[Libvirt-cim] [PATCH 2 of 3] Make alloc_cap_instances() available for external use by EC

[Heidi Eckhart]

Dan Smith wrote:
> HE> Mhh, as we have many free operations now that can handle NULL
> HE> pointers, I suggest to also make inst_list_free() able to handle
> HE> NULL pointers.
>
> But they're not NULL pointers at that point, the list.list is a
> garbage pointer.  Unless you define them as:
>
>   struct inst_list list = {NULL, 0, 0};
>
> Otherwise, the pointer will be garbage and a free() will smash the
> heap.
>
> The inst_list_init() call doesn't allocate any memory, it just
> initializes the contents of the struct, so why not always do that
> before proceeding?
>   
Ok, thank you for this clarification.
> HE> Agreed. I will cook up a patch for inst_list_free(). The intention
> HE> to move the inst_list_init() functions below
> HE> connect_by_classname() was to avoid some cycles, because the case
> HE> where the provider exits right after provider_is_responsible() or
> HE> connect_by_classname() can happen often.
>
> I think this optimization is likely lost in the noise of the roaring
> CIMOM above us, so I'm not sure it's all that important.  However, a
> macro could help make this cleaner I think.  Something like what they
> do in the kernel might be helpful:
>
>   #define DECLARE_INST_LIST(x) struct inst_list x = {NULL, 0, 0}
>
> so that we can just do this in a function to have pre-initialized
> lists and avoid the inst_list_init() calls:
>
>   int function_foo(...) {
>     int a;
>     char b;
>     DECLARE_INST_LIST(list_one);
>     DECLARE_INST_LIST(list_two);
>
>     ...
>   }
>
> I still question the value of this optimization, as I think the
> compiler will inline the inst_list_init() function.  At that point,
> this:
>
>   struct inst_list foo = {NULL, 0, 0};
>
> surely becomes the same code as this:
>
>   struct inst_list foo;
>
>   foo.list = NULL;
>   foo.max = foo.cur = 0;
>
> Anyone else have thoughts on this?
>   
Your explanation is absolutely clear and shows me, that I was nitpickier 
than a nitpicker ;). I can only agree that the "optimization" will get 
"lost in the noise of the roaring CIMOM above us". I like the suggestion 
of the DECLARE macro, but understand, that we have more important things 
to do and fix. So skipping it.
> HE> Agreed. I saw that we already have a task for "Fix up all the
> HE> error codes in returned status values (everything is currently
> HE> CMPI_RC_ERR_FAILED)". So we should leave this discussion for
> HE> there. I will remove this change.
>
> Yes, we definitely have work to do on our return codes and error
> messages, but I'd rather address them as a group than sprinkle them in
> with other changes :)
>
> Thanks!
>
>   


-- 
Regards

Heidi Eckhart
Software Engineer
IBM Linux Technology Center - Open Hypervisor