systemd-nspawn: Clarify detect_unified_cgroup_hierarchy().

3 files changed, 34 insertions, 12 deletions

diff --git a/src/libsystemd-basic/include/systemd-basic/cgroup-util.h b/src/libsystemd-basic/include/systemd-basic/cgroup-util.h
index 0aa27c4cd7..d730f3490c 100644
--- a/src/libsystemd-basic/include/systemd-basic/cgroup-util.h
+++ b/src/libsystemd-basic/include/systemd-basic/cgroup-util.h
@@ -242,6 +242,7 @@ bool cg_ns_supported(void);
 
 int cg_all_unified(void);
 int cg_unified(const char *controller);
+int cg_version(CGroupUnified *ver);
 void cg_unified_flush(void);
 
 bool cg_is_unified_wanted(void);
diff --git a/src/libsystemd-basic/src/cgroup-util.c b/src/libsystemd-basic/src/cgroup-util.c
index cf9c682599..929101e558 100644
--- a/src/libsystemd-basic/src/cgroup-util.c
+++ b/src/libsystemd-basic/src/cgroup-util.c
@@ -2311,6 +2311,17 @@ int cg_all_unified(void) {
         return cg_unified(NULL);
 }
 
+int cg_version(CGroupUnified *ver) {
+        int r;
+
+        r = cg_update_unified();
+        if (r < 0)
+                return r;
+
+        *ver = unified_cache;
+        return 0;
+}
+
 void cg_unified_flush(void) {
         unified_cache = CGROUP_UNIFIED_UNKNOWN;
 }
diff --git a/src/systemd-nspawn/nspawn.c b/src/systemd-nspawn/nspawn.c
index 5f5e21c0f4..7c9b32fbc2 100644
--- a/src/systemd-nspawn/nspawn.c
+++ b/src/systemd-nspawn/nspawn.c
@@ -323,7 +323,8 @@ static int custom_mounts_prepare(void) {
 
 static int detect_unified_cgroup_hierarchy(const char *directory) {
         const char *e;
-        int r, all_unified, systemd_unified;
+        int r;
+        CGroupUnified outer;
 
         /* Allow the user to control whether the unified hierarchy is used */
         e = getenv("UNIFIED_CGROUP_HIERARCHY");
@@ -339,16 +340,24 @@ static int detect_unified_cgroup_hierarchy(const char *directory) {
                 return 0;
         }
 
-        all_unified = cg_all_unified();
-        systemd_unified = cg_unified(SYSTEMD_CGROUP_CONTROLLER);
-
-        if (all_unified < 0 || systemd_unified < 0)
+        r = cg_version(&outer);
+        if (r < 0)
                 return log_error_errno(r, "Failed to decide cgroup version to use: Failed to determine what the host system uses: %m");
 
-        /* Otherwise inherit the default from the host system */
-        if (all_unified > 0) {
-                /* Unified cgroup hierarchy support was added in 230. Unfortunately the detection
-                 * routine only detects 231, so we'll have a false negative here for 230. */
+        /* Otherwise inherit the default from the host system, unless
+         * the container doesn't have a new enough systemd (detected
+         * by checking libsystemd-shared). */
+        switch (outer) {
+        case CGROUP_UNIFIED_UNKNOWN:
+                assert_not_reached("Unknown host cgroup version");
+                break;
+        case CGROUP_UNIFIED_NONE: /* cgroup v1 */
+                arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_NONE;
+                break;
+        case CGROUP_UNIFIED_ALL: /* cgroup v2 */
+                /* Unified cgroup hierarchy support was added in 230. Unfortunately libsystemd-shared,
+                 * which we use to sniff the systemd version, was only added in 231, so we'll have a
+                 * false negative here for 230. */
                 r = systemd_installation_has_version(directory, 230);
                 if (r < 0)
                         return log_error_errno(r, "Failed to decide cgroup version to use: Failed to determine systemd version in container: %m");
@@ -356,7 +365,8 @@ static int detect_unified_cgroup_hierarchy(const char *directory) {
                         arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_ALL;
                 else
                         arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_NONE;
-        } else if (systemd_unified > 0) {
+                break;
+        case CGROUP_UNIFIED_SYSTEMD: /* cgroup v1 & v2 mixed; but v2 for systemd */
                 /* Mixed cgroup hierarchy support was added in 232 */
                 r = systemd_installation_has_version(directory, 232);
                 if (r < 0)
@@ -365,8 +375,8 @@ static int detect_unified_cgroup_hierarchy(const char *directory) {
                         arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_SYSTEMD;
                 else
                         arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_NONE;
-        } else
-                arg_unified_cgroup_hierarchy = CGROUP_UNIFIED_NONE;
+                break;
+        }
 
         return 0;
 }