From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [PATCH] [Target_Core_Mod/pSCSI]: Add optional legacy scsi_execute_async() usage for Linux/SCSI passthrough Date: Wed, 22 Apr 2009 15:06:13 -0400 Message-ID: <49EF6AA5.80500@interlog.com> References: <1239930560.4176.577.camel@haakon2.linux-iscsi.org> <49EB036B.8090607@panasas.com> <49EDB8EF.7040503@vlnb.net> <49EF1A88.1040105@panasas.com> Reply-To: dgilbert@interlog.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.infotech.no ([82.134.31.41]:53708 "EHLO elrond2.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756754AbZDVTGY (ORCPT ); Wed, 22 Apr 2009 15:06:24 -0400 In-Reply-To: <49EF1A88.1040105@panasas.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Boaz Harrosh Cc: Vladislav Bolkhovitin , Tejun Heo , "Nicholas A. Bellinger" , linux-scsi , LKML , James Bottomley , FUJITA Tomonori , Mike Christie , Jens Axboe , Geert Uytterhoeven , Geoff Levand , Christoph Hellwig , Paul Mundt Boaz Harrosh wrote: > On 04/21/2009 03:15 PM, Vladislav Bolkhovitin wrote: >> Boaz Harrosh, on 04/19/2009 02:56 PM wrote: >>> On 04/17/2009 04:09 AM, Nicholas A. Bellinger wrote: >> [..] >> >>> Are you aware that scsi_execute_async() has gone in 2.6.30-rc1? >>> >>> I'm not sure what would be the best alternative for you. I would say >>> a bio, but it is still being debated. Your current options are: >>> >>> 1. bio_alloc then loop () bio_add_pc_page, and finally blk_rq_append_bio >>> (Which block people don't like) >>> 2. sglist => page-pointers-array translation and blk_rq_map_user with >>> struct rq_map_data mode. (not possible with all kind of sglists) >>> 2. sglist => iovec translation and blk_rq_map_user_iov() >>> (Very very ugly mapping of pages to virtual pointers) >>> >>> I have a similar situation with my OSD code. >> Do you have somewhere in it a need to run an arbitrary CDB with data >> pages stored in an sglist? Is that code accepted in the mainline? >> > > No, I have a direct bio which comes from two sources. > 1. A bio prepared by a filesystem to describe a write/read to a file (osd object) > 2. A cloned bio that comes from a stacking block-device over osd-object. > > So I do not have an sglist at all, anywhere in code. > >> If yes, why not to resurrect the necessary bits of scsi_execute_async() >> (option (1) above)? It was deleted, because in 2.6.30 there are no users >> of it left, but if there are users (OSD), then why not to return it? >> Seems nothing better for the sg->bio case can be invented. >> > > I hate scsi_execute_async() for lots of reasons, > 1. The cover-up of an historical abuse of sglists by sg/sr > 2. Override of use_sg/data-pointer crap Hate, abuse, crap?? [I believe the author of scsi_execute_async() is cc-ed on your post.] It served a purpose when the block layer was taking over sglist handling and was synchronous. Block error handling was non-existent or poor at the time. The block layer wanted to disown the sg and st drivers because they didn't fit its crude model. So scsi_execute_async() was our "get out of the !@#$ing block system" card. Happily the block system has evolved to being able to provide the async handling and error processing that it, sg and st need. It is now a non-block system. So scsi_execute_async() has become superfluous. > 3. What is data-format got to do with sync/async execution A fair bit in async. For example I'd like to know when data-out buffers can be re-used and data-in buffers are ready. If it was really clever it could alert me when thresholds were met in the data-in buffer. Doug Gilbert > 4. the need of all that scsi_io_context and the re-invention > of async_done API. > 5. ... > Good riddence > > But you might be looking into an API introduced by an RFC by > Tejun Heo in the form of blk_rq_map_kern_sgl() which should > be a more appropriate general API for your use. > (And is not directly usable for me in OSD) > >> Vlad > > Boaz >