[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>hifive-unleashed-5.1
Pavel Machek
Linus Torvalds
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48c8b11342
commit
d7ae79c72d
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@ -1,22 +1,20 @@
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From kernel/suspend.c:
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Some warnings, first.
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* BIG FAT WARNING *********************************************************
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*
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* If you have unsupported (*) devices using DMA...
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* ...say goodbye to your data.
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*
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* If you touch anything on disk between suspend and resume...
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* ...kiss your data goodbye.
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*
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* If your disk driver does not support suspend... (IDE does)
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* ...you'd better find out how to get along
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* without your data.
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* If you do resume from initrd after your filesystems are mounted...
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* ...bye bye root partition.
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* [this is actually same case as above]
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*
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* If you change kernel command line between suspend and resume...
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* ...prepare for nasty fsck or worse.
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*
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* If you change your hardware while system is suspended...
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* ...well, it was not good idea.
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* If you have unsupported (*) devices using DMA, you may have some
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* problems. If your disk driver does not support suspend... (IDE does),
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* it may cause some problems, too. If you change kernel command line
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* between suspend and resume, it may do something wrong. If you change
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* your hardware while system is suspended... well, it was not good idea;
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* but it will probably only crash.
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*
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* (*) suspend/resume support is needed to make it safe.
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@ -30,6 +28,13 @@ echo shutdown > /sys/power/disk; echo disk > /sys/power/state
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echo platform > /sys/power/disk; echo disk > /sys/power/state
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Encrypted suspend image:
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------------------------
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If you want to store your suspend image encrypted with a temporary
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key to prevent data gathering after resume you must compile
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crypto and the aes algorithm into the kernel - modules won't work
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as they cannot be loaded at resume time.
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Article about goals and implementation of Software Suspend for Linux
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -85,11 +90,6 @@ resume.
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You have your server on UPS. Power died, and UPS is indicating 30
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seconds to failure. What do you do? Suspend to disk.
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Ethernet card in your server died. You want to replace it. Your
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server is not hotplug capable. What do you do? Suspend to disk,
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replace ethernet card, resume. If you are fast your users will not
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even see broken connections.
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Q: Maybe I'm missing something, but why don't the regular I/O paths work?
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@ -117,31 +117,6 @@ Q: Does linux support ACPI S4?
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A: Yes. That's what echo platform > /sys/power/disk does.
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Q: My machine doesn't work with ACPI. How can I use swsusp than ?
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A: Do a reboot() syscall with right parameters. Warning: glibc gets in
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its way, so check with strace:
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reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 0xd000fce2)
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(Thanks to Peter Osterlund:)
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#include <unistd.h>
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#include <syscall.h>
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#define LINUX_REBOOT_MAGIC1 0xfee1dead
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#define LINUX_REBOOT_MAGIC2 672274793
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#define LINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2
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int main()
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{
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syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
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LINUX_REBOOT_CMD_SW_SUSPEND, 0);
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return 0;
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}
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Also /sys/ interface should be still present.
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Q: What is 'suspend2'?
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A: suspend2 is 'Software Suspend 2', a forked implementation of
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@ -312,9 +287,45 @@ system is shut down or suspended. Additionally use the encrypted
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suspend image to prevent sensitive data from being stolen after
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resume.
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Q: Why we cannot suspend to a swap file?
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Q: Why can't we suspend to a swap file?
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A: Because accessing swap file needs the filesystem mounted, and
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filesystem might do something wrong (like replaying the journal)
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during mount. [Probably could be solved by modifying every filesystem
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to support some kind of "really read-only!" option. Patches welcome.]
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during mount.
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There are few ways to get that fixed:
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1) Probably could be solved by modifying every filesystem to support
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some kind of "really read-only!" option. Patches welcome.
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2) suspend2 gets around that by storing absolute positions in on-disk
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image (and blocksize), with resume parameter pointing directly to
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suspend header.
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Q: Is there a maximum system RAM size that is supported by swsusp?
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A: It should work okay with highmem.
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Q: Does swsusp (to disk) use only one swap partition or can it use
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multiple swap partitions (aggregate them into one logical space)?
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A: Only one swap partition, sorry.
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Q: If my application(s) causes lots of memory & swap space to be used
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(over half of the total system RAM), is it correct that it is likely
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to be useless to try to suspend to disk while that app is running?
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A: No, it should work okay, as long as your app does not mlock()
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it. Just prepare big enough swap partition.
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Q: What information is usefull for debugging suspend-to-disk problems?
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A: Well, last messages on the screen are always useful. If something
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is broken, it is usually some kernel driver, therefore trying with as
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little as possible modules loaded helps a lot. I also prefer people to
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suspend from console, preferably without X running. Booting with
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init=/bin/bash, then swapon and starting suspend sequence manually
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usually does the trick. Then it is good idea to try with latest
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vanilla kernel.
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@ -120,6 +120,7 @@ IBM ThinkPad T42p (2373-GTG) s3_bios (2)
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IBM TP X20 ??? (*)
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IBM TP X30 s3_bios (2)
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IBM TP X31 / Type 2672-XXH none (1), use radeontool (http://fdd.com/software/radeon/) to turn off backlight.
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IBM TP X32 none (1), but backlight is on and video is trashed after long suspend
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IBM Thinkpad X40 Type 2371-7JG s3_bios,s3_mode (4)
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Medion MD4220 ??? (*)
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Samsung P35 vbetool needed (6)
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@ -28,7 +28,7 @@ config PM_DEBUG
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config SOFTWARE_SUSPEND
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bool "Software Suspend"
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depends on EXPERIMENTAL && PM && SWAP && ((X86 && SMP) || ((FVR || PPC32 || X86) && !SMP))
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depends on PM && SWAP && (X86 || ((FVR || PPC32) && !SMP))
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---help---
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Enable the possibility of suspending the machine.
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It doesn't need APM.
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