From gd78059@sac.sfbay.sun.com Fri Jun 6 12:59:04 2008 Received: from newsunmail1brm.central.sun.com (newsunmail1brm.Central.Sun.COM [129.147.62.245]) by sac.sfbay.sun.com (8.13.8+Sun/8.13.8) with ESMTP id m56Jx3Y9003553 for ; Fri, 6 Jun 2008 12:59:04 -0700 (PDT) Received: from nwk-avmta-1.SFBay.Sun.COM (nwk-avmta-1.SFBay.Sun.COM [129.146.11.74]) by newsunmail1brm.central.sun.com (8.13.7+Sun/8.13.7/ENSMAIL,v2.2) with ESMTP id m56Jx27W028226; Fri, 6 Jun 2008 13:59:03 -0600 (MDT) Received: from pmxchannel-daemon.nwk-avmta-1.sfbay.Sun.COM by nwk-avmta-1.sfbay.Sun.COM (Sun Java System Messaging Server 6.2-3.04 (built Jul 15 2005)) id <0K22003054UEKA00@nwk-avmta-1.sfbay.Sun.COM>; Fri, 06 Jun 2008 12:59:02 -0700 (PDT) Received: from dm-sfbay-02.sfbay.sun.com ([129.146.11.31]) by nwk-avmta-1.sfbay.Sun.COM (Sun Java System Messaging Server 6.2-3.04 (built Jul 15 2005)) with ESMTP id <0K22004044UDF6D0@nwk-avmta-1.sfbay.Sun.COM>; Fri, 06 Jun 2008 12:59:01 -0700 (PDT) Received: from sac.sfbay.sun.com (new-sac.SFBay.Sun.COM [129.146.175.65]) by dm-sfbay-02.sfbay.sun.com (8.13.8+Sun/8.13.8/ENSMAIL,v2.2) with ESMTP id m56Jx1lU007773; Fri, 06 Jun 2008 12:59:01 -0700 (PDT) Received: from sac.sfbay.sun.com (localhost [127.0.0.1]) by sac.sfbay.sun.com (8.13.8+Sun/8.13.8) with ESMTP id m56JwxeN003548; Fri, 06 Jun 2008 12:58:59 -0700 (PDT) Received: (from gd78059@localhost) by sac.sfbay.sun.com (8.13.8+Sun/8.13.8/Submit) id m56Jwx67003544; Fri, 06 Jun 2008 12:58:59 -0700 (PDT) Date: Fri, 06 Jun 2008 12:58:59 -0700 (PDT) From: "Garrett D'Amore - sun microsystems" Subject: Remove MAXIOCBSZ [PSARC/2008/367 Self Review] To: PSARC-ext@sun.com Cc: Garrett.Damore@sun.com Message-id: <200806061958.m56Jwx67003544@sac.sfbay.sun.com> Content-transfer-encoding: 7BIT X-PMX-Version: 5.4.1.325704 Status: RO Content-Length: 2408 Following self-review case on my own behalf, with possible benefits for some STREAMS device drivers. Template Version: @(#)sac_nextcase 1.66 04/17/08 SMI This information is Copyright 2008 Sun Microsystems 1. Introduction 1.1. Project/Component Working Name: Remove MAXIOCBSZ 1.2. Name of Document Author/Supplier: Author: Garrett D'Amore 1.3 Date of This Document: 06 June, 2008 4. Technical Description Self-Review: Removal of MAXIOCBSZ Binding: Patch Description: In , there is a macro called MAXIOCBSZ, which is assigned value 1024. This macro is used in only one place, uts/common/os/strsubr.c, in the function putiocd(). The macro limits the amount of data that will be copied into a single msgb data block, when the data is being copied in either in response to I_STR ioctls, or as part of a driver initiated request via M_COPYIN. Note that the macro doesn't limit the amount of data copied in, as that check is handled via strmsgsz (but only for I_STR data; drivers are expected to provide sane values for the data size in M_COPYIN messages). Rather what it does is cause a single copyin to be split across smaller M_DATA messages. This is a piece of SVR3 legacy that actually inhibits performance, since the stream head must now perform extra processing, and the receiving driver may need to copy the data via msgpullup() if it desires a contiguous amount of data. We therefore propose to remove the MAXIOCBSZ macro. We further propose to promise device drivers that on Solaris versions with this change, they can avoid the check and msgpullup() if they so desire. (Basically, we can promise that the data will already be contiguous.) Drivers that don't care to depend on this promise, or that are from older releases of Solaris, should still check for additional trailing message blocks and do msgpullup() if appropriate. We don't believe that any consumers have ever used, referenced, or relied on MAXIOCBSZ (at least in "modern" times), and we can find no evidence that the old behavior was ever specifically documented. So we don't think this represents any compatibility issues for older drivers. (There is absolutely *no* change for userland applications.) 6. Resources and Schedule 6.4. Steering Committee requested information 6.4.1. Consolidation C-team Name: ON 6.5. ARC review type: Automatic 6.6. ARC Exposure: open