Article about goals and implementation of Software Suspend for Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Author: G\82ábor Kuti
+Author: G\82ábor Kuti
Last revised: 2003-10-20 by Pavel Machek
Idea and goals to achieve
If the thread is needed for writing the image to storage, you should
instead set the PF_NOFREEZE process flag when creating the thread (and
-be very carefull).
+be very careful).
-Q: What is the difference between "platform", "shutdown" and
-"firmware" in /sys/power/disk?
+Q: What is the difference between "platform" and "shutdown"?
A:
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.
+"platform" is actually right thing to do where supported, but
+"shutdown" is most reliable (except on ACPI systems).
Q: I do not understand why you have such strong objections to idea of
selective suspend.
suspend image to prevent sensitive data from being stolen after
resume.
-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.
-
-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.
+Q: Can I suspend to a swap file?
-2) suspend2 gets around that by storing absolute positions in on-disk
-image (and blocksize), with resume parameter pointing directly to
-suspend header.
+A: Generally, yes, you can. However, it requires you to use the "resume=" and
+"resume_offset=" kernel command line parameters, so the resume from a swap file
+cannot be initiated from an initrd or initramfs image. See
+swsusp-and-swap-files.txt for details.
Q: Is there a maximum system RAM size that is supported by swsusp?
modes like "suspend-to-RAM" or "standby". (Don't write "disk" to the
/sys/power/state file; write "standby" or "mem".) We've not seen any
hardware that can use these modes through software suspend, although in
-theory some systems might support "platform" or "firmware" modes that
-won't break the USB connections.
+theory some systems might support "platform" modes that won't break the
+USB connections.
Remember that it's always a bad idea to unplug a disk drive containing a
mounted filesystem. That's true even when your system is asleep! The