Hi On Tue, Mar 8, 2022 at 6:43 PM Akihiko Odaki <akihiko.od...@gmail.com> wrote:
> On 2022/03/08 23:26, Marc-André Lureau wrote: > > Hi > > > > On Mon, Mar 7, 2022 at 4:49 PM Akihiko Odaki <akihiko.od...@gmail.com> > wrote: > >> > > > > (taking notes, mostly for myself) > > > >>> Could you provide a failing test case or a more concrete suggestion on > >>> what to do instead? I am all ears :) > >>> > >>> thanks > >>> > >> > >> Let me describe a more concrete case. Think that egl-headless and vnc > >> are enabled. The guest devices are serial virtio-gpu-gl. vnc selects > >> serial at first. > > > > (I am not sure how you would select serial first, but let's assume you > did) > > > >> > >> vnc uses register_displaychangelistener and console_select to switch > >> consoles. > >> > >> displaychangelistener_display_console does the actual switching, and > >> calls dpy_gfx_switch and dpy_gfx_update if con->scanout.kind is > >> SCANOUT_SURFACE. It calls dpy_gl_scanout_texture or > >> dpy_gl_scanout_dmabuf if con->scanout.kind is SCANOUT_TEXTURE or > >> SCANOUT_DMABUF. It works for a OpenGL display, but it doesn't vnc in > >> combination with egl-headless. > > > > (hmm, what doesn't work? With this patch, the DisplaySurface is always > > switched, no matter what con->scanout.kind is) > > > >> > >> virtio-gpu-gl starts scanning out texture. It would happen in the > >> following sequence: > >> 1. virtio-gpu-gl calls qemu_console_resize. con->scanout.kind will be > >> SCANOUT_SURFACE. > >> 2. qemu_console_resize calls dpy_gfx_switch, delivering DisplaySurface > >> to egl-headless. con->scanout.kind will be SCANOUT_TEXTURE. > > > > (qemu_console_resize calls dpy_gfx_replace_surface. con.scanout.kind > > is still SCANOUT_SURFACE) > > > > (It calls displaychangelistener_gfx_switch() which will call > > egl_gfx_switch() and update the current surface) > > > >> 3. virtio-gpu-gl calls dpy_gl_scanout_texture. egl-headless starts > >> rendering the texture to the DisplaySurface. > > > > (now con.scanout.kind becomes SCANOUT_TEXTURE) > > > >> > >> In the end, the DisplaySurface will have the image rendered, and > >> con->scanout.kind will be SCANOUT_TEXTURE. > > > > (so far it works as expected, right?) > > > > > > > >> > >> Now vnc switches to virtio-gpu-gl. > >> > >> 4. vnc calls console_select > >> 5. displaychangelistener_display_console finds con->scanout.kind is > >> SCANOUT_TEXTURE so it tries to scanout texture, but vnc is not an OpenGL > >> display. It essentially becomes no-op and the display would be blank. > >> > >> This patch will change it to call dpy_gfx_switch but not to call > >> dpy_gfx_update. > > > > Alright, I think I see what you mean. egl-headless is associated with > > a specific con, and thus is not involved during vnc console switching. > > > > However, dpy_gfx_switch on vnc is not a no-op. It updates the surface, > > resize the client and mark the area dirty. Because the con.surface is > > kept updated by egl-headless, the client gets the updated content. > > Iow, it still works. > > > > If we always called dpy_gfx_update() during > > displaychangelistener_display_console(), it would mean for the > > listener to display the surface content, even when the scanout kind is > > set for a texture. Or we need to change the behaviour of > > dpy_gfx_update() to depend on the current scanout kind. > > vnc has to display the surface content so dpy_gfx_update should be > called for vnc, but not for OpenGL displays. > > VNC already marks the whole surface as dirty during vnc_dpy_switch(). This is like calling dpy_gfx_update(). -- Marc-André Lureau
