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

[Tetsuya Mukawa <mukawa@igel.co.jp>]

On 2015/04/22 5:19, Nikolay Nikolaev wrote:
> On Tue, Apr 21, 2015 at 9:36 AM, Tetsuya Mukawa <mukawa@igel.co.jp> 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(+)
>>
>> diff --git a/net/vhost-user.c b/net/vhost-user.c
>> index 1d86a2b..55c05a5 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));
> So you read the date from the buffer and just discard it?
> Are you going to miss messages this way?
>
> Please clarify.

Hi Nikolay,

Thanks for comment.
Yes, some messages might be lost, but it will be only happened after
unix domain socket is closed by vhost-user backend.
So I guess there is no side effect.
Anyway, I just want to know vhost-user disconnection, so other ways are
also nice.
Do you have any suggestions about how to implement?

Regards,
Tetsuya

> regards,
> Nikolay Nikolaev
>
>> +    return FALSE;
>> +}
>> +
>>  static void net_vhost_user_event(void *opaque, int event)
>>  {
>>      VhostUserState *s = opaque;
>>
>>      switch (event) {
>>      case CHR_EVENT_OPENED:
>> +        s->watch = qemu_chr_fe_add_watch(s->chr, G_IO_HUP, net_vhost_user_watch, s);
>>          vhost_user_start(s);
>>          net_vhost_link_down(s, false);
>>          error_report("chardev \"%s\" went up", s->chr->label);
>> @@ -126,6 +138,8 @@ static void net_vhost_user_event(void *opaque, int event)
>>      case CHR_EVENT_CLOSED:
>>          net_vhost_link_down(s, true);
>>          vhost_user_stop(s);
>> +        g_source_remove(s->watch);
>> +        s->watch = 0;
>>          error_report("chardev \"%s\" went down", s->chr->label);
>>          break;
>>      }
>> --
>> 1.9.1
>>
>>