[PULL 76/91] qmp: add QMP command x-query-virtio-queue-element

[Michael S. Tsirkin]

From: Laurent Vivier <lvivier@redhat.com>

This new command shows the information of a VirtQueue element.

[Note: Up until v10 of this patch series, virtio.json had many (15+)
 enums defined (e.g. decoded device features, statuses, etc.). In v10
 most of these enums were removed and replaced with string literals.
 By doing this we get (1) simpler schema, (2) smaller generated code,
 and (3) less maintenance burden for when new things are added (e.g.
 devices, device features, etc.).]

Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
Message-Id: <1648819405-25696-8-git-send-email-jonah.palmer@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 qapi/virtio.json        | 183 ++++++++++++++++++++++++++++++++++++++++
 hw/virtio/virtio-stub.c |   9 ++
 hw/virtio/virtio.c      | 154 +++++++++++++++++++++++++++++++++
 3 files changed, 346 insertions(+)

diff --git a/qapi/virtio.json b/qapi/virtio.json
index 44cc05ceeb..99b9064902 100644
--- a/qapi/virtio.json
+++ b/qapi/virtio.json
@@ -656,3 +656,186 @@
   'data': { 'path': 'str', 'queue': 'uint16' },
   'returns': 'VirtVhostQueueStatus',
   'features': [ 'unstable' ] }
+
+##
+# @VirtioRingDesc:
+#
+# Information regarding the vring descriptor area
+#
+# @addr: Guest physical address of the descriptor area
+#
+# @len: Length of the descriptor area
+#
+# @flags: List of descriptor flags
+#
+# Since: 7.0
+#
+##
+
+{ 'struct': 'VirtioRingDesc',
+  'data': { 'addr': 'uint64',
+            'len': 'uint32',
+            'flags': [ 'str' ] } }
+
+##
+# @VirtioRingAvail:
+#
+# Information regarding the avail vring (a.k.a. driver area)
+#
+# @flags: VRingAvail flags
+#
+# @idx: VRingAvail index
+#
+# @ring: VRingAvail ring[] entry at provided index
+#
+# Since: 7.0
+#
+##
+
+{ 'struct': 'VirtioRingAvail',
+  'data': { 'flags': 'uint16',
+            'idx': 'uint16',
+            'ring': 'uint16' } }
+
+##
+# @VirtioRingUsed:
+#
+# Information regarding the used vring (a.k.a. device area)
+#
+# @flags: VRingUsed flags
+#
+# @idx: VRingUsed index
+#
+# Since: 7.0
+#
+##
+
+{ 'struct': 'VirtioRingUsed',
+  'data': { 'flags': 'uint16',
+            'idx': 'uint16' } }
+
+##
+# @VirtioQueueElement:
+#
+# Information regarding a VirtQueue's VirtQueueElement including
+# descriptor, driver, and device areas
+#
+# @name: Name of the VirtIODevice that uses this VirtQueue
+#
+# @index: Index of the element in the queue
+#
+# @descs: List of descriptors (VirtioRingDesc)
+#
+# @avail: VRingAvail info
+#
+# @used: VRingUsed info
+#
+# Since: 7.0
+#
+##
+
+{ 'struct': 'VirtioQueueElement',
+  'data': { 'name': 'str',
+            'index': 'uint32',
+            'descs': [ 'VirtioRingDesc' ],
+            'avail': 'VirtioRingAvail',
+            'used': 'VirtioRingUsed' } }
+
+##
+# @x-query-virtio-queue-element:
+#
+# Return the information about a VirtQueue's VirtQueueElement
+#
+# @path: VirtIODevice canonical QOM path
+#
+# @queue: VirtQueue index to examine
+#
+# @index: Index of the element in the queue
+#         (default: head of the queue)
+#
+# Features:
+# @unstable: This command is meant for debugging.
+#
+# Returns: VirtioQueueElement information
+#
+# Since: 7.0
+#
+# Examples:
+#
+# 1. Introspect on virtio-net's VirtQueue 0 at index 5
+#
+# -> { "execute": "x-query-virtio-queue-element",
+#      "arguments": { "path": 
"/machine/peripheral-anon/device[1]/virtio-backend",
+#                     "queue": 0,
+#                     "index": 5 }
+#    }
+# <- { "return": {
+#            "index": 5,
+#            "name": "virtio-net",
+#            "descs": [
+#               { "flags": ["write"], "len": 1536, "addr": 5257305600 }
+#            ],
+#            "avail": {
+#               "idx": 256,
+#               "flags": 0,
+#               "ring": 5
+#            },
+#            "used": {
+#               "idx": 13,
+#               "flags": 0
+#            },
+#    }
+#
+# 2. Introspect on virtio-crypto's VirtQueue 1 at head
+#
+# -> { "execute": "x-query-virtio-queue-element",
+#      "arguments": { "path": "/machine/peripheral/crypto0/virtio-backend",
+#                     "queue": 1 }
+#    }
+# <- { "return": {
+#            "index": 0,
+#            "name": "virtio-crypto",
+#            "descs": [
+#               { "flags": [], "len": 0, "addr": 8080268923184214134 }
+#            ],
+#            "avail": {
+#               "idx": 280,
+#               "flags": 0,
+#               "ring": 0
+#            },
+#            "used": {
+#               "idx": 280,
+#               "flags": 0
+#            }
+#    }
+#
+# 3. Introspect on virtio-scsi's VirtQueue 2 at head
+#
+# -> { "execute": "x-query-virtio-queue-element",
+#      "arguments": { "path": 
"/machine/peripheral-anon/device[2]/virtio-backend",
+#                     "queue": 2 }
+#    }
+# <- { "return": {
+#            "index": 19,
+#            "name": "virtio-scsi",
+#            "descs": [
+#               { "flags": ["used", "indirect", "write"], "len": 4099327944,
+#                 "addr": 12055409292258155293 }
+#            ],
+#            "avail": {
+#               "idx": 1147,
+#               "flags": 0,
+#               "ring": 19
+#            },
+#            "used": {
+#               "idx": 280,
+#               "flags": 0
+#            }
+#    }
+#
+##
+
+{ 'command': 'x-query-virtio-queue-element',
+  'data': { 'path': 'str', 'queue': 'uint16', '*index': 'uint16' },
+  'returns': 'VirtioQueueElement',
+  'features': [ 'unstable' ] }
diff --git a/hw/virtio/virtio-stub.c b/hw/virtio/virtio-stub.c
index 13e5f93652..7ddb22cc5e 100644
--- a/hw/virtio/virtio-stub.c
+++ b/hw/virtio/virtio-stub.c
@@ -31,3 +31,12 @@ VirtQueueStatus *qmp_x_query_virtio_queue_status(const char 
*path,
 {
     return qmp_virtio_unsupported(errp);
 }
+
+VirtioQueueElement *qmp_x_query_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 0a4cf62bbe..716b64c43a 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -489,6 +489,19 @@ static inline void vring_used_write(VirtQueue *vq, 
VRingUsedElem *uelem,
     address_space_cache_invalidate(&caches->used, pa, sizeof(VRingUsedElem));
 }
 
