Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 20 Jul 2001 06:53:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 20 Jul 2001 06:53:20 -0400 Received: from adsl-204-0-249-112.corp.se.verio.net ([204.0.249.112]:4349 "EHLO tabby.cats-chateau.net") by vger.kernel.org with ESMTP id ; Fri, 20 Jul 2001 06:53:10 -0400 From: Jesse Pollard Reply-To: jesse@cats-chateau.net To: stimits@idcomm.com, "D. Stimits" , kernel-list Subject: Re: bzImage, root device Q Date: Fri, 20 Jul 2001 05:46:52 -0500 X-Mailer: KMail [version 1.0.28] Content-Type: text/plain; charset=US-ASCII In-Reply-To: <3B57E0AB.F5D6B2E2@idcomm.com> In-Reply-To: <3B57E0AB.F5D6B2E2@idcomm.com> MIME-Version: 1.0 Message-Id: <01072005531200.07975@tabby> Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Original-Recipient: rfc822;linux-kernel-outgoing On Fri, 20 Jul 2001, D. Stimits wrote: >When booting to a bzImage kernel, bytes 508 and 509 can be used to name >the minor and major number of the intended root device (although it can >be overridden with a command line parameter). Other characteristics are >also available this way, through bytes in the kernel. rdev makes a >convenient way to hex edit those bytes. > >What I'm more curious about is how does the kernel know what filesystem >_type_ the root is? Are there similar bytes in the bzImage, and can rdev >change this? And is there a command line syntax to allow specifying >filesystem type (e.g., something like "vmlinuz root=/dev/scd0,iso9660" >or "vmlinuz root=/dev/scd0,xfs")? Or is this limited in some way, >requiring mount on one or a few known filesystem types ("linux native" >subset comes to mind), followed by a chroot or pivot_root style command >(which in turn means no direct root mount of some filesystem types)? Take a look at fs/super.c - function mount_root(). It reads the file system superblock (from the major/minor specified root device) and determines the filesystem from that. There is a loop that cycles through all known (ie built in) file systems until one works. If none do, then it panics. -- ------------------------------------------------------------------------- Jesse I Pollard, II Email: jesse@cats-chateau.net Any opinions expressed are solely my own. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/