[Cocci] how to find missing initializer

[lars@metafoo.de (Lars-Peter Clausen)]

On 12/03/2015 02:04 PM, Peter Hurley wrote:
> Hi all,
> 
> I'm struggling with the grammar necessary to find struct definitions
> missing an initializer.
> 
> The background is that many tty interfaces include a method/operations
> table (named fields of function ptrs). For example, given a declaration
> like,
> 
>     struct tty_operations {
>             int (*install)( /* ... */ );
>             int (*remove)( /* ... */ );
>             void (*cleanup)( /* ... * );
>     ...
>     };
> 
> a tty driver might define its method table like,
> 
>     static const struct tty_operations ops = {
>             .install = uart_install,
> 	    .remove = uart_remove,
>             .cleanup = uart_cleanup,
>     ...
>     };
> 
> 
> (actually, this is a common pattern throughout the kernel)
> 
> Many operations are optional; a NULL method is simply not executed.
> For example,
> 
>     if (tty->ops->cleanup)
>             tty->ops->cleanup(tty);
> 
> So trying to find those in-tree drivers which _do not_ define a cleanup
> method with coccinelle, led to this fragment which has a parse error.
> 
> Apologies if my question is obvious or trivial; I'm still learning
> coccinelle.

Usually you'd do something like first find all that have the initializer and
then match all that where not matched before using a position metavariable. E.g.

@r1@
identifier fops;
identifier fn;
position p;
@@
struct tty_operations fops at p = {
    ...,
    .cleanup = fn,
    ...
};

@@
identifier fops;
identifier fn;
position p != r1.p;
@@
*struct tty_operations fops at p = {
    ...
};