6ed9fcec85
The attached patch contains a mini howto for using dm-crypt together with swsusp. Signed-off-by: Andreas Steinmetz <ast@domdv.de> Signed-off-by: Pavel Machek <pavel@suse.cz> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
138 lines
4.6 KiB
Text
138 lines
4.6 KiB
Text
Author: Andreas Steinmetz <ast@domdv.de>
|
|
|
|
|
|
How to use dm-crypt and swsusp together:
|
|
========================================
|
|
|
|
Some prerequisites:
|
|
You know how dm-crypt works. If not, visit the following web page:
|
|
http://www.saout.de/misc/dm-crypt/
|
|
You have read Documentation/power/swsusp.txt and understand it.
|
|
You did read Documentation/initrd.txt and know how an initrd works.
|
|
You know how to create or how to modify an initrd.
|
|
|
|
Now your system is properly set up, your disk is encrypted except for
|
|
the swap device(s) and the boot partition which may contain a mini
|
|
system for crypto setup and/or rescue purposes. You may even have
|
|
an initrd that does your current crypto setup already.
|
|
|
|
At this point you want to encrypt your swap, too. Still you want to
|
|
be able to suspend using swsusp. This, however, means that you
|
|
have to be able to either enter a passphrase or that you read
|
|
the key(s) from an external device like a pcmcia flash disk
|
|
or an usb stick prior to resume. So you need an initrd, that sets
|
|
up dm-crypt and then asks swsusp to resume from the encrypted
|
|
swap device.
|
|
|
|
The most important thing is that you set up dm-crypt in such
|
|
a way that the swap device you suspend to/resume from has
|
|
always the same major/minor within the initrd as well as
|
|
within your running system. The easiest way to achieve this is
|
|
to always set up this swap device first with dmsetup, so that
|
|
it will always look like the following:
|
|
|
|
brw------- 1 root root 254, 0 Jul 28 13:37 /dev/mapper/swap0
|
|
|
|
Now set up your kernel to use /dev/mapper/swap0 as the default
|
|
resume partition, so your kernel .config contains:
|
|
|
|
CONFIG_PM_STD_PARTITION="/dev/mapper/swap0"
|
|
|
|
Prepare your boot loader to use the initrd you will create or
|
|
modify. For lilo the simplest setup looks like the following
|
|
lines:
|
|
|
|
image=/boot/vmlinuz
|
|
initrd=/boot/initrd.gz
|
|
label=linux
|
|
append="root=/dev/ram0 init=/linuxrc rw"
|
|
|
|
Finally you need to create or modify your initrd. Lets assume
|
|
you create an initrd that reads the required dm-crypt setup
|
|
from a pcmcia flash disk card. The card is formatted with an ext2
|
|
fs which resides on /dev/hde1 when the card is inserted. The
|
|
card contains at least the encrypted swap setup in a file
|
|
named "swapkey". /etc/fstab of your initrd contains something
|
|
like the following:
|
|
|
|
/dev/hda1 /mnt ext3 ro 0 0
|
|
none /proc proc defaults,noatime,nodiratime 0 0
|
|
none /sys sysfs defaults,noatime,nodiratime 0 0
|
|
|
|
/dev/hda1 contains an unencrypted mini system that sets up all
|
|
of your crypto devices, again by reading the setup from the
|
|
pcmcia flash disk. What follows now is a /linuxrc for your
|
|
initrd that allows you to resume from encrypted swap and that
|
|
continues boot with your mini system on /dev/hda1 if resume
|
|
does not happen:
|
|
|
|
#!/bin/sh
|
|
PATH=/sbin:/bin:/usr/sbin:/usr/bin
|
|
mount /proc
|
|
mount /sys
|
|
mapped=0
|
|
noresume=`grep -c noresume /proc/cmdline`
|
|
if [ "$*" != "" ]
|
|
then
|
|
noresume=1
|
|
fi
|
|
dmesg -n 1
|
|
/sbin/cardmgr -q
|
|
for i in 1 2 3 4 5 6 7 8 9 0
|
|
do
|
|
if [ -f /proc/ide/hde/media ]
|
|
then
|
|
usleep 500000
|
|
mount -t ext2 -o ro /dev/hde1 /mnt
|
|
if [ -f /mnt/swapkey ]
|
|
then
|
|
dmsetup create swap0 /mnt/swapkey > /dev/null 2>&1 && mapped=1
|
|
fi
|
|
umount /mnt
|
|
break
|
|
fi
|
|
usleep 500000
|
|
done
|
|
killproc /sbin/cardmgr
|
|
dmesg -n 6
|
|
if [ $mapped = 1 ]
|
|
then
|
|
if [ $noresume != 0 ]
|
|
then
|
|
mkswap /dev/mapper/swap0 > /dev/null 2>&1
|
|
fi
|
|
echo 254:0 > /sys/power/resume
|
|
dmsetup remove swap0
|
|
fi
|
|
umount /sys
|
|
mount /mnt
|
|
umount /proc
|
|
cd /mnt
|
|
pivot_root . mnt
|
|
mount /proc
|
|
umount -l /mnt
|
|
umount /proc
|
|
exec chroot . /sbin/init $* < dev/console > dev/console 2>&1
|
|
|
|
Please don't mind the weird loop above, busybox's msh doesn't know
|
|
the let statement. Now, what is happening in the script?
|
|
First we have to decide if we want to try to resume, or not.
|
|
We will not resume if booting with "noresume" or any parameters
|
|
for init like "single" or "emergency" as boot parameters.
|
|
|
|
Then we need to set up dmcrypt with the setup data from the
|
|
pcmcia flash disk. If this succeeds we need to reset the swap
|
|
device if we don't want to resume. The line "echo 254:0 > /sys/power/resume"
|
|
then attempts to resume from the first device mapper device.
|
|
Note that it is important to set the device in /sys/power/resume,
|
|
regardless if resuming or not, otherwise later suspend will fail.
|
|
If resume starts, script execution terminates here.
|
|
|
|
Otherwise we just remove the encrypted swap device and leave it to the
|
|
mini system on /dev/hda1 to set the whole crypto up (it is up to
|
|
you to modify this to your taste).
|
|
|
|
What then follows is the well known process to change the root
|
|
file system and continue booting from there. I prefer to unmount
|
|
the initrd prior to continue booting but it is up to you to modify
|
|
this.
|