From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752463AbcBAIlo (ORCPT <rfc822;w@1wt.eu>);
	Mon, 1 Feb 2016 03:41:44 -0500
Received: from mga04.intel.com ([192.55.52.120]:37128 "EHLO mga04.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751853AbcBAIln (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 1 Feb 2016 03:41:43 -0500
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="5.22,379,1449561600"; 
   d="scan'208";a="893620609"
Subject: Re: [PATCH 06/10] staging/android: turn fence_info into a __64
 pointer
To: Gustavo Padovan <gustavo@padovan.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <1454102426-20637-1-git-send-email-gustavo@padovan.org>
 <1454102426-20637-7-git-send-email-gustavo@padovan.org>
Cc: linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
        dri-devel@lists.freedesktop.org, Daniel Stone <daniels@collabora.com>,
        =?UTF-8?Q?Arve_Hj=c3=b8nnev=c3=a5g?= <arve@android.com>,
        Riley Andrews <riandrews@android.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Rob Clark <robdclark@gmail.com>, Greg Hackmann <ghackmann@google.com>,
        John Harrison <John.C.Harrison@Intel.com>,
        Gustavo Padovan <gustavo.padovan@collabora.co.uk>
From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <56AF1A43.5010900@linux.intel.com>
Date: Mon, 1 Feb 2016 09:41:39 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.1.0
MIME-Version: 1.0
In-Reply-To: <1454102426-20637-7-git-send-email-gustavo@padovan.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Op 29-01-16 om 22:20 schreef Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
>
> Making fence_info a pointer enables us to extend the struct in the future
> without breaking the ABI.
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  drivers/staging/android/sync.c      | 2 +-
>  drivers/staging/android/uapi/sync.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
> index f7530f0..51d4f47 100644
> --- a/drivers/staging/android/sync.c
> +++ b/drivers/staging/android/sync.c
> @@ -525,7 +525,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>  	if (info->status >= 0)
>  		info->status = !info->status;
>  
> -	len = sizeof(struct sync_file_info);
> +	len = sizeof(struct sync_file_info) - sizeof(__u64 *);
>  
>  	for (i = 0; i < sync_file->num_fences; ++i) {
>  		struct fence *fence = sync_file->cbs[i].fence;
> diff --git a/drivers/staging/android/uapi/sync.h b/drivers/staging/android/uapi/sync.h
> index ed281fc..9f07aa7 100644
> --- a/drivers/staging/android/uapi/sync.h
> +++ b/drivers/staging/android/uapi/sync.h
> @@ -54,7 +54,7 @@ struct sync_file_info {
>  	char	name[32];
>  	__s32	status;
>  
> -	__u8	fence_info[0];
> +	__u64	*fence_info;
>  };
>
Pointers are awful, it should be a __u64 since it's a pointer type. Userspace should cast it to a uintptr_t in userspace.
This structure also won't work on 64-bits systems, there may be a hole between fence_info and status (or num_fences in next patch).

It's probably best to move it to the top and ensure the struct is 64-bits aligned.