libvhost-user: handle shared_object msg

In the libvhost-user library we need to
handle VHOST_USER_GET_SHARED_OBJECT requests,
and add helper functions to allow sending messages
to interact with the virtio shared objects
hash table.

Signed-off-by: Albert Esteve <aesteve@redhat.com>
Message-Id: <20231002065706.94707-5-aesteve@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -161,6 +161,7 @@ vu_request_to_string(unsigned int req)
         REQ(VHOST_USER_GET_MAX_MEM_SLOTS),
         REQ(VHOST_USER_ADD_MEM_REG),
         REQ(VHOST_USER_REM_MEM_REG),
+        REQ(VHOST_USER_GET_SHARED_OBJECT),
         REQ(VHOST_USER_MAX),
     };
 #undef REQ
@@ -901,6 +902,24 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
     return false;
 }
 
+static bool
+vu_get_shared_object(VuDev *dev, VhostUserMsg *vmsg)
+{
+    int fd_num = 0;
+    int dmabuf_fd = -1;
+    if (dev->iface->get_shared_object) {
+        dmabuf_fd = dev->iface->get_shared_object(
+            dev, &vmsg->payload.object.uuid[0]);
+    }
+    if (dmabuf_fd != -1) {
+        DPRINT("dmabuf_fd found for requested UUID\n");
+        vmsg->fds[fd_num++] = dmabuf_fd;
+    }
+    vmsg->fd_num = fd_num;
+
+    return true;
+}
+
 static bool
 vu_set_mem_table_exec_postcopy(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1404,6 +1423,105 @@ bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, int fd,
     return vu_process_message_reply(dev, &vmsg);
 }
 
+bool
+vu_lookup_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN],
+                        int *dmabuf_fd)
+{
+    bool result = false;
+    VhostUserMsg msg_reply;
+    VhostUserMsg msg = {
+        .request = VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP,
+        .size = sizeof(msg.payload.object),
+        .flags = VHOST_USER_VERSION | VHOST_USER_NEED_REPLY_MASK,
+    };
+
+    memcpy(msg.payload.object.uuid, uuid, sizeof(uuid[0]) * UUID_LEN);
+
+    if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHARED_OBJECT)) {
+        return false;
+    }
+
+    pthread_mutex_lock(&dev->backend_mutex);
+    if (!vu_message_write(dev, dev->backend_fd, &msg)) {
+        goto out;
+    }
+
+    if (!vu_message_read_default(dev, dev->backend_fd, &msg_reply)) {
+        goto out;
+    }
+
+    if (msg_reply.request != msg.request) {
+        DPRINT("Received unexpected msg type. Expected %d, received %d",
+               msg.request, msg_reply.request);
+        goto out;
+    }
+
+    if (msg_reply.fd_num != 1) {
+        DPRINT("Received unexpected number of fds. Expected 1, received %d",
+               msg_reply.fd_num);
+        goto out;
+    }
+
+    *dmabuf_fd = msg_reply.fds[0];
+    result = *dmabuf_fd > 0 && msg_reply.payload.u64 == 0;
+out:
+    pthread_mutex_unlock(&dev->backend_mutex);
+
+    return result;
+}
+
+static bool
+vu_send_message(VuDev *dev, VhostUserMsg *vmsg)
+{
+    bool result = false;
+    pthread_mutex_lock(&dev->backend_mutex);
+    if (!vu_message_write(dev, dev->backend_fd, vmsg)) {
+        goto out;
+    }
+
+    result = true;
+out:
+    pthread_mutex_unlock(&dev->backend_mutex);
+
+    return result;
+}
+
+bool
+vu_add_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN])
+{
+    VhostUserMsg msg = {
+        .request = VHOST_USER_BACKEND_SHARED_OBJECT_ADD,
+        .size = sizeof(msg.payload.object),
+        .flags = VHOST_USER_VERSION,
+    };
+
+    memcpy(msg.payload.object.uuid, uuid, sizeof(uuid[0]) * UUID_LEN);
+
+    if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHARED_OBJECT)) {
+        return false;
+    }
+
+    return vu_send_message(dev, &msg);
+}
+
+bool
+vu_rm_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN])
+{
+    VhostUserMsg msg = {
+        .request = VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE,
+        .size = sizeof(msg.payload.object),
+        .flags = VHOST_USER_VERSION,
+    };
+
+    memcpy(msg.payload.object.uuid, uuid, sizeof(uuid[0]) * UUID_LEN);
+
+    if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHARED_OBJECT)) {
+        return false;
+    }
+
+    return vu_send_message(dev, &msg);
+}
+
 static bool
 vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
 {
@@ -1944,6 +2062,8 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
         return vu_add_mem_reg(dev, vmsg);
     case VHOST_USER_REM_MEM_REG:
         return vu_rem_mem_reg(dev, vmsg);
+    case VHOST_USER_GET_SHARED_OBJECT:
+        return vu_get_shared_object(dev, vmsg);
     default:
         vmsg_close_fds(vmsg);
         vu_panic(dev, "Unhandled request: %d", vmsg->request);

subprojects/libvhost-user/libvhost-user.h

@@ -64,7 +64,8 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
     VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS = 14,
     VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS = 15,
-
+    /* Feature 16 is reserved for VHOST_USER_PROTOCOL_F_STATUS. */
+    VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 17,
     VHOST_USER_PROTOCOL_F_MAX
 };
 
