linux-ext4 - Re: [PATCH v2] ext4:Let ext4_ext_fiemap_cb() handle blocks before request range correctly.

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Date:	Tue, 10 May 2011 23:08:47 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH v2] ext4:Let ext4_ext_fiemap_cb() handle blocks before
 request range correctly.

On Tue, May 10, 2011 at 10:35 PM, Lukas Czerner <lczerner@...hat.com> wrote:
> On Tue, 10 May 2011, Yongqiang Yang wrote:
>
>> v1->v2:
>>   Add more specific description.
>>
>> To get delayed-extent information, ext4_ext_fiemap_cb() lookups pagecache,
>> it thus collects information starting from a page's head block.
>> If blockszie < pagesize, the beginning blocks of a page may lie before the
>> range.  ext4_ext_fiemap_cb() should proceed ignoring them, because they
>> has been handled before.
>
> Thanks for the description, but I have one question below.
>
>>
>> Reported-by: Amir Goldstein <amir73il@...rs.sf.net>
>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.com>
>> ---
>>  fs/ext4/extents.c |    7 ++++++-
>>  1 files changed, 6 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index e363f21..ec37109 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -3718,9 +3718,14 @@ out:
>>
>>                       bh = head;
>>                       do {
>> +                             if (end < newex->ec_block)
>> +                                     /* The buffer is not in
>> +                                      * the request range.
>> +                                      */
>> +                                     continue;
> So if the condition is true, then we might leave the loop, because (bh ==
> head) in the first iteration, is that desired behavior? Also if we hit
> this condition in other than first iteration we will spin forever. I do
> not think this is right. How did you tested this case ?
You are right.  Maybe the patch sent out is not same as the patch with
which I tested.  What a stupid error!
I am not sure what happened now.  I will check the patch with which I
tested tomorrow.

My working tree passed xfstests 225 in both 1k blocksize and 4k
blocksize cases.

Sorry!

Yongqiang.
>
> Thanks!
> -Lukas
>
>>                               if (buffer_mapped(bh)) {
>>                                       /* get the 1st mapped buffer. */
>> -                                     if (end > newex->ec_block +
>> +                                     if (end >= newex->ec_block +
>>                                               newex->ec_len)
>>                                               /* The buffer is out of
>>                                                * the request range.
>>
>



-- 
Best Wishes
Yongqiang Yang
--
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