[bug#74510] [PATCH] doc: Document the (possible) need for network-online for NFS.

[Maxim Cournoyer]

Hi Tomas,

Tomas Volf <~@wolfsden.cz> writes:

> Depending on networking is not enough in some setups, so a language clarifying
> that and an example of network-online service.
>
> * doc/guix.texi (File Systems): Document the possible need for network-online.
>
> Change-Id: I8abe07cc9d6dc61f28eeea7ffa785eb8c9e8fd09
> ---
>  doc/guix.texi | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/doc/guix.texi b/doc/guix.texi
> index 26488b41c8..861e78e6d2 100644
> --- a/doc/guix.texi
> +++ b/doc/guix.texi
> @@ -18018,7 +18018,33 @@ File Systems
>  met before mounting the file system.
>  
>  As an example, an NFS file system would typically have a requirement for
> -@code{networking}.
> +@code{networking}.  However be aware that depending on @code{networking}
> +might not be sufficient in some setups and a variant of custom
> +@code{network-online} service might be necessary.

Could we be more precise and detail a simple case or example of when
requiring 'network-online is needed over just 'network for NFS?

> Example:
> +
> +@lisp
> +(simple-service 'network-online shepherd-root-service-type
> +  (list
> +   (shepherd-service
> +    (requirement '(networking))
> +    (provision '(network-online))
> +    (documentation "Wait for the network to come up.")
> +    (start #~(lambda _
> +               (let* ((cmd
> +                       "set -eux
> +c=0
> +while ! /run/setuid-programs/ping -qc1 -W1 example.org; do
> +     sleep 1
> +     [ \"$((c += 1))\" -lt 30 ] || exit 1  # Limit the wait time
> +done
> +")
> +                    (status (system cmd)))
> +               (= 0 (status:exit-val status)))))

I'm pretty sure we have connectivity tests already in the Guix test
suite that must make use of Guile; that would be nicer, I think; for
example, the (guix tests) module has:

--8<---------------cut here---------------start------------->8---
(define (network-reachable?)
  "Return true if we can reach the Internet."
  (false-if-exception (getaddrinfo "www.gnu.org" "80" AI_NUMERICSERV)))
--8<---------------cut here---------------end--------------->8---

> +   ;; Ordering for one-shot? services does not currently work.
> +   ;; https://issues.guix.gnu.org/74284
> +   ;; (one-shot? #t)
> +   )))
> +@end lisp

Otherwise, it looks like a useful addition.

-- 
Thanks,
Maxim