systemd.bbclass: generate preset for templates

There was a regression introduced by the change to use
systemd-systemctl-native rather than a python fake implementation,
which caused template units to not be properly enabled when set in
the SYSTEMD_SERVICE variable.  Through investigation, it seems that
the best way to re-enable template instances is to handle them
explicitly in the systemd.bbclass and enable them with `preset`, like
most units are handled[1,2].

Per the systemd.preset manpage, the format for template units is
different than for regular units[3].  We need to coalesce all the
template instances onto a single line and emit them as an additional
space-deliminated argument.

Ran this against openbmc's phosphor-ipmi-net recipe and generated
the following preset file:
```
$ cat packages-split/phosphor-ipmi-net/usr/lib/systemd/system-preset/98-phosphor-ipmi-net.preset
enable phosphor-ipmi-net@.service eth0
enable phosphor-ipmi-net@.socket eth0
```

[1]: https://lore.kernel.org/openembedded-core/Z2ch.1747051947055246176.oktf@lists.openembedded.org/
[2]: https://lore.kernel.org/openembedded-core/aDdoTVtCmElpURYD@heinlein/
[3]: https://www.freedesktop.org/software/systemd/man/latest/systemd.preset.html

Fixes: 7a580800db39 ("systemd: Build the systemctl executable")
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
---
 meta/classes-recipe/systemd.bbclass | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

On Wed, May 28, 2025 at 05:33:06PM -0400, Patrick Williams wrote:
> There was a regression introduced by the change to use
> systemd-systemctl-native rather than a python fake implementation,
> which caused template units to not be properly enabled when set in
> the SYSTEMD_SERVICE variable.  Through investigation, it seems that
> the best way to re-enable template instances is to handle them
> explicitly in the systemd.bbclass and enable them with `preset`, like
> most units are handled[1,2].
> 
> Per the systemd.preset manpage, the format for template units is
> different than for regular units[3].  We need to coalesce all the
> template instances onto a single line and emit them as an additional
> space-deliminated argument.
> 
> Ran this against openbmc's phosphor-ipmi-net recipe and generated
> the following preset file:
> ```
> $ cat packages-split/phosphor-ipmi-net/usr/lib/systemd/system-preset/98-phosphor-ipmi-net.preset
> enable phosphor-ipmi-net@.service eth0
> enable phosphor-ipmi-net@.socket eth0
> ```
> 
> [1]: https://lore.kernel.org/openembedded-core/Z2ch.1747051947055246176.oktf@lists.openembedded.org/
> [2]: https://lore.kernel.org/openembedded-core/aDdoTVtCmElpURYD@heinlein/
> [3]: https://www.freedesktop.org/software/systemd/man/latest/systemd.preset.html
> 
> Fixes: 7a580800db39 ("systemd: Build the systemctl executable")
> Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
> ---
>  meta/classes-recipe/systemd.bbclass | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/meta/classes-recipe/systemd.bbclass b/meta/classes-recipe/systemd.bbclass
> index e1fe4ed072..3cc53c44d9 100644
> --- a/meta/classes-recipe/systemd.bbclass
> +++ b/meta/classes-recipe/systemd.bbclass
> @@ -224,6 +224,8 @@ python systemd_populate_packages() {
>                          service, pkg_systemd, "Also looked for service unit '{0}'.".format(base) if base is not None else ""))
>  
>      def systemd_create_presets(pkg, action, user):
> +        import re
> +
>          # Check there is at least one service of given type (system/user), don't
>          # create empty files.
>          needs_preset = False
> @@ -239,10 +241,17 @@ python systemd_populate_packages() {
>          presetf = oe.path.join(d.getVar("PKGD"), d.getVar("systemd_unitdir"), "%s-preset/98-%s.preset" % (prefix, pkg))
>          bb.utils.mkdirhier(os.path.dirname(presetf))
>          with open(presetf, 'a') as fd:
> +            template_services = {}
>              for service in d.getVar('SYSTEMD_SERVICE:%s' % pkg).split():
>                  if not systemd_service_exists(service, user, d):
>                      continue
> -                fd.write("%s %s\n" % (action,service))
> +                if '@' in service:

I somehow sent out an older version of this patch.  Will send an update.

If a service is "@.service", this is just a template file, and shouldn't
be added to the instance registration.

> +                    (subservice, instance, service_type) = re.split('[@.]', service)
> +                    template_services.setdefault(subservice + '@.' + service_type, []).append(instance)
> +                else:
> +                    fd.write("%s %s\n" % (action,service))
> +            for template, instances in template_services.items():
> +                fd.write("%s %s %s\n" % (action, template, ' '.join(instances)))
>          d.appendVar("FILES:%s" % pkg, ' ' + oe.path.join(d.getVar("systemd_unitdir"), "%s-preset/98-%s.preset" % (prefix, pkg)))
>  
>      # Run all modifications once when creating package
> -- 
> 2.49.0
>