Re: [Qemu-devel] [PATCH 2/2] nbd: fix max_discard

[Peter Lieven <pl@kamp.de>]

Am 02.02.2015 um 19:29 schrieb Denis V. Lunev:
> nbd_co_discard calls nbd_client_session_co_discard which uses uint32_t
> as the length in bytes of the data to discard due to the following
> definition:
>
> struct nbd_request {
>     uint32_t magic;
>     uint32_t type;
>     uint64_t handle;
>     uint64_t from;
>     uint32_t len; <-- the length of data to be discarded, in bytes
> } QEMU_PACKED;
>
> Thus we should limit bl_max_discard to UINT32_MAX >> BDRV_SECTOR_BITS to
> avoid overflow.
>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Peter Lieven <pl@kamp.de>
> ---
>  block/nbd.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/block/nbd.c b/block/nbd.c
> index 04cc845..99af713 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -301,6 +301,11 @@ static int nbd_co_flush(BlockDriverState *bs)
>      return nbd_client_session_co_flush(&s->client);
>  }
>  
> +static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
> +{
> +    bs->bl.max_discard = UINT32_MAX >> BDRV_SECTOR_BITS;
> +}
> +
>  static int nbd_co_discard(BlockDriverState *bs, int64_t sector_num,
>                            int nb_sectors)
>  {
> @@ -396,6 +401,7 @@ static BlockDriver bdrv_nbd = {
>      .bdrv_close                 = nbd_close,
>      .bdrv_co_flush_to_os        = nbd_co_flush,
>      .bdrv_co_discard            = nbd_co_discard,
> +    .bdrv_refresh_limits        = nbd_refresh_limits,
>      .bdrv_getlength             = nbd_getlength,
>      .bdrv_detach_aio_context    = nbd_detach_aio_context,
>      .bdrv_attach_aio_context    = nbd_attach_aio_context,
> @@ -413,6 +419,7 @@ static BlockDriver bdrv_nbd_tcp = {
>      .bdrv_close                 = nbd_close,
>      .bdrv_co_flush_to_os        = nbd_co_flush,
>      .bdrv_co_discard            = nbd_co_discard,
> +    .bdrv_refresh_limits        = nbd_refresh_limits,
>      .bdrv_getlength             = nbd_getlength,
>      .bdrv_detach_aio_context    = nbd_detach_aio_context,
>      .bdrv_attach_aio_context    = nbd_attach_aio_context,
> @@ -430,6 +437,7 @@ static BlockDriver bdrv_nbd_unix = {
>      .bdrv_close                 = nbd_close,
>      .bdrv_co_flush_to_os        = nbd_co_flush,
>      .bdrv_co_discard            = nbd_co_discard,
> +    .bdrv_refresh_limits        = nbd_refresh_limits,
>      .bdrv_getlength             = nbd_getlength,
>      .bdrv_detach_aio_context    = nbd_detach_aio_context,
>      .bdrv_attach_aio_context    = nbd_attach_aio_context,

Reviewed-by: Peter Lieven <pl@kamp.de>