Re: [PATCH v3 3/9] vnc: h264: send additional frames after the display is clean

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

On Fri, Apr 18, 2025 at 01:29:47PM +0200, Dietmar Maurer wrote:
> The H264 implementation only sends frames when it detects changes in
> the server's framebuffer. This leads to artifacts when there are no
> further changes, as the internal H264 encoder may still contain data.
> 
> This patch modifies the code to send a few additional frames in such
> situations to flush the H264 encoder data.
> 
> Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>
> ---
>  ui/vnc.c | 25 ++++++++++++++++++++++++-
>  ui/vnc.h |  3 +++
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/ui/vnc.c b/ui/vnc.c
> index aed25b0183..badc7912c0 100644
> --- a/ui/vnc.c
> +++ b/ui/vnc.c
> @@ -3239,7 +3239,30 @@ static void vnc_refresh(DisplayChangeListener *dcl)
>      vnc_unlock_display(vd);
>  
>      QTAILQ_FOREACH_SAFE(vs, &vd->clients, next, vn) {
> -        rects += vnc_update_client(vs, has_dirty);
> +        int client_dirty = has_dirty;
> +        if (vs->h264) {
> +            if (client_dirty) {
> +                vs->h264->keep_dirty = VNC_H264_KEEP_DIRTY;
> +            } else {
> +                if (vs->h264->keep_dirty > 0) {
> +                    client_dirty = 1;
> +                    vs->h264->keep_dirty--;
> +                }
> +            }
> +        }
> +
> +        int count = vnc_update_client(vs, client_dirty);
> +        rects += count;
> +
> +        if (vs->h264 && !count && vs->h264->keep_dirty) {
> +            VncJob *job = vnc_job_new(vs);
> +            int height = pixman_image_get_height(vd->server);
> +            int width = pixman_image_get_width(vd->server);
> +            vs->job_update = vs->update;
> +            vs->update = VNC_STATE_UPDATE_NONE;
> +            vnc_job_add_rect(job, 0, 0, width, height);
> +            vnc_job_push(job);
> +        }
>          /* vs might be free()ed here */

This comment is telling you that 'vnc_update_client' may have
released 'vs', and yet this code is referencing 'vs->...'
and so will be liable to crash.

>      }
>  

With regards,
Daniel
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