From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: [Stgt-devel] Question for pass-through target design Date: Mon, 07 May 2007 19:27:23 +0400 Message-ID: <463F455B.3000209@vlnb.net> References: <463B72F6.3000207@torque.net> <20070506053629P.fujita.tomonori@lab.ntt.co.jp> <463F36AC.3010207@vlnb.net> <20070507182837E.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-relay-02.mailcluster.net ([85.249.135.243]:60322 "EHLO mail-relay-02.mailcluster.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965055AbXEGP1h (ORCPT ); Mon, 7 May 2007 11:27:37 -0400 In-Reply-To: <20070507182837E.fujita.tomonori@lab.ntt.co.jp> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: FUJITA Tomonori Cc: stgt-devel@lists.berlios.de, scst-devel@lists.sourceforge.net, linux-scsi@vger.kernel.org FUJITA Tomonori wrote: > From: Vladislav Bolkhovitin > Subject: Re: [Stgt-devel] Question for pass-through target design > Date: Mon, 07 May 2007 18:24:44 +0400 > > >>FUJITA Tomonori wrote: >> >>>>>>It looks like the pass-through target support is currently broken, at >>>>>>least as I've checked for ibmvstgt, but I think it's a general problem. >>>>>>I wanted to check my assumptions and get ideas. >>>>> >>>>>Yeah, unfortunately, it works only with the iSCSI target driver (which >>>>>runs in user space). >>>>> >>>>> >>>>> >>>>> >>>>>>The code isn't allocating any memory to pass along to the sg code to store >>>>>>the result of a read or data for a write. Currently, dxferp for sg_io_hdr >>>>>>or dout_xferp/din_xferp for sg_io_v4 are assigned to the value of uaddr, >>>>>>which is set to 0 in kern_queue_cmd. With the pointer set to NULL, >>>>>>the pass-through target isn't going to function. Even if we had memory >>>>>>allocated, there isn't a means of getting data to be written via sg down >>>>>>this code path. >>>>>> >>>>>>What ideas are there as to how the data will get to user-space so that >>>>>>we can use sg? >>>>> >>>>>For kernel-space drivers, we don't need to go to user-space. We can do >>>>>the pass-through in kernel space. I talked with James about this last >>>>>year and he said that if the code is implemented cleanly, he would >>>>>merges it into mainline. >>>> >>>>We already have a pass-through in the kernel space for >>>>kernel space drivers. It is the scsi_tgt* code. >>> >>> >>>Could you elaborate more? >>> >>>What I meant that is that the kernel tgt code (scsi_tgt*) receives >>>SCSI commands from one lld and send them to another lld instead of >>>sending them to user space. >> >>Although the approach of passing SCSI commands from a target LLD to an >>initiator one without any significant interventions from the target >>software looks to be nice and simple, you should realize how limited, >>unsafe and illegal it is, since it badly violates SCSI specs. > > > I think that 'implemented cleanly' means that one scsi_host is assigned > to only one initiator. Sorry, I don't fully understand you. If you mean you are going to limit only one remote initiator per-target device, then, well, is it even more limited (and limiting) or not? > _______________________________________________ > Stgt-devel mailing list > Stgt-devel@lists.berlios.de > https://lists.berlios.de/mailman/listinfo/stgt-devel >