core: wrap cgroup path with empty_to_root() in log messages

This fixes e.g. the following log message:
---
systemd[1]: -.slice: Failed to migrate controller cgroups from , ignoring: Read-only file system
---

(cherry picked from commit 6178e2f88956e1900f445908ed053865cc22e879)

3 files changed, 28 insertions, 27 deletions

diff --git a/src/core/bpf-devices.c b/src/core/bpf-devices.c
index 8a345a4498..4daa7f76b0 100644
--- a/src/core/bpf-devices.c
+++ b/src/core/bpf-devices.c
@@ -9,6 +9,7 @@
 #include "fileio.h"
 #include "nulstr-util.h"
 #include "parse-util.h"
+#include "path-util.h"
 #include "stat-util.h"
 #include "stdio-util.h"
 #include "string-util.h"
@@ -260,7 +261,7 @@ int bpf_devices_apply_policy(
         r = bpf_program_cgroup_attach(prog, BPF_CGROUP_DEVICE, controller_path, BPF_F_ALLOW_MULTI);
         if (r < 0)
                 return log_error_errno(r, "Attaching device control BPF program to cgroup %s failed: %m",
-                                       cgroup_path);
+                                       empty_to_root(cgroup_path));
 
  finish:
         /* Unref the old BPF program (which will implicitly detach it) right before attaching the new program. */
diff --git a/src/core/cgroup.c b/src/core/cgroup.c
index eab0929dc5..3a6f768c60 100644
--- a/src/core/cgroup.c
+++ b/src/core/cgroup.c
@@ -84,7 +84,7 @@ static int set_attribute_and_warn(Unit *u, const char *controller, const char *a
         r = cg_set_attribute(controller, u->cgroup_path, attribute, value);
         if (r < 0)
                 log_unit_full_errno(u, LOG_LEVEL_CGROUP_WRITE(r), r, "Failed to set '%s' attribute on '%s' to '%.*s': %m",
-                                    strna(attribute), isempty(u->cgroup_path) ? "/" : u->cgroup_path, (int) strcspn(value, NEWLINE), value);
+                                    strna(attribute), empty_to_root(u->cgroup_path), (int) strcspn(value, NEWLINE), value);
 
         return r;
 }
@@ -713,25 +713,25 @@ void cgroup_oomd_xattr_apply(Unit *u, const char *cgroup_path) {
         if (c->moom_preference == MANAGED_OOM_PREFERENCE_OMIT) {
                 r = cg_set_xattr(SYSTEMD_CGROUP_CONTROLLER, cgroup_path, "user.oomd_omit", "1", 1, 0);
                 if (r < 0)
-                        log_unit_debug_errno(u, r, "Failed to set oomd_omit flag on control group %s, ignoring: %m", cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to set oomd_omit flag on control group %s, ignoring: %m", empty_to_root(cgroup_path));
         }
 
         if (c->moom_preference == MANAGED_OOM_PREFERENCE_AVOID) {
                 r = cg_set_xattr(SYSTEMD_CGROUP_CONTROLLER, cgroup_path, "user.oomd_avoid", "1", 1, 0);
                 if (r < 0)
-                        log_unit_debug_errno(u, r, "Failed to set oomd_avoid flag on control group %s, ignoring: %m", cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to set oomd_avoid flag on control group %s, ignoring: %m", empty_to_root(cgroup_path));
         }
 
         if (c->moom_preference != MANAGED_OOM_PREFERENCE_AVOID) {
                 r = cg_remove_xattr(SYSTEMD_CGROUP_CONTROLLER, cgroup_path, "user.oomd_avoid");
                 if (r < 0 && r != -ENODATA)
-                        log_unit_debug_errno(u, r, "Failed to remove oomd_avoid flag on control group %s, ignoring: %m", cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to remove oomd_avoid flag on control group %s, ignoring: %m", empty_to_root(cgroup_path));
         }
 
         if (c->moom_preference != MANAGED_OOM_PREFERENCE_OMIT) {
                 r = cg_remove_xattr(SYSTEMD_CGROUP_CONTROLLER, cgroup_path, "user.oomd_omit");
                 if (r < 0 && r != -ENODATA)
-                        log_unit_debug_errno(u, r, "Failed to remove oomd_omit flag on control group %s, ignoring: %m", cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to remove oomd_omit flag on control group %s, ignoring: %m", empty_to_root(cgroup_path));
         }
 }
 