@@ -109,6 +110,7 @@ typedef enum VhostUserRequest {
     VHOST_USER_GET_MAX_MEM_SLOTS = 36,
     VHOST_USER_ADD_MEM_REG = 37,
     VHOST_USER_REM_MEM_REG = 38,
+    VHOST_USER_GET_SHARED_OBJECT = 41,
     VHOST_USER_MAX
 } VhostUserRequest;
 
@@ -119,6 +121,9 @@ typedef enum VhostUserBackendRequest {
     VHOST_USER_BACKEND_VRING_HOST_NOTIFIER_MSG = 3,
     VHOST_USER_BACKEND_VRING_CALL = 4,
     VHOST_USER_BACKEND_VRING_ERR = 5,
+    VHOST_USER_BACKEND_SHARED_OBJECT_ADD = 6,
+    VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE = 7,
+    VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP = 8,
     VHOST_USER_BACKEND_MAX
 }  VhostUserBackendRequest;
 
@@ -172,6 +177,12 @@ typedef struct VhostUserInflight {
     uint16_t queue_size;
 } VhostUserInflight;
 
+#define UUID_LEN 16
+
+typedef struct VhostUserShared {
+    unsigned char uuid[UUID_LEN];
+} VhostUserShared;
+
 #if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
 # define VU_PACKED __attribute__((gcc_struct, packed))
 #else
@@ -199,6 +210,7 @@ typedef struct VhostUserMsg {
         VhostUserConfig config;
         VhostUserVringArea area;
         VhostUserInflight inflight;
+        VhostUserShared object;
     } payload;
 
     int fds[VHOST_MEMORY_BASELINE_NREGIONS];
@@ -232,6 +244,7 @@ typedef int (*vu_get_config_cb) (VuDev *dev, uint8_t *config, uint32_t len);
 typedef int (*vu_set_config_cb) (VuDev *dev, const uint8_t *data,
                                  uint32_t offset, uint32_t size,
                                  uint32_t flags);
+typedef int (*vu_get_shared_object_cb) (VuDev *dev, const unsigned char *uuid);
 
 typedef struct VuDevIface {
     /* called by VHOST_USER_GET_FEATURES to get the features bitmask */
@@ -258,6 +271,8 @@ typedef struct VuDevIface {
     vu_get_config_cb get_config;
     /* set the config space of the device */
     vu_set_config_cb set_config;
+    /* get virtio shared object from the underlying vhost implementation. */
+    vu_get_shared_object_cb get_shared_object;
 } VuDevIface;
 
 typedef void (*vu_queue_handler_cb) (VuDev *dev, int qidx);
@@ -541,6 +556,44 @@ void vu_set_queue_handler(VuDev *dev, VuVirtq *vq,
 bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq *vq, int fd,
                                 int size, int offset);
 
+/**
+ * vu_lookup_shared_object:
+ * @dev: a VuDev context
+ * @uuid: UUID of the shared object
+ * @dmabuf_fd: output dma-buf file descriptor
+ *
+ * Lookup for a virtio shared object (i.e., dma-buf fd) associated with the
+ * received UUID. Result, if found, is stored in the dmabuf_fd argument.
+ *
+ * Returns: whether the virtio object was found.
+ */
+bool vu_lookup_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN],
+                             int *dmabuf_fd);
+
+/**
+ * vu_add_shared_object:
+ * @dev: a VuDev context
+ * @uuid: UUID of the shared object
+ *
+ * Registers this back-end as the exporter for the object associated with
+ * the received UUID.
+ *
+ * Returns: TRUE on success, FALSE on failure.
+ */
+bool vu_add_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN]);
+
+/**
+ * vu_rm_shared_object:
+ * @dev: a VuDev context
+ * @uuid: UUID of the shared object
+ *
+ * Removes a shared object entry (i.e., back-end entry) associated with the
+ * received UUID key from the hash table.
+ *
+ * Returns: TRUE on success, FALSE on failure.
+ */
+bool vu_rm_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN]);
+
 /**
  * vu_queue_set_notification:
  * @dev: a VuDev context