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

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Message-ID: <4ECDB87A.90106@redhat.com>
Date:	Thu, 24 Nov 2011 11:22:34 +0800
From:	Cong Wang <amwang@...hat.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.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

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@...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
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