Re: [Qemu-devel] [PATCH v9 03/10] virtio-blk: don't use pointer for configuration.

[Kevin Wolf <kwolf@redhat.com>]

Am 15.03.2013 um 19:48 hat fred.konrad@greensocs.com geschrieben:
> From: KONRAD Frederic <fred.konrad@greensocs.com>
> 
> The configuration field must not be a pointer as it will be used for virtio-blk
> properties. So *blk is replaced by blk in VirtIOBlock structure.
> 
> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/virtio-blk.c | 8 ++++----
>  hw/virtio-blk.h | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
> index 6714b01..908c316 100644
> --- a/hw/virtio-blk.c
> +++ b/hw/virtio-blk.c
> @@ -151,7 +151,7 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
>       */
>      req->scsi = (void *)req->elem.in_sg[req->elem.in_num - 2].iov_base;
>  
> -    if (!req->dev->blk->scsi) {
> +    if (!req->dev->blk.scsi) {
>          status = VIRTIO_BLK_S_UNSUPP;
>          goto fail;
>      }
> @@ -371,7 +371,7 @@ static void virtio_blk_handle_request(VirtIOBlockReq *req,
>           * terminated by '\0' only when shorter than buffer.
>           */
>          strncpy(req->elem.in_sg[0].iov_base,
> -                s->blk->serial ? s->blk->serial : "",
> +                s->blk.serial ? s->blk.serial : "",
>                  MIN(req->elem.in_sg[0].iov_len, VIRTIO_BLK_ID_BYTES));
>          virtio_blk_req_complete(req, VIRTIO_BLK_S_OK);
>          g_free(req);
> @@ -534,7 +534,7 @@ static uint32_t virtio_blk_get_features(VirtIODevice *vdev, uint32_t features)
>      features |= (1 << VIRTIO_BLK_F_BLK_SIZE);
>      features |= (1 << VIRTIO_BLK_F_SCSI);
>  
> -    if (s->blk->config_wce) {
> +    if (s->blk.config_wce) {
>          features |= (1 << VIRTIO_BLK_F_CONFIG_WCE);
>      }
>      if (bdrv_enable_write_cache(s->bs))
> @@ -650,7 +650,7 @@ VirtIODevice *virtio_blk_init(DeviceState *dev, VirtIOBlkConf *blk)
>      s->vdev.reset = virtio_blk_reset;
>      s->bs = blk->conf.bs;
>      s->conf = &blk->conf;
> -    s->blk = blk;
> +    memcpy(&(s->blk), blk, sizeof(struct VirtIOBlkConf));

Why not simply s->blk = *blk?

The reason why copying this works is that blk is read-only after
initialisation. We also get an additional reference to blk->serial, but
we know that it can only go away after this device has been destroyed
(the same assumption was necessary for the s->blk pointer in the old
code).

Is my understanding of this correct?

Kevin