vhost-user: support receiving file descriptors in slave_read

Signed-off-by: NTiwei Bie <tiwei.bie@intel.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/vhost-user.c

@@ -852,14 +852,44 @@ static void slave_read(void *opaque)
     VhostUserHeader hdr = { 0, };
     VhostUserPayload payload = { 0, };
     int size, ret = 0;
+    struct iovec iov;
+    struct msghdr msgh;
+    int fd = -1;
+    char control[CMSG_SPACE(sizeof(fd))];
+    struct cmsghdr *cmsg;
+    size_t fdsize;
+
+    memset(&msgh, 0, sizeof(msgh));
+    msgh.msg_iov = &iov;
+    msgh.msg_iovlen = 1;
+    msgh.msg_control = control;
+    msgh.msg_controllen = sizeof(control);
 
     /* Read header */
-    size = read(u->slave_fd, &hdr, VHOST_USER_HDR_SIZE);
+    iov.iov_base = &hdr;
+    iov.iov_len = VHOST_USER_HDR_SIZE;
+
+    size = recvmsg(u->slave_fd, &msgh, 0);
     if (size != VHOST_USER_HDR_SIZE) {
         error_report("Failed to read from slave.");
         goto err;
     }
 
+    if (msgh.msg_flags & MSG_CTRUNC) {
+        error_report("Truncated message.");
+        goto err;
+    }
+
+    for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg != NULL;
+         cmsg = CMSG_NXTHDR(&msgh, cmsg)) {
+            if (cmsg->cmsg_level == SOL_SOCKET &&
+                cmsg->cmsg_type == SCM_RIGHTS) {
+                    fdsize = cmsg->cmsg_len - CMSG_LEN(0);
+                    memcpy(&fd, CMSG_DATA(cmsg), fdsize);
+                    break;
+            }
+    }
+
     if (hdr.size > VHOST_USER_PAYLOAD_SIZE) {
         error_report("Failed to read msg header."
                 " Size %d exceeds the maximum %zu.", hdr.size,
@@ -883,9 +913,15 @@ static void slave_read(void *opaque)
         break;
     default:
         error_report("Received unexpected msg type.");
+        if (fd != -1) {
+            close(fd);
+        }
         ret = -EINVAL;
     }
 
+    /* Message handlers need to make sure that fd will be consumed. */
+    fd = -1;
+
     /*
      * REPLY_ACK feature handling. Other reply types has to be managed
      * directly in their request handlers.
@@ -918,6 +954,9 @@ err:
     qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
     close(u->slave_fd);
     u->slave_fd = -1;
+    if (fd != -1) {
+        close(fd);
+    }
     return;
 }