Re: kmem_cache_attr (was Re: [PATCH 04/36] usercopy: Prepare for usercopy whitelisting)

[Christopher Lameter]

On Tue, 16 Jan 2018, Matthew Wilcox wrote:

> > Sure this data is never changed. It can be const.
>
> It's changed at initialisation.  Look:
>
> kmem_cache_create(const char *name, size_t size, size_t align,
>                   slab_flags_t flags, void (*ctor)(void *))
>         s = create_cache(cache_name, size, size,
>                          calculate_alignment(flags, align, size),
>                          flags, ctor, NULL, NULL);
>
> The 'align' that ends up in s->align, is not the user-specified align.
> It's also dependent on runtime information (cache_line_size()), so it
> can't be calculated at compile time.

Then we would need another align field in struct kmem_cache that takes the
changes value?

> 'flags' also gets mangled:
>         flags &= CACHE_CREATE_MASK;

Well ok then that also belongs into kmem_cache and the original value
stays in kmem_cache_attr.

> unsigned int would be my preference.

Great.