Re: [PATCH v2 3/7] mm/memory_hotplug: prepare passing flags to add_memory() and friends

[David Hildenbrand <david@redhat.com>]

On 09.09.20 13:37, David Hildenbrand wrote:
> On 09.09.20 13:24, Michael Ellerman wrote:
>> David Hildenbrand <david@redhat.com> writes:
>>> On 09.09.20 09:17, Greg Kroah-Hartman wrote:
>>>> On Tue, Sep 08, 2020 at 10:10:08PM +0200, David Hildenbrand wrote:
>>>>> We soon want to pass flags, e.g., to mark added System RAM resources.
>>>>> mergeable. Prepare for that.
>>>>
>>>> What are these random "flags", and how do we know what should be passed
>>>> to them?
>>>>
>>>> Why not make this an enumerated type so that we know it all works
>>>> properly, like the GPF_* flags are?  Passing around a random unsigned
>>>> long feels very odd/broken...
>>>
>>> Agreed, an enum (mhp_flags) seems to give a better hint what can
>>> actually be passed. Thanks!
>>
>> You probably know this but ...
>>
>> Just using a C enum doesn't get you any type safety.
>>
>> You can get some checking via sparse by using __bitwise, which is what
>> gfp_t does. You don't actually have to use an enum for that, it works
>> with #defines also.
> 
> Yeah, we seem to be using different approaches. And there is always a
> way to mess things up :)
> 
> gfp_t is one (extreme) example, enum memblock_flags is another example.
> I tend to prefer an enum in this particular case, because it's simple
> and at least tells the user which values are expected.
> 

Gave it another try, looks like mhp_t (like gfp_t) is actually nicer.

-- 
Thanks,

David / dhildenb
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