On Wed, 28 Sep 2005, Nigel Cunningham wrote: > Yes, that's true. If the usb modules are loaded when suspending and not > loaded when resuming or vice versa, you'll get inconsistencies: > > State at suspend State at resume Image state > > Built in Built in Freeze->Freeze > Loaded modules Unloaded modules Undefined->Freeze > Unloaded modules Loaded modules Freeze->Undefined This table is misleading. Better to describe it like this: If the image doesn't contain USB drivers, the device state doesn't matter. If the image does contain USB drivers and the boot kernel did not meddle with the device states, then the devices will be suspended even though the image thinks they are frozen. If the image does contain USB drivers and the boot kernel did meddle with the device states, then the devices probably will not be resumable by the image kernel. They will have to be rediscovered. > I guess there are three possible solutions: > 1) Leave things as they are and say it is the user's problem if they > make the state inconsistent. > 2) Keep knowledge of the device states across the atomic restore and use > that information in deciding what to do in device resume/powerup. > 3) Make device drivers handle the situation properly without knowledge > of what state the hardware is really in (or check the real state - where > possible - and rely on that in deciding what to do). > > 2 seems to me to make for the most reliable solution. No. The best answer is to (A) tell the boot kernel that the impending freeze is for a restore-from-disk, so that it can wipe out the state of any devices it has changed, and (B) tell the image kernel that it is resuming from disk, so that it can know that the devices are really suspended even though its internal records say they are frozen. Better than (A) would be to tell the boot kernel that it _is_ only a boot kernel, so that its drivers will know not to mess up the state of any devices. This would have the side effect of making it impossible to reload an image from a USB drive, but that's pretty much unavoidable anyway. Alan Stern
