From mboxrd@z Thu Jan  1 00:00:00 1970
From: Miklos Szeredi <mszeredi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH v8 1/6] fs/posix_acl: Update the comments and support
	lightweight cache skipping
Date: Mon, 5 Mar 2018 10:53:41 +0100
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To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Linux Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, lkml <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Seth Forshee <seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org>, Alban Crequy <alban-lYLaGTFnO9sWenYVfaLwtA@public.gmane.org>, Sargun Dhillon <sargun-GaZTRHToo+CzQB+pC5nmwQ@public.gmane.org>, linux-fsdevel <linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
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On Fri, Mar 2, 2018 at 10:59 PM, Eric W. Biederman
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> 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