units: rework growfs units to be just a regular unit that is instantiated

The systemd-growfs@.service units are currently written in full for each
file system to grow. Which is kinda pointless given that (besides an
optional ordering dep) they contain always the same definition. Let's
fix that and add a static template for this logic, that the generator
simply instantiates (and adds an ordering dep for).

This mimics how systemd-fsck@.service is handled. Similar to the wait
that for root fs there's a special instance systemd-fsck-root.service
we also add a special instance systemd-growfs-root.service for the root
fs, since it has slightly different deps.

Fixes: #20788
See: #10014

5 files changed, 126 insertions, 49 deletions

diff --git a/src/basic/special.h b/src/basic/special.h
index 5d1111fd71..9bb36c5732 100644
--- a/src/basic/special.h
+++ b/src/basic/special.h
@@ -87,6 +87,8 @@
 #define SPECIAL_REMOUNT_FS_SERVICE "systemd-remount-fs.service"
 #define SPECIAL_VOLATILE_ROOT_SERVICE "systemd-volatile-root.service"
 #define SPECIAL_UDEVD_SERVICE "systemd-udevd.service"
+#define SPECIAL_GROWFS_SERVICE "systemd-growfs@.service"
+#define SPECIAL_GROWFS_ROOT_SERVICE "systemd-growfs-root.service"
 
 /* Services systemd relies on */
 #define SPECIAL_DBUS_SERVICE "dbus.service"
diff --git a/src/shared/generator.c b/src/shared/generator.c
index ec0182d05e..6c82d0f0ef 100644
--- a/src/shared/generator.c
+++ b/src/shared/generator.c
@@ -110,6 +110,64 @@ int generator_add_symlink_full(
         return 0;
 }
 
+static int generator_add_ordering(
+                const char *dir,
+                const char *src,
+                const char *order,
+                const char *dst,
+                const char *instance) {
+
+        _cleanup_free_ char *instantiated = NULL, *p = NULL, *fn = NULL;
+        _cleanup_fclose_ FILE *f = NULL;
+        const char *to;
+        int r;
+
+        assert(dir);
+        assert(src);
+        assert(order);
+        assert(dst);
+
+        /* Adds in an explicit ordering dependency of type <order> from <src> to <dst>. If <instance> is
+         * specified, it is inserted into <dst>. */
+
+        if (instance) {
+                r = unit_name_replace_instance(dst, instance, &instantiated);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to instantiate '%s' for '%s': %m", dst, instance);
+
+                to = instantiated;
+        } else
+                to = dst;
+
+        fn = strjoin(src, ".d/50-order-", to, ".conf");
+        if (!fn)
+                return log_oom();
+
+        p = path_join(dir, fn);
+        if (!p)
+                return log_oom();
+
+        (void) mkdir_parents_label(p, 0755);
+
+        r = fopen_unlocked(p, "wxe", &f);
+        if (r < 0)
+                return log_error_errno(r, "Failed to create '%s': %m", p);
+
+        fprintf(f,
+                "# Automatically generated by %s\n\n"
+                "[Unit]\n"
+                "%s=%s\n",
+                program_invocation_short_name,
+                order,
+                to);
+
+        r = fflush_and_check(f);
+        if (r < 0)
+                return log_error_errno(r, "Failed to write drop-in '%s': %m", p);
+
+        return 0;
+}
+
 static int write_fsck_sysroot_service(
                 const char *unit, /* Either SPECIAL_FSCK_ROOT_SERVICE or SPECIAL_FSCK_USR_SERVICE */
                 const char *dir,
@@ -560,66 +618,36 @@ int generator_hook_up_growfs(
                 const char *where,
                 const char *target) {
 
-        _cleanup_free_ char *unit = NULL, *escaped = NULL, *where_unit = NULL, *unit_file = NULL;
-        _cleanup_fclose_ FILE *f = NULL;
+        const char *growfs_unit, *growfs_unit_path;
+        _cleanup_free_ char *where_unit = NULL, *instance = NULL;
         int r;
 
         assert(dir);
         assert(where);
 
