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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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- *
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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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+ * 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 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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+
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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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-
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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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-
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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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-
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-reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 0xd000fce2)
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-
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-(Thanks to Peter Osterlund:)
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-
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-#include <unistd.h>
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-#include <syscall.h>
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-
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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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-
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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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-
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-Also /sys/ interface should be still present.
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-
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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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+
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+There are few ways to get that fixed:
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+
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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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+
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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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+
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+Q: Is there a maximum system RAM size that is supported by swsusp?
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+
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+A: It should work okay with highmem.
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+
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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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+
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+A: Only one swap partition, sorry.
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+
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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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+
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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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+
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+Q: What information is usefull for debugging suspend-to-disk problems?
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+
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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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+
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+
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Pavel Machek