core/mount-setup: if unified hierarchy is not supported, fall back to legacy

We need this to gracefully support older or strangely configured kernels.

v2:
- do not install a callback handler, just embed the right conditions into
  cg_is_*_wanted()

v3:
- fix bug in cg_is_legacy_wanted()

diff --git a/src/basic/cgroup-util.c b/src/basic/cgroup-util.c
index ad412235347b6376dc9336c31e6505236a460dc4..0079ff9a49d1f936ac94674c7202d7a6df8601ba 100644 (file)
--- a/src/basic/cgroup-util.c
+++ b/src/basic/cgroup-util.c
@@ -2495,7 +2495,14 @@ bool cg_is_unified_wanted(void) {
 }
 
 bool cg_is_legacy_wanted(void) {
-        return !cg_is_unified_wanted();
+        /* Check if we have cgroups2 already mounted. */
+        if (cg_unified_flush() >= 0 &&
+            unified_cache == CGROUP_UNIFIED_ALL)
+                return false;
+
+        /* Otherwise, assume that at least partial legacy is wanted,
+         * since cgroups2 should already be mounted at this point. */
+        return true;
 }
 
 bool cg_is_hybrid_wanted(void) {
@@ -2504,11 +2511,6 @@ bool cg_is_hybrid_wanted(void) {
         bool b;
         const bool is_default = DEFAULT_HIERARCHY == CGROUP_UNIFIED_SYSTEMD;
 
-        /* If the unified hierarchy is requested in full, no need to
-         * bother with this. */
-        if (cg_is_unified_wanted())
-                return 0;
-
         /* If the hierarchy is already mounted, then follow whatever
          * was chosen for it. */
         if (cg_unified_flush() >= 0)

diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index 694a03cc84c267b73d9b7366aee3b5a77659941a..d8140bea903e5d3aac8b0f150621112406cc1b18 100644 (file)
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -100,7 +100,7 @@ static const MountPoint mount_table[] = {
         { "tmpfs",       "/run",                      "tmpfs",      "mode=755",                MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
         { "cgroup",      "/sys/fs/cgroup",            "cgroup2",    NULL,                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
-          cg_is_unified_wanted, MNT_FATAL|MNT_IN_CONTAINER },
+          cg_is_unified_wanted, MNT_IN_CONTAINER },
 #endif // 0
         { "tmpfs",       "/sys/fs/cgroup",            "tmpfs",      "mode=755",                MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
           cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
@@ -114,10 +114,9 @@ static const MountPoint mount_table[] = {
         { "cgroup",      "/sys/fs/cgroup/elogind",    "cgroup",     "none,name=elogind,xattr", MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_legacy_wanted, MNT_IN_CONTAINER  },
         { "cgroup",      "/sys/fs/cgroup/elogind",    "cgroup",     "none,name=elogind",       MS_NOSUID|MS_NOEXEC|MS_NODEV,
-          cg_is_legacy_wanted, MNT_IN_CONTAINER  },
 #endif // 0
+          cg_is_legacy_wanted, MNT_IN_CONTAINER  },
 #if 0 /// UNNEEDED by elogind
-          cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
         { "pstore",      "/sys/fs/pstore",            "pstore",     NULL,                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_NONE                   },
 #ifdef ENABLE_EFI