On Wed, 06/22 15:51, John Snow wrote:
> mirror_do_read intends to return the number of sectors processed after
> the starting sector, without regard to how many sectors were processed
> before the starting sector due to alignment.
>
> Clean up the comments and code to hopefully illustrate this more clearly.
>
> This also fixes an issue in initialization where if the mirror buffer size
> is initialized to smaller than the number of sectors being requested for
> transfer, we report back an incorrectly large number to the caller.
Good catch!
Reviewed-by: Fam Zheng <f...@redhat.com>
>
> Signed-off-by: John Snow <js...@redhat.com>
> ---
> block/mirror.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/block/mirror.c b/block/mirror.c
> index a04ed9c..2ba9642 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -218,7 +218,9 @@ static inline void mirror_wait_for_io(MirrorBlockJob *s)
> }
>
> /* Submit async read while handling COW.
> - * Returns: nb_sectors if no alignment is necessary, or
> + * Returns: The number of sectors copied after and including sector_num,
> + * excluding any sectors copied prior to sector_num due to
> alignment.
> + * This will be nb_sectors if no alignment is necessary, or
> * (new_end - sector_num) if tail is rounded up or down due to
> * alignment or buffer limit.
> */
> @@ -227,7 +229,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t
> sector_num,
> {
> BlockBackend *source = s->common.blk;
> int sectors_per_chunk, nb_chunks;
> - int ret = nb_sectors;
> + int ret;
> MirrorOp *op;
>
> sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
> @@ -235,6 +237,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t
> sector_num,
> /* We can only handle as much as buf_size at a time. */
> nb_sectors = MIN(s->buf_size >> BDRV_SECTOR_BITS, nb_sectors);
> assert(nb_sectors);
> + ret = nb_sectors;
>
> if (s->cow_bitmap) {
> ret += mirror_cow_align(s, §or_num, &nb_sectors);
> --
> 2.4.11
>
