linux-kernel - Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

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Message-ID: <20120803223634.GO15477@google.com>
Date:	Fri, 3 Aug 2012 15:36:34 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sasha Levin <levinsasha928@...il.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	paul.gortmaker@...driver.com, davem@...emloft.net,
	rostedt@...dmis.org, mingo@...e.hu, ebiederm@...ssion.com,
	aarcange@...hat.com, ericvh@...il.com, netdev@...r.kernel.org
Subject: Re: [RFC v2 1/7] hashtable: introduce a small and naive hashtable

On Fri, Aug 03, 2012 at 03:29:10PM -0700, Linus Torvalds wrote:
> On Fri, Aug 3, 2012 at 3:23 PM, Tejun Heo <tj@...nel.org> wrote:
> >
> > I actually meant an enclosing struct.  When you're defining a struct
> > member, simply putting the storage after a struct with var array
> > should be good enough.  If that doesn't work, quite a few things in
> > the kernel will break.
> 
> The unsigned member of a struct has to be the last one, so your struct
> won't work.

I suppose you mean unsized.  I remember this working.  Maybe I'm
confusing it with zero-sized array.  Hmm... gcc doesn't complain about
the following.  --std=c99 seems happy too.

  #include <stdio.h>

  struct A {
	  int i;
	  long ar[];
  };

  struct B {
	  struct A a;
	  long ar_storage[32];
  };

  int main(void)
  {
	  printf("sizeof(A)=%zd sizeof(B)=%zd\n", sizeof(struct A), sizeof(struct B));
	  return 0;
  }

$ ./a.out
sizeof(A)=8 sizeof(B)=264

-- 
tejun
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