Re: [9fans] union directories

[Geoff Collyer <geoff@collyer.net>]

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`bind -c 9 9' remains useful, however, to retain createability of the
directory in which a union mount is then performed:

; cd /tmp
; mkdir x
; bind -a /sys/lib x
; ns|tail -4
mount -b '#s/rio.geoff.73279' /dev
bind  /tmp/x /tmp/x
bind -a /sys/lib /tmp/x
cd /tmp
; >x/FOO
x/FOO: rc: can't open: mounted directory forbids creation

versus

; unmount x
; bind -c x x
; bind -a /sys/lib x
; ns|tail -4
mount -b '#s/rio.geoff.73279' /dev
bind -c /tmp/x /tmp/x
bind -a /sys/lib /tmp/x
cd /tmp
; >x/FOO
; unmount x; ls x
x/FOO

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From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] union directories
Date: Fri, 28 Feb 2003 13:56:18 -0500
Message-ID: <1f229e0b2b861ffeebd62738b74c9cd3@plan9.bell-labs.com>

You used to need to say "bind foo foo" to set up a mount
point for future union mounts.  (A long time ago.)
Now the system inserts these for you, though they're
still visible in the /proc/$pid/ns file (and thus the
output of ns).

Bind -bc 9 9 is a different thing, and almost
certainly not what is wanted, especially in the
example given -- it doesn't have any effect except
to make everything appear twice in the directory.
(Bind -bc 9 9 is like:

	bind 9 9
	bind -bc 9 9

hence everything appears twice.)

Russ