From: Mark Hindley <mark@hindley.org.uk>
Date: Wed, 1 Nov 2023 20:04:48 +0000
Subject: Use libsystemd0 compatible cgroups layout.

Fixes:

../meson_options.txt:272: WARNING: Newline character in a string detected, use ''' (three single quotes) for multiline strings instead.
This will become a hard error in a future Meson release.
option('libsystemd-compat-cgroups', type : 'boolean', description : 'Use a libsystemd
                                                                    ^
---
 meson.build                |  1 +
 meson_options.txt          |  1 +
 src/basic/cgroup-util.c    | 66 +++++++++++++++++++++++++---------------------
 src/basic/cgroup-util.h    | 24 ++++++++++-------
 src/basic/unit-name.c      |  4 +--
 src/basic/unit-name.h      |  4 +--
 src/login/logind-core.c    | 19 ++++++-------
 src/login/logind-session.c | 20 +++++++++++---
 src/login/logind.h         |  4 +--
 9 files changed, 85 insertions(+), 58 deletions(-)

diff --git a/meson.build b/meson.build
index 4fa7bbd..f63942b 100644
--- a/meson.build
+++ b/meson.build
@@ -999,6 +999,7 @@ conf.set_quoted('SYSTEMD_CGROUP_CONTROLLER_LEGACY',
                 '='.join(['name', with_cgroupctrl]))
 conf.set_quoted('SYSTEMD_CGROUP_CONTROLLER_HYBRID',
                 '='.join(['name', with_cgroupctrl]))
+conf.set10('LIBSYSTEMD_COMPATIBLE_CGROUPS', get_option('libsystemd-compat-cgroups'))
 ############################################################
 #endif // 0
 
diff --git a/meson_options.txt b/meson_options.txt
index 83d5688..4eae6ca 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -283,6 +283,7 @@ option('default-hierarchy', type : 'combo',
                 "unified" assumes cgroups version 2 on /sys/fs/cgroup''')
 option('cgroup-controller', type : 'string',
        description : 'Name of the cgroup controller to use')
+option('libsystemd-compat-cgroups', type : 'boolean', description : 'Use a libsystemd compatible cgroups layout')
 #endif // 0
 #if 0 /// UNNEEDED by elogind
 # option('extra-net-naming-schemes', type : 'string',
diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index fdffa2d..c01bf50 100644
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -20,7 +20,9 @@
 #include "format-util.h"
 #include "fs-util.h"
 #include "log.h"
-// #include "login-util.h"
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+#include "login-util.h"
+#endif
 #include "macro.h"
 #include "missing_magic.h"
 #include "missing_threads.h"
@@ -29,13 +31,17 @@
 #include "path-util.h"
 #include "process-util.h"
 #include "set.h"
-//#include "special.h"
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+#include "special.h"
+#endif
 #include "stat-util.h"
 #include "stdio-util.h"
 #include "string-table.h"
 #include "string-util.h"
 //#include "strv.h"
-//#include "unit-name.h"
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+#include "unit-name.h"
+#endif
 #include "user-util.h"
 //#include "xattr-util.h"
 /// Additional includes needed by elogind
@@ -1131,18 +1137,18 @@ int cg_get_root_path(char **ret_path) {
         if (r < 0)
                 return r;
 
-#if 0 /// elogind does not support systemd scopes and slices but other controllers
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support systemd scopes and slices but other controllers
         e = endswith(p, "/" SPECIAL_INIT_SCOPE);
         if (!e)
                 e = endswith(p, "/" SPECIAL_SYSTEM_SLICE); /* legacy */
         if (!e)
                 e = endswith(p, "/system"); /* even more legacy */
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         log_debug_elogind("Determined PID 1 root path: \"%s\"", p);
         e = endswith(p, "/" CGROUP_CONTROLLER_NAME);
         if (!e)
                 e = endswith(p, "/elogind"); /* elogind pseudo-controller? */
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         if (e)
                 *e = 0;
 
@@ -1218,7 +1224,7 @@ int cg_pid_get_path_shifted(pid_t pid, const char *root, char **ret_cgroup) {
         return 0;
 }
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_path_decode_unit(const char *cgroup, char **ret_unit) {
         char *c, *s;
         size_t n;
@@ -1523,10 +1529,10 @@ int cg_path_get_cgroupid(const char *path, uint64_t *ret) {
         *ret = CG_FILE_HANDLE_CGROUPID(fh);
         return 0;
 }
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
 int cg_path_get_session(const char *path, char **ret_session) {
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
         _cleanup_free_ char *unit = NULL;
         char *start, *end;
         int r;
@@ -1547,7 +1553,7 @@ int cg_path_get_session(const char *path, char **ret_session) {
         *end = 0;
         if (!session_id_valid(start))
                 return -ENXIO;
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         /* Elogind uses a flat hierarchy, just "/SESSION".  The only
            wrinkle is that SESSION might be escaped.  */
         const char *e, *n, *start;
@@ -1571,7 +1577,7 @@ int cg_path_get_session(const char *path, char **ret_session) {
 
