|From:||"Rafael J. Wysocki" <firstname.lastname@example.org>|
|To:||Linux PM list <email@example.com>|
|Subject:||[RFC][PATCH 0/2] PM / Sleep: Extended control of suspend/hibernate interfaces|
|Date:||Thu, 13 Oct 2011 21:45:42 +0200|
|Cc:||mark gross <firstname.lastname@example.org>, LKML <email@example.com>, John Stultz <firstname.lastname@example.org>, Alan Stern <email@example.com>, NeilBrown <firstname.lastname@example.org>|
Hi, There is an ongoing discussion about possible ways to avoid some probles related to suspend/hibernate interfaces, such as races with the handling of wakeup events (in user space) and (destructive) interference with some important system maintenance tasks (such as firmware updates). It follows from this discussion that whatever the kernel has to offer in this area is either too complicated to use in practice or inadequate for other reasons. The two use case examples given by John, that is the firmware update problem (i.e. system suspend or hibernation should not be allowed to happen while the system's firmware is being updated) and the backup problem (i.e. is should be possible to wake up the system from sleep in the middle of the night via a timer event, create a backup of it and make it go to sleep again automatically when the backup is ready without implementing the backup feature in a power manager) are quite convincing to me, but also it seems to me that previous attempts to address them go a bit too far in complexity. For this reason, I thought it might be a good idea to propose a simpler approach. It is not bullet proof, but it should be suitable to address at least those two issues. First, to address the firmware update problem, I think we need a big hammer switch allowing a root-owned process to disable/enable all suspend/hibernate interfaces. This is introduced by the first patch in the form of a new sysfs attribute, /sys/power/sleep_mode, that can be used to disable the suspend/hibernate functionality (it does that with the help of the existing wakeup events detection mechanism). Second, to address the backup problem, we need to allow user space processes other than the suspend/hibernate process itself to prevent the system from being put into sleep states. A mechanism for that is introduced by the second patch in the form of the /dev/sleepctl special device working kind of like user space wakelocks on Android (although in a simplified fashion). More details are in the changelogs and (of course) in the code itself. The patches haven't been tested (I had tested the first one, but then I made some changes to it afterwards), so most likely there are some bugs in them, but I didn't want to lose time on testing things that people may not like in principle. :-) Thanks, Rafael
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