Re: [9fans] using GitHub.com/u-root/cpu on plan9 to connect to linux guests in vmx

[ron minnich <rminnich@gmail.com>]

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I'll be submitting a PR to fix it, we'll see how that goes, because the
code, as written, doesn't even give you some idea how many variables had
the problem.

I don't see that exposing those names is that big a deal, but we'll see.


On Tue, Jun 3, 2025 at 5:15 PM Daniel Maslowski via 9fans <9fans@9fans.net>
wrote:

> The author of that error message might have chosen to not expose/disclose
> the information.
>
> Anyway, interesting - would be really nice to see both systems integrate
> seamlessly!
> I have a good collection of hardware by now that would really like to see
> this.
>
> On Wed, Jun 4, 2025 at 1:57 AM ron minnich <rminnich@gmail.com> wrote:
>
>> well, here's a fun one.
>>
>> I've got my golang cpu command working on plan 9. So I'm working to have
>> my plan 9 cpu connect to a linux vmx guest running my golang cpud.
>>
>> The linux kernel has the initramfs builtin, so ... one file for vmx to
>> worry about, and 0 disk images.
>>
>> side note: qemu was choking on this kernel somehow, but vmx ran it just
>> fine. I like vmx much more than qemu at this point. I prefer to test these
>> linux kernels on vmx now.
>>
>> The goal is to have a linux appliance process, where it is easy to (e.g.)
>> run python3. So the only thing embedded in the linux kernel is u-root
>> programs and a cpud. You should be able to cd to the root of a linux file
>> system, and say
>> linux usr/bin/python3
>> where linux is a wrapper for vmx, and have it work. We had this on
>> akaros. It's handy.
>>
>> The only big problem will be the plethora of symlinks in linux images,
>> but I have a workaround for that, so we'll see.
>>
>> Anyway, plan 9 cpu was connecting to linux cpud, mounts were happening,
>> and so on, then I got this on the cpud side:
>> "exec: environment variable contains NUL"
>> and the cpud exec failed.
>> WTH? Well, it turns out, it's this in src/os/exec/exec.go.
>>
>>                 // Reject NUL in environment variables to prevent
>> security issues (#56284);
>>                 // except on Plan 9, which uses NUL as
>> os.PathListSeparator (#56544).
>>
>> The problem is, this doesn't work if you are communicating plan 9
>> environment variables to Linux, and that's what we're doing. You kind of
>> have to for cpu. I will guess I'm the first person to see this ... kind of
>> funny. Working on it.
>>
>> I'm a bit annoyed that whoever wrote the test and error did this:
>> err = errors.New("exec: environment variable contains NUL"
>> instead of this:
>> err = fmt.Errorf"%q:exec: environment variable contains NUL", kv)
>> since it's always kind of nice to produce useful error messages :-)
>> but at least I got something!
>>
>> btw, my talk, the paper, and the code for vmthreads is mirrored to
>> github.com/rminnich/vmproc.
>>
>>
>>
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