Re: [RFC RFC PATCH] mm: convert VM flags from macros to enum

[David Hildenbrand <david@redhat.com>]

On 13.10.25 14:31, David Hildenbrand wrote:
> On 13.10.25 13:33, Lorenzo Stoakes wrote:
>> On Mon, Oct 13, 2025 at 01:12:20PM +0200, David Hildenbrand wrote:
>>> On 13.10.25 13:04, Lorenzo Stoakes wrote:
>>>> On Sat, Oct 11, 2025 at 05:30:52PM +0800, Ye Liu wrote:
>>>>> From: Ye Liu <liuye@kylinos.cn>
>>>>>
>>>>> Hello MM maintainers and drgn community,
>>>>>
>>>>> This RFC proposes to convert VM_* flags from #define macros to enum
>>>>> vm_flags. The motivation comes from recent drgn development where we
>>>>> encountered difficulties in implementing VM flag parsing due to the
>>>>> current macro-based approach.
>>>>
>>>> This isn't going to work sorry, it's not valid to have flag values as an enum
>>>
>>> I don't follow, can you elaborate? IIRC, the compiler will use an integer
>>> type to back the enum that will fit all values.
>>
>> switch (flags) {
>> 	case VAL1:
>> 	case VAL2:
>> 	etc.
>> }
>>
>> Is broken (compiler will say you cover all cases when you don't...)
> 
> I assume you mean theoretically, because there is no such code, right?
> 
>>
>> An enum implies independent values that exhaustively describe all state, however
>> these flag values are not that - they're intended to be bit fields.
>>
> 
> Observe how we use an enum for FOLL_* flags, vm_fault_reason, fault_flag
> and probably other things.
> 
> But more importantly,
> 
> enum pageflags { ... :)

Okay, that one is different, because it's the actual bit numbers today.

-- 
Cheers

David / dhildenb