vhost-user: Don't pass file descriptor for VHOST_USER_REM_MEM_REG

The spec clarifies now that QEMU should not send a file descriptor in a
request to remove a memory region. Change it accordingly.

For libvhost-user, this is a bug fix that makes it compatible with
rust-vmm's implementation that doesn't send a file descriptor. Keep
accepting, but ignoring a file descriptor for compatibility with older
QEMU versions.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20220407133657.155281-4-kwolf@redhat.com>
Reviewed-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/virtio/vhost-user.c

@@ -751,7 +751,7 @@ static int send_remove_regions(struct vhost_dev *dev,
             vhost_user_fill_msg_region(&region_buffer, shadow_reg, 0);
             msg->payload.mem_reg.region = region_buffer;
 
-            ret = vhost_user_write(dev, msg, &fd, 1);
+            ret = vhost_user_write(dev, msg, NULL, 0);
             if (ret < 0) {
                 return ret;
             }

subprojects/libvhost-user/libvhost-user.c

@@ -822,15 +822,15 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
     int i;
     bool found = false;
 
-    if (vmsg->fd_num != 1) {
+    if (vmsg->fd_num > 1) {
         vmsg_close_fds(vmsg);
-        vu_panic(dev, "VHOST_USER_REM_MEM_REG received %d fds - only 1 fd "
+        vu_panic(dev, "VHOST_USER_REM_MEM_REG received %d fds - at most 1 fd "
                       "should be sent for this message type", vmsg->fd_num);
         return false;
     }
 
     if (vmsg->size < VHOST_USER_MEM_REG_SIZE) {
-        close(vmsg->fds[0]);
+        vmsg_close_fds(vmsg);
         vu_panic(dev, "VHOST_USER_REM_MEM_REG requires a message size of at "
                       "least %d bytes and only %d bytes were received",
                       VHOST_USER_MEM_REG_SIZE, vmsg->size);
@@ -877,7 +877,7 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
         vu_panic(dev, "Specified region not found\n");
     }
 
-    close(vmsg->fds[0]);
+    vmsg_close_fds(vmsg);
 
     return false;
 }