Re: Latest guile-daemon changes and bewilderment

[ludo@gnu.org (Ludovic Courtès)]

Hi reepca,

Caleb Ristvedt <caleb.ristvedt@cune.org> skribis:

>> Is there a line above or below the backtrace mentioning the uncaught
>> exception?  Could you ‘strace -f’ the daemon process?
>
> No, no line above or below. Very strange.

And strace?  :-)  It could be that it fails to load some of the
(system *) helper modules when displaying the error, something like
that.

>> BTW, I see the code uses ‘clone’ directly.  It would be safer to use
>> ‘call-with-container’, which already handles bind mounts, non-local
>> exits, and so on.  Would it be an option?
>
> There are a couple of issues with using call-with-container. In
> decreasing order of perceived difficulty to solve:

[...]

> ... and then I paused writing this for 2 days while I checked whether my
> in-theory solutions would work in practice. And it seems like they
> actually do (see recent branch update). Mostly. I need to figure out why
> it fails when a new user namespace is created - for some reason
> pivot-root fails when new-root was mounted from a different user
> namespace.

Heheh.  :-)

The commit “build-derivations: use call-with-container” does two things:
adjust ‘call-with-container’, and actually use it in the new daemon
code.  I think it would be great to split this into two logical changes.

I don’t get the use of ‘try-umount’ in an unwind handler of
‘call-with-container’.  Since ‘call-with-container’ uses
‘call-with-temporary-directory’, ROOT is never a mount point, no?

> But on the bright side, it somehow solved the bug I described earlier. I
> still haven't managed to make it all the way to building hello (a
> libunistring test hangs), but it's getting much farther.

If the hanging test is ‘test-lock’, that’s a “known problem” on machines
with more than ~8 cores, and it’s fixed in core-updates.

>> Let’s maybe try to further debug this interactively on IRC.
>
> ... and then I promptly fell asleep and spent the next few days
> (nights?) tinkering. Oops.

No problem.  :-)

Next time feel free to ping me when you’re at the peak of your debugging
activity, in case I can help out!

Thanks,
Ludo’.