execute: add support for XDG_STATE_HOME for placing service state data in --user mode

This adds support for the new XDG_STATE_HOME env var that was added to
the xdg basedir spec. Previously, because the basedir spec didn't know
the concept we'd alias the backing dir for StateDirectory= to the one
for ConfigurationDirectory= when runnin in --user mode. With this change
we'll make separate. This brings us various benefits, such as proper
"systemctl clean" support, where we can clear service state separately
from service configuration, now in user mode too.

This does not come without complications: retaining compatibility with
older setups is difficult, because we cannot possibly identitfy which
files in existing populated config dirs are actually "state" and which
one are true" configuration.

Hence let's deal with this pragmatically: if we detect that a service
that has both dirs configured only has the configuration dir existing,
then symlink the state dir to the configuration dir to retain
compatibility.

This is not great, but it's the only somewhat reasonable way out I can
see.

Fixes: #25739

1 files changed, 2 insertions, 2 deletions

diff --git a/src/core/unit-printf.c b/src/core/unit-printf.c
index 3977082cc1..9f95984eb6 100644
--- a/src/core/unit-printf.c
+++ b/src/core/unit-printf.c
@@ -209,8 +209,8 @@ int unit_full_printf_full(const Unit *u, const char *format, size_t max_length,
          * %C: the cache directory root (e.g. /var/cache or $XDG_CACHE_HOME)
          * %d: the credentials directory ($CREDENTIALS_DIRECTORY)
          * %E: the configuration directory root (e.g. /etc or $XDG_CONFIG_HOME)
-         * %L: the log directory root (e.g. /var/log or $XDG_CONFIG_HOME/log)
-         * %S: the state directory root (e.g. /var/lib or $XDG_CONFIG_HOME)
+         * %L: the log directory root (e.g. /var/log or $XDG_STATE_HOME/log)
+         * %S: the state directory root (e.g. /var/lib or $XDG_STATE_HOME)
          * %t: the runtime directory root (e.g. /run or $XDG_RUNTIME_DIR)
          *
          * %h: the homedir of the running user