         if (!start[0])
                 return -ENXIO;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
         if (ret_session) {
                 char *rr;
@@ -1599,12 +1605,12 @@ int cg_pid_get_session(pid_t pid, char **ret_session) {
 }
 
 int cg_path_get_owner_uid(const char *path, uid_t *ret_uid) {
-#if 0 /// elogind needs one more value
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind needs one more value
         _cleanup_free_ char *slice = NULL;
         char *start, *end;
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         _cleanup_free_ char *slice = NULL, *p = NULL, *s = NULL;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         int r;
 
         assert(path);
@@ -1613,7 +1619,7 @@ int cg_path_get_owner_uid(const char *path, uid_t *ret_uid) {
         if (r < 0)
                 return r;
 
-#if 0 /// elogind does not support systemd slices
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support systemd slices
         start = startswith(slice, "user-");
         if (!start)
                 return -ENXIO;
@@ -1625,7 +1631,7 @@ int cg_path_get_owner_uid(const char *path, uid_t *ret_uid) {
         *end = 0;
         if (parse_uid(start, ret_uid) < 0)
                 return -ENXIO;
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         p = strjoin("/run/systemd/sessions/", slice);
 
         r = parse_env_file(NULL, p, "UID", &s);
@@ -1638,7 +1644,7 @@ int cg_path_get_owner_uid(const char *path, uid_t *ret_uid) {
 
         if (parse_uid(s, ret_uid) < 0)
                 return -ENXIO;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
         return 0;
 }
@@ -1661,7 +1667,7 @@ int cg_path_get_slice(const char *p, char **ret_slice) {
         assert(p);
         assert(ret_slice);
 
-#if 0 /// elogind does not support systemd slices
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support systemd slices
         /* Finds the right-most slice unit from the beginning, but
          * stops before we come to the first non-slice unit. */
 
@@ -1690,7 +1696,7 @@ int cg_path_get_slice(const char *p, char **ret_slice) {
                 e = p;
                 p += n;
         }
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         /* In elogind, what is reported here, is the location of
          * the session. This is derived from /proc/<self|PID>/cgroup.
          * In there we look at the controller, which will look something
@@ -1710,7 +1716,7 @@ int cg_path_get_slice(const char *p, char **ret_slice) {
                 *ret_slice = strdup(p);
 
         return 0;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 }
 
 int cg_pid_get_slice(pid_t pid, char **ret_slice) {
@@ -1729,28 +1735,28 @@ int cg_pid_get_slice(pid_t pid, char **ret_slice) {
 }
 
 int cg_path_get_user_slice(const char *p, char **ret_slice) {
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
         const char *t;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         assert(p);
         assert(ret_slice);
 
-#if 0 /// nothing to skip in elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// nothing to skip in elogind
         t = skip_user_prefix(p);
         if (!t)
                 return -ENXIO;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
         /* And now it looks pretty much the same as for a system slice, so let's just use the same parser
          * from here on. */
         return cg_path_get_slice(t, ret_slice);
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         /* In elogind there is nothing to skip, we can use the path
          * directly. Generally speaking this is always a session id
          * to user mapping. */
         return cg_path_get_slice(p, ret_slice);
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 }
 
 int cg_pid_get_user_slice(pid_t pid, char **ret_slice) {
@@ -1943,7 +1949,7 @@ int cg_slice_to_path(const char *unit, char **ret) {
         *ret = TAKE_PTR(s);
         return 0;
 }
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
 int cg_is_threaded(const char *path) {
         _cleanup_free_ char *fs = NULL, *contents = NULL;
@@ -1991,7 +1997,7 @@ int cg_get_attribute(const char *controller, const char *path, const char *attri
         return read_one_line_file(p, ret);
 }
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_get_attribute_as_uint64(const char *controller, const char *path, const char *attribute, uint64_t *ret) {
         _cleanup_free_ char *value = NULL;
         uint64_t v;
@@ -2185,7 +2191,7 @@ int cg_mask_to_string(CGroupMask mask, char **ret) {
 
         return 0;
 }
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
 int cg_mask_from_string(const char *value, CGroupMask *ret) {
         CGroupMask m = 0;
diff --git a/src/basic/cgroup-util.h b/src/basic/cgroup-util.h
index 1b170fd..e61d595 100644
--- a/src/basic/cgroup-util.h
+++ b/src/basic/cgroup-util.h
@@ -238,7 +238,7 @@ typedef enum  {
 
