Re: [PATCH 4/4] ui/vnc: notify client of clipboard peer status

Hi Marc-Andre

I quickly became aware of the shortcomings of my v1 series and I've 
already drafted a v2 where the cover is a bit more detailed and the 
commits were fixed to remove the Change-IDs.

On 8/18/26 15:33, Marc-André Lureau wrote:
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>
> |-------------------------------------------------------------------!
>
> Hi Lukasz
>
> On Tue, Aug 18, 2026 at 4:15 PM Lukasz Kornicki
> <[email protected]> wrote:
>> Introduce a new vnc message (VNC_MSG_SERVER_QEMU_CLIPBOARD_STATUS) and
>> the corresponding feature/encoding.
>>
>> When a client requests this feature, the server will inform the client
>> whether a guest clipboard peer is present. The server will repeat the
>> notification each time availability of a guest clipboard peer changes.
>>
>> This change enables the VNC client to determine if a guest side
>> clipboard peer is available for clipboard exchange and react to
>> changes of its availability.
>>
>> Until now the VNC clipboard peer was only registered when
>> VNC_FEATURE_CLIPBOARD_EXT was enabled. With this change the VNC peer
>> can be registered just for the purpose of receiving peer status
>> updates. This requires introducing a VNC_FEATURE_CLIPBOARD_EXT guard
>> before the QEMU_CLIPBOARD_UPDATE_INFO handler which previously only ran
>> if VNC_FEATURE_CLIPBOARD_EXT was enabled.
>>
> The series looks good, but this extension is not documented afaict.
> Can you make a PR for it?

Sure. I've found this repo before but was not aware that it functions in 
any official capacity.

