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

From: Alex Kost <[email-masked]>
Date: Thu, 04 Jun 2015 17:43:55 +0300

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

> Alex Kost <[email-masked]> skribis:
>
>> I see some inconsistency in specifying text / text files in an
>> operating-system declaration:
>
> Yeah, I agree it is somewhat annoying that there’s no single way to
> handle this.  But...
>
>> - ‘sudoers’ and ‘issue’ want plain strings;
>>
>> - ‘hosts-file’ and ‘mingetty-service’ (#:motd argument) want a
>>   'text-file' monadic procedure;
>>
>> - some other services (‘syslog-service’, ‘lirc-service’, ...) want file
>>   names (of the configuration files).
>
> In reality they take a “file”, not a file name.  A file is an object
> that within a gexp expands to a file name.  So it can be a ‘local-file’
> object, a derivation, etc.

Ah, thanks!  I didn't realize that ‘local-file’ or a derivation may be
used there.

>> As for me, I prefer the latter variant.  But I think the best would
>> be to add support for any of the above possibilities for all services
>> or operating-system fields.
>
> 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.

> 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" "..."))

> This brings up the question of how far we should go on the declarative
> side: Similar to ‘local-file’ and ‘plain-file’, should we add more
> declarative types, say for ‘gexp->derivation’?
>
> My current inclination would be to not add anything beyond ‘local-file’
> and ‘plain-file’: These two are useful in OS configurations, so that’s
> fine, but for more elaborate things people should just use the
> procedural interface.  Thoughts?

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’).

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.

-- 
Thanks,
Alex