@@ -750,7 +750,7 @@ static void cgroup_xattr_apply(Unit *u) {
                                  sd_id128_to_string(u->invocation_id, ids), 32,
                                  0);
                 if (r < 0)
-                        log_unit_debug_errno(u, r, "Failed to set invocation ID on control group %s, ignoring: %m", u->cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to set invocation ID on control group %s, ignoring: %m", empty_to_root(u->cgroup_path));
         }
 
         if (unit_cgroup_delegate(u)) {
@@ -759,11 +759,11 @@ static void cgroup_xattr_apply(Unit *u) {
                                  "1", 1,
                                  0);
                 if (r < 0)
-                        log_unit_debug_errno(u, r, "Failed to set delegate flag on control group %s, ignoring: %m", u->cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to set delegate flag on control group %s, ignoring: %m", empty_to_root(u->cgroup_path));
         } else {
                 r = cg_remove_xattr(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, "trusted.delegate");
                 if (r < 0 && r != -ENODATA)
-                        log_unit_debug_errno(u, r, "Failed to remove delegate flag on control group %s, ignoring: %m", u->cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to remove delegate flag on control group %s, ignoring: %m", empty_to_root(u->cgroup_path));
         }
 
         cgroup_oomd_xattr_apply(u, u->cgroup_path);
@@ -1921,12 +1921,12 @@ int unit_watch_cgroup(Unit *u) {
                                       * is not an error */
                         return 0;
 
-                return log_unit_error_errno(u, errno, "Failed to add control inotify watch descriptor for control group %s: %m", u->cgroup_path);
+                return log_unit_error_errno(u, errno, "Failed to add control inotify watch descriptor for control group %s: %m", empty_to_root(u->cgroup_path));
         }
 
         r = hashmap_put(u->manager->cgroup_control_inotify_wd_unit, INT_TO_PTR(u->cgroup_control_inotify_wd), u);
         if (r < 0)
-                return log_unit_error_errno(u, r, "Failed to add control inotify watch descriptor to hash map: %m");
+                return log_unit_error_errno(u, r, "Failed to add control inotify watch descriptor for control group %s to hash map: %m", empty_to_root(u->cgroup_path));
 
         return 0;
 }
@@ -1984,12 +1984,12 @@ int unit_watch_cgroup_memory(Unit *u) {
                                       * is not an error */
                         return 0;
 
-                return log_unit_error_errno(u, errno, "Failed to add memory inotify watch descriptor for control group %s: %m", u->cgroup_path);
+                return log_unit_error_errno(u, errno, "Failed to add memory inotify watch descriptor for control group %s: %m", empty_to_root(u->cgroup_path));
         }
 
         r = hashmap_put(u->manager->cgroup_memory_inotify_wd_unit, INT_TO_PTR(u->cgroup_memory_inotify_wd), u);
         if (r < 0)
-                return log_unit_error_errno(u, r, "Failed to add memory inotify watch descriptor to hash map: %m");
+                return log_unit_error_errno(u, r, "Failed to add memory inotify watch descriptor for control group %s to hash map: %m", empty_to_root(u->cgroup_path));
 
         return 0;
 }
@@ -2012,9 +2012,9 @@ int unit_pick_cgroup_path(Unit *u) {
 
         r = unit_set_cgroup_path(u, path);
         if (r == -EEXIST)
-                return log_unit_error_errno(u, r, "Control group %s exists already.", path);
+                return log_unit_error_errno(u, r, "Control group %s exists already.", empty_to_root(path));
         if (r < 0)
-                return log_unit_error_errno(u, r, "Failed to set unit's control group path to %s: %m", path);
+                return log_unit_error_errno(u, r, "Failed to set unit's control group path to %s: %m", empty_to_root(path));
 
         return 0;
 }
@@ -2042,7 +2042,7 @@ static int unit_update_cgroup(
         /* First, create our own group */
         r = cg_create_everywhere(u->manager->cgroup_supported, target_mask, u->cgroup_path);
         if (r < 0)
-                return log_unit_error_errno(u, r, "Failed to create cgroup %s: %m", u->cgroup_path);
+                return log_unit_error_errno(u, r, "Failed to create cgroup %s: %m", empty_to_root(u->cgroup_path));
         created = r;
 
         /* Start watching it */
@@ -2058,7 +2058,7 @@ static int unit_update_cgroup(
                 /* Enable all controllers we need */
                 r = cg_enable_everywhere(u->manager->cgroup_supported, enable_mask, u->cgroup_path, &result_mask);
                 if (r < 0)
-                        log_unit_warning_errno(u, r, "Failed to enable/disable controllers on cgroup %s, ignoring: %m", u->cgroup_path);
+                        log_unit_warning_errno(u, r, "Failed to enable/disable controllers on cgroup %s, ignoring: %m", empty_to_root(u->cgroup_path));
 
                 /* Remember what's actually enabled now */
                 u->cgroup_enabled_mask = result_mask;
@@ -2080,12 +2080,12 @@ static int unit_update_cgroup(
         if (cg_all_unified() == 0) {
                 r = cg_migrate_v1_controllers(u->manager->cgroup_supported, migrate_mask, u->cgroup_path, migrate_callback, u);
                 if (r < 0)
-                        log_unit_warning_errno(u, r, "Failed to migrate controller cgroups from %s, ignoring: %m", u->cgroup_path);
+                        log_unit_warning_errno(u, r, "Failed to migrate controller cgroups from %s, ignoring: %m", empty_to_root(u->cgroup_path));
 
                 is_root_slice = unit_has_name(u, SPECIAL_ROOT_SLICE);
                 r = cg_trim_v1_controllers(u->manager->cgroup_supported, ~target_mask, u->cgroup_path, !is_root_slice);
                 if (r < 0)
-                        log_unit_warning_errno(u, r, "Failed to delete controller cgroups %s, ignoring: %m", u->cgroup_path);
+                        log_unit_warning_errno(u, r, "Failed to delete controller cgroups %s, ignoring: %m", empty_to_root(u->cgroup_path));
         }
 
