Re: [swsusp] separate snapshot functionality to separate file

[Pavel Machek <pavel@ucw.cz>]

Hi!

> OK, but if we decide to move some functions from one file to another,
> we'll have to wait for another "settle down" period, I think.

Yes...

> > > Well, aren't there any problems with handling kernel addresses from the user
> > > space and vice versa?
> > 
> > Nothing we could not handle. Kernel needs to use get_user, while
> > userspace needs to seek/read/write on /dev/kmem (when accessing "the
> > other" addresses).
> 
> Shouldn't we avoid using /dev/kmem?  Especially that some people wanted it
> to go already.

Well, I believe it is okay for suspend.

> > > Anyway, I think on resume we should send data from the user space to the
> > > kernel and let the kernel arrange them in memory instead of placing them in
> > > memory directly from the used space.  By symmetry, on suspend we should send
> > > data from the kernel to the user space instead of allowing the users space
> > > to read memory at will.  IMO the arrangement of the data in memory should
> > > not be visible to the user space at all.
> > 
> > I thought about that -- user/kernel interface would certainly be nicer
> > -- but I do not think it is feasible without writing a lot of code. 
> 
> I thought of two in-kernel subsystems with a well defined interface
> between them first, such that one of them could be replaced with a
> user space implementation (partially or as a whole) in the future.
> 
> I think I can come up with a proof-of-concept patch if that helps.

Yes, it would help. (But notice that I have proof-of-concenpt ready in
sw3 tree :-).

> > [I agree that assymetry I have in there is ugly, but I don't see a way
> > to do alloc_pagedir() in userspace, and I'd like to keep page
> > relocation in userspace.]
> 
> I'd think the page relocation is easier in the kernel, as we have access to
> zones and we can use swsusp_free() to clean things up if something goes
> wrong (of course that's after some changes).

It is quite a lot of ugly code, and being in kernel does not really
help. swsusp_free() will need to be exported, but we need it for
normal (non-error) code path, too, so that should not be big problem.

								Pavel
-- 
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