Re: [PATCH v3] ext4:Let ext4_ext_fiemap_cb() handle blocks before request range correctly.

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On Sun, May 22, 2011 at 4:35 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> On Mon, May 16, 2011 at 4:15 PM, Yongqiang Yang <xiaoqiangnk@xxxxxxxxx> wrote:
>> On Mon, May 16, 2011 at 7:53 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>>> On Mon, May 16, 2011 at 2:27 PM, Yongqiang Yang <xiaoqiangnk@xxxxxxxxx> wrote:
>>>> To get delayed-extent information, ext4_ext_fiemap_cb() looks up
>>>> pagecache, it thus collects information starting from a page's
>>>> head block.
>>>>
>>>> If blocksize < pagesize, the beginning blocks of a page may lies
>>>> before the request range. So ext4_ext_fiemap_cb() should proceed
>>>> ignoring them, because they has been handled before. If no mapped
>>>> buffer in the range is found in the 1st page, we need to look up
>>>> the 2nd page, otherwise delayed-extents after a hole will be ignored.
>>>
>>> Does this patch fix the endless loop I encountered?
>> Yes, it fixes another bug.
>>> If so, you may want to add to commit message:
>>> - Reported-by: Amir..
>>> - that the patch fixes a hang bug
>>> - how was it reproduced
>>> - which commit introduced the bug
>> Sorry, I forgot to add these.   I rewrote the xfstests 225 and found
>> another bug which the old 225 could not find.
>> I think I should resend this patch.
>
> Hi Yongqiang,
>
> Did you resend this patch? I see that Ted hasn't picked it up yet.
> Apparently, he is expecting to get a new version from you with proper
> commit log (I think he mentioned that on last week's confcall).
Sorry,  I had a travel in last three days without a computer.   I will
send it out tomorrow.

>
> Amir.
>
>>
>>>
>>>>
>>>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
>>>> ---
>>>>  fs/ext4/extents.c |   51 ++++++++++++++++++++++++++++++++++++---------------
>>>>  1 files changed, 36 insertions(+), 15 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>>> index e363f21..474eaad 100644
>>>> --- a/fs/ext4/extents.c
>>>> +++ b/fs/ext4/extents.c
>>>> @@ -3680,6 +3680,7 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
>>>>                pgoff_t         last_offset;
>>>>                pgoff_t         offset;
>>>>                pgoff_t         index;
>>>> +               pgoff_t         start_index = 0;
>>>>                struct page     **pages = NULL;
>>>>                struct buffer_head *bh = NULL;
>>>>                struct buffer_head *head = NULL;
>>>> @@ -3706,39 +3707,57 @@ out:
>>>>                                kfree(pages);
>>>>                                return EXT_CONTINUE;
>>>>                        }
>>>> +                       index = 0;
>>>>
>>>> +next_page:
>>>>                        /* Try to find the 1st mapped buffer. */
>>>> -                       end = ((__u64)pages[0]->index << PAGE_SHIFT) >>
>>>> +                       end = ((__u64)pages[index]->index << PAGE_SHIFT) >>
>>>>                                  blksize_bits;
>>>> -                       if (!page_has_buffers(pages[0]))
>>>> +                       if (!page_has_buffers(pages[index]))
>>>>                                goto out;
>>>> -                       head = page_buffers(pages[0]);
>>>> +                       head = page_buffers(pages[index]);
>>>>                        if (!head)
>>>>                                goto out;
>>>> -
>>>> +
>>>> +                       index++;
>>>>                        bh = head;
>>>>                        do {
>>>> -                               if (buffer_mapped(bh)) {
>>>> +                               if (end >= newex->ec_block +
>>>> +                                       newex->ec_len)
>>>> +                                       /* The buffer is out of
>>>> +                                        * the request range.
>>>> +                                        */
>>>> +                                       goto out;
>>>> +
>>>> +                               if (buffer_mapped(bh) &&
>>>> +                                   end >= newex->ec_block) {
>>>> +                                       start_index = index - 1;
>>>>                                        /* get the 1st mapped buffer. */
>>>> -                                       if (end > newex->ec_block +
>>>> -                                               newex->ec_len)
>>>> -                                               /* The buffer is out of
>>>> -                                                * the request range.
>>>> -                                                */
>>>> -                                               goto out;
>>>>                                        goto found_mapped_buffer;
>>>>                                }
>>>> +
>>>>                                bh = bh->b_this_page;
>>>>                                end++;
>>>>                        } while (bh != head);
>>>>
>>>> -                       /* No mapped buffer found. */
>>>> -                       goto out;
>>>> +                       /* No mapped buffer in the range found in this page,
>>>> +                        * We need to look up next page.
>>>> +                        */
>>>> +                       if (index >= ret) {
>>>> +                               /* There is no page left, but we need to limit
>>>> +                                * newex->ec_len.
>>>> +                                */
>>>> +                               newex->ec_len = end - newex->ec_block;
>>>> +                               goto out;
>>>> +                       }
>>>> +                       goto next_page;
>>>>                } else {
>>>>                        /*Find contiguous delayed buffers. */
>>>>                        if (ret > 0 && pages[0]->index == last_offset)
>>>>                                head = page_buffers(pages[0]);
>>>>                        bh = head;
>>>> +                       index = 1;
>>>> +                       start_index = 0;
>>>>                }
>>>>
>>>>  found_mapped_buffer:
>>>> @@ -3761,7 +3780,7 @@ found_mapped_buffer:
>>>>                                end++;
>>>>                        } while (bh != head);
>>>>
>>>> -                       for (index = 1; index < ret; index++) {
>>>> +                       for (; index < ret; index++) {
>>>>                                if (!page_has_buffers(pages[index])) {
>>>>                                        bh = NULL;
>>>>                                        break;
>>>> @@ -3771,8 +3790,10 @@ found_mapped_buffer:
>>>>                                        bh = NULL;
>>>>                                        break;
>>>>                                }
>>>> +
>>>>                                if (pages[index]->index !=
>>>> -                                       pages[0]->index + index) {
>>>> +                                   pages[start_index]->index + index
>>>> +                                   - start_index) {
>>>>                                        /* Blocks are not contiguous. */
>>>>                                        bh = NULL;
>>>>                                        break;
>>>> --
>>>> 1.7.5.1
>>>>
>>>> --
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>>>>
>>>
>>
>>
>>
>> --
>> Best Wishes
>> Yongqiang Yang
>>
>



-- 
Best Wishes
Yongqiang Yang
--
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