Hi, On Tuesday 14 March 2006 21:33, Pavel Machek wrote: > > > We need to be able to rollback the state of the filesystem in memory and on > > > disk to the point where the last checkpoint was made. Memory would be > > > straight forward if we want to do it dumbly and slowly - just reload the > > > whole check pointed image. If we want to be more efficient, we'd want to just > > > load the pages that had changed (Mark on (first) write?). But filesystems > > > seem to be a whole different story. Do any of the commonly used fses have > > > support for checkpointing and rollback back at the moment? > > > > I'm not sure if we need a rollback as such. What we need is to make sure > > the filesystems state will be consistent before as well as after we have > > "reloaded" the snapshot. > > Even if you make sure *kernel* is consistent with changed filesystem, > userland is going to be badly confused. Imagine what will happen with > memory mapped files, for example. Something like what happens when you suspend with a mounted CD and mmapped files from there, then you replace the CD while suspended and resume. Not a wise thing to do, but I think people will do such things from time to time and we'd better be prepared to handle them nicely. > I'm not sure how it could work... IMO memory mapped files are the most difficult problem here, but the rest seems to be doable in general. Rafael
