On Fri, 16 Jun 2006, Benjamin Herrenschmidt wrote: > > You can't save a consistent system image if your drivers aren't all > stopped and DMA is stopped. Read the whole thread to an end. You don't _need_ to save a consistent system image. There's no "single snapshot in time" needed. The only thing needed is to save a _workign_ system image, and that's very different. > Example is USB for example: to save a consistent state, the USB host > controller must stop DMA processing (for both STD and kexec). But that > means it can't process requests. No. It means no such thing. It just means that trying to save a total snapshot is insane and fundamentally impossible. Instead, you save a snapshot of the stuff you care about afterwards. All the while realizing that when you resume, you cannot rely on any temporary data structures (that did get saved off - because trying to teach the STD logic the meaning of all memory is obviously _also_ insane) in the drivers. But you have a perfect callback for that. It's called the "resume" part. The driver _knows_ which parts of its data it changes on its own as part of normal operation, and it re-creates those parts rather than depend on them being saved away atomically, since doing it atomically is _impossible_. Why can't people accept that simple statement? If you give up on doing the impossible, suddenly everything else becomes much easier. Don't work so hard at doing something that must not be done in the first place! Linus
