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

[Amir Goldstein <amir73il@gmail.com>]

On Mon, May 16, 2011 at 4:15 PM, Yongqiang Yang <xiaoqiangnk@gmail.com> wrote:
> On Mon, May 16, 2011 at 7:53 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>> On Mon, May 16, 2011 at 2:27 PM, Yongqiang Yang <xiaoqiangnk@gmail.com> 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).

Amir.

>
>>
>>>
>>> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
>>> ---
>>>  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
>