Re: [Qemu-devel] [PATCH RFC 3/3] libvhost-user: quit when no more data received

[Marc-André Lureau]

Hi

On Wed, Jul 12, 2017 at 1:47 PM Jens Freimann <address@hidden> wrote:

> From: Jens Freimann <address@hidden>
>
> When recvmsg() returns a message size of zero and
> errno is ENOENT end processing of vhost-user messages.
>
> Without this we run into a vubr_panic() call and get
>      PANIC: Error while recvmsg: No such file or directory
>      Error while dispatching.
>
>
How do you get ENOENT on recvmsg()?

Add a switch "quit" to the vhost user device and set true to stop
> processing messages.
>
> Signed-off-by: Jens Freimann <address@hidden>
> ---
>  contrib/libvhost-user/libvhost-user.c | 12 +++++++++++-
>  contrib/libvhost-user/libvhost-user.h |  1 +
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c
> b/contrib/libvhost-user/libvhost-user.c
> index 9efb9da..5538859 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -161,7 +161,10 @@ vu_message_read(VuDev *dev, int conn_fd, VhostUserMsg
> *vmsg)
>          rc = recvmsg(conn_fd, &msg, 0);
>      } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
>
> -    if (rc <= 0) {
> +    if (rc == 0 && (errno == ENOENT)) {
> +        vmsg->size = 0;
> +        dev->quit = true;
> +    } else if (rc < 0) {
>          vu_panic(dev, "Error while recvmsg: %s", strerror(errno));
>          return false;
>      }
> @@ -755,6 +758,10 @@ vu_process_message(VuDev *dev, VhostUserMsg *vmsg)
>      DPRINT("Flags:   0x%x\n", vmsg->flags);
>      DPRINT("Size:    %d\n", vmsg->size);
>
> +    if (dev->quit) {
> +        return true;
> +    }
>

Make it false, as no reply is expected then


> +
>      if (vmsg->fd_num) {
>          int i;
>          DPRINT("Fds:");
> @@ -822,6 +829,9 @@ vu_dispatch(VuDev *dev)
>      bool success = false;
>
>      if (!vu_message_read(dev, dev->sock, &vmsg)) {
> +        if (vmsg.size == 0) {
> +            success = true;
> +        }
>

There might be better ways to indicate a disconnection than modifying and
checking vmsg.size. Perhaps dev->quit alone is enough?

         goto end;
>      }
>
> diff --git a/contrib/libvhost-user/libvhost-user.h
> b/contrib/libvhost-user/libvhost-user.h
> index 53ef222..c02215a 100644
> --- a/contrib/libvhost-user/libvhost-user.h
> +++ b/contrib/libvhost-user/libvhost-user.h
> @@ -217,6 +217,7 @@ struct VuDev {
>      uint64_t features;
>      uint64_t protocol_features;
>      bool broken;
> +    bool quit;
>

I also think you could re-use broken in this case.


>
>      /* @set_watch: add or update the given fd to the watch set,
>       * call cb when condition is met */
> --
> 2.9.4
>
>
> --
Marc-André Lureau