Re: [Qemu-devel] [PATCH] block: Avoid bogus flags during mirroring

[Fam Zheng <famz@redhat.com>]

On Sat, 06/11 19:18, Eric Blake wrote:
> Commit e253f4b8 converted mirroring from sector-based bdrv_aio_*
> to byte-based blk_aio_*, but failed to account for the subtle
> difference in signatures (the former takes a semi-redundant length,
> the latter takes a flags parameter).  Since all of our flags are
> currently smaller in size than BDRV_SECTOR_SIZE, it has no ill
> effects until we either perform sub-sector mirroring, or we start
> asserting that no unexpected flags are set.  I found it while
> testing new asserts when qemu-iotests 132 started warning about an
> unknown flag 0x200000.
> 
> Add an assert to help us catch any other improper flags.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  block/block-backend.c | 2 ++
>  block/mirror.c        | 6 ++----
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/block-backend.c b/block/block-backend.c
> index 34500e6..a5dc6e3 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -945,6 +945,8 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes,
>      acb->bh = NULL;
>      acb->has_returned = false;
> 
> +    assert(flags <= 0x1f);
> +

Maybe define BDRV_REQ_FLAGS_MAX in include/block/block.h so it's easier to keep
this assertion valid when we introduce more flags in the future?

Otherwise the patch looks good.

Fam

>      co = qemu_coroutine_create(co_entry);
>      qemu_coroutine_enter(co, acb);
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index fbbc496..41848b2 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -157,8 +157,7 @@ static void mirror_read_complete(void *opaque, int ret)
>          return;
>      }
>      blk_aio_pwritev(s->target, op->sector_num * BDRV_SECTOR_SIZE, &op->qiov,
> -                    op->nb_sectors * BDRV_SECTOR_SIZE,
> -                    mirror_write_complete, op);
> +                    0, mirror_write_complete, op);
>  }
> 
>  static inline void mirror_clip_sectors(MirrorBlockJob *s,
> @@ -275,8 +274,7 @@ static int mirror_do_read(MirrorBlockJob *s, int64_t sector_num,
>      s->sectors_in_flight += nb_sectors;
>      trace_mirror_one_iteration(s, sector_num, nb_sectors);
> 
> -    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov,
> -                   nb_sectors * BDRV_SECTOR_SIZE,
> +    blk_aio_preadv(source, sector_num * BDRV_SECTOR_SIZE, &op->qiov, 0,
>                     mirror_read_complete, op);
>      return ret;
>  }
> -- 
> 2.5.5
> 
>