From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Mason <chris.mason@oracle.com>
Subject: Re: [PATCH 29/35] Btrfs ioctl code
Date: Thu, 15 Jan 2009 15:49:49 -0500
Message-ID: <1232052589.8269.124.camel@think.oraclecorp.com>
References: <1231387045-27838-1-git-send-email-chris.mason@oracle.com>
	 <1231387045-27838-30-git-send-email-chris.mason@oracle.com>
	 <20090116.032900.03617624.ryusuke@osrg.net>
	 <alpine.LFD.2.00.0901151215130.6528@localhost.localdomain>
	 <1232051302.8269.99.camel@think.oraclecorp.com>
	 <alpine.LFD.2.00.0901151242450.6528@localhost.localdomain>
Mime-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>,
	akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org
To: Linus Torvalds <torvalds@linux-foundation.org>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from acsinet12.oracle.com ([141.146.126.234]:53731 "EHLO
	acsinet12.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S933858AbZAOUuw (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Thu, 15 Jan 2009 15:50:52 -0500
In-Reply-To: <alpine.LFD.2.00.0901151242450.6528@localhost.localdomain>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Thu, 2009-01-15 at 12:44 -0800, Linus Torvalds wrote:
> 
> On Thu, 15 Jan 2009, Chris Mason wrote:
> > > 
> > > Grr. Different alignment for 64-bit values, coupled with "name" not 
> > > having a size that is a multiple-of-eight.
> > 
> > Will the fd and the start of the name get aligned differently?  I'll fix
> > it up
> 
> No, since the name is byte-aligned, the only thing that happens is that 
> the total alignment (which comes from the alignment of __s64) affects the 
> final size - think about having an array of those things, and the 
> "sizeof()" gives you what the offset to the next entry in the array would 
> be.
> 
> So they'll look _exactly_ the same in all ways, except for padding at the 
> end.

Ok, that makes more sense thanks.  The kernel does:

if (copy_from_user(vol_args, arg, sizeof(*vol_args))) {
	ret = -EFAULT;
	goto out;
}

So I'll try to get something that works as expected and just trims some
bytes off the end to align things.

-chris