Re: [PATCH 07/15] build: syscalls: Add pivot-root.

["Thompson, David" <dthompson2@worcester.edu>]

On Tue, Jul 7, 2015 at 9:35 AM, Ludovic Courtès <ludo@gnu.org> wrote:
> David Thompson <dthompson2@worcester.edu> skribis:
>
>> From: David Thompson <davet@gnu.org>
>>
>> * guix/build/syscalls.scm (pivot-root): New procedure.
>> * tests/syscalls.scm: Test it.
>
> [...]
>
>> +(test-assert "pivot-root"
>> +  (match (pipe)
>> +    ((in . out)
>> +     (match (clone (logior CLONE_NEWUSER CLONE_NEWNS))
>> +       (0
>> +        (close in)
>> +        (call-with-temporary-directory
>> +         (lambda (root)
>> +           (let ((put-old (string-append root "/real-root")))
>> +             (mount "none" root "tmpfs")
>> +             (mkdir put-old)
>> +             (call-with-output-file (string-append root "/test")
>> +               (lambda (port)
>> +                 (display "testing\n" port)))
>> +             (pivot-root root put-old)
>> +             ;; The test file should now be located inside the root directory.
>> +             (write (file-exists "/test") out)
>> +             (close out))))
>> +        (primitive-exit 0))
>> +       (pid
>> +        (close out)
>> +        (read in))))))
>
> Shouldn’t it be:
>
>   (file-exists? (string-append put-old "/test"))

No, because put-old contains the current system root directory.  I
wanted to test that the file I made in the temporary directory is now
located in the new root file system.  I hope this makes sense.

> To be on the safe side, the last line should probably be:
>
>   (eq? #t (read in))
>
> Otherwise a return value of *unspecified* works as well.

Good call.  I had a typo ('file-exists' instead of 'file-exists?')
that was making this test pass when it should've failed.  That's bad
"test driven development" on my part. ;)

> Also, ‘waidpid’:
>
>   (pid
>     (close out)
>     (let ((result (read in)))
>       (close in)
>       (and (zero? (status:exit-val (waitpid pid)))
>            (eq? #t result))))
>
> OK with these changes.

Fixed and pushed.  Thanks!

- Dave