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Date: Mon, 16 May 2011 14:53:18 +0300
From: Amir Goldstein <amir73il@...il.com>
To: Yongqiang Yang <xiaoqiangnk@...il.com>
Cc: linux-ext4@...r.kernel.org, lczerner@...hat.com, tytso@....edu
Subject: Re: [PATCH v3] ext4:Let ext4_ext_fiemap_cb() handle blocks before
request range correctly.
On Mon, May 16, 2011 at 2:27 PM, Yongqiang Yang <xiaoqiangnk@...il.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?
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
>
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@...il.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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