[PATCH wayland] client: Use a 0 version to mean indeterminate proxy version

[Pekka Paalanen]

On Thu, 26 Nov 2015 15:23:52 -0600
Derek Foreman <derekf at osg.samsung.com> wrote:

> This sets wl_display's version (for proxy version query purposes)
> to 0.  Any proxy created with unversioned API (this happens when
> a client compiled with old headers links against new wayland)
> will inherit this 0.
> 
> This gives us a way for new libraries linked by old clients to
> realize they can't know a proxy's version.
> 
> wl_display's version being unqueryable (always returning 0) is
> an acceptable side effect, since it's a special object you can't
> bind specific versions of anyway.
> 
> Signed-off-by: Derek Foreman <derekf at osg.samsung.com>
> ---
> 
> This follows on Jason's proxy version patch that I rebased
> and reposted a little while ago.
> 
>  src/wayland-client.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/src/wayland-client.c b/src/wayland-client.c
> index f2df0b9..5ba6edc 100644
> --- a/src/wayland-client.c
> +++ b/src/wayland-client.c
> @@ -928,7 +928,25 @@ wl_display_connect_to_fd(int fd)
>  	display->proxy.queue = &display->default_queue;
>  	display->proxy.flags = 0;
>  	display->proxy.refcount = 1;
> -	display->proxy.version = 1;
> +
> +	/* We set this version to 0 for backwards compatibility.
> +	 *
> +	 * If a client is using old versions of protocol headers,
> +	 * it will use unversioned API to create proxies.  Those
> +	 * proxies will inherit this 0.
> +	 *
> +	 * A client could be passing these proxies into library
> +	 * code newer than the headers that checks proxy
> +	 * versions.  When the proxy version is reported as 0
> +	 * the library will know that it can't reliably determine
> +	 * the proxy version, and should do whatever fallback is
> +	 * required.
> +	 *
> +	 * This trick forces wl_display to always report 0, but
> +	 * since it's a special object that we can't bind
> +	 * specific versions of anyway, this should be fine.
> +	 */
> +	display->proxy.version = 0;
>  
>  	display->connection = wl_connection_create(display->fd);
>  	if (display->connection == NULL)
> @@ -1923,7 +1941,18 @@ wl_proxy_get_user_data(struct wl_proxy *proxy)
>  /** Get the protocol object version of a proxy object
>   *
>   * \param proxy The proxy object
> - * \return The protocol object version of the proxy
> + * \return The protocol object version of the proxy or 0
> + *
> + * Gets the protocol object version of a proxy object, or 0
> + * if the proxy was created with unversioned API.
> + *
> + * A returned value of 0 means that no version information is
> + * available, so the caller must make safe assumptions about
> + * the object's real version.
> + *
> + * wl_display's version will always return 0.
> + *
> + * \note This should not normally be used by non-generated code.

Hi,

this note does not seem to belong here.

>   *
>   * \memberof wl_proxy
>   */

With the note fixed:
Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>


Thanks,
pq
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