From owner-freebsd-fs@FreeBSD.ORG Tue Apr 26 18:57:18 2011 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E9A35106564A for ; Tue, 26 Apr 2011 18:57:18 +0000 (UTC) (envelope-from mavbsd@gmail.com) Received: from mail-bw0-f54.google.com (mail-bw0-f54.google.com [209.85.214.54]) by mx1.freebsd.org (Postfix) with ESMTP id 6F7848FC08 for ; Tue, 26 Apr 2011 18:57:18 +0000 (UTC) Received: by bwz12 with SMTP id 12so1126572bwz.13 for ; Tue, 26 Apr 2011 11:57:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:sender:message-id:date:from:user-agent :mime-version:to:cc:subject:references:in-reply-to :x-enigmail-version:content-type:content-transfer-encoding; bh=A74fnpAPvmZQ5LURRfld/rkx/TwmOR8gDEMY+0aA50A=; b=CeXYNDap6erZxnycSdxP7eC+fQ3rkNd4c82phcgdca7KdE5OffBHWv1y910PXEV5Pt 3Su+2aT4vP+n+wJpDBHhAFr4SchVEknmViriwrq4xXq65tpMPhlLxrZRJIZLbVLU3wov CT1/yXDjpajv9imFZClGlDGn+sY3/DNQt6m+U= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:x-enigmail-version:content-type :content-transfer-encoding; b=GHChLIXh5ii9r783XghzthgbwxKKYukx71bgGWKeKK2Nq7ZzwIJycliCMx12z1y98P z2Aw2joj4sYM1W3oYRflT5JGBSIbXb+ac5B31R7tgeP/n2+2a1h+zwSdGa58FXFx87+M NqJROuWP9agKWDzBouLl3EKAawuBI5ut089Is= Received: by 10.204.49.87 with SMTP id u23mr1040392bkf.171.1303842719978; Tue, 26 Apr 2011 11:31:59 -0700 (PDT) Received: from mavbook2.mavhome.dp.ua (pc.mavhome.dp.ua [212.86.226.226]) by mx.google.com with ESMTPS id 16sm4012788bkm.6.2011.04.26.11.31.58 (version=SSLv3 cipher=OTHER); Tue, 26 Apr 2011 11:31:59 -0700 (PDT) Sender: Alexander Motin Message-ID: <4DB70F97.1070809@FreeBSD.org> Date: Tue, 26 Apr 2011 21:31:51 +0300 From: Alexander Motin User-Agent: Thunderbird 2.0.0.23 (X11/20091212) MIME-Version: 1.0 To: Doug Barton References: <4DB70949.6090104@FreeBSD.org> In-Reply-To: <4DB70949.6090104@FreeBSD.org> X-Enigmail-Version: 0.96.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: freebsd-fs@FreeBSD.org Subject: Re: Why not just name the cam-ata devices the same as the old names? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Apr 2011 18:57:19 -0000 Hi. Doug Barton wrote: > I'm not nearly as smart as you are, so please explain to me like I'm > dense. :) Why can we not simply give the devices created by ata-cam the > same names they have under the old ata system? Don't underestimate yourself, or don't make me blush. ;) There are two problems: names and unit numbers. We can't use same names because old and new stacks coexisting last 18 months (and they will forever in 8.x), and it was possible to just load single ahci module of new stack for SATA devices, while PATA were working via old stack. Using same name would cause collisions. Now when we are going to switch to the new stack completely, coexistence could be a bit less important, but there is already number of migrated systems and they would suffer from the second renaming. Even if we do something with names, there is a problem with device unit numbers. Previous numbering scheme of ATA_STATIC_ID reserved only two device numbers per ATA channel. It was working fine for PATA times, but it is not now. When SATA port multipliers are used (and it is not so rare now), there could be up to 15 devices per channel, plus multiplier itself. They just won't fit. -- Alexander Motin