On Thu, 26 Apr 2007, Nigel Cunningham wrote: > > * Doing things in the right order? (Prepare the image, then do the > atomic copy, then save).
I'd actually like to discuss this a bit.. I'm obviously not a huge fan of the whole user/kernel level split and interfaces, but I actually do think that there is *one* split that makes sense: - generate the (whole) snapshot image entirely inside the kernel - do nothing else (ie no IO at all), and just export it as a single image to user space (literally just mapping the pages into user space). *one* interface. None of the "pretty UI update" crap. Just a single system call: void *snapshot_system(u32 *size); which will map in the snapshot, return the mapped address and the size (and if you want to support snapshots > 4GB, be my guest, but I suspect you're actually *better* off just admitting that if you cannot shrink the snapshot to less than 32 bits, it's not worth doing) User space gets a fully running system, with that one process having that one image mapped into its address space. It can then compress/write/do whatever to that snapshot. You need one other system call, of course, which is int resume_snapshot(void *snapshot, u32 size); and for testing, you should be able to basically do u32 size; void *buffer = snapshot_system(&size); if (buffer != MAP_FAILED) resume_snapshot(buffer, size); and it should obviously work. And btw, the device model changes are a big part of this. Because I don't think it's even remotely debuggable with the full suspend/resume of the devices being part of generating the image! That freeze/snapshot/unfreeze sequence is likely a lot more debuggable, if only because freeze/unfreeze is actually a no-op for most devices, and snapshotting is trivial too. Once you have that snapshot image in user space you can do anything you want. And again: you'd hav a fully working system: not any degradation *at*all*. If you're in X, then X will continue running etc even after the snapshotting, although obviously the snapshotting will have tried to page a lot of stuff out in order to make the snapshot smaller, so you'll likely be crawling. > * Mulithreaded I/O (might as well use multiple cores to compress the > image, now that we're hotplugging later). > * Support for > 1 swap device. > * Support for ordinary files. > * Full image option. > * Modular design? I'd really suggest _just_ the "full image". Nothing else is probably ever worth supporting. Your "snapshot to disk" wouldn't be _quite_ as simple as "echo disk > /sys/power/state", but it should not necessarily be much worse than snapshot_kernel | gzip -9 > /dev/snapshot either (and resuming from the snapshot would just be the reverse)! And if you want to send the snapshot over a TCP connection to another host, be my guest. With pretty images while it's transferring. Whatever. Linus - 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/