linux-kernel - Re: [V3 PATCH 1/2] tmpfs: add fallocate support

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Date:	Thu, 24 Nov 2011 12:01:26 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Cong Wang <amwang@...hat.com>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Pekka Enberg <penberg@...nel.org>,
	Christoph Hellwig <hch@....de>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay.sievers@...y.org>, linux-mm@...ck.org
Subject: Re: [V3 PATCH 1/2] tmpfs: add fallocate support

On Wed, 23 Nov 2011 21:46:39 -0500
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> >> +     while (index < end) {
> >> +             ret = shmem_getpage(inode, index, &page, SGP_WRITE, NULL);
> >
> > If the 'page' for index exists before this call, this will return the page without
> > allocaton.
> >
> > Then, the page may not be zero-cleared. I think the page should be zero-cleared.
> 
> No. fallocate shouldn't destroy existing data. It only ensure
> subsequent file access don't make ENOSPC error.
> 
      FALLOC_FL_KEEP_SIZE
              This flag allocates and initializes to zero the disk  space
              within the range specified by offset and len. ....

just manual is unclear ? it seems that the range [offset, offset+len) is
zero cleared after the call.

Thanks,
-kame

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