On Friday, 27 April 2007 12:12, Pekka J Enberg wrote:
Well, swsusp currently does almost the same, except that you can read the
image from the kernel as a stream of bytes, using read() and, during the
restore phase, upload the same image using write(). The advantage of this
is that the interface is symmetrical from the user space's point of view.
[You're cancelling the hibernation by closing /dev/snapshot, which also is
quite natural.]
If you look at the interface in user.c, there are only two ioctls really needed
for that in there, SNAPSHOT_ATOMIC_SNAPSHOT and
SNAPSHOT_ATOMIC_RESTORE. Two more are handy for freezing
tasks, SNAPSHOT_FREEZE and SNAPSHOT_UNFREEZE. The others were added
later, to make the user space part simpler or capable of doing some fancy
stuff, which I am ready to admit was a mistake.
Yes, and that's why we wanted to introduce the userland part. The problem
with this approach, as it's turned out, is that the userland part must be a
very specialized piece of software, really careful of what it's doing, mainly
because of the inability to checkpoint filesystems. If we could checkpoint
filesystems and were able to unfreeze the user space after creating the
snapshot without the risk of corrupting filesystems in the restore phase,
the userland part could be much simpler (even as simple as Linus suggested).
Greetings,
Rafael
-
