Re: [uml-devel] [UML combo patch] 2.6.0 host-skas kernel & UML kernel patch

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 22:16, venerdì 19 dicembre 2003, Ingo Molnar ha scritto:
> * BlaisorBlade <blaisorblade_spam@yahoo.it> wrote:
> > > WARNING: this is an experimental patch, UML kernels compiled with this
> > > patch wont work in skas mode on older host-skas patched kernels.

You mean that they won't work on 2.4 SKAS kernels or on 2.6 skas kernels 
without your change(i.e. there have been some other ports of Skas to 2.5/2.6, 
which didn't touch the actual code logic)? If I've understood you correctly, 
you must just re-add the MM_COPY_SEGMENTS call in the UML arch, while still 
making its implementation in the i386 arch as a no-op, to make us happy. 
Right? Could you do this?

> > Does this warning refers to any of the other patches you posted? To
> > which one especially? Is this related to the removal of
> > MM_COPY_SEGMENTS ?
>
> yes, it refers mostly to the removal of MM_COPY_SEGMENTS.

> > Also, if there is any incompatibility, it should be named skas4. But
> > since Jeff Dike's will release skas4, even improving skas3 by breaking
> > compatibility is not useful. And if it is accepted, it should at least
> > be released also for 2.4(the guest 2.4/2.6 choice must be unrelated to
> > the host choice).
>
> skas4 will be nice, and since it will most likely be 2.6 based (?), it
> doesnt have the copy_segments problem.

The patch is very useful, but I think that at least the MM_COPY_SEGMENTS 
change should be split out, since it is not backward compatible. Anything 
required to fix a bug can be put inside, but preserving it. So preserve 
binary compatibility with old host-skas kernels and old guest kernels.

Jeff has already refused patches for skas3(a cleanup actually, the one of 
renaming do_mmap_pgoff as __do_mmap_pgoff as I said you), which hadn't got 
any problem, just because he wants to release skas4.

Such a speedup could be useful maybe for skas4, but only maybe(i.e. since 
skas4 will have to be for 2.4 also, I think that MM_COPY_SEGMENTS can be made 
a no-op, but the guest must call it).

In fact, I think he planned skas 4 for 2.4; he said also it is almost ready, 
just has some problems with the two new syscall numbers. And UML development 
is still mainly on 2.4; fixes are applied currently on 2.4 tree, and at some 
moment will appear on the 2.6 one.

However, the one to refer to for such issues is actually Jeff Dike; this is 
only my VERY HUMBLE opinion; I'm answering just because I've been lurking on 
the ML's from enough time to understand the Jeff's plans.

> Jeff, do you know how the new skas4 syscall API will look like, exactly?
>
> 	Ingo

He mentioned that /proc/mm will be removed, and there will be two new 
syscalls: one will be to create a new address space, and the second will be 
to use a certain context(i.e. a certain mm_struct) for any syscall from the 
guest to the host(I am not able to find his message, so this is what I 
remember). This design was agreed on by Jeff and Linus.

Btw: some changes in your patch are just build-generated files(headers, and 
symlinks in the arch/um/sys-i386 dir). Pay attention to making clean(or 
mrproper) next time before creating the patch. If you get some error from 
"sh" about SIZE and shell arithmetic, it's already fixed(in a thread from a 
few days ago).

Bye
-- 
cat <<EOSIGN
Paolo Giarrusso, aka Blaisorblade
Linux Kernel 2.4.21/2.6.0-test on an i686; Linux registered user n. 292729
EOSIGN



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