[Xcb] Using Coccinelle to automatically transform Xlib-based code to use XCB

[Barton C Massey]

Really interesting!  Thanks for posting.

	Bart

In message <20100613220850.GA16387 at feather> you wrote:
> [CCing the Coccinelle list for interest.]
> 
> I've done some experiments with transforming Xlib-based code to use XCB
> by using Coccinelle, the "semantic patch" tool.
> 
> I've managed to successfully handle common usage of XOpenDisplay,
> XCloseDisplay, and the error-handling around them.  I can also
> automatically transform Display * variables into xcb_connection_t *
> variables, and transform functions that pass around a Display * to pass
> around an xcb_connection_t * instead.
> 
> Note that these transformations target applications based on Xlib, using
> the assumption that no function signatures have a fixed API.
> Transforming library code would require a different set of
> transformations, using XGetXCBConnection.  I can do that kind of
> transformation too, though, making an arbitrary function that takes a
> dpy argument define an xcb_connection_t *conn at the top and set it
> equal to XGetXCBConnection(dpy).
> 
> I've attached my work-in-progress Coccinelle patch.  You can use it like
> this:
> 
> spatch -sp_file xcb.cocci xlib-app.c
> 
> Actually transforming requests and (in particular) responses will
> require more work to figure out the right equivalences, and these
> sometimes involve several different cases, particularly to make
> efficient translations (avoiding extra data copies, for instance).
> However, if we can come up with the right general rules to apply, we can
> probably express those rules in Coccinelle.
> 
> - Josh Triplett
> 
> --CE+1k2dSO48ffgeK
> Content-Type: text/plain; charset=us-ascii
> Content-Disposition: attachment; filename="xcb.cocci"
> 
> @@
> identifier dpy;
> @@
> (
> -static Display *dpy;
> +static xcb_connection_t *conn;
> |
> -Display *dpy = NULL;
> +xcb_connection_t *conn = NULL;
> |
> -Display *dpy;
> +xcb_connection_t *conn;
> )
> 
> @localfunc@
> identifier dpy;
> identifier f;
> @@
>  f(...,
> -Display *dpy
> +xcb_connection_t *conn
>  ,...) { ... }
> 
> @@
> identifier localfunc.f;
> Display *dpy;
> @@
>  f(...,
> -dpy
> +conn
>  ,...)
> 
> @@
> Display *dpy;
> identifier displayname;
> identifier screen;
> @@
> (
> -dpy = XOpenDisplay(displayname);
> +conn = xcb_connect(displayname, &screen);
> ... when != screen
> -screen = DefaultScreen(dpy);
> |
> -dpy = XOpenDisplay(displayname);
> +conn = xcb_connect(displayname, NULL);
> )
> 
> @@
> identifier displayname;
> @@
> (
> -XDisplayName(NULL)
> +getenv("DISPLAY")
> |
> -XDisplayName(displayname)
> +displayname ? displayname : getenv("DISPLAY")
> )
> 
> @@
> Display *dpy;
> @@
> (
> -if (dpy) { XCloseDisplay(dpy); }
> +if (conn) xcb_disconnect(conn);
> |
>  if (
> -    !dpy
> +    xcb_connection_has_error(conn)
>     ) { ... }
> )