         /* Set attributes */
@@ -2175,7 +2175,7 @@ int unit_attach_pids_to_cgroup(Unit *u, Set *pids, const char *suffix_path) {
 
                         log_unit_full_errno(u, again ? LOG_DEBUG : LOG_INFO,  q,
                                             "Couldn't move process "PID_FMT" to%s requested cgroup '%s': %m",
-                                            pid, again ? " directly" : "", p);
+                                            pid, again ? " directly" : "", empty_to_root(p));
 
                         if (again) {
                                 int z;
@@ -2187,7 +2187,7 @@ int unit_attach_pids_to_cgroup(Unit *u, Set *pids, const char *suffix_path) {
 
                                 z = unit_attach_pid_to_cgroup_via_bus(u, pid, suffix_path);
                                 if (z < 0)
-                                        log_unit_info_errno(u, z, "Couldn't move process "PID_FMT" to requested cgroup '%s' (directly or via the system bus): %m", pid, p);
+                                        log_unit_info_errno(u, z, "Couldn't move process "PID_FMT" to requested cgroup '%s' (directly or via the system bus): %m", pid, empty_to_root(p));
                                 else
                                         continue; /* When the bus thing worked via the bus we are fully done for this PID. */
                         }
@@ -2221,7 +2221,7 @@ int unit_attach_pids_to_cgroup(Unit *u, Set *pids, const char *suffix_path) {
                                         continue; /* Success! */
 
                                 log_unit_debug_errno(u, q, "Failed to attach PID " PID_FMT " to requested cgroup %s in controller %s, falling back to unit's cgroup: %m",
-                                                     pid, p, cgroup_controller_to_string(c));
+                                                     pid, empty_to_root(p), cgroup_controller_to_string(c));
                         }
 
                         /* So this controller is either not delegate or realized, or something else weird happened. In
@@ -2656,7 +2656,7 @@ void unit_prune_cgroup(Unit *u) {
                  * the containing slice is stopped. So even if we failed now, this unit shouldn't assume
                  * that the cgroup is still realized the next time it is started. Do not return early
                  * on error, continue cleanup. */
-                log_unit_full_errno(u, r == -EBUSY ? LOG_DEBUG : LOG_WARNING, r, "Failed to destroy cgroup %s, ignoring: %m", u->cgroup_path);
+                log_unit_full_errno(u, r == -EBUSY ? LOG_DEBUG : LOG_WARNING, r, "Failed to destroy cgroup %s, ignoring: %m", empty_to_root(u->cgroup_path));
 
         if (is_root_slice)
                 return;
@@ -2869,7 +2869,7 @@ void unit_add_to_cgroup_empty_queue(Unit *u) {
 
         r = cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path);
         if (r < 0) {
-                log_unit_debug_errno(u, r, "Failed to determine whether cgroup %s is empty: %m", u->cgroup_path);
+                log_unit_debug_errno(u, r, "Failed to determine whether cgroup %s is empty: %m", empty_to_root(u->cgroup_path));
                 return;
         }
         if (r == 0)
diff --git a/src/core/unit.c b/src/core/unit.c
index 30afd5a776..47966bcf0d 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -427,7 +427,7 @@ bool unit_may_gc(Unit *u) {
 
                 r = cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path);
                 if (r < 0)
-                        log_unit_debug_errno(u, r, "Failed to determine whether cgroup %s is empty: %m", u->cgroup_path);
+                        log_unit_debug_errno(u, r, "Failed to determine whether cgroup %s is empty: %m", empty_to_root(u->cgroup_path));
                 if (r <= 0)
                         return false;
         }
@@ -4553,7 +4553,7 @@ int unit_kill_context(
                                       log_func, u);
                 if (r < 0) {
                         if (!IN_SET(r, -EAGAIN, -ESRCH, -ENOENT))
-                                log_unit_warning_errno(u, r, "Failed to kill control group %s, ignoring: %m", u->cgroup_path);
+                                log_unit_warning_errno(u, r, "Failed to kill control group %s, ignoring: %m", empty_to_root(u->cgroup_path));
 
                 } else if (r > 0) {
 
@@ -5011,7 +5011,7 @@ int unit_fork_helper_process(Unit *u, const char *name, pid_t *ret) {
         if (u->cgroup_path) {
                 r = cg_attach_everywhere(u->manager->cgroup_supported, u->cgroup_path, 0, NULL, NULL);
                 if (r < 0) {
-                        log_unit_error_errno(u, r, "Failed to join unit cgroup %s: %m", u->cgroup_path);
+                        log_unit_error_errno(u, r, "Failed to join unit cgroup %s: %m", empty_to_root(u->cgroup_path));
                         _exit(EXIT_CGROUP);
                 }
         }