> > 
> > Please don't make this always happen. c/mtime updates should be dependent
> > on the mode being used and whether there is visible change to the file. If no
> > userspace visible changes to the file occurred, then timestamps should not
> > be changed.
> 
> i_blocks will be updated, so it seems reasonable to update ctime.  mtime
> shouldn't be changed, though, since the contents of the file will be
> unchanged.

That's assuming blocks were actually allocated - if the prealloc range already
has underlying blocks there is no change and so we should not be changing
mtime either. Only the filesystem will know if it has changed the file, so I
think that timestamp updates need to be driven down to that level, not done
blindy at the highest layer....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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