Re: [PATCH v8 1/6] fs/posix_acl: Update the comments and support lightweight cache skipping

[Miklos Szeredi]

On Fri, Mar 2, 2018 at 10:59 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> The code has been missing a way for a ->get_acl method to not cache
> a return value without risking invalidating a cached value
> that was set while get_acl() was returning.
>
> Add that support by implementing to_uncachable_acl, to_cachable_acl,
> is_uncacheable_acl, and dealing with uncachable acls in get_acl().

I don't like the pointer magic here.  Can't the uncachable bit just be
added to struct posix_acl?

 AFAICS that can be done even without increasing the size of that
struct (e.g. by unioning it with the rcu_head).

Thanks,
Miklos