+/* Called within rcu_read_lock(). */
+static inline uint16_t vring_used_flags(VirtQueue *vq)
+{
+    VRingMemoryRegionCaches *caches = vring_get_region_caches(vq);
+    hwaddr pa = offsetof(VRingUsed, flags);
+
+    if (!caches) {
+        return 0;
+    }
+
+    return virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
+}
+
 /* Called within rcu_read_lock().  */
 static uint16_t vring_used_idx(VirtQueue *vq)
 {
@@ -4432,6 +4445,147 @@ VirtQueueStatus *qmp_x_query_virtio_queue_status(const 
char *path,
     return status;
 }
 
+static strList *qmp_decode_vring_desc_flags(uint16_t flags)
+{
+    strList *list = NULL;
+    strList *node;
+    int i;
+
+    struct {
+        uint16_t flag;
+        const char *value;
+    } map[] = {
+        { VRING_DESC_F_NEXT, "next" },
+        { VRING_DESC_F_WRITE, "write" },
+        { VRING_DESC_F_INDIRECT, "indirect" },
+        { 1 << VRING_PACKED_DESC_F_AVAIL, "avail" },
+        { 1 << VRING_PACKED_DESC_F_USED, "used" },
+        { 0, "" }
+    };
+
+    for (i = 0; map[i].flag; i++) {
+        if ((map[i].flag & flags) == 0) {
+            continue;
+        }
+        node = g_malloc0(sizeof(strList));
+        node->value = g_strdup(map[i].value);
+        node->next = list;
+        list = node;
+    }
+
+    return list;
+}
+
+VirtioQueueElement *qmp_x_query_virtio_queue_element(const char *path,
+                                                     uint16_t queue,
+                                                     bool has_index,
+                                                     uint16_t index,
+                                                     Error **errp)
+{
+    VirtIODevice *vdev;
+    VirtQueue *vq;
+    VirtioQueueElement *element = NULL;
+
+    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 indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
+        MemoryRegionCache *desc_cache;
+        VRingDesc desc;
+        VirtioRingDescList *list = NULL;
+        VirtioRingDescList *node;
+        int rc; int ndescs;
+
+        RCU_READ_LOCK_GUARD();
+
+        max = vq->vring.num;
+
+        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) {
+            int64_t len;
+            len = address_space_cache_init(&indirect_desc_cache, vdev->dma_as,
+                                           desc.addr, desc.len, false);
+            desc_cache = &indirect_desc_cache;
+            if (len < desc.len) {
+                error_setg(errp, "Cannot map indirect buffer");
+                goto done;
+            }
+
+            max = desc.len / sizeof(VRingDesc);
+            i = 0;
+            vring_split_desc_read(vdev, &desc, desc_cache, i);
+        }
+
+        element = g_new0(VirtioQueueElement, 1);
+        element->avail = g_new0(VirtioRingAvail, 1);
+        element->used = g_new0(VirtioRingUsed, 1);
+        element->name = g_strdup(vdev->name);
+        element->index = head;
+        element->avail->flags = vring_avail_flags(vq);
+        element->avail->idx = vring_avail_idx(vq);
+        element->avail->ring = head;
+        element->used->flags = vring_used_flags(vq);
+        element->used->idx = vring_used_idx(vq);
+        ndescs = 0;
+
+        do {
+            /* A buggy driver may produce an infinite loop */
+            if (ndescs >= max) {
+                break;
+            }
+            node = g_new0(VirtioRingDescList, 1);
+            node->value = g_new0(VirtioRingDesc, 1);
+            node->value->addr = desc.addr;
+            node->value->len = desc.len;
+            node->value->flags = qmp_decode_vring_desc_flags(desc.flags);
+            node->next = list;
+            list = node;
+
+            ndescs++;
+            rc = virtqueue_split_read_next_desc(vdev, &desc, desc_cache,
+                                                max, &i);
+        } while (rc == VIRTQUEUE_READ_DESC_MORE);
+        element->descs = list;
+done:
+        address_space_cache_destroy(&indirect_desc_cache);
+    }
+
+    return element;
+}
+
 static const TypeInfo virtio_device_info = {
     .name = TYPE_VIRTIO_DEVICE,
     .parent = TYPE_DEVICE,
-- 
MST