Re: [PATCH v2] net: vhost-user: add QAPI events to report connection state

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Feb 14, 2025 at 10:31:10AM +0100, Laurent Vivier wrote:
> The netdev reports NETDEV_VHOST_USER_CONNECTED event when
> the chardev is connected, and NETDEV_VHOST_USER_DISCONNECTED
> when it is disconnected.
> 
> The NETDEV_VHOST_USER_CONNECTED event includes the ChardevInfo
> (label, filename and frontend_open).
> 
> This allows a system manager like libvirt to detect when the server
> fails.
> 
> For instance with passt:
> 
> { 'execute': 'qmp_capabilities' }
> { "return": { } }
> 
> [killing passt here]
> 
> { "timestamp": { "seconds": 1739517243, "microseconds": 115081 },
>   "event": "NETDEV_VHOST_USER_DISCONNECTED",
>   "data": { "netdev-id": "netdev0" } }
> 
> [automatic reconnection with reconnect-ms]
> 
> { "timestamp": { "seconds": 1739517290, "microseconds": 343777 },
>   "event": "NETDEV_VHOST_USER_CONNECTED",
>   "data": { "netdev-id": "netdev0",
>             "info": { "frontend-open": true,
>                       "filename": "unix:",
>                       "label": "chr0" } } }

I'm wondering what the benefit of including the chardev info
is here ? It seems like the netdev-id is sufficient for the
mgmt app to handle the situation

The 'filename' is a legacy representation of the ChardevBackend
struct info, that we shouldn't propagate to new places IMHO.

The 'frontend-open' flag meanwhile is liable to be out of date
since events are delivered asychronously.

So at most the chardev 'id' is appropriate to be included (yes,
'id' not 'label' which is another legacy internal term). None
the less, I still figure that the mgmt app would lookup the
details via the netdev-id, not chardev, so not convinced we
even need the chardev.

> 
> Tested-by: Stefano Brivio <sbrivio@redhat.com>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
> 
> Notes:
>     v2:
>       - remove duplicate line info.frontend_open
> 
>  qapi/char.json   | 43 +++++++++++++++++++++++++++++++++++++++++++
>  net/vhost-user.c |  7 +++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/qapi/char.json b/qapi/char.json
> index f02b66c06b3e..a8094c86fb49 100644
> --- a/qapi/char.json
> +++ b/qapi/char.json
> @@ -902,3 +902,46 @@
>  { 'event': 'VSERPORT_CHANGE',
>    'data': { 'id': 'str',
>              'open': 'bool' } }
> +
> +##
> +# @NETDEV_VHOST_USER_CONNECTED:
> +#
> +# Emitted when the vhost-user chardev is connected
> +#
> +# @netdev-id: QEMU netdev id that is connected
> +#
> +# @info: The chardev information
> +#
> +# Since: 10.0
> +#
> +# .. qmp-example::
> +#
> +#     <- { "timestamp": { "seconds": 1739469793, "microseconds": 683713 },
> +#          "event": "NETDEV_VHOST_USER_CONNECTED",
> +#          "data": { "netdev-id": "netdev0",
> +#                   "info": { "frontend-open": true,
> +#                             "filename": "unix:",
> +#                             "label": "chr0" } } }
> +#
> +##
> +{ 'event': 'NETDEV_VHOST_USER_CONNECTED',
> +  'data': { 'netdev-id': 'str', 'info': 'ChardevInfo' } }
> +
> +##
> +# @NETDEV_VHOST_USER_DISCONNECTED:
> +#
> +# Emitted when the vhost-user chardev is disconnected
> +#
> +# @netdev-id: QEMU netdev id that is disconnected
> +#
> +# Since: 10.0
> +#
> +# .. qmp-example::
> +#
> +#     <- { "timestamp": { "seconds": 1739469786, "microseconds": 822220 },
> +#          "event": "NETDEV_VHOST_USER_DISCONNECTED",
> +#          "data": { "netdev-id": "netdev0" } }
> +#
> +##
> +{ 'event': 'NETDEV_VHOST_USER_DISCONNECTED',
> +  'data': { 'netdev-id': 'str' } }
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 12555518e838..049174f704cd 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -16,6 +16,7 @@
>  #include "chardev/char-fe.h"
>  #include "qapi/error.h"
>  #include "qapi/qapi-commands-net.h"
> +#include "qapi/qapi-events-char.h"
>  #include "qemu/config-file.h"
>  #include "qemu/error-report.h"
>  #include "qemu/option.h"
> @@ -271,6 +272,7 @@ static void chr_closed_bh(void *opaque)
>      if (err) {
>          error_report_err(err);
>      }
> +    qapi_event_send_netdev_vhost_user_disconnected(name);
>  }
>  
>  static void net_vhost_user_event(void *opaque, QEMUChrEvent event)
> @@ -278,6 +280,7 @@ static void net_vhost_user_event(void *opaque, QEMUChrEvent event)
>      const char *name = opaque;
>      NetClientState *ncs[MAX_QUEUE_NUM];
>      NetVhostUserState *s;
> +    ChardevInfo info;
>      Chardev *chr;
>      Error *err = NULL;
>      int queues;
> @@ -300,6 +303,10 @@ static void net_vhost_user_event(void *opaque, QEMUChrEvent event)
>                                           net_vhost_user_watch, s);
>          qmp_set_link(name, true, &err);
>          s->started = true;
> +        info.label = chr->label;
> +        info.filename = chr->filename;
> +        info.frontend_open = chr->be && chr->be->fe_is_open;

I gues 

> +        qapi_event_send_netdev_vhost_user_connected(name, &info);
>          break;
>      case CHR_EVENT_CLOSED:
>          /* a close event may happen during a read/write, but vhost
> -- 
> 2.48.1
> 
> 

With regards,
Daniel
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