nilfs2: avoid double error caused by nilfs_transaction_end

[linux-2.6-omap-h63xx.git] / Documentation / power / swsusp.txt

diff --git a/Documentation/power/swsusp.txt b/Documentation/power/swsusp.txt
index e635e6f1e316ca549834716c95fccc3c61b35748..9d60ab717a7b3c8dc0daa4d14e6a914884965bf0 100644 (file)
--- a/Documentation/power/swsusp.txt
+++ b/Documentation/power/swsusp.txt
@@ -48,7 +48,7 @@ before suspend (it is limited to 500 MB by default).
 
 Article about goals and implementation of Software Suspend for Linux
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 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
 Last revised: 2003-10-20 by Pavel Machek
 
 Idea and goals to achieve


@@ -140,24 +140,13 @@ 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.
 
 website, and not to the Linux Kernel Mailing List. We are working
 toward merging suspend2 into the mainline kernel.
 

-Q: A kernel thread must voluntarily freeze itself (call 'refrigerator').
-I found some kernel threads that don't do it, and they don't freeze
-so the system can't sleep. Is this a known behavior?
+Q: What is the freezing of tasks and why are we using it?

 
 

-A: All such kernel threads need to be fixed, one by one. Select the
-place where the thread is safe to be frozen (no kernel semaphores
-should be held at that point and it must be safe to sleep there), and
-add:
+A: The freezing of tasks is a mechanism by which user space processes and some
+kernel threads are controlled during hibernation or system-wide suspend (on some
+architectures).  See freezing-of-tasks.txt for details.

 
 

-       try_to_freeze();
-
-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 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:
 
 
 A:
 


@@ -166,11 +155,8 @@ shutdown: save state in linux, then tell bios to powerdown
 platform: save state in linux, then tell bios to powerdown and blink
           "suspended led"
 
 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.
 
 Q: I do not understand why you have such strong objections to idea of
 selective suspend.


@@ -297,20 +283,12 @@ system is shut down or suspended. Additionally use the encrypted
 suspend image to prevent sensitive data from being stolen after
 resume.
 
 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.
+Q: Can I suspend to a swap file?

 
 

-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.
+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?
 
 
 Q: Is there a maximum system RAM size that is supported by swsusp?
 


@@ -396,8 +374,8 @@ while the system is asleep, maintaining the connection, using true sleep
 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
 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
 
 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


@@ -405,6 +383,14 @@ safest thing is to unmount all filesystems on removable media (such USB,
 Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays)
 before suspending; then remount them after resuming.
 
 Firewire, CompactFlash, MMC, external SATA, or even IDE hotplug bays)
 before suspending; then remount them after resuming.
 

+There is a work-around for this problem.  For more information, see
+Documentation/usb/persist.txt.
+
+Q: Can I suspend-to-disk using a swap partition under LVM?
+
+A: No. You can suspend successfully, but you'll not be able to
+resume. uswsusp should be able to work with LVM. See suspend.sf.net.
+

 Q: I upgraded the kernel from 2.6.15 to 2.6.16. Both kernels were
 compiled with the similar configuration files. Anyway I found that
 suspend to disk (and resume) is much slower on 2.6.16 compared to
 Q: I upgraded the kernel from 2.6.15 to 2.6.16. Both kernels were
 compiled with the similar configuration files. Anyway I found that
 suspend to disk (and resume) is much slower on 2.6.16 compared to