From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.fusionio.com ([66.114.96.30]:38627 "EHLO mx1.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751491Ab2FTNh5 (ORCPT ); Wed, 20 Jun 2012 09:37:57 -0400 Date: Wed, 20 Jun 2012 09:37:54 -0400 From: Chris Mason To: "H. Peter Anvin" CC: "linux-btrfs@vger.kernel.org" Subject: Re: Device names Message-ID: <20120620133754.GE4102@shiny> References: <4FDFC807.2080209@zytor.com> <20120619235129.GB4102@shiny> <4FE1128B.5080004@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: <4FE1128B.5080004@zytor.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Tue, Jun 19, 2012 at 06:00:11PM -0600, H. Peter Anvin wrote: > On 06/19/2012 04:51 PM, Chris Mason wrote: > > > > At mount time, we go through and verify the path names still belong to > > the filesystem you thought they belonged to. The bdev is locked during > > the verification, so it won't be able to go away or change. > > > > This is a long way of saying right we don't spit out device numbers. > > Even device numbers can change. We can easily add a uuid based listing, > > which I think is what you want. > > > > No, I want to find the actual devices. I know I can get the UUID, but > scanning all the block devices in the system looking for that UUID is a > nonstarter. > > Device path names can change while the system is operating (and, worse, > are dependent on namespace changes and chroot); device *numbers* cannot > as long as the device is in use (e.g. mounted.) They can indeed change > while not in use, of course. Ok, my two choices for exporting this to you are a /sys/btrfs kind of directory (representing the mounted filesystems) or an ioctl. Which one is most usable for you? You want to map from /some_dir to a definitive list of devices you need to find in syslinux to later boot off that FS, right? -chris