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Date: Tue, 19 Jun 2012 16:35:59 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Calvin Walton <calvin.walton@kepstin.ca>
CC: linux-btrfs@vger.kernel.org
Subject: Re: Subvolumes and /proc/self/mountinfo
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On 06/19/2012 07:22 AM, Calvin Walton wrote:
> 
> All subvolumes are accessible from the volume mounted when you use -o
> subvolid=0. (Note that 0 is not the real ID of the root volume, it's
> just a shortcut for mounting it.)
> 

Could you clarify this bit?  Specifically, what is the real ID of the
root volume, then?

I found that after having set the default subvolume to something other
than the root, and then mounting it without the -o subvol= option, then
the subvolume name does *not* show in /proc/self/mountinfo; the same
happens if a subvolume is mounted by -o subvolid= rather than -o subvol=.

Is this a bug?  This would seem to give the worst of both worlds in
terms of actually knowing what the underlying filesystem path would end
up looking like.

	-hpa