Subject: bug#20720: Inconsistency in text fields for 'operating-system'

From: [email-masked] (Ludovic Courtès)
Date: Fri, 05 Jun 2015 14:30:35 +0200

Alex Kost <[email-masked]> skribis:

> Ludovic Courtès (2015-06-03 12:52 +0300) wrote:

[...]

>> An important criterion is whether the file needs to contain references
>> to store items or not.  For ‘sudoers’ and ‘issue’, that’s normally not
>> the case, and these are usually small files or computable files, so I
>> think it’s fine to use strings here (more convenient than files.)
>
> Well, I don't agree about ‘sudoers’.  It may be a really big file.  Mine
> is not so big, but it is 40 lines long (including some useful comments),
> so I have to use some additional guile code to convert the contents of
> the file into string.

Ah, good point.  So let’s turn ‘sudoers’ into a file-like object.

>> Using monadic values as for ‘hosts-file’ and #:motd is not nice.  These
>> should be changed to use either a string or a file.
>>
>> The best would be to always use a file-like object.  I’ve just added
>> ‘plain-file’ for that reason.  Now I would change #:motd and
>> ‘hosts-file’ to take a file-like object rather than a monadic value.
>>
>> WDYT?
>
> I beg a pardon, but if I inderstand it correctly (probably not), I don't
> see a difference from the user point of view.  Previously it was:
>
>   (hosts-file (text-file "hosts" "..."))
>
> and now it would be:
>
>   (hosts-file (plain-file "hosts" "..."))

Right.  But it could also be:

  (hosts-file (local-file "/home/foo/my-hosts-file.txt"))

This form is pleasant when the file can be long or when it has special
syntax and you’d rather use the editor’s syntax highlighting.

> I think I'm not competent as I have a vague understanding of all this
> stuff and of user's needs (except mine ☺).  What I would like to have,
> is a possibility to specify my configuration files for various services
> and operating-system fields.  I don't want to write text configs in my
> os-config.scm file (as it happens now with ‘hosts-file’).

OK.  So that’s definitely in favor of using file-like objects pretty
much everywhere.

> I'm very happy with the current behaviour of ‘syslog-service’,
> ‘lirc-service’ and ‘console-keymap-service’ where I just specify file
> names, e.g.:
>
>   (syslog-service #:config-file "/home/me/my-favourite-syslog.conf")
>
> and I like this ↑ way of specifying configurations very much!  That's
> what I would like to see in ‘sudoers’ and ‘hosts-file’ fields.

OK.  Note that this form (directly using a local file name) works
somewhat by chance and should not be used because it defeats
reproducibility.  That is, your OS configuration actually depends on
that file in /home, which may be modified or deleted anytime, thereby
changing the syslogd behavior in unpredicable ways.

The right thing to do is:

  (syslog-service #:config-file
                  (local-file "/home/me/my-favourite-syslog.conf"))

This means that the config file is automatically added to the store and
made part of the closure of the OS config.  Now if
"/home/me/my-favourite-syslog.conf" is removed/modified, the OS behavior
remains unchanged.

I’ll prepare a patch for that and report back.

Thank you!

Ludo’.