bus-control: Fix cgroup handling

On systems without properly setup systemd, cg_get_root_path returns
-ENOENT.  This means that busctl doesn't display much information.

busctl monitor also fails whenever it intercepts messages.

This fix fakes creates a fake "/" root cgroup which lets busctl work
on such systems.

4 files changed, 26 insertions, 10 deletions

diff --git a/src/libsystemd/sd-bus/bus-control.c b/src/libsystemd/sd-bus/bus-control.c
index 076bbce6b1..ad372f6772 100644
--- a/src/libsystemd/sd-bus/bus-control.c
+++ b/src/libsystemd/sd-bus/bus-control.c
@@ -495,11 +495,9 @@ static int bus_get_owner_kdbus(
                                         goto fail;
                                 }
 
-                                if (!bus->cgroup_root) {
-                                        r = cg_get_root_path(&bus->cgroup_root);
-                                        if (r < 0)
-                                                goto fail;
-                                }
+                                r = bus_get_root_path(bus);
+                                if (r < 0)
+                                        goto fail;
 
                                 c->cgroup_root = strdup(bus->cgroup_root);
                                 if (!c->cgroup_root) {
diff --git a/src/libsystemd/sd-bus/bus-internal.h b/src/libsystemd/sd-bus/bus-internal.h
index f2ccdfd177..601ea5afb1 100644
--- a/src/libsystemd/sd-bus/bus-internal.h
+++ b/src/libsystemd/sd-bus/bus-internal.h
@@ -383,3 +383,5 @@ int bus_set_address_system_remote(sd_bus *b, const char *host);
 int bus_set_address_system_container(sd_bus *b, const char *machine);
 
 int bus_remove_match_by_string(sd_bus *bus, const char *match, sd_bus_message_handler_t callback, void *userdata);
+
+int bus_get_root_path(sd_bus *bus);
diff --git a/src/libsystemd/sd-bus/bus-kernel.c b/src/libsystemd/sd-bus/bus-kernel.c
index d384f846b9..3ca271c704 100644
--- a/src/libsystemd/sd-bus/bus-kernel.c
+++ b/src/libsystemd/sd-bus/bus-kernel.c
@@ -542,11 +542,9 @@ static int bus_kernel_make_message(sd_bus *bus, struct kdbus_msg *k) {
                         m->creds.cgroup = d->str;
                         m->creds.mask |= (SD_BUS_CREDS_CGROUP|SD_BUS_CREDS_UNIT|SD_BUS_CREDS_USER_UNIT|SD_BUS_CREDS_SLICE|SD_BUS_CREDS_SESSION|SD_BUS_CREDS_OWNER_UID) & bus->creds_mask;
 
-                        if (!bus->cgroup_root) {
-                                r = cg_get_root_path(&bus->cgroup_root);
-                                if (r < 0)
-                                        goto fail;
-                        }
+                        r = bus_get_root_path(bus);
+                        if (r < 0)
+                                goto fail;
 
                         m->creds.cgroup_root = bus->cgroup_root;
 
diff --git a/src/libsystemd/sd-bus/sd-bus.c b/src/libsystemd/sd-bus/sd-bus.c
index 83233fd7e6..a204d67590 100644
--- a/src/libsystemd/sd-bus/sd-bus.c
+++ b/src/libsystemd/sd-bus/sd-bus.c
@@ -3358,3 +3358,21 @@ _public_ int sd_bus_get_name(sd_bus *bus, const char **name) {
         *name = bus->connection_name;
         return 0;
 }
+
+int bus_get_root_path(sd_bus *bus) {
+        int r;
+
+        if (bus->cgroup_root)
+                return 0;
+
+        r = cg_get_root_path(&bus->cgroup_root);
+        if (r == -ENOENT) {
+                bus->cgroup_root = strdup("/");
+                if (!bus->cgroup_root)
+                        return -ENOMEM;
+
+                r = 0;
+        }
+
+        return r;
+}