Re: [Qemu-devel] [PATCH v2 6/9] block: Use common req handling for discard

[Kevin Wolf <kwolf@redhat.com>]

Am 05.07.2018 um 09:36 hat Fam Zheng geschrieben:
> Reuse the new bdrv_co_write_req_prepare/finish helpers. The variation
> here is that discard requests don't affect bs->wr_highest_offset.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/io.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index f06978dda0..912fcb962a 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1582,7 +1582,18 @@ bdrv_co_write_req_finish(BdrvChild *child, BdrvTrackedRequest *req, int ret)
>          bdrv_parent_cb_resize(bs);
>          bdrv_dirty_bitmap_truncate(bs, end_sector << BDRV_SECTOR_BITS);
>      }
> -    bdrv_set_dirty(bs, req->offset, req->bytes);
> +    if (req->bytes) {
> +        switch (req->type) {
> +        case BDRV_TRACKED_WRITE:
> +            stat64_max(&bs->wr_highest_offset, req->offset + req->bytes);

You forgot to remove this line above, so now this one is redundant and
we still execute it always.

Apart from that, why shouldn't discard be included in
bs->wr_highest_offset? It's an access to an area in the image that must
be present, so it indicates a larger file size, doesn't it?

> +            /* fall through, to set dirty bits */
> +        case BDRV_TRACKED_DISCARD:
> +            bdrv_set_dirty(bs, req->offset, req->bytes);
> +            break;
> +        default:
> +            break;
> +        }
> +    }
>  }

Kevin