split on-disk cgroup validation from parent name generation

Split cgroup_find_parent cgroup/parent on-disk validation from cgroup parent
name generation.  This solves a chicken-and-egg problem for callers that need
to obtain a parent name from a cgroup that has not yet been created, such as
cgroup_create_cgroup_from_parent().  The new function enforces the documented
behavior (return NULL) when a "root" cgroup is specified.

Modify cgroup_create_cgroup_from_parent() to use this new function, and clean up
a few possibly-erroneous return values.

Signed-off-by: Eric Brower <ebrower@gmail.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Dhaval Giani <dhaval.giani@gmail.com>

diff --git a/src/api.c b/src/api.c
index c8332f98f7bf4e6758bce817059ad44dfb688284..5092ac96b27ad6decae93c542b2b633141c8fd33 100644 (file)
--- a/src/api.c
+++ b/src/api.c
@@ -1434,9 +1434,57 @@ err:
        return error;
 }
 
+/**
+ * Obtain the calculated parent name of specified cgroup; no validation
+ * of the existence of the child or parent group is performed.
+ *
+ * Given the path-like hierarchy of cgroup names, this function returns
+ * the dirname() of the cgroup name as the likely parent name; the caller
+ * is responsible for validating parent as appropriate.
+ *
+ * @param cgroup The cgroup to query for parent's name
+ * @param parent Output, name of parent's group, or NULL if the
+ *     provided cgroup is the root group.
+ *     Caller is responsible to free the returned string.
+ * @return 0 on success, > 0 on error
+ */
+static int cgroup_get_parent_name(struct cgroup *cgroup, char **parent)
+{
+       int ret = 0;
+       char *dir = NULL;
+       char *pdir = NULL;
+
+       dir = strdup(cgroup->name);
+       if (!dir) {
+               return ECGFAIL;
+       }
+       cgroup_dbg("group name is %s\n", dir);
+
+       pdir = dirname(dir);
+       cgroup_dbg("parent's group name is %s\n", pdir);
+
+       /* check for root group */
+       if (strlen(cgroup->name) == 0 || !strcmp(cgroup->name, pdir)) {
+               cgroup_dbg("specified cgroup \"%s\" is root group\n",
+                       cgroup->name);
+               *parent = NULL;
+       }
+       else {
+               *parent = strdup(pdir);
+       }
+       free(dir);
+
+       if (*parent == NULL)
+               ret = ECGFAIL;
+
+       return ret;
+}
+
 /**
  * Find the parent of the specified directory. It returns the parent (the
- * parent is usually name/.. unless name is a mount point.
+ * parent is usually name/.. unless name is a mount point.  It is assumed
+ * both the cgroup (and, therefore, parent) already exist, and will fail
+ * otherwise.
  *
  * @param cgroup The cgroup
  * @param parent Output, name of parent's group (if the group has parent) or
@@ -1450,7 +1498,6 @@ static int cgroup_find_parent(struct cgroup *cgroup, char **parent)
        char *parent_path = NULL;
        struct stat stat_child, stat_parent;
        char *controller = NULL;
-       char *dir = NULL, *parent_dir = NULL;
        int ret = 0;
 
        *parent = NULL;
@@ -1490,20 +1537,7 @@ static int cgroup_find_parent(struct cgroup *cgroup, char **parent)
                ret = 0;
                cgroup_dbg("Parent is on different device\n");
        } else {
-               dir = strdup(cgroup->name);
-               cgroup_dbg("group name is %s\n", dir);
-               if (!dir) {
-                       ret = ECGFAIL;
-                       goto free_parent;
-               }
-
-               parent_dir = dirname(dir);
-               cgroup_dbg("parent's group name is %s\n", parent_dir);
-               *parent = strdup(parent_dir);
-               free(dir);
-
-               if (*parent == NULL)
-                       ret = ECGFAIL;
+               ret = cgroup_get_parent_name(cgroup, parent);
        }
 
 free_parent:
@@ -1529,7 +1563,7 @@ int cgroup_create_cgroup_from_parent(struct cgroup *cgroup,
        if (!cgroup_initialized)
                return ECGROUPNOTINITIALIZED;
 
-       ret = cgroup_find_parent(cgroup, &parent);
+       ret = cgroup_get_parent_name(cgroup, &parent);
        if (ret)
                return ret;
 
@@ -1543,16 +1577,21 @@ int cgroup_create_cgroup_from_parent(struct cgroup *cgroup,
 
        cgroup_dbg("parent is %s\n", parent);
        parent_cgroup = cgroup_new_cgroup(parent);
-       if (!parent_cgroup)
+       if (!parent_cgroup) {
+               ret = ECGFAIL;
                goto err_nomem;
+       }
 
-       if (cgroup_get_cgroup(parent_cgroup))
+       if (cgroup_get_cgroup(parent_cgroup)) {
+               ret = ECGFAIL;
                goto err_parent;
+       }
 
        cgroup_dbg("got parent group for %s\n", parent_cgroup->name);
        ret = cgroup_copy_cgroup(cgroup, parent_cgroup);
-       if (ret)
+       if (ret) {
                goto err_parent;
+       }
 
        cgroup_dbg("copied parent group %s to %s\n", parent_cgroup->name,
                                                        cgroup->name);