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Re: [PATCH 0/15] Add preliminary support for Linux containers
From: |
Ludovic Courtès |
Subject: |
Re: [PATCH 0/15] Add preliminary support for Linux containers |
Date: |
Wed, 08 Jul 2015 14:46:26 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
"Thompson, David" <address@hidden> skribis:
> On Tue, Jul 7, 2015 at 6:28 AM, Ludovic Courtès <address@hidden> wrote:
[...]
>>> (lambda ()
>>> (sethostname "guix-0.8.3"))
>>
>> Surprisingly, calling ‘getpid’ in the thunk returns the PID of the
>> parent (I was expecting it to return 1.) Not sure why that is the
>> case. I’m still amazed that this works as non-root, BTW.
>
> The first process created inside the PID namespace gets the honor of
> being PID 1, not the process created with the 'clone' call.
>
> For more information, see: https://lwn.net/Articles/532748/
To me, the thunk above is just like ‘childFunc’ in
<https://lwn.net/Articles/533492/>–i.e., it’s the procedure that ‘clone’
calls in the first child process of the new PID name space.
What am I missing?
>> There’s an issue when the parent’s Guile is not mapped into the
>> container’s file system: ‘use-modules’ forms and auto-loading will fail.
>> For instance, I did (use-modules (ice-9 ftw)) in the parent and called
>> ‘scandir’ in the child, but that failed because of an attempt to
>> auto-load (ice-9 i18n), which is unavailable in the container.
>
> Hmm, I don't know of a way to deal with that other than the user being
> careful to bind-mount in the Guile modules they need.
Right. Maybe the best we can do is to add a word of caution in the
docstring or something.
> Hmm, there's various reasons that EINVAL would be thrown. Could you
> readlink "those" files, that is /proc/<pid-outside-container>/ns/user
> and /proc/<pid-inside-container>/ns/user, and tell me if the contents
> are the same? They shouldn't be, but this will eliminate one of the
> possible causes of EINVAL.
It turns out I was targeting the wrong PID.
>> Also, I think we should add --expose and --share as for ‘guix system’,
>> though that can come later.
>
> Yes, I also really want that, but it's a task for another time.
Sure.
>>> Here's how you build it:
>>>
>>> guix system container container.scm
>>
>> Very neat. I wonder if that should automatically override the
>> ‘file-systems’ field to be ‘%container-file-systems’, so that one can
>> reuse existing OS declarations unmodified. WDYT?
>
> This would be a better user experience, for sure. I thought about
> this, but I don't know how to do it in a way that isn't surprising or
> just broken. Ideas?
IMO it’d be fine to simply override the subset of ‘file-systems’ that
clashes with ‘%container-file-systems’, similar to what
‘virtualized-operating-system’ does in (gnu system vm).
WDYT?
Thanks,
Ludo’.