[Spice-devel] [RFC 2/2] add shared memory display channel support

[Marc-André Lureau]

All of this makes sense for me,
I think this is good enough for a first iteration.

Nice work, ack

----- Mensaje original -----
> The new protocol is an extension optionally supported by the client if
> setting this capability bit.
> 
> It includes 4 new messages, 3 are new messages (SHM_OFFER, SHM_REPLY,
> SHM_DAMAGE) and one replaces an existing message (SURFACE_CREATE_SHM replaces
> SURFACE_CREATE), plus a capability bit that both server and client advertise
> (SPICE_DISPLAY_CAP_SHARED_MEMORY).
> 
> If the server sees the client capability, it will send MSG_DISPLAY_SHM_OFFER
> right after the display channel handshake.
> 
> client replies with MSGC_DISPLAY_SHM_REPLY
>  - accepted = 0
>   - nothing changes, return to normal behavior
>  - accepted = 1
>   - shared memory behavior commences as described below.
> 
> In shared memory mode:
> 1. every message read from the qxl device (via the qxl interface
> interface_get_command) is:
> 1.1 immediately rendered into the framebuffer
>     * since the framebuffer is a shared memory segment, the client can
>     immediately use it.
> 1.2 server will send a MSG_DISPLAY_SHM_DAMAGE message with the clips buffer
> from the render command
> 2. no offscreen surfaces will ever be sent
> 3. all messages creating/destroying the primary surface (i.e. resolution
> changes) will be sent as usual, with SURFACE_CREATE_SHM being used, it
> includes a new field, shm_offset, which allows having multiple primary
> surfaces on the qemu side being switched between. This is useful for the vga
> mode where the qxl framebuffer has bpp != 32 and there exists a shadow
> framebuffer at 32 bpp which will then be used as the primary surface for the
> spice client.
> 4. the cursor channel is unaffected (possible future optimization).
> 
> Future: preventing tearing by adding a MSGC_DISPLAY_SHM_DAMAGE_HANDLED:
> 
> Server      render DAMAGE\              /render DAMAGE\
> Client                    \     HANDLED/               \ ...
> -------->------->------->------->------->------->------->------->
> ---
>  spice/enums.h    | 4 ++++
>  spice/protocol.h | 1 +
>  2 files changed, 5 insertions(+)
> 
> diff --git a/spice/enums.h b/spice/enums.h
> index 7be34eb..720dcf5 100644
> --- a/spice/enums.h
> +++ b/spice/enums.h
> @@ -472,6 +472,9 @@ enum {
>      SPICE_MSG_DISPLAY_MONITORS_CONFIG,
>      SPICE_MSG_DISPLAY_DRAW_COMPOSITE,
>      SPICE_MSG_DISPLAY_STREAM_ACTIVATE_REPORT,
> +    SPICE_MSG_DISPLAY_SHM_OFFER,
> +    SPICE_MSG_DISPLAY_SHM_DAMAGE,
> +    SPICE_MSG_DISPLAY_SURFACE_CREATE_SHM,
>  
>      SPICE_MSG_END_DISPLAY
>  };
> @@ -479,6 +482,7 @@ enum {
>  enum {
>      SPICE_MSGC_DISPLAY_INIT = 101,
>      SPICE_MSGC_DISPLAY_STREAM_REPORT,
> +    SPICE_MSGC_DISPLAY_SHM_REPLY,
>  
>      SPICE_MSGC_END_DISPLAY
>  };
> diff --git a/spice/protocol.h b/spice/protocol.h
> index e11f384..cc69892 100644
> --- a/spice/protocol.h
> +++ b/spice/protocol.h
> @@ -131,6 +131,7 @@ enum {
>      SPICE_DISPLAY_CAP_COMPOSITE,
>      SPICE_DISPLAY_CAP_A8_SURFACE,
>      SPICE_DISPLAY_CAP_STREAM_REPORT,
> +    SPICE_DISPLAY_CAP_SHARED_MEMORY,
>  };
>  
>  enum {
> --
> 1.8.3.1
> 
> _______________________________________________
> Spice-devel mailing list
> Spice-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/spice-devel
>