| Message ID | 1471015978-1123-4-git-send-email-stefanha@redhat.com |
|---|---|
| State | New |
| Headers | show |
On Fri, 12 Aug 2016 16:32:57 +0100 Stefan Hajnoczi <stefanha@redhat.com> wrote: > virtqueue_discard() requires a VirtQueueElement but virtio-balloon does > not migrate its in-use element. Introduce a new function that is > similar to virtqueue_discard() but doesn't require a VirtQueueElement. > > This will allow virtio-balloon to access element again after migration > with the usual proviso that the guest may have modified the vring since > last time. > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > hw/virtio/virtio.c | 22 ++++++++++++++++++++++ > include/hw/virtio/virtio.h | 1 + > 2 files changed, 23 insertions(+) > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 00158b6..22727ba 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -272,6 +272,28 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem, > virtqueue_unmap_sg(vq, elem, len); > } > > +/* virtqueue_rewind: > + * @vq: The #VirtQueue > + * @num: Number of elements to push back > + * > + * Pretend that elements weren't popped from the virtqueue. The next > + * virtqueue_pop() will refetch the oldest element. > + * > + * Use virtqueue_discard() instead if you have a VirtQueueElement. > + * > + * Returns: true on success, false if @num is greater than the number of in use > + * elements. Does it make sense at all to rewind multiple elements at once? Or does it make more sense for the caller to rewind one-by-one until they know that there are no more elements that could be refetched? > + */ > +bool virtqueue_rewind(VirtQueue *vq, unsigned int num) > +{ > + if (num > vq->inuse) { > + return false; > + } > + vq->last_avail_idx -= num; > + vq->inuse -= num; > + return true; > +} > + > void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, > unsigned int len, unsigned int idx) > {
On Mon, Aug 15, 2016 at 10:36:25AM +0200, Cornelia Huck wrote: > On Fri, 12 Aug 2016 16:32:57 +0100 > Stefan Hajnoczi <stefanha@redhat.com> wrote: > > > virtqueue_discard() requires a VirtQueueElement but virtio-balloon does > > not migrate its in-use element. Introduce a new function that is > > similar to virtqueue_discard() but doesn't require a VirtQueueElement. > > > > This will allow virtio-balloon to access element again after migration > > with the usual proviso that the guest may have modified the vring since > > last time. > > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > --- > > hw/virtio/virtio.c | 22 ++++++++++++++++++++++ > > include/hw/virtio/virtio.h | 1 + > > 2 files changed, 23 insertions(+) > > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > index 00158b6..22727ba 100644 > > --- a/hw/virtio/virtio.c > > +++ b/hw/virtio/virtio.c > > @@ -272,6 +272,28 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem, > > virtqueue_unmap_sg(vq, elem, len); > > } > > > > +/* virtqueue_rewind: > > + * @vq: The #VirtQueue > > + * @num: Number of elements to push back > > + * > > + * Pretend that elements weren't popped from the virtqueue. The next > > + * virtqueue_pop() will refetch the oldest element. > > + * > > + * Use virtqueue_discard() instead if you have a VirtQueueElement. > > + * > > + * Returns: true on success, false if @num is greater than the number of in use > > + * elements. > > Does it make sense at all to rewind multiple elements at once? Or does > it make more sense for the caller to rewind one-by-one until they know > that there are no more elements that could be refetched? I think Ladi's virtio-balloon stats fix using the vmchange callback is preferrable. I'll drop this and the next patch. Stefan
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 00158b6..22727ba 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -272,6 +272,28 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem, virtqueue_unmap_sg(vq, elem, len); } +/* virtqueue_rewind: + * @vq: The #VirtQueue + * @num: Number of elements to push back + * + * Pretend that elements weren't popped from the virtqueue. The next + * virtqueue_pop() will refetch the oldest element. + * + * Use virtqueue_discard() instead if you have a VirtQueueElement. + * + * Returns: true on success, false if @num is greater than the number of in use + * elements. + */ +bool virtqueue_rewind(VirtQueue *vq, unsigned int num) +{ + if (num > vq->inuse) { + return false; + } + vq->last_avail_idx -= num; + vq->inuse -= num; + return true; +} + void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, unsigned int len, unsigned int idx) { diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index d2490c1..f05559d 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -154,6 +154,7 @@ void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem, void virtqueue_flush(VirtQueue *vq, unsigned int count); void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem, unsigned int len); +bool virtqueue_rewind(VirtQueue *vq, unsigned int num); void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, unsigned int len, unsigned int idx);
virtqueue_discard() requires a VirtQueueElement but virtio-balloon does not migrate its in-use element. Introduce a new function that is similar to virtqueue_discard() but doesn't require a VirtQueueElement. This will allow virtio-balloon to access element again after migration with the usual proviso that the guest may have modified the vring since last time. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- hw/virtio/virtio.c | 22 ++++++++++++++++++++++ include/hw/virtio/virtio.h | 1 + 2 files changed, 23 insertions(+)