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-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.