* ...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.
+ *
* (*) pm interface support is needed to make it safe.
You need to append resume=/dev/your_swap_partition to kernel command
line. Then you suspend by echo 4 > /proc/acpi/sleep.
-Pavel's unreliable guide to swsusp mess
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-There are currently two versions of swap suspend in the kernel, the old
-"Pavel's" version in kernel/power/swsusp.c and the new "Patrick's"
-version in kernel/power/pmdisk.c. They provide the same functionality;
-the old version looks ugly but was tested, while the new version looks
-nicer but did not receive so much testing. echo 4 > /proc/acpi/sleep
-calls the old version, echo disk > /sys/power/state calls the new one.
-
-[In the future, when the new version is stable enough, two things can
-happen:
-
-* the new version is moved into swsusp.c, and swsusp is renamed to swap
- suspend (Pavel prefers this)
-
-* pmdisk is kept as is and swsusp.c is removed from the kernel]
-
-
-
Article about goals and implementation of Software Suspend for Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Author: G\82ábor Kuti
About the code
Things to implement
-- SMP support. I've done an SMP support but since I don't have access to a kind
- of this one I cannot test it. Please SMP people test it. .. Tested it,
- doesn't work. Had no time to figure out why. There is some mess with
- interrupts AFAIK..
- We should only make a copy of data related to kernel segment, since any
process data won't be changed.
- Should make more sanity checks. Or are these enough?
- We should not free pages at the beginning so aggressively, most of them
go there anyway..
-Drivers that need support
-- pc_keyb -- perhaps we can wait for vojtech's input patches
-- do IDE cdroms need some kind of support?
-- IDE CD-RW -- how to deal with that?
-
Sleep states summary (thanx, Ducrot)
====================================
echo 4b > /proc/acpi/sleep # for suspend to disk via s4bios
-FAQ:
+Frequently Asked Questions
+==========================
Q: well, suspending a server is IMHO a really stupid thing,
but... (Diego Zuccato):
replace ethernet card, resume. If you are fast your users will not
even see broken connections.
-Any other idea you might have tell me!
-Contacting the author
-If you have any question or any patch that solves the above or detected
-problems please contact me at seasons@falcon.sch.bme.hu. I might delay
-answering, sorry about that.
+Q: Maybe I'm missing something, but why don't the regular I/O paths work?
+
+A: We do use the regular I/O paths. However we cannot restore the data
+to its original location as we load it. That would create an
+inconsistent kernel state which would certainly result in an oops.
+Instead, we load the image into unused memory and then atomically copy
+it back to it original location. This implies, of course, a maximum
+image size of half the amount of memory.
+
+There are two solutions to this:
+
+* require half of memory to be free during suspend. That way you can
+read "new" data onto free spots, then cli and copy
+
+* assume we had special "polling" ide driver that only uses memory
+between 0-640KB. That way, I'd have to make sure that 0-640KB is free
+during suspending, but otherwise it would work...
+
+suspend2 shares this fundamental limitation, but does not include user
+data and disk caches into "used memory" by saving them in
+advance. That means that the limitation goes away in practice.
+
+Q: Does linux support ACPI S4?
+
+A: No.
+
+When swsusp was created, ACPI was not too widespread, so we tried to
+avoid using ACPI-specific stuff. ACPI also is/was notoriously
+buggy. These days swsusp works on APM-only i386 machines and even
+without any power managment at all. Some versions also work on PPC.
+
+That means that machine does not enter S4 on suspend-to-disk, but
+simply enters S5. That has few advantages, you can for example boot
+windows on next boot, and return to your Linux session later. You
+could even have few different Linuxes on your box (not sharing any
+partitions), and switch between them.
+
+It also has disadvantages. On HP nx5000, if you unplug power cord
+while machine is suspended-to-disk, Linux will fail to notice that.
+
+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;
+}
+
+Q: What is 'suspend2'?
+
+A: suspend2 is 'Software Suspend 2', a forked implementation of
+suspend-to-disk which is available as separate patches for 2.4 and 2.6
+kernels from swsusp.sourceforge.net. It includes support for SMP, 4GB
+highmem and preemption. It also has a extensible architecture that
+allows for arbitrary transformations on the image (compression,
+encryption) and arbitrary backends for writing the image (eg to swap
+or an NFS share[Work In Progress]). Questions regarding suspend2
+should be sent to the mailing list available through the suspend2
+website, and not to the Linux Kernel Mailing List. We are working
+toward merging suspend2 into the mainline kernel.
+
+Q: Kernel thread must voluntarily freeze itself (call 'refrigerator'). But
+I found some kernel threads don't do it, and they don't freeze, and
+so the system can't sleep. Is this a known behavior?
+
+A: All such kernel threads need to be fixed, one by one. Select place
+where it is safe to be frozen (no kernel semaphores should be held at
+that point and it must be safe to sleep there), and add:
+
+ if (current->flags & PF_FREEZE)
+ refrigerator(PF_FREEZE);
+
+Q: What is the difference between between "platform", "shutdown" and
+"firmware" in /sys/power/disk?
+
+A:
+
+shutdown: save state in linux, then tell bios to powerdown
+
+platform: save state in linux, then tell bios to powerdown and blink
+ "suspended led"
+
+firmware: tell bios to save state itself [needs BIOS-specific suspend
+ partition, and has very little to do with swsusp]
+"platform" is actually right thing to do, but "shutdown" is most
+reliable.
git://git.onelab.eu / linux-2.6.git / blobdiff