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 S970626AbdAELvA (ORCPT <rfc822;w@1wt.eu>);
        Thu, 5 Jan 2017 06:51:00 -0500
Received: from aserp1050.oracle.com ([141.146.126.70]:21112 "EHLO
        aserp1050.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1762251AbdAELts (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 5 Jan 2017 06:49:48 -0500
Date: Thu, 5 Jan 2017 14:48:04 +0300
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Long Li <longli@exchange.microsoft.com>
Cc: devel@linuxdriverproject.org, Haiyang Zhang <haiyangz@microsoft.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] hv: use substraction to update ring buffer index
Message-ID: <20170105114804.GE13756@mwanda>
References: <1483589302-27177-1-git-send-email-longli@exchange.microsoft.com>
 <20170105113955.GD13756@mwanda>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170105113955.GD13756@mwanda>
User-Agent: Mutt/1.5.21 (2010-09-15)
X-Source-IP: aserp1040.oracle.com [141.146.126.69]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Jan 05, 2017 at 02:39:55PM +0300, Dan Carpenter wrote:
> > @@ -179,7 +180,8 @@ static u32 hv_copyfrom_ringbuffer(
> >  	memcpy(dest, ring_buffer + start_read_offset, destlen);
> >  
> >  	start_read_offset += destlen;
> > -	start_read_offset %= ring_buffer_size;
> > +	if (start_read_offset >= ring_buffer_size)
> > +		start_read_offset -= ring_buffer_size;
> 
> I totally don't understand the original code here.  We do the memset

I meant memcpy() not memset.

regards,
dan carpenter