From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Anderson Subject: Re: Request for review of Linux iSCSI driver version 4.0.0.1 Date: Tue, 2 Dec 2003 09:42:02 -0800 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20031202174202.GA1960@beaverton.ibm.com> References: <03120118001300.08627@naveenb-lnx.cisco.com> <03120217260300.01630@naveenb-lnx.cisco.com> <1070383028.2345.8.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e34.co.us.ibm.com ([32.97.110.132]:41140 "EHLO e34.co.us.ibm.com") by vger.kernel.org with ESMTP id S262601AbTLBRjo (ORCPT ); Tue, 2 Dec 2003 12:39:44 -0500 Content-Disposition: inline In-Reply-To: <1070383028.2345.8.camel@mulgrave> List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: naveenb@cisco.com, Roman Zippel , hch@infradead.org, SCSI Mailing List James Bottomley [James.Bottomley@steeleye.com] wrote: > On Tue, 2003-12-02 at 05:56, Naveen Burmi wrote: > > Our assumption so far was that if a buffer is given to SCSI HBA driver, then > > nobody can touch the buffer until the HBA says that he is done with the > > buffer. It seems that this assumption isn't true. Can you give an instance > > where somebody (probably buffer cache) will modify the buffer which is handed > > over to an HBA driver? > > This is an incorrect assumption. The Linux SCSI subsystem is > architected for zero copy, meaning that if the user maps a copy of the > data, they can alter it at will, even if it is in flight within the > driver. The only thing you can guarantee is that you will get another > write request for any page the user dirtied. The user would need to generate another write request and the "guarantee" is up to the user (correct?)? -andmike -- Michael Anderson andmike@us.ibm.com