Re: [PULL v2 10/16] block: introduce zone append write for zoned devices

[Peter Maydell]

On Mon, 15 May 2023 at 17:06, Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> From: Sam Li <faithilikerun@gmail.com>
>
> A zone append command is a write operation that specifies the first
> logical block of a zone as the write position. When writing to a zoned
> block device using zone append, the byte offset of the call may point at
> any position within the zone to which the data is being appended. Upon
> completion the device will respond with the position where the data has
> been written in the zone.
>
> Signed-off-by: Sam Li <faithilikerun@gmail.com>
> Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Message-id: 20230508051510.177850-3-faithilikerun@gmail.com
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Hi; Coverity flagged up a possible bug here (CID 1512459):

> @@ -2453,8 +2454,12 @@ static int coroutine_fn raw_co_prw(BlockDriverState 
> *bs, uint64_t offset,
>      if (fd_open(bs) < 0)
>          return -EIO;
>  #if defined(CONFIG_BLKZONED)
> -    if (type & QEMU_AIO_WRITE && bs->wps) {
> +    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) && bs->wps) {

Here we check for bs->wps being NULL, which implies that it might be NULL...

>          qemu_co_mutex_lock(&bs->wps->colock);
> +        if (type & QEMU_AIO_ZONE_APPEND && bs->bl.zone_size) {
> +            int index = offset / bs->bl.zone_size;
> +            offset = bs->wps->wp[index];
> +        }
>      }
>  #endif
>
> @@ -2502,9 +2507,13 @@ out:
>  {
>      BlockZoneWps *wps = bs->wps;
>      if (ret == 0) {
> -        if (type & QEMU_AIO_WRITE && wps && bs->bl.zone_size) {
> +        if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND))
> +            && wps && bs->bl.zone_size) {
>              uint64_t *wp = &wps->wp[offset / bs->bl.zone_size];
>              if (!BDRV_ZT_IS_CONV(*wp)) {
> +                if (type & QEMU_AIO_ZONE_APPEND) {
> +                    *s->offset = *wp;
> +                }
>                  /* Advance the wp if needed */
>                  if (offset + bytes > *wp) {
>                      *wp = offset + bytes;
> @@ -2512,12 +2521,12 @@ out:
>              }
>          }
>      } else {
> -        if (type & QEMU_AIO_WRITE) {
> +        if (type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) {

...but here we do not, even though update_zones_wp() can
dereference bs->wps in some code paths.

Should we be checking for NULL here before calling, or
should update_zones_wp() handle a NULL bs->wps, or something else?

>              update_zones_wp(bs, s->fd, 0, 1);
>          }
>      }
>
> -    if (type & QEMU_AIO_WRITE && wps) {
> +    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) && wps) {
>          qemu_co_mutex_unlock(&wps->colock);
>      }
>  }

thanks
-- PMM