Re: [WIP Patch] Adding an FHS container to guix shell

[Ludovic Courtès]

Hello!

John Kehayias <john.kehayias@protonmail.com> skribis:

> 2. Typically binaries will expect the ld loader to use
> /etc/ld.so.cache for finding libraries.

Not necessarily.  /etc/ld.so.cache is an optimization, but it’s entirely
possible to opt out: if that file is missing, things will work fine, but
libc will ‘stat’ more to find files.  That would make glibc-for-fhs
unnecessary.

> +(define* (launch-environment/container #:key command bash fhs-container? user
> +                                       user-mappings profile manifest
> +                                       link-profile? network? map-cwd?
> +                                       (white-list '()))
>    "Run COMMAND within a container that features the software in PROFILE.
>  Environment variables are set according to the search paths of MANIFEST.
>  The global shell is BASH, a file name for a GNU Bash binary in the
> @@ -709,6 +718,49 @@ (define* (launch-environment/container #:key command 
> bash user user-mappings
>              (mkdir-p home-dir)
>              (setenv "HOME" home-dir)
>  
> +            ;; Set up an FHS container.
> +            (when fhs-container?
> +              ;; Set up the expected bin and library directories as symlinks 
> to
> +              ;; the profile lib directory.  Note that this is assuming a 
> 64bit
> +              ;; architecture.
> +              (let ((lib-dir (string-append profile "/lib")))
> +                (symlink lib-dir "/lib64")
> +                (symlink lib-dir "/lib")
> +                (mkdir-p "/usr")
> +                (symlink lib-dir "/usr/lib"))

Instead of adding code here, maybe you could do in a more declarative
fashion, like:

  (define fhs-mappings
    (list (file-system-mapping
            (source (string-append profile "/bin")) (target "/bin"))
          …))

and append that to the ‘mappings’ variable there.  It’s not necessarily
more compact, but maybe marginally easier to read?

> +              ;; Define an entry script to start the container: generate
> +              ;; ld.so.cache, supplement $PATH, and include command.

I’d leave ld.so.cache generation out.

> +              (call-with-output-file "/tmp/fhs.sh"
> +                (lambda (port)
> +                  (display "ldconfig -X -f /tmp/ld.so.conf" port)
> +                  (newline port)
> +                  (display "export PATH=/bin:/usr/bin:/sbin:/usr/sbin:$PATH" 
> port)

I think the default value of PATH in our libc is the FHS one:

--8<---------------cut here---------------start------------->8---
$ env -i $(type -P strace) -e execve -f $(type -P guile) -c '(system* 
"whatever")'
execve("/gnu/store/lpcjxka7hx3ypv4nz47g08k4m2syqwlj-profile/bin/guile", 
["/gnu/store/lpcjxka7hx3ypv4nz47g0"..., "-c", "(system* \"whatever\")"], 
0x7ffede27ad38 /* 0 vars */) = 0
/home/ludo/.guix-home/profile/bin/strace: Process 9727 attached
/home/ludo/.guix-home/profile/bin/strace: Process 9728 attached
/home/ludo/.guix-home/profile/bin/strace: Process 9729 attached
/home/ludo/.guix-home/profile/bin/strace: Process 9730 attached
/home/ludo/.guix-home/profile/bin/strace: Process 9731 attached
/home/ludo/.guix-home/profile/bin/strace: Process 9732 attached
[pid  9732] execve("/bin/whatever", ["whatever"], 0x7ffed6d967c8 /* 0 vars */) 
= -1 ENOENT (No such file or directory)
[pid  9732] execve("/usr/bin/whatever", ["whatever"], 0x7ffed6d967c8 /* 0 vars 
*/) = -1 ENOENT (No such file or directory)
In execvp of whatever: No such file or directory
--8<---------------cut here---------------end--------------->8---

So you could leave it undefined, but ‘load-profile’ in
‘launch-environment’ will define it.

Instead of the wrapper script, maybe you could extend
‘launch-environment’ so the caller can make it override certain
variables?  I would find it a bit clearer.

Thanks,
Ludo’.