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SubjectRe: try module get code understanding
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On Thu, 27 Sep 2007 05:19:06 -0000, Shreyansh Jain said:

> -----
> static inline int try_module_get(struct module *module){
> int ret = 1; <--- error case when !module
> if (module) {
> unsigned int cpu = get_cpu();
> if (likely(module_is_live(module)))
> local_inc(&module->ref[cpu].count);
> else
> ret = 0; <--- error case
> put_cpu();
> }
> return ret; <----
> }

> 1. In case the module pointer passed is invalid (NULL) this function would
> return 1 (error case)
> 2. In case the module pointer is OK, and module is currently not being removed,
> reference count would be incremented and 1 returned (non error case)
> 3. In case the module pointer is OK, and module reference count can NOT be
> increased, 0 would be returned (error case).
>
> As you can observe from above points, 0 and 1 are returned for error cases. I am
> a little confused and wondering if there is something which I am missing in this
> code??.

Go look at the call sites for this function - I bet that most of them, if they
check the return code at all, only check for zero or nonzero, because they only
*care* about the case that returns zero. Since they already know they're not
passing a NULL pointer, they don't worry about that case returning a 1. So
there's only two realistic returns - either the module is live or it isn't.
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