On 2018年04月04日 20:53, w...@redhat.com wrote:
From: Wei Xu <w...@redhat.com>
helper for ring empty check.
And descriptor read.
Signed-off-by: Wei Xu <w...@redhat.com>
---
hw/virtio/virtio.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 59 insertions(+), 3 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 73a35a4..478df3d 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -24,6 +24,9 @@
#include "hw/virtio/virtio-access.h"
#include "sysemu/dma.h"
+#define AVAIL_DESC_PACKED(b) ((b) << 7)
+#define USED_DESC_PACKED(b) ((b) << 15)
Can we pass value other than 1 to this macro?
+
/*
* The alignment to use between consumer and producer parts of vring.
* x86 pagesize again. This is the default, used by transports like PCI
@@ -446,10 +449,27 @@ int virtio_queue_ready(VirtQueue *vq)
return vq->vring.avail != 0;
}
+static void vring_desc_read_packed(VirtIODevice *vdev, VRingDescPacked *desc,
+ MemoryRegionCache *cache, int i)
+{
+ address_space_read_cached(cache, i * sizeof(VRingDescPacked),
+ desc, sizeof(VRingDescPacked));
+ virtio_tswap64s(vdev, &desc->addr);
+ virtio_tswap32s(vdev, &desc->len);
+ virtio_tswap16s(vdev, &desc->id);
+ virtio_tswap16s(vdev, &desc->flags);
+}
+
+static inline bool is_desc_avail(struct VRingDescPacked* desc)
+{
+ return (!!(desc->flags & AVAIL_DESC_PACKED(1)) !=
+ !!(desc->flags & USED_DESC_PACKED(1)));
Don't we need to care about endian here?
+}
+
/* Fetch avail_idx from VQ memory only when we really need to know if
* guest has added some buffers.
* Called within rcu_read_lock(). */
-static int virtio_queue_empty_rcu(VirtQueue *vq)
+static int virtio_queue_empty_split_rcu(VirtQueue *vq)
{
if (unlikely(!vq->vring.avail)) {
return 1;
@@ -462,7 +482,7 @@ static int virtio_queue_empty_rcu(VirtQueue *vq)
return vring_avail_idx(vq) == vq->last_avail_idx;
}
-int virtio_queue_empty(VirtQueue *vq)
+static int virtio_queue_empty_split(VirtQueue *vq)
{
bool empty;
@@ -480,6 +500,42 @@ int virtio_queue_empty(VirtQueue *vq)
return empty;
}
+static int virtio_queue_empty_packed_rcu(VirtQueue *vq)
+{
+ struct VRingDescPacked desc;
+ VRingMemoryRegionCaches *cache;
+
+ if (unlikely(!vq->packed.desc)) {
+ return 1;
+ }
+
+ cache = vring_get_region_caches(vq);
+ vring_desc_read_packed(vq->vdev, &desc, &cache->desc_packed,
vq->last_avail_idx);
+
+ /* Make sure we see the updated flag */
+ smp_mb();
What we need here is to make sure flag is read before all other fields,
looks like this barrier can't.
+ return !is_desc_avail(&desc);
+}
+
+static int virtio_queue_empty_packed(VirtQueue *vq)
+{
+ bool empty;
+
+ rcu_read_lock();
+ empty = virtio_queue_empty_packed_rcu(vq);
+ rcu_read_unlock();
+ return empty;
+}
+
+int virtio_queue_empty(VirtQueue *vq)
+{
+ if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+ return virtio_queue_empty_packed(vq);
+ } else {
+ return virtio_queue_empty_split(vq);
+ }
+}
+
static void virtqueue_unmap_sg(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len)
{
@@ -951,7 +1007,7 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz)
return NULL;
}
rcu_read_lock();
- if (virtio_queue_empty_rcu(vq)) {
+ if (virtio_queue_empty_split_rcu(vq)) {
I think you'd better have a switch inside virtio_queue_empty_rcu() like
virtio_queue_empty() here.
Thanks
goto done;
}
/* Needed after virtio_queue_empty(), see comment in