From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH RFC 0/4] use scatter lists for all blockpc requests and simplify hw handlers Date: Tue, 7 Jun 2005 20:43:36 +0200 Message-ID: <20050607184335.GD8172@suse.de> References: <1118162097.4813.38.camel@mulgrave> <007e01c56b90$1a09a6f0$e0019d89@cybernetics.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from ns.virtualhost.dk ([195.184.98.160]:14487 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S261872AbVFGSml (ORCPT ); Tue, 7 Jun 2005 14:42:41 -0400 Content-Disposition: inline In-Reply-To: <007e01c56b90$1a09a6f0$e0019d89@cybernetics.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Tony Battersby Cc: 'James Bottomley' , 'Douglas Gilbert' , 'Mike Christie' , 'device-mapper development' , 'linux-scsi' , LIRANS@il.ibm.com On Tue, Jun 07 2005, Tony Battersby wrote: > > > My company (Cybernetics) sells several products that run embedded > Linux > > > which use the userspace scatter-gather capability of the SG driver. > > > They are still running the 2.4 kernel series, but we will probably > > > switch to 2.6 at some point. > > > > What do they actually use it for? As in why is the data scattered > even > > in the virtual address space? > > One of our products is a RAID-like controller for SCSI tape drives. > Parallel SCSI or iSCSI in via a target-mode SCSI driver and parallel > SCSI, iSCSI, or FC out via the SG driver, with various functions in > between for data buffering, emulation, striping, mirroring, etc. The > program that controls everything has a complex internal buffering scheme > that uses userspace scatter-gather for the main read/write I/O path to > the tape drives. That sounds like a valid use. Either way, I don't think we should remove such a feature. It's a sane feature, and people might be using it - there's no excuse for removing it. Should we kill readv next? :) -- Jens Axboe