diff options
Diffstat (limited to 'Documentation/power/swsusp.txt')
| -rw-r--r-- | Documentation/power/swsusp.txt | 101 |
1 files changed, 56 insertions, 45 deletions
diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt index ddf907fbcc0..b0d50840788 100644 --- a/Documentation/power/swsusp.txt +++ b/Documentation/power/swsusp.txt @@ -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 change kernel command line between suspend and resume... - * ...prepare for nasty fsck or worse. + * 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 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. + + |