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Date: Thu, 29 Aug 2013 07:50:07 +0200
From: Milan Broz <gmazyland@gmail.com>
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Subject: Re: [dm-crypt] u?mount (8) helper script for luks encrypted disks
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To: Matthias Schniedermeyer <ms@citd.de>
Cc: dm-crypt@saout.de, Debian Cryptsetup Team <pkg-cryptsetup-devel@lists.alioth.debian.org>, Steffen Vogel <post@steffenvogel.de>

On 26.8.2013 10:23, Matthias Schniedermeyer wrote:
> Personally i "solved" this by renaming /bin/mount to /bin/mount.orig
> and putting a shell-script as /bin/mount that checks if i want to mount
> a /dev/mapper/XXX and does the setup of XXX before it calls
> /bin/mount.orig.

Underlying device construction can be very complex task sometimes
(it can be combination of lvm, mdraid, multipath, partitions and whatever.)

So while it works for your use case, it will not work for other.

> "Back then" when i implemented that about 1.5 years ago i tried to
> explain to Karel Zak (util-linux maintainer) that a generic "premount"
> and "postumount" command in (u)mount could solve this generic problem.
> The Problem that all cryptographic-setups need (at least) one more step
> to setup(/tear-down) a device. But that didn't happen and i didn't try
> to open the issue again.


For that particular case, LUKS tear down, I think we had a better approach.
Just implement auto removal on last device close (similar to loop device
autoclear flag.)

For more info see
https://bugzilla.redhat.com/show_bug.cgi?id=873734


Milan

p.s.
Be very careful with shell scripts in mount helpers here.
It will run under the same UID as mount, which means root for LUKS here.