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Date: Thu, 24 Nov 2011 11:22:34 +0800
From: Cong Wang <amwang@redhat.com>
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To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        Pekka Enberg <penberg@kernel.org>, Christoph Hellwig <hch@lst.de>,
        Hugh Dickins <hughd@google.com>, Dave Hansen <dave@linux.vnet.ibm.com>,
        Lennart Poettering <lennart@poettering.net>,
        Kay Sievers <kay.sievers@vrfy.org>, linux-mm@kvack.org
Subject: Re: [V3 PATCH 1/2] tmpfs: add fallocate support
References: <1322038412-29013-1-git-send-email-amwang@redhat.com>	<20111124105245.b252c65f.kamezawa.hiroyu@jp.fujitsu.com>	<CAHGf_=oD0Coc=k5kAAQoP=GqK+nc0jd3qq3TmLZaitSjH-ZPmQ@mail.gmail.com> <20111124120126.9361b2c9.kamezawa.hiroyu@jp.fujitsu.com>
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于 2011年11月24日 11:01, KAMEZAWA Hiroyuki 写道:
> On Wed, 23 Nov 2011 21:46:39 -0500
> KOSAKI Motohiro<kosaki.motohiro@jp.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.

I think we should fix the man page, because at least ext4 doesn't clear
the original contents,

% echo hi > /tmp/foobar
% fallocate -n -l 1 -o 10 /tmp/foobar
% hexdump -Cv /tmp/foobar
00000000  68 69 0a                                          |hi.|
00000003