Re: [Qemu-devel] [PATCH v2 22/23] vhost-user: wait until backend init is completed

[Yuanhan Liu]

On Fri, Jun 24, 2016 at 03:51:09PM +0200, address@hidden wrote:
> From: Marc-André Lureau <address@hidden>
> 
> The chardev waits for an initial connection before starting qemu,
> vhost-user wants the backend negotiation to be completed. vhost-user is
> started in the net_vhost_user_event callback, which is synchronously
> called after the socket is connected.
> 
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  net/vhost-user.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 95ed2d2..4badd9e 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -24,6 +24,7 @@ typedef struct VhostUserState {
>      VHostNetState *vhost_net;
>      int watch;
>      uint64_t acked_features;
> +    bool started;
>  } VhostUserState;
>  
>  typedef struct VhostUserChardevProps {
> @@ -211,6 +212,7 @@ static void net_vhost_user_event(void *opaque, int event)
>              return;
>          }
>          qmp_set_link(name, true, &err);
> +        s->started = true;
>          break;
>      case CHR_EVENT_CLOSED:
>          qmp_set_link(name, false, &err);
> @@ -248,7 +250,15 @@ static int net_vhost_user_init(NetClientState *peer, 
> const char *device,
>          s->chr = chr;
>      }
>  
> -    qemu_chr_add_handlers(chr, NULL, NULL, net_vhost_user_event, nc[0].name);
> +    do {
> +        Error *err = NULL;
> +        if (qemu_chr_wait_connected(chr, &err) < 0) {
> +            error_report_err(err);
> +            return -1;
> +        }
> +        qemu_chr_add_handlers(chr, NULL, NULL,
> +                              net_vhost_user_event, nc[0].name);
> +    } while (!s->started);


I haven't looked at your patchset carefully yet, but I did a quick test,
and showed that above code piece just breaks vhost-user: it's a dead loop
that vhost-user net will be initiated again and again.

The dead loop is due to, we check "s->started" corresponding to last nc,
while we set "s->started" corresponding to the first nc.

        --yliu