This new command shows the information of a VirtQueue element.
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
hw/virtio/virtio-stub.c | 7 ++++
hw/virtio/virtio.c | 85 +++++++++++++++++++++++++++++++++++++++++
qapi/virtio.json | 85 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 177 insertions(+)
diff --git a/hw/virtio/virtio-stub.c b/hw/virtio/virtio-stub.c
index 5b4ed6fd531e..693f5eac409f 100644
--- a/hw/virtio/virtio-stub.c
+++ b/hw/virtio/virtio-stub.c
@@ -23,3 +23,10 @@ VirtQueueStatus *qmp_virtio_queue_status(const char *path, uint16_t queue,
{
return qmp_virtio_unsupported(errp);
}
+
+VirtioQueueElement *qmp_virtio_queue_element(const char* path, uint16_t queue,
+ bool has_index, uint16_t index,
+ Error **errp)
+{
+ return qmp_virtio_unsupported(errp);
+}
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 271d4ca3417f..28848b9e64cf 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3925,6 +3925,91 @@ VirtioStatus *qmp_virtio_status(const char* path, Error **errp)
return status;
}
+VirtioQueueElement *qmp_virtio_queue_element(const char* path, uint16_t queue,
+ bool has_index, uint16_t index,
+ Error **errp)
+{
+ VirtIODevice *vdev;
+ VirtQueue *vq;
+ VirtioQueueElement *element;
+
+ vdev = virtio_device_find(path);
+ if (vdev == NULL) {
+ error_setg(errp, "Path %s is not a VirtIO device", path);
+ return NULL;
+ }
+
+ if (queue >= VIRTIO_QUEUE_MAX || !virtio_queue_get_num(vdev, queue)) {
+ error_setg(errp, "Invalid virtqueue number %d", queue);
+ return NULL;
+ }
+ vq = &vdev->vq[queue];
+
+ if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) {
+ error_setg(errp, "Packed ring not supported");
+ return NULL;
+ } else {
+ unsigned int head, i, max;
+ VRingMemoryRegionCaches *caches;
+ MemoryRegionCache *desc_cache;
+ VRingDesc desc;
+
+ RCU_READ_LOCK_GUARD();
+ if (virtio_queue_empty_rcu(vq)) {
+ error_setg(errp, "Queue is empty");
+ return NULL;
+ }
+ /*
+ * Needed after virtio_queue_empty(), see comment in
+ * virtqueue_num_heads().
+ */
+ smp_rmb();
+
+ max = vq->vring.num;
+
+ if (vq->inuse >= vq->vring.num) {
+ error_setg(errp, "Queue size exceeded");
+ return NULL;
+ }
+
+ if (!has_index) {
+ head = vring_avail_ring(vq, vq->last_avail_idx % vq->vring.num);
+ } else {
+ head = vring_avail_ring(vq, index % vq->vring.num);
+ }
+ i = head;
+
+ caches = vring_get_region_caches(vq);
+ if (!caches) {
+ error_setg(errp, "Region caches not initialized");
+ return NULL;
+ }
+
+ if (caches->desc.len < max * sizeof(VRingDesc)) {
+ error_setg(errp, "Cannot map descriptor ring");
+ return NULL;
+ }
+
+ desc_cache = &caches->desc;
+ vring_split_desc_read(vdev, &desc, desc_cache, i);
+ if (desc.flags & VRING_DESC_F_INDIRECT) {
+ error_setg(errp, "Unsupported indirect buffer feature");
+ return NULL;
+ }
+
+ element = g_new0(VirtioQueueElement, 1);
+ element->index = head;
+ element->ndescs = 1;
+ element->descs = g_new0(VirtioRingDescList, 1);
+ element->descs->value = g_new0(VirtioRingDesc, 1);
+ element->descs->value->addr = desc.addr;
+ element->descs->value->len = desc.len;
+ element->descs->value->flags = desc.flags;
+ }
+
+ return element;
+}
+
static const TypeInfo virtio_device_info = {
.name = TYPE_VIRTIO_DEVICE,
.parent = TYPE_DEVICE,
diff --git a/qapi/virtio.json b/qapi/virtio.json
index ab70500d919b..3e8865511217 100644
--- a/qapi/virtio.json
+++ b/qapi/virtio.json
@@ -215,3 +215,88 @@
'data': { 'path': 'str', 'queue': 'uint16' },
'returns': 'VirtQueueStatus'
}
+
+##
+# @VirtioRingDesc:
+#
+# @addr: guest physical address of the descriptor data
+#
+# @len: length of the descriptor data
+#
+# @flags: descriptor flags (write-only, read-only, ...)
