From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Smart Subject: Re: [RFC] Netlink and user-space buffer pointers Date: Thu, 20 Apr 2006 10:33:12 -0400 Message-ID: <44479BA8.1000405@emulex.com> References: <1145306661.4151.0.camel@localhost.localdomain> <20060418160121.GA2707@us.ibm.com> <444633B5.5030208@emulex.com> <4446AC80.6040604@cs.wisc.edu> Reply-To: James.Smart@Emulex.Com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-scsi@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: To: Mike Christie In-Reply-To: <4446AC80.6040604@cs.wisc.edu> Sender: linux-scsi-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Mike Christie wrote: > For the tasks you want to do for the fc class is performance critical? No, it should not be. > If not, you could do what the iscsi class (for the netdev people this is > drivers/scsi/scsi_transport_iscsi.c) does and just suffer a couple > copies. For iscsi we do this in userspace to send down a login pdu: > > /* > * xmitbuf is a buffer that is large enough for the iscsi_event, > * iscsi pdu (hdr_size) and iscsi pdu data (data_size) > */ Well, the real difference is that the payload of the "message" is actually the payload of the SCSI command or ELS/CT Request. Thus, the payload may range in size from a few hundred bytes to several kbytes (> 1 page) to Mbyte's in size. Rather than buffer all of this, and push it over the socket, thus the extra copies - it would best to have the LLDD simply DMA the payload like on a typical SCSI command. Additionally, there will be response data that can be several kbytes in length. > ... I think there may be issues with packing structs or 32 bit > userspace and 64 bit kernels and other fun things like this so the iscsi > pdu and iscsi event have to be defined correctly and I guess we are back > to some of the problems with ioctls :( Agreed. In this use of netlink, there's not a lot of wins for netlink over ioctls. It all comes down to 2 things: a) proper portable message definition; and b) what do you do with that non-portable user space buffer pointer ? -- james s