Re: [Qemu-devel] [PATCH v1 1/4] vhost-user: Add ability to know vhost-user backend disconnection

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, May 29, 2015 at 01:42:27PM +0900, Tetsuya Mukawa wrote:
> Current QEMU cannot detect vhost-user backend disconnection. The
> patch adds ability to know it.
> To know disconnection, add watcher to detect G_IO_HUP event. When
> G_IO_HUP event is detected, the disconnected socket will be read
> to cause a CHR_EVENT_CLOSED.
> 
> Signed-off-by: Tetsuya Mukawa <mukawa@igel.co.jp>
> ---
>  net/vhost-user.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)

It is unfortunate that qemu-chr.c doesn't have a built-in way to handle
G_IO_HUP and raise the CHR_EVENT_CLOSED event.  This is not really
specific to vhost-user.

CCing Paolo Bonzini (Character Devices).  He is currently on vacation so
let's not hold up this patch.  It can be made generic later, if
necessary.

> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 11899c5..1967ff4 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -19,6 +19,7 @@ typedef struct VhostUserState {
>      NetClientState nc;
>      CharDriverState *chr;
>      VHostNetState *vhost_net;
> +    int watch;
>  } VhostUserState;
>  
>  typedef struct VhostUserChardevProps {
> @@ -113,12 +114,23 @@ static void net_vhost_link_down(VhostUserState *s, bool link_down)
>      }
>  }
>  
> +static gboolean net_vhost_user_watch(GIOChannel *chan, GIOCondition cond,
> +                                           void *opaque)
> +{
> +    VhostUserState *s = opaque;
> +    uint8_t buf[1];
> +
> +    qemu_chr_fe_read_all(s->chr, buf, sizeof(buf));
> +    return FALSE;
> +}

If you respin this patch, please add a comment like:

/* We don't actually want to read anything, but CHR_EVENT_CLOSED will be
 * raised as a side-effect of the read.
 */

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