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

[Kevin Wolf]

Am 19.03.2013 um 14:38 hat KONRAD Frédéric geschrieben:
> On 18/03/2013 09:59, Kevin Wolf wrote:
> >Am 15.03.2013 um 19:48 hat address@hidden geschrieben:
> >>From: KONRAD Frederic <address@hidden>
> >>
> >>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 <address@hidden>
> >>Reviewed-by: Peter Maydell <address@hidden>
> >>---
> >>  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).
> 
> You mean this copying (s->blk = *blk) ?

Or the memcpy() in your code, which should be equivalent.

Kevin

> >Is my understanding of this correct?
> >
> >Kevin
>