On 8/27/24 9:33 AM, Jann Horn wrote:
> On Tue, Aug 27, 2024 at 4:05?PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>> On 8/26/24 18:04, Christian Brauner wrote:
>>> diff --git a/include/linux/slab.h b/include/linux/slab.h
>>> index eb2bf4629157..fc3c3cc9f689 100644
>>> --- a/include/linux/slab.h
>>> +++ b/include/linux/slab.h
>>> @@ -242,6 +242,10 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
>>> slab_flags_t flags,
>>> unsigned int useroffset, unsigned int usersize,
>>> void (*ctor)(void *));
>>> +struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size,
>>> + unsigned int offset,
>>> + slab_flags_t flags,
>>> + void (*ctor)(void *));
>>
>> I wonder if there's a way to do this in a more generic way, we'd now have 3
>> variants and neither supports everything (what about both rcu offset and
>> usercopy?).
>
> The "pass all arguments as a struct" pattern might not look too bad
> (or alternatively, "pass all optional arguments as a struct"), as long
> as it's fine for unused arguments to be zero-initialized? Like:
>
> struct kcr_options {
> const char *name;
> unsigned int size;
> ...
> };
>
> struct kmem_cache *kmem_cache_create(struct kcr_options opt);
>
> void blah() {
> kmem_cache_create((struct kcr_options){
> .name = "blah",
> .size = ...,
> ...
> });
> }
>
> I think maybe we can do this now that the kernel is C11?
Yep should work.
I like this approach as a way of unifying the various ways of creating a
slab cache. Particularly as I'd want to use a free ptr myself for an
in-kernel use case that currently creates a cache with
kmem_cache_create_usercopy().
> But I guess if we want to allow leaving out the freeptr_offset
> parameter, we'd have to have a flag to say whether the freeptr_offset
> parameter value should be used... Maybe my proposal is too overly
> fancy...
I think we'll end up going down that route eventually anyway to cover
all cases, so may as well do a prep patch that does that first. At least
that's my opinion...
--
Jens Axboe
