[PATCH] swsusp: update documentation

This updates documentation a bit (mostly removing obsolete stuff), and
marks swsusp as no longer experimental in config.

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Pavel Machek 2005-09-06 15:16:21 -07:00 committed by Linus Torvalds
parent 48c8b11342
commit d7ae79c72d
3 changed files with 58 additions and 46 deletions

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@ -1,22 +1,20 @@
From kernel/suspend.c:
Some warnings, first.
* BIG FAT WARNING *********************************************************
*
* If you have unsupported (*) devices using DMA...
* ...say goodbye to your data.
*
* If you touch anything on disk between suspend and resume...
* ...kiss your data goodbye.
*
* If your disk driver does not support suspend... (IDE does)
* ...you'd better find out how to get along
* without your data.
* If you do resume from initrd after your filesystems are mounted...
* ...bye bye root partition.
* [this is actually same case as above]
*
* If you change kernel command line between suspend and resume...
* ...prepare for nasty fsck or worse.
*
* If you change your hardware while system is suspended...
* ...well, it was not good idea.
* If you have unsupported (*) devices using DMA, you may have some
* problems. If your disk driver does not support suspend... (IDE does),
* it may cause some problems, too. If you change kernel command line
* between suspend and resume, it may do something wrong. If you change
* your hardware while system is suspended... well, it was not good idea;
* but it will probably only crash.
*
* (*) suspend/resume support is needed to make it safe.
@ -30,6 +28,13 @@ echo shutdown > /sys/power/disk; echo disk > /sys/power/state
echo platform > /sys/power/disk; echo disk > /sys/power/state
Encrypted suspend image:
------------------------
If you want to store your suspend image encrypted with a temporary
key to prevent data gathering after resume you must compile
crypto and the aes algorithm into the kernel - modules won't work
as they cannot be loaded at resume time.
Article about goals and implementation of Software Suspend for Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -85,11 +90,6 @@ resume.
You have your server on UPS. Power died, and UPS is indicating 30
seconds to failure. What do you do? Suspend to disk.
Ethernet card in your server died. You want to replace it. Your
server is not hotplug capable. What do you do? Suspend to disk,
replace ethernet card, resume. If you are fast your users will not
even see broken connections.
Q: Maybe I'm missing something, but why don't the regular I/O paths work?
@ -117,31 +117,6 @@ Q: Does linux support ACPI S4?
A: Yes. That's what echo platform > /sys/power/disk does.
Q: My machine doesn't work with ACPI. How can I use swsusp than ?
A: Do a reboot() syscall with right parameters. Warning: glibc gets in
its way, so check with strace:
reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 0xd000fce2)
(Thanks to Peter Osterlund:)
#include <unistd.h>
#include <syscall.h>
#define LINUX_REBOOT_MAGIC1 0xfee1dead
#define LINUX_REBOOT_MAGIC2 672274793
#define LINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2
int main()
{
syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_SW_SUSPEND, 0);
return 0;
}
Also /sys/ interface should be still present.
Q: What is 'suspend2'?
A: suspend2 is 'Software Suspend 2', a forked implementation of
@ -312,9 +287,45 @@ system is shut down or suspended. Additionally use the encrypted
suspend image to prevent sensitive data from being stolen after
resume.
Q: Why we cannot suspend to a swap file?
Q: Why can't we suspend to a swap file?
A: Because accessing swap file needs the filesystem mounted, and
filesystem might do something wrong (like replaying the journal)
during mount. [Probably could be solved by modifying every filesystem
to support some kind of "really read-only!" option. Patches welcome.]
during mount.
There are few ways to get that fixed:
1) Probably could be solved by modifying every filesystem to support
some kind of "really read-only!" option. Patches welcome.
2) suspend2 gets around that by storing absolute positions in on-disk
image (and blocksize), with resume parameter pointing directly to
suspend header.
Q: Is there a maximum system RAM size that is supported by swsusp?
A: It should work okay with highmem.
Q: Does swsusp (to disk) use only one swap partition or can it use
multiple swap partitions (aggregate them into one logical space)?
A: Only one swap partition, sorry.
Q: If my application(s) causes lots of memory & swap space to be used
(over half of the total system RAM), is it correct that it is likely
to be useless to try to suspend to disk while that app is running?
A: No, it should work okay, as long as your app does not mlock()
it. Just prepare big enough swap partition.
Q: What information is usefull for debugging suspend-to-disk problems?
A: Well, last messages on the screen are always useful. If something
is broken, it is usually some kernel driver, therefore trying with as
little as possible modules loaded helps a lot. I also prefer people to
suspend from console, preferably without X running. Booting with
init=/bin/bash, then swapon and starting suspend sequence manually
usually does the trick. Then it is good idea to try with latest
vanilla kernel.

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@ -120,6 +120,7 @@ IBM ThinkPad T42p (2373-GTG) s3_bios (2)
IBM TP X20 ??? (*)
IBM TP X30 s3_bios (2)
IBM TP X31 / Type 2672-XXH none (1), use radeontool (http://fdd.com/software/radeon/) to turn off backlight.
IBM TP X32 none (1), but backlight is on and video is trashed after long suspend
IBM Thinkpad X40 Type 2371-7JG s3_bios,s3_mode (4)
Medion MD4220 ??? (*)
Samsung P35 vbetool needed (6)

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@ -28,7 +28,7 @@ config PM_DEBUG
config SOFTWARE_SUSPEND
bool "Software Suspend"
depends on EXPERIMENTAL && PM && SWAP && ((X86 && SMP) || ((FVR || PPC32 || X86) && !SMP))
depends on PM && SWAP && (X86 || ((FVR || PPC32) && !SMP))
---help---
Enable the possibility of suspending the machine.
It doesn't need APM.