Re: [Qemu-devel] [PATCH] libvhost-user: handle NOFD flag in call/kick/err better

[Stefan Hajnoczi]

On Tue, Sep 17, 2019 at 02:25:59PM +0200, Johannes Berg wrote:
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index f1677da21201..17b7833d1f6b 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -920,6 +920,7 @@ static bool
>  vu_check_queue_msg_file(VuDev *dev, VhostUserMsg *vmsg)
>  {
>      int index = vmsg->payload.u64 & VHOST_USER_VRING_IDX_MASK;
> +    bool nofd = vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK;
>  
>      if (index >= dev->max_queues) {
>          vmsg_close_fds(vmsg);
> @@ -927,8 +928,12 @@ vu_check_queue_msg_file(VuDev *dev, VhostUserMsg *vmsg)
>          return false;
>      }
>  
> -    if (vmsg->payload.u64 & VHOST_USER_VRING_NOFD_MASK ||
> -        vmsg->fd_num != 1) {
> +    if (nofd) {
> +        vmsg_close_fds(vmsg);
> +        return true;
> +    }

With the following change to vmsg_close_fds():

  for (i = 0; i < vmsg->fd_num; i++) {
      close(vmsg->fds[i]);
  }
+ for (i = 0; i < sizeof(vmsg->fd_num) / sizeof(vmsg->fd_num[0]); i++) {
+     vmsg->fds[i] = -1;
+ }
+ vmsg->fd_num = 0;

...the message handler functions below can use vmsg->fds[0] (-1) without
worrying about NOFD.  This makes the code simpler.

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