Re: [Libguestfs] [PATCH libnbd v2 04/10] lib: Permit .callback = NULL, .free != NULL.

>> >> /* Test if a callback is "null" or not, and set it to null. */ >> -#define CALLBACK_IS_NULL(cb) ((cb).callback == NULL) >> +#define CALLBACK_IS_NULL(cb) ((cb).callback == NULL && (cb).free == NULL) > > Semantic change. In generator, you used CALLBACK_IS_NULL() for both > Closure and OClosure. For OClosure, the new semantics are still > correct. But for Closure, we now no longer return EFAULT when the > callback itself is missing but a .free was provided. This changes > pread_structured and block_status to accept NULL for the callback; which > is probably not a good idea. I'm unclear on this. This is the point of the patch - that you can register a callback which has no callback action but still performs the free action, and that's not considered a null callback. (It's considered to be a callback that does nothing and returns 0.) Does something bad happen to those two calls in this case?