>> Change-Id: Id0897a24fae103288c399f73e808ed6c07018359
> What is this? Is it a gerrit thing?
Yes, I forgot to remove the commit-msg hook and they got regenerated 
right after I removed them :)
>> Signed-off-by: Lukasz Kornicki <[email protected]>
>> ---
>>   ui/trace-events    |  1 +
>>   ui/vnc-clipboard.c | 31 ++++++++++++++++++++++++++++++-
>>   ui/vnc.c           |  6 ++++++
>>   ui/vnc.h           |  8 ++++++++
>>   4 files changed, 45 insertions(+), 1 deletion(-)
>>
>> diff --git a/ui/trace-events b/ui/trace-events
>> index 917d116d90..d2fe153b7d 100644
>> --- a/ui/trace-events
>> +++ b/ui/trace-events
>> @@ -48,6 +48,7 @@ vnc_msg_server_ext_desktop_resize(void *state, void *ioc, int width, int height,
>>   vnc_msg_client_audio_enable(void *state, void *ioc) "VNC client msg audio enable state=%p ioc=%p"
>>   vnc_msg_client_audio_disable(void *state, void *ioc) "VNC client msg audio disable state=%p ioc=%p"
>>   vnc_msg_client_audio_format(void *state, void *ioc, int fmt, int channels, int freq) "VNC client msg audio format state=%p ioc=%p fmt=%d channels=%d freq=%d"
>> +vnc_clipboard_peer_status_send(void *state, bool present) "VNC server clipboard peer status state=%p present=%d"
>>   vnc_msg_client_cut_text(void *state, void *ioc, int len) "VNC client msg cut text state=%p ioc=%p len=%u"
>>   vnc_msg_client_cut_text_ext(void *state, void *ioc, int len, int flags) "VNC client msg cut text state=%p ioc=%p len=%u flags=%u"
>>   vnc_msg_client_ext_key_event(void *state, void *ioc, int down, int sym, int keycode) "VNC client msg ext key event state=%p ioc=%p down=%u sym=%u keycode=%u"
>> diff --git a/ui/vnc-clipboard.c b/ui/vnc-clipboard.c
>> index 67f710f6ed..4ecc4489e4 100644
>> --- a/ui/vnc-clipboard.c
>> +++ b/ui/vnc-clipboard.c
>> @@ -26,6 +26,7 @@
>>   #include "qemu/error-report.h"
>>   #include "vnc.h"
>>   #include "vnc-jobs.h"
>> +#include "trace.h"
>>
>>   static uint8_t *inflate_buffer(uint8_t *in, uint32_t in_len, uint32_t *size)
>>   {
>> @@ -224,6 +225,23 @@ static void vnc_clipboard_update_info(VncState *vs, QemuClipboardInfo *info)
>>       }
>>   }
>>
>> +void vnc_clipboard_peer_status_send(VncState *vs, bool present)
>> +{
>> +    if (!vnc_has_feature(vs, VNC_FEATURE_CLIPBOARD_STATUS)) {
>> +        return;
>> +    }
>> +
>> +    trace_vnc_clipboard_peer_status_send(vs, present);
>> +
>> +    vnc_lock_output(vs);
>> +    vnc_write_u8(vs, VNC_MSG_SERVER_QEMU);
>> +    vnc_write_u8(vs, VNC_MSG_SERVER_QEMU_CLIPBOARD_STATUS);
>> +    vnc_write_u16(vs, present ? VNC_CLIPBOARD_PEER_PRESENT
>> +                              : VNC_CLIPBOARD_PEER_ABSENT);
>> +    vnc_unlock_output(vs);
>> +    vnc_flush(vs);
>> +}
>> +
>>   static void vnc_clipboard_notify(Notifier *notifier, void *data)
>>   {
>>       VncState *vs = container_of(notifier, VncState, cbpeer.notifier);
>> @@ -231,13 +249,24 @@ static void vnc_clipboard_notify(Notifier *notifier, void *data)
>>
>>       switch (notify->type) {
>>       case QEMU_CLIPBOARD_UPDATE_INFO:
>> +        /* ignore the update if client does not want ext messages */
>> +        if (!vnc_has_feature(vs, VNC_FEATURE_CLIPBOARD_EXT)) {
>> +            return;
>> +        }
>> +
>>           vnc_clipboard_update_info(vs, notify->info);
>>           return;
>>       case QEMU_CLIPBOARD_RESET_SERIAL:
>>           /* ignore */
>>           return;
>>       case QEMU_CLIPBOARD_PEER_UPDATE:
>> -        /* ignore */
>> +        /* only guest side peers affect the status we relay to the client */
>> +        if (!notify->peer_update.peer->guest) {
>> +            return;
>> +        }
>> +
>> +        vnc_clipboard_peer_status_send(vs,
>> +            qemu_clipboard_guest_peer_present());
>>           return;
>>       }
>>   }
>> diff --git a/ui/vnc.c b/ui/vnc.c
>> index 656768f9c9..9e44a20311 100644
>> --- a/ui/vnc.c
>> +++ b/ui/vnc.c
>> @@ -2191,6 +2191,12 @@ static void set_encodings(VncState *vs, int32_t *encodings, size_t n_encodings)
>>               vnc_set_feature(vs, VNC_FEATURE_CLIPBOARD_EXT);
>>               vnc_server_cut_text_caps(vs);
>>               break;
>> +        case VNC_ENCODING_CLIPBOARD_STATUS:
>> +            vnc_set_feature(vs, VNC_FEATURE_CLIPBOARD_STATUS);
>> +            vnc_clipboard_peer_register(vs);
>> +            vnc_clipboard_peer_status_send(vs,
>> +                qemu_clipboard_guest_peer_present());
>> +            break;
>>           case VNC_ENCODING_COMPRESSLEVEL0 ... VNC_ENCODING_COMPRESSLEVEL0 + 9:
>>               vc->worker.tight.compression = (enc & 0x0F);
>>               break;
>> diff --git a/ui/vnc.h b/ui/vnc.h
>> index d8b0070396..6e8fa66e9c 100644
>> --- a/ui/vnc.h
>> +++ b/ui/vnc.h
>> @@ -422,6 +422,7 @@ enum {
>>   #define VNC_ENCODING_DESKTOP_RESIZE_EXT   0XFFFFFECC /* -308 */
>>   #define VNC_ENCODING_XVP                  0XFFFFFECB /* -309 */
>>   #define VNC_ENCODING_ALPHA_CURSOR         0XFFFFFEC6 /* -314 */
>> +#define VNC_ENCODING_CLIPBOARD_STATUS     0XFFFFFEC5 /* -315 */
>>   #define VNC_ENCODING_WMVi                 0x574D5669
>>   #define VNC_ENCODING_CLIPBOARD_EXT        0xc0a1e5ce
>>
>> @@ -466,6 +467,7 @@ enum VncFeatures {
>>       VNC_FEATURE_LED_STATE,
>>       VNC_FEATURE_XVP,
>>       VNC_FEATURE_CLIPBOARD_EXT,
>> +    VNC_FEATURE_CLIPBOARD_STATUS,
>>       VNC_FEATURE_AUDIO,
>>   };
>>
>> @@ -507,6 +509,7 @@ enum VncFeatures {
>>
>>   /* QEMU server -> client message IDs */
>>   #define VNC_MSG_SERVER_QEMU_AUDIO                 1
>> +#define VNC_MSG_SERVER_QEMU_CLIPBOARD_STATUS      2
>>
>>
>>
>> @@ -541,6 +544,10 @@ enum VncFeatures {
>>   #define VNC_CLIPBOARD_NOTIFY   (1 << 27)
>>   #define VNC_CLIPBOARD_PROVIDE  (1 << 28)
>>
>> +/* guest side clipboard peer status */
>> +#define VNC_CLIPBOARD_PEER_ABSENT  0
>> +#define VNC_CLIPBOARD_PEER_PRESENT 1
>> +
>>   VncDisplay *vnc_display_new(const char *id, Error **errp);
>>   void vnc_display_free(VncDisplay *vd);
>>
>> @@ -637,6 +644,7 @@ void vnc_zrle_clear(VncWorker *worker);
>>
>>   /* vnc-clipboard.c */
>>   void vnc_clipboard_peer_register(VncState *vs);
>> +void vnc_clipboard_peer_status_send(VncState *vs, bool present);
>>   void vnc_server_cut_text_caps(VncState *vs);
>>   void vnc_client_cut_text(VncState *vs, size_t len, uint8_t *text);
>>   void vnc_client_cut_text_ext(VncState *vs, int32_t len, uint32_t flags, uint8_t *data);
>> --
>> 2.43.0
>>
>>