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

[Cong Wang <amwang@redhat.com>]

ao? 2011a1'11ae??24ae?JPY 11:01, KAMEZAWA Hiroyuki a??e??:
> 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

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