 int cg_set_attribute(const char *controller, const char *path, const char *attribute, const char *value);
 int cg_get_attribute(const char *controller, const char *path, const char *attribute, char **ret);
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_get_keyed_attribute_full(const char *controller, const char *path, const char *attribute, char **keys, char **values, CGroupKeyMode mode);
 
 static inline int cg_get_keyed_attribute(
@@ -265,7 +265,9 @@ int cg_get_attribute_as_uint64(const char *controller, const char *path, const c
 int cg_get_attribute_as_bool(const char *controller, const char *path, const char *attribute, bool *ret);
 
 int cg_get_owner(const char *path, uid_t *ret_uid);
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
+#if 0 /// UNNEEDED by elogind
 int cg_set_xattr(const char *path, const char *name, const void *value, size_t size, int flags);
 int cg_get_xattr(const char *path, const char *name, void *value, size_t size);
 int cg_get_xattr_malloc(const char *path, const char *name, char **ret);
@@ -282,9 +284,9 @@ int cg_is_empty_recursive(const char *controller, const char *path);
 
 int cg_get_root_path(char **path);
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_path_get_cgroupid(const char *path, uint64_t *ret);
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 int cg_path_get_session(const char *path, char **ret_session);
 int cg_path_get_owner_uid(const char *path, uid_t *ret_uid);
 int cg_path_get_unit(const char *path, char **ret_unit);
@@ -306,28 +308,30 @@ int cg_pid_get_machine_name(pid_t pid, char **ret_machine);
 int cg_pid_get_slice(pid_t pid, char **ret_slice);
 int cg_pid_get_user_slice(pid_t pid, char **ret_slice);
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_path_decode_unit(const char *cgroup, char **ret_unit);
 
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 bool cg_needs_escape(const char *p);
 int cg_escape(const char *p, char **ret);
 char *cg_unescape(const char *p) _pure_;
 
 bool cg_controller_is_valid(const char *p);
 
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_slice_to_path(const char *unit, char **ret);
 
 typedef const char* (*cg_migrate_callback_t)(CGroupMask mask, void *userdata);
 
 int cg_mask_supported(CGroupMask *ret);
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 int cg_mask_supported_subtree(const char *root, CGroupMask *ret);
 int cg_mask_from_string(const char *s, CGroupMask *ret);
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 int cg_mask_to_string(CGroupMask mask, char **ret);
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
+#if 0 /// UNNEEDED by elogind
 int cg_kernel_controllers(Set **controllers);
 #endif // 0
 
@@ -373,6 +377,8 @@ typedef enum ManagedOOMPreference {
 const char* managed_oom_preference_to_string(ManagedOOMPreference a) _const_;
 ManagedOOMPreference managed_oom_preference_from_string(const char *s) _pure_;
 
+#endif // 0
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
 /* The structure to pass to name_to_handle_at() on cgroupfs2 */
 typedef union {
         struct file_handle file_handle;
@@ -381,4 +387,4 @@ typedef union {
 
 #define CG_FILE_HANDLE_INIT { .file_handle.handle_bytes = sizeof(uint64_t) }
 #define CG_FILE_HANDLE_CGROUPID(fh) (*(uint64_t*) (fh).file_handle.f_handle)
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
diff --git a/src/basic/unit-name.c b/src/basic/unit-name.c
index 32a0991..35423fd 100644
--- a/src/basic/unit-name.c
+++ b/src/basic/unit-name.c
@@ -110,7 +110,7 @@ bool unit_instance_is_valid(const char *i) {
 
         return in_charset(i, "@" VALID_CHARS);
 }
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 
 bool unit_suffix_is_valid(const char *s) {
         if (isempty(s))
@@ -249,7 +249,7 @@ int unit_name_change_suffix(const char *n, const char *suffix, char **ret) {
         *ret = TAKE_PTR(s);
         return 0;
 }
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
 int unit_name_build(const char *prefix, const char *instance, const char *suffix, char **ret) {
         UnitType type;
diff --git a/src/basic/unit-name.h b/src/basic/unit-name.h
index 80c3282..40bc721 100644
--- a/src/basic/unit-name.h
+++ b/src/basic/unit-name.h
@@ -19,7 +19,7 @@ typedef enum UnitNameFlags {
 bool unit_name_is_valid(const char *n, UnitNameFlags flags) _pure_;
 bool unit_prefix_is_valid(const char *p) _pure_;
 bool unit_instance_is_valid(const char *i) _pure_;
-#if 0 /// UNNEEDED by elogind
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// UNNEEDED by elogind
 bool unit_suffix_is_valid(const char *s) _pure_;
 
 int unit_name_to_prefix(const char *n, char **ret);
@@ -32,7 +32,7 @@ int unit_name_to_prefix_and_instance(const char *n, char **ret);
 UnitType unit_name_to_type(const char *n) _pure_;
 
