> On Jan 10, 2016, at 11:27 PM, Fan Li <fanofcode.li@xxxxxxxxxxx> wrote:
>
> When len is less than one block, it will be extended to
> one block. If start + len exceeds the boundary of the
> original block because of the extension, one needless block
> will be returned.
>
> And this patch only tries to map blocks within range instead
> of mapping as many contiguous blocks as possible at once.
> That's because comparing to extent-based files, find mapping
> for indirect-based files could be time-consuming, especially
> after we found the last extent we need, we don't care how
> long the next extent, and should return right after find
> a mapped block or EOF.
>
> Signed-off-by: Fan Li <fanofcode.li@xxxxxxxxxxx>
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> fs/ioctl.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 13a3e96..5d54377 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -276,23 +276,21 @@ int __generic_block_fiemap(struct inode *inode,
> len = isize - start;
> }
>
> - /*
> - * Some filesystems can't deal with being asked to map less than
> - * blocksize, so make sure our len is at least block length.
> - */
> - if (logical_to_blk(inode, len) == 0)
> - len = blk_to_logical(inode, 1);
> -
> start_blk = logical_to_blk(inode, start);
> last_blk = logical_to_blk(inode, start + len - 1);
>
> do {
> + memset(&map_bh, 0, sizeof(struct buffer_head));
> /*
> - * we set b_size to the total size we want so it will map as
> - * many contiguous blocks as possible at once
> + * Some filesystems would round down b_size to align
> + * with block size, if len isn't aligned already, the last
> + * block may not be returned. Let's round it up first.
> */
> - memset(&map_bh, 0, sizeof(struct buffer_head));
> - map_bh.b_size = len;
> + if (last_blk > start_blk)
> + map_bh.b_size = blk_to_logical(inode,
> + last_blk - start_blk + 1);
> + else
> + map_bh.b_size = blk_to_logical(inode, 1);
>
> ret = get_block(inode, start_blk, &map_bh, 0);
> if (ret)
> --
> 1.7.9.5
>
> --
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Cheers, Andreas
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