cgroup: add support for unified cgroup v2

add support for: opencontainers/runtime-spec#1040

Signed-off-by: Giuseppe Scrivano <[email protected]>

src/libcrun/cgroup.c

@@ -2828,6 +2828,26 @@ update_cgroup_v2_resources (runtime_spec_schema_config_linux_resources *resource
         return ret;
     }
 
+  /* Write unified resources if any.  They have higher precedence and override any previous setting.  */
+  if (resources->unified)
+    {
+      size_t i;
+
+      for (i = 0; i < resources->unified->len; i++)
+        {
+          size_t len;
+
+          if (strchr (resources->unified->keys[i], '/'))
+            return crun_make_error (err, 0, "key `%s` must be a file name without any slash", resources->unified->keys[i]);
+
+          len = strlen (resources->unified->values[i]);
+          ret = write_file_at (cgroup_dirfd, resources->unified->keys[i], resources->unified->values[i], len, err);
+          if (UNLIKELY (ret < 0))
+            return ret;
+        }
+
+    }
+
   return 0;
 }