On Wednesday, 25 April 2007 22:44, Linus Torvalds wrote: > > On Wed, 25 Apr 2007, Pavel Machek wrote: > > > > Can I get you on IRC somewhere? No, I do not think I'm a moron, and > > yes, I need to suspend^Wsnapshot the devices before, so I have that in > > the snapshot. Of course, I'll need to resume^Wrestore the devices > > before writing snapshot. That's okay, it does not take long. > > You do NOT need to "suspend" the devices, and that's the whole point. > > You may want to save the device info somewhere, BUT THAT IS SOMETHING > TOTALLY DIFFERENT! > > This is *exactly* the confusion I'm talking about. The STD and STR > codepaths try to use the same function for two TOTALLY DIFFERENT things. > > STR actually wants to "suspend". > > STD actually wants to "atomic snapshot", and it must not allow allocations > or anything like that, because the whole snapshot image should be done > atomically as one event. But it should *not* suspend, because that device > may actually be needed afterwards. > > So not the same thing at all. > > So here's what "suspend()" wants: > - suspend() - preparatory work, can error our, can delay, can park the > disk, etc etc. > - suspend_late() - called late, with interrupts disabled, should actually > suspend if the early suspend didn't do it already > > And here is what "snapshot()" wants: > - prepare_to_snapshot() (for memory allocation) > - snapshot() - called late, with interrupts disabled, save state. > > and there is absolutely _zero_ overlap between them. There just isn't > anything in common. Yes, both are two-phase (for the simple reason that > both want an "atomic" part), but there's really no real overlap. > > Just trying to *make* them be the same operations is just going to > introduce flags that then cause them to be totally different *and* > confusing and generate bugs. It also means that people do one of them, and > "it works" for that case, and the other case is totally broken, but it's > not obvious, because doing one means that the system _thinks_ that you did > both! > > In the very unlikely case that some driver actually *wants* to use the > same function for snapshots and suspending, that driver could just go > ahead and _use_ the same function pointer. But now, as things are set up, > we force a total confusion on drivers by calling them through the same > interface for two totally different things.
I agree, except there are surprisingly many drivers like that. You're right, we should be doing all of it in a different way, but this means a lot of changes and we can't do them overnight. As I wrote in the reply to Pavel, I think we can introduce .freeze(), .thaw() (and .prethaw() for that matter) callbacks for hibernation and make drivers use them, but that will be a long series of patches. Still, I think it's doable. Greetings, Rafael - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
