Subject: Re: [PATCH v4 01/10] fwctl: Add basic structure for a class subsystem with a cdev

From: Jason Gunthorpe <[email-masked]>
Date: Fri, 7 Feb 2025 19:55:36 -0400

On Fri, Feb 07, 2025 at 03:32:00PM -0800, Dan Williams wrote:

> > +#define fwctl_alloc_device(parent, ops, drv_struct, member)               \
> > +	({                                                                \
> > +		static_assert(__same_type(struct fwctl_device,            \
> > +					  ((drv_struct *)NULL)->member)); \
> > +		static_assert(offsetof(drv_struct, member) == 0);         \
> > +		(drv_struct *)_fwctl_alloc_device(parent, ops,            \
> > +						  sizeof(drv_struct));    \
> > +	})
> 
> I have already suggested someone else copy this approach to context
> allocation. What do you think of generalizing this in
> include/linux/container_of.h as:

I also have several places doing that too in iommufd and I think we
have a variation in rdma as well.

Let me suggest we go around after the fact and propose a consolidation
patch. I think it will be easier to understand like that?

> #define container_alloc(core_struct, drv_struct, member, alloc_fn, ...)    \
>        ({                                                                 \
>                static_assert(__same_type(core_struct,                     \
>                                          ((drv_struct *)NULL)->member));  \
>                static_assert(offsetof(drv_struct, member) == 0);          \
>                (drv_struct *)(alloc_fn)(sizeof(drv_struct), __VA_ARGS__); \
>        })

It makes sense to me

Jason