+#
+# Since: 5.1
+#
+##
+
+{ 'struct': 'VirtioRingDesc',
+ 'data': {
+ 'addr': 'uint64',
+ 'len': 'uint32',
+ 'flags': 'uint16'
+ }
+}
+
+##
+# @VirtioQueueElement:
+#
+# @index: index of the element in the queue
+#
+# @len: length of the element data
+#
+# @ndescs: number of descriptors
+#
+# @descs: list of the descriptors
+#
+# Since: 5.1
+#
+##
+
+{ 'struct': 'VirtioQueueElement',
+ 'data': {
+ 'index': 'uint32',
+ 'len': 'uint32',
+ 'ndescs': 'uint32',
+ 'descs': ['VirtioRingDesc']
+ }
+}
+
+##
+# @virtio-queue-element:
+#
+# Return the information about an element queue (by default head)
+#
+# @path: QOBject path of the VirtIODevice
+#
+# @queue: queue number to examine
+#
+# @index: the index in the queue, by default head
+#
+# Returns: the element information
+#
+# Since: 5.1
+#
+# Example:
+#
+# -> { "execute": "virtio-queue-element",
+# "arguments": {
+# "path": "/machine/peripheral-anon/device[3]/virtio-backend",
+# "queue": 0
+# }
+# }
+# -> { "return": {
+# "index": 109,
+# "len": 0,
+# "ndescs": 1,
+# "descs": [
+# { "flags": 2, "len": 2048, "addr": 853145600 }
+# ]
+# }
+# }
+#
+##
+
+{ 'command': 'virtio-queue-element',
+ 'data': { 'path': 'str', 'queue': 'uint16', '*index': 'uint16' },
+ 'returns': 'VirtioQueueElement'
+}
--
2.25.1
On 4/2/20 5:03 AM, Laurent Vivier wrote:
> This new command shows the information of a VirtQueue element.
>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> hw/virtio/virtio-stub.c | 7 ++++
> hw/virtio/virtio.c | 85 +++++++++++++++++++++++++++++++++++++++++
> qapi/virtio.json | 85 +++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 177 insertions(+)
>
> +##
> +# @VirtioRingDesc:
> +#
> +# @addr: guest physical address of the descriptor data
> +#
> +# @len: length of the descriptor data
> +#
> +# @flags: descriptor flags (write-only, read-only, ...)
> +#
> +# Since: 5.1
> +#
> +##
> +
> +{ 'struct': 'VirtioRingDesc',
> + 'data': {
> + 'addr': 'uint64',
> + 'len': 'uint32',
> + 'flags': 'uint16'
Again, flags should probably be an array of enum values, rather than a
bare int.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
* Laurent Vivier (lvivier@redhat.com) wrote:
> This new command shows the information of a VirtQueue element.
Having had a few second play with this, I think I've always seen it say
that the ring is empty; is this pretty much always the case when the VM
is running and the device is consuming elements off the queue - so most
cases where this is useful is where the VM is paused?
> + desc_cache = &caches->desc;
> + vring_split_desc_read(vdev, &desc, desc_cache, i);
> + if (desc.flags & VRING_DESC_F_INDIRECT) {
> + error_setg(errp, "Unsupported indirect buffer feature");
> + return NULL;
> + }
I did trigger this in the case I was playing with.
Dave
> + element = g_new0(VirtioQueueElement, 1);
> + element->index = head;
> + element->ndescs = 1;
> + element->descs = g_new0(VirtioRingDescList, 1);
> + element->descs->value = g_new0(VirtioRingDesc, 1);
> + element->descs->value->addr = desc.addr;
> + element->descs->value->len = desc.len;
> + element->descs->value->flags = desc.flags;
> + }
> +
> + return element;
> +}
> +
> static const TypeInfo virtio_device_info = {
> .name = TYPE_VIRTIO_DEVICE,
> .parent = TYPE_DEVICE,
> diff --git a/qapi/virtio.json b/qapi/virtio.json
> index ab70500d919b..3e8865511217 100644
> --- a/qapi/virtio.json
> +++ b/qapi/virtio.json
> @@ -215,3 +215,88 @@
> 'data': { 'path': 'str', 'queue': 'uint16' },
> 'returns': 'VirtQueueStatus'
> }
> +
> +##
> +# @VirtioRingDesc:
> +#
> +# @addr: guest physical address of the descriptor data
> +#
> +# @len: length of the descriptor data
> +#
> +# @flags: descriptor flags (write-only, read-only, ...)
> +#
> +# Since: 5.1
> +#
> +##
> +
> +{ 'struct': 'VirtioRingDesc',
> + 'data': {
> + 'addr': 'uint64',
> + 'len': 'uint32',
> + 'flags': 'uint16'
> + }
> +}
> +
> +##
> +# @VirtioQueueElement:
> +#
> +# @index: index of the element in the queue
> +#
> +# @len: length of the element data
> +#
> +# @ndescs: number of descriptors
> +#
> +# @descs: list of the descriptors
> +#
> +# Since: 5.1
> +#
> +##
> +
> +{ 'struct': 'VirtioQueueElement',
> + 'data': {
> + 'index': 'uint32',
> + 'len': 'uint32',
> + 'ndescs': 'uint32',
> + 'descs': ['VirtioRingDesc']
> + }
> +}
> +
> +##
> +# @virtio-queue-element:
> +#
> +# Return the information about an element queue (by default head)
> +#
> +# @path: QOBject path of the VirtIODevice
> +#
> +# @queue: queue number to examine
> +#
> +# @index: the index in the queue, by default head
> +#
> +# Returns: the element information
> +#
> +# Since: 5.1
> +#
> +# Example:
> +#
> +# -> { "execute": "virtio-queue-element",
> +# "arguments": {
> +# "path": "/machine/peripheral-anon/device[3]/virtio-backend",
> +# "queue": 0
> +# }
> +# }
> +# -> { "return": {
> +# "index": 109,
> +# "len": 0,
> +# "ndescs": 1,
> +# "descs": [
> +# { "flags": 2, "len": 2048, "addr": 853145600 }
> +# ]
> +# }
> +# }
> +#
> +##
> +
> +{ 'command': 'virtio-queue-element',
> + 'data': { 'path': 'str', 'queue': 'uint16', '*index': 'uint16' },
> + 'returns': 'VirtioQueueElement'
> +}
> --
> 2.25.1
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
© 2016 - 2025 Red Hat, Inc.