From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benny Halevy Subject: Re: [PATCH 3/3] iscsi_tcp: Enable large commands Date: Tue, 15 Apr 2008 16:57:20 +0300 Message-ID: <4804B440.20109@gmail.com> References: <20080414010112W.tomof@acm.org> <1208170266-1676-1-git-send-email-fujita.tomonori@lab.ntt.co.jp> <48049E8A.7030700@panasas.com> <4804A16D.7000002@panasas.com> <4804A8C7.504@emulex.com> <4804AFBA.1070105@panasas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from bzq-219-195-70.pop.bezeqint.net ([62.219.195.70]:56918 "EHLO bh-buildlin1.bhalevy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755782AbYDON7Y (ORCPT ); Tue, 15 Apr 2008 09:59:24 -0400 In-Reply-To: <4804AFBA.1070105@panasas.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Boaz Harrosh Cc: James.Smart@Emulex.Com, FUJITA Tomonori , James Bottomley , Mike Christie , linux-scsi@vger.kernel.org, Jens Axboe , Bartlomiej Zolnierkiewicz , Alasdair G Kergon , Geert Uytterhoeven On Apr. 15, 2008, 16:38 +0300, Boaz Harrosh wrote: > On Tue, Apr 15 2008 at 16:08 +0300, James Smart wrote: >> Boaz Harrosh wrote: >>> Let through up to the largest command of 260 defined by the scsi standard. >>> iscsi core supports this already. Now that the scsi-ml supports it we can >>> start using large commands. >> Just to double-check: >> if we use sg_io to pass through requests from user-land, which are addressed to >> drivers or transports, and which may not be a SCSI command but rather just something >> utilizing the sg_io infrastructure for management or pass-thru, are we limited to >> 260 bytes for request/cmd payload ? >> >> -- james s > > I think that only bsg, after the pending patches get accepted, will let you > pass larger then 16 bytes commands from user-land. sg_io is I think limited > to 16. However this could be fixed. (With sg_io, did you mean commands going > through the sg.c driver?) > > The block layer imposes no limits, and so is scsi-ml. The only limits are from > ULDs, and LLDs, like here, iscsi protocol does not support more then > SCSI_MAX_VARLEN_CDB_SIZE (260). Actually the 260 byte limit comes from SCSI variable length CDB maximum length. iSCSI allows to send larger CDBs with the Extended CDB AHS that has a 16 bit length field. Within the protocol constraints, the longest CDB would be 16 (in BHS) + 65532 (in AHS) = 65548 bytes long :) Benny > > If you need support in any other ULD, I will be happy to help. > > Boaz > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html