linux-kernel - Re: Adding subroot information to /proc/mounts, or obtaining that through other means

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Message-ID: <467B7F6F.4030007@zytor.com>
Date:	Fri, 22 Jun 2007 00:51:11 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ram Pai <linuxram@...ibm.com>
CC:	Al Viro <viro@....linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, util-linux-ng@...r.kernel.org
Subject: Re: Adding subroot information to /proc/mounts, or obtaining that
 through other means

Ram Pai wrote:
> 
> Ok. so you think /proc/mounts can be extended easily without breaking
> any userspace commands?
> 
> well lets see..
> 1. to disambiguate bind mounts, we have to add a field that displays the
> 	 path to the mount's root dentry from the filesystem's root
> 	 dentry. Agree?
> 
> 2. For filesystems that do not have a backing store, it becomes hard
> 	to disambiguate bind mounts in (1). So we need to add a
> 	filesystem-id field.
> 
> 3. if we need to add the propagation status of the mount we need a
> 	 propagation flag added in the output.
> 
> 4. To be able to construct the propagation tree, we need a way to refer
> 	to the other mounts, since some mounts are peers and some other
> 	mounts are master. Which means we need a mount-id field.
> 	Agree?
> 
> If you agree to the above 4 new fields, it becomes challenging to
> extend /proc/mounts to incorporate these new fields without
> breaking any existing applications. 
> 

No, I don't think so.  I suspect, in fact, that as long as we add the
new fields to the right (obviously) we should be fine.  There aren't all
that many users of /proc/mounts, and even fewer that don't use the
library functions (getmntent et al.)

	-hpa
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