Re: [PATCH] cgroup: reorder flexible array members of struct cgroup_root

[Tejun Heo <tj@kernel.org>]

Hello,

On Mon, Oct 16, 2017 at 11:33:21PM -0700, Nick Desaulniers wrote:
> When compiling arch/x86/boot/compressed/eboot.c with HOSTCC=clang, the
> following warning is observed:
> 
> ./include/linux/cgroup-defs.h:391:16: warning: field 'cgrp' with
> variable sized type 'struct cgroup' not at the end of a struct or class
> is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
>         struct cgroup cgrp;
>                       ^
> Flexible array members are a C99 feature, but must be the last member of
> a struct. Structs with flexible members composed in other structs must
> also be the final members, unless using GNU C extensions.
> 
> struct cgroup_root's member cgrp is a struct cgroup, struct cgroup's
> member ancestor_ids is a flexible member.

This is silly tho.  We know the the root group embedded there won't
have any ancestor_ids.  Also, in general, nothing prevents us from
doing something like the following.

	struct outer_struct {
		blah blah;
		struct inner_struct_with_flexible_array_member inner;
		unsigned long storage_for_flexible_array[NR_ENTRIES];
		blah blah;
	};

I think we should just silence the bogus warning.

Thanks.

-- 
tejun