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

On Tue, 16 Jan 2018, Matthew Wilcox wrote:

quoted

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.

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