[PATCH]adding documentation about power management
From: Oliver Neukum
Date: Mon Oct 04 2004 - 06:56:51 EST
Hi,
this is the first part of added documentation about power management
in drivers.
Regards
Oliver
Signed-Off-By: Oliver Neukum <oliver@xxxxxxxxxxx>
You can import this changeset into BK by piping this whole message to:
'| bk receive [path to repository]' or apply the patch as usual.
===================================================================
ChangeSet@xxxxxx, 2004-10-04 13:50:42+02:00, oliver@xxxxxxxxxxxxxxxxxxxx
- adding Documentation about kernel threads and power management
kernel_threads.txt | 41 +++++++++++++++++++++++++++++++++++++++++
1 files changed, 41 insertions(+)
diff -Nru a/Documentation/power/kernel_threads.txt b/Documentation/power/kernel_threads.txt
--- /dev/null Wed Dec 31 16:00:00 1969
+++ b/Documentation/power/kernel_threads.txt Mon Oct 4 13:51:47 2004
@@ -0,0 +1,41 @@
+KERNEL THREADS
+
+
+Freezer
+
+Upon entering a suspended state the system will freeze all
+tasks. This is done by delivering pseudosignals. This affects
+kernel threads, too. To successfully freeze a kernel thread
+the thread has to check for the pseudosignal and enter the
+refrigerator. Code to do this looks like this:
+
+ do {
+ hub_events();
+ wait_event_interruptible(khubd_wait, !list_empty(&hub_event_list));
+ if (current->flags & PF_FREEZE)
+ refrigerator(PF_FREEZE);
+ } while (!signal_pending(current));
+
+from drivers/usb/core/hub.c::hub_thread()
+
+
+The Unfreezable
+
+Some kernel threads however, must not be frozen. The kernel must
+be able to finish pending IO operations and later on be able to
+write the memory image to disk. Kernel threads needed to do IO
+must stay awake. Such threads must mark themselves unfreezable
+like this:
+
+ /*
+ * This thread doesn't need any user-level access,
+ * so get rid of all our resources.
+ */
+ daemonize("usb-storage");
+
+ current->flags |= PF_NOFREEZE;
+
+from drivers/usb/storage/usb.c::usb_stor_control_thread()
+
+Such drivers are themselves responsible for staying quiet during
+the actual snapshotting.
===================================================================
This BitKeeper patch contains the following changesets:
1.2047
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