User-mode Linux kernel port

Hi Martin,

On Sat, Apr 16, 2011 at 4:04 PM, Martin Walch <walch.martin@...> wrote:
> Hello UML maintainers,
>
> I have run into a problem making a uml kernel for SUBARCH=i386 with support
> for XFS. This looks like a regression. Can you please take a look at
>
> https://bugzilla.kernel.org/show_bug.cgi?id=32812

The cmpxchg8b_emu issue is already known and fixed.
See:
http://git.kernel.org/linus/084189a

For the atomic64_read_386 issue I've attached a patch.
WARING: It's only compile time tested. :)

Please apply both and retry.

Thanks,
//richard

> Thank you.
>
> Martin Walch
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>
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-- 
Thanks,
//richard

On Sat, Apr 16, 2011 at 5:09 PM, richard -rw- weinberger
<richard.weinberger@...> wrote:
> Hi Martin,
>
> On Sat, Apr 16, 2011 at 4:04 PM, Martin Walch <walch.martin@...> wrote:
>> Hello UML maintainers,
>>
>> I have run into a problem making a uml kernel for SUBARCH=i386 with support
>> for XFS. This looks like a regression. Can you please take a look at
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=32812
>
> The cmpxchg8b_emu issue is already known and fixed.
> See:
> http://git.kernel.org/linus/084189a
>
> For the atomic64_read_386 issue I've attached a patch.
> WARING: It's only compile time tested. :)
>
> Please apply both and retry.

Forget the patch.
We need something better.
I'm working on it.

-- 
Thanks,
//richard

Martin,

On Sat, Apr 16, 2011 at 4:04 PM, Martin Walch <walch.martin@...> wrote:
> Hello UML maintainers,
>
> I have run into a problem making a uml kernel for SUBARCH=i386 with support
> for XFS. This looks like a regression. Can you please take a look at
>
> https://bugzilla.kernel.org/show_bug.cgi?id=32812
>
> Thank you.

Can you please test the attached patch?
Don't forget to apply http://git.kernel.org/linus/084189a in case you're
not using Linus' tree.

BTW: Please configure your kernel for a CPU newer than i486,
Pentium Pro would be a good choice. :-)

-- 
Thanks,
//richard

> Can you please test the attached patch?
> Don't forget to apply http://git.kernel.org/linus/084189a in case you're
> not using Linus' tree.

Works fine. At least make successfully creates a uml binary and I can create, 
mount and unmount an xfs file system. Creating and deleting a file also works 
fine.

I did not do any intensive testing as I am not going to use it now anyway, as 
hostfs has become the better choice. (Actually, I had already decided against 
xfs before reporting the bug.)

> BTW: Please configure your kernel for a CPU newer than i486,
> Pentium Pro would be a good choice. :-)

I never intended to actually use an i486 comaptible build. I will be using 
"Opteron/Athlon64/Hammer/K8". However, I wonder if there are any problems 
using i486 besides performance loss. Will this break things?

--

On Sun, Apr 17, 2011 at 7:52 PM, Martin Walch <walch.martin@...> wrote:
>> Can you please test the attached patch?
>> Don't forget to apply http://git.kernel.org/linus/084189a in case you're
>> not using Linus' tree.
>
> Works fine. At least make successfully creates a uml binary and I can create,
> mount and unmount an xfs file system. Creating and deleting a file also works
> fine.

Fine.

> I never intended to actually use an i486 comaptible build. I will be using
> "Opteron/Athlon64/Hammer/K8". However, I wonder if there are any problems
> using i486 besides performance loss. Will this break things?

XFS needs atomic 64 bit operations. To emulate them on 32 bit systems we need
the cmpxchg8b instruction.
Old CPUs don't offer this instruction. So we would have to emulate
cmpxchg8b too.
For now UML does not have a cmpxchg8b emulation because this would be
quite hacky
to realize it in pure user mode.

--
Thanks,
//richard