-        escaped = cescape(where);
-        if (!escaped)
-                return log_oom();
-
-        r = unit_name_from_path_instance("systemd-growfs", where, ".service", &unit);
-        if (r < 0)
-                return log_error_errno(r, "Failed to make unit instance name from path \"%s\": %m",
-                                       where);
-
         r = unit_name_from_path(where, ".mount", &where_unit);
         if (r < 0)
-                return log_error_errno(r, "Failed to make unit name from path \"%s\": %m",
-                                       where);
-
-        unit_file = path_join(dir, unit);
-        if (!unit_file)
-                return log_oom();
-
-        log_debug("Creating %s", unit_file);
-
-        f = fopen(unit_file, "wxe");
-        if (!f)
-                return log_error_errno(errno, "Failed to create unit file %s: %m",
-                                       unit_file);
+                return log_error_errno(r, "Failed to make unit name from path '%s': %m", where);
 
-        fprintf(f,
-                "# Automatically generated by %s\n\n"
-                "[Unit]\n"
-                "Description=Grow File System on %%f\n"
-                "Documentation=man:systemd-growfs@.service(8)\n"
-                "DefaultDependencies=no\n"
-                "BindsTo=%%i.mount\n"
-                "Conflicts=shutdown.target\n"
-                "After=systemd-repart.service %%i.mount\n"
-                "Before=shutdown.target%s%s\n",
-                program_invocation_short_name,
-                target ? " " : "",
-                strempty(target));
+        if (empty_or_root(where)) {
+                growfs_unit = SPECIAL_GROWFS_ROOT_SERVICE;
+                growfs_unit_path = SYSTEM_DATA_UNIT_DIR "/" SPECIAL_GROWFS_ROOT_SERVICE;
+        } else {
+                growfs_unit = SPECIAL_GROWFS_SERVICE;
+                growfs_unit_path = SYSTEM_DATA_UNIT_DIR "/" SPECIAL_GROWFS_SERVICE;
 
-        if (empty_or_root(where)) /* Make sure the root fs is actually writable before we resize it */
-                fprintf(f,
-                        "After=systemd-remount-fs.service\n");
+                r = unit_name_path_escape(where, &instance);
+                if (r < 0)
+                        return log_error_errno(r, "Failed to escape path '%s': %m", where);
+        }
 
-        fprintf(f,
-                "\n"
-                "[Service]\n"
-                "Type=oneshot\n"
-                "RemainAfterExit=yes\n"
-                "ExecStart="SYSTEMD_GROWFS_PATH " %s\n"
-                "TimeoutSec=0\n",
-                escaped);
+        if (target) {
+                r = generator_add_ordering(dir, target, "After", growfs_unit, instance);
+                if (r < 0)
+                        return r;
+        }
 
-        return generator_add_symlink(dir, where_unit, "wants", unit);
+        return generator_add_symlink_full(dir, where_unit, "wants", growfs_unit_path, instance);
 }
 
 int generator_enable_remount_fs_service(const char *dir) {
diff --git a/units/meson.build b/units/meson.build
index 48b24f05c1..62ce438a3f 100644
--- a/units/meson.build
+++ b/units/meson.build
@@ -267,6 +267,8 @@ in_units = [
          'sysinit.target.wants/'],
         ['systemd-pcrmachine.service',           'HAVE_GNU_EFI HAVE_OPENSSL HAVE_TPM2',
          'sysinit.target.wants/'],
+        ['systemd-growfs-root.service',          ''],
+        ['systemd-growfs@.service',              ''],
 ]
 
 add_wants = []
diff --git a/units/systemd-growfs-root.service.in b/units/systemd-growfs-root.service.in
new file mode 100644
index 0000000000..295bafd5af
--- /dev/null
+++ b/units/systemd-growfs-root.service.in
@@ -0,0 +1,22 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Grow Root File System
+Documentation=man:systemd-growfs-root.service(8)
+DefaultDependencies=no
+Conflicts=shutdown.target
+After=systemd-repart.service systemd-remount-fs.service
+Before=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart={{ROOTLIBEXECDIR}}/systemd-growfs /
+TimeoutSec=0
diff --git a/units/systemd-growfs@.service.in b/units/systemd-growfs@.service.in
new file mode 100644
index 0000000000..7154e4ca76
--- /dev/null
+++ b/units/systemd-growfs@.service.in
@@ -0,0 +1,23 @@
+#  SPDX-License-Identifier: LGPL-2.1-or-later
+#
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=Grow File System on %f
+Documentation=man:systemd-growfs@.service(8)
+DefaultDependencies=no
+BindsTo=%i.mount
+Conflicts=shutdown.target
+After=systemd-repart.service %i.mount
+Before=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart={{ROOTLIBEXECDIR}}/systemd-growfs %f
+TimeoutSec=0