From owner-freebsd-arch@FreeBSD.ORG Mon Jan 7 05:13:39 2008 Return-Path: Delivered-To: freebsd-arch@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9723A16A419; Mon, 7 Jan 2008 05:13:39 +0000 (UTC) (envelope-from delphij@delphij.net) Received: from tarsier.delphij.net (delphij-pt.tunnel.tserv2.fmt.ipv6.he.net [IPv6:2001:470:1f03:2c9::2]) by mx1.freebsd.org (Postfix) with ESMTP id 2BBDF13C46E; Mon, 7 Jan 2008 05:13:39 +0000 (UTC) (envelope-from delphij@delphij.net) Received: from tarsier.geekcn.org (unknown [202.108.54.204]) (using TLSv1 with cipher ADH-CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by tarsier.delphij.net (Postfix) with ESMTP id D63DB28448; Mon, 7 Jan 2008 13:13:37 +0800 (CST) Received: from localhost (unknown [202.108.54.204]) by tarsier.geekcn.org (Postfix) with ESMTP id 75D18EB2CE2; Mon, 7 Jan 2008 13:13:37 +0800 (CST) X-Virus-Scanned: amavisd-new at geekcn.org Received: from tarsier.geekcn.org ([202.108.54.204]) by localhost (mail.geekcn.org [202.108.54.204]) (amavisd-new, port 10024) with ESMTP id 83o3pk4e7piZ; Mon, 7 Jan 2008 13:13:27 +0800 (CST) Received: from charlie.delphij.net (c-67-161-39-180.hsd1.ca.comcast.net [67.161.39.180]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by tarsier.geekcn.org (Postfix) with ESMTP id A4C95EB0A25; Mon, 7 Jan 2008 13:13:25 +0800 (CST) DomainKey-Signature: a=rsa-sha1; s=default; d=delphij.net; c=nofws; q=dns; h=message-id:date:from:reply-to:organization:user-agent: mime-version:to:cc:subject:x-enigmail-version:openpgp:content-type:content-transfer-encoding; b=brhI+YDv5sOq4w42lTtBdJYKEbCZFm4fi2JvxwBgT+Aqz103gqEPu6qB7VJbVnr50 mxQeuCO11uDU1fVuCr7OA== Message-ID: <4781B4F2.9040707@delphij.net> Date: Sun, 06 Jan 2008 21:13:22 -0800 From: Xin LI Organization: The FreeBSD Project User-Agent: Thunderbird 2.0.0.9 (X11/20071125) MIME-Version: 1.0 To: freebsd-arch@FreeBSD.org X-Enigmail-Version: 0.95.5 OpenPGP: id=18EDEBA0; url=http://www.delphij.net/delphij.asc Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: dfr@FreeBSD.org, mengguang@staff.sina.com.cn Subject: Why it does not make sense if msginfo.msgssz is greater than 256? X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: d@delphij.net List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 07 Jan 2008 05:13:39 -0000 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi, While pursuing sys/kern/sysv_msg.c, we found the following comment: * Each message is broken up and stored in segments that are msgssz bytes * long. For efficiency reasons, this should be a power of two. Also, * it doesn't make sense if it is less than 8 or greater than about 256. * Consequently, msginit in kern/sysv_msg.c checks that msgssz is a power of * two between 8 and 1024 inclusive (and panic's if it isn't). And it seems to be come from the following comment: /* * msginfo.msgssz should be a power of two for efficiency reasons. * It is also pretty silly if msginfo.msgssz is less than 8 * or greater than about 256 so ... */ Why is there the limitation (recommendation)? Thanks in advance! Cheers, - -- Xin LI http://www.delphij.net/ FreeBSD - The Power to Serve! -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFHgbTyi+vbBBjt66ARAuJmAKCAw8qZuYtVMIxjY1BXkNad57BVTACgt6zF 3l5/4Bd55EoNy8aFhm+RXyc= =qWJk -----END PGP SIGNATURE-----