 int unit_name_change_suffix(const char *n, const char *suffix, char **ret);
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
 
 int unit_name_build(const char *prefix, const char *instance, const char *suffix, char **ret);
 int unit_name_build_from_type(const char *prefix, const char *instance, UnitType, char **ret);
diff --git a/src/login/logind-core.c b/src/login/logind-core.c
index 7807a49..63d2112 100644
--- a/src/login/logind-core.c
+++ b/src/login/logind-core.c
@@ -372,11 +372,11 @@ int manager_process_button_device(Manager *m, sd_device *d) {
 }
 
 int manager_get_session_by_pidref(Manager *m, const PidRef *pid, Session **ret) {
-#if 0 /// elogind does not support systemd units, but its own session system
+#if LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support systemd units, but its own session system
         _cleanup_free_ char *unit = NULL;
-#else // 0
+#else // LIBSYSTEMD_COMPATIBLE_CGROUPS
         _cleanup_free_ char *session_name = NULL;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         Session *s;
         int r;
 
@@ -385,13 +385,14 @@ int manager_get_session_by_pidref(Manager *m, const PidRef *pid, Session **ret)
         if (!pidref_is_set(pid))
                 return -EINVAL;
 
+
         s = hashmap_get(m->sessions_by_leader, pid);
         if (s) {
-                r = pidref_verify(pid);
-                if (r < 0)
-                        return r;
-        } else {
-#if 0 /// elogind does not support systemd units, but its own session system
+               r = pidref_verify(pid);
+               if (r < 0)
+                       return r;
+       } else  {
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support systemd units, but its own session system
                 r = cg_pidref_get_unit(pid, &unit);
                 if (r >= 0)
                         s = hashmap_get(m->session_units, unit);
@@ -404,7 +405,7 @@ int manager_get_session_by_pidref(Manager *m, const PidRef *pid, Session **ret)
 
                 log_debug_elogind("Session Name \"%s\" -> Session \"%s\"",
                                   strnull(session_name), s && s->id ? s->id : "(null)");
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         }
 
         if (ret)
diff --git a/src/login/logind-session.c b/src/login/logind-session.c
index 4a2cde9..b13ddb4 100644
--- a/src/login/logind-session.c
+++ b/src/login/logind-session.c
@@ -43,6 +43,9 @@
 #include "cgroup-setup.h"
 #include "extract-word.h"
 #include "musl_missing.h"
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+#include "special.h"
+#endif
 
 #define RELEASE_USEC (20*USEC_PER_SEC)
 
@@ -746,19 +749,25 @@ static int session_start_scope(Session *s, sd_bus_message *properties, sd_bus_er
 #else // 0
 static int session_start_cgroup(Session *s) {
         int r;
+        const char *path;
 
         assert(s);
         assert(s->user);
         assert(s->leader.pid > 0);
 
         /* First, create our own group */
-        r = cg_create(SYSTEMD_CGROUP_CONTROLLER, s->id);
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+        path = path_join(SPECIAL_USER_SLICE, s->user->slice, strjoin("session-", s->id, ".scope"));
+#else
+        path = s->id;
+#endif
+        r = cg_create(SYSTEMD_CGROUP_CONTROLLER, path);
         if (r < 0)
-                return log_error_errno(r, "Failed to create cgroup %s: %m", s->id);
+                return log_error_errno(r, "Failed to create cgroup %s: %m", path);
 
-        r = cg_attach(SYSTEMD_CGROUP_CONTROLLER, s->id, s->leader.pid);
+        r = cg_attach(SYSTEMD_CGROUP_CONTROLLER, path, s->leader.pid);
         if (r < 0)
-                log_warning_errno(r, "Failed to attach PID %d to cgroup %s: %m", s->leader.pid, s->id);
+                log_warning_errno(r, "Failed to attach PID %d to cgroup %s: %m", s->leader.pid, path);
 
         return 0;
 }
@@ -1464,6 +1473,9 @@ SessionState session_get_state(Session *s) {
 
 int session_kill(Session *s, KillWho who, int signo) {
         assert(s);
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS
+        const char *path;
+#endif
 
         switch (who) {
 
diff --git a/src/login/logind.h b/src/login/logind.h
index 5c4b1f1..8c83bd0 100644
--- a/src/login/logind.h
+++ b/src/login/logind.h
@@ -97,9 +97,9 @@ struct Manager {
         uint64_t session_counter;
         uint64_t inhibit_counter;
 
-#if 0 /// elogind does not support session units
+#ifdef LIBSYSTEMD_COMPATIBLE_CGROUPS /// elogind does not support session units
         Hashmap *session_units;
-#endif // 0
+#endif // LIBSYSTEMD_COMPATIBLE_CGROUPS
         Hashmap *user_units;
 
         usec_t inhibit_delay_max;