+ struct cgroupfs_root *root = cgrp->root;
+ struct list_head *l = &init_css_set.list;
+
+ /* Built the set of subsystem state objects that we want to
+ * see in the new css_set */
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ if (root->subsys_bits & (1ull << i)) {
+ /* Subsystem is in this hierarchy. So we want
+ * the subsystem state from the new
+ * cgroup */
+ template[i] = cgrp->subsys[i];
+ } else {
+ /* Subsystem is not in this hierarchy, so we
+ * don't want to change the subsystem state */
+ template[i] = oldcg->subsys[i];
+ }
+ }
+
+ /* Look through existing cgroup groups to find one to reuse */
+ do {
+ struct css_set *cg =
+ list_entry(l, struct css_set, list);
+
+ if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
+ /* All subsystems matched */
+ return cg;
+ }
+ /* Try the next cgroup group */
+ l = l->next;
+ } while (l != &init_css_set.list);
+
+ /* No existing cgroup group matched */
+ return NULL;
+}
+
+/*
+ * allocate_cg_links() allocates "count" cg_cgroup_link structures
+ * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
+ * success or a negative error
+ */
+
+static int allocate_cg_links(int count, struct list_head *tmp)
+{
+ struct cg_cgroup_link *link;
+ int i;
+ INIT_LIST_HEAD(tmp);
+ for (i = 0; i < count; i++) {
+ link = kmalloc(sizeof(*link), GFP_KERNEL);
+ if (!link) {
+ while (!list_empty(tmp)) {
+ link = list_entry(tmp->next,
+ struct cg_cgroup_link,
+ cgrp_link_list);
+ list_del(&link->cgrp_link_list);
+ kfree(link);
+ }
+ return -ENOMEM;
+ }
+ list_add(&link->cgrp_link_list, tmp);
+ }
+ return 0;
+}
+
+static void free_cg_links(struct list_head *tmp)
+{
+ while (!list_empty(tmp)) {
+ struct cg_cgroup_link *link;
+ link = list_entry(tmp->next,
+ struct cg_cgroup_link,
+ cgrp_link_list);
+ list_del(&link->cgrp_link_list);
+ kfree(link);
+ }
+}
+
+/*
+ * find_css_set() takes an existing cgroup group and a
+ * cgroup object, and returns a css_set object that's
+ * equivalent to the old group, but with the given cgroup
+ * substituted into the appropriate hierarchy. Must be called with
+ * cgroup_mutex held
+ */
+
+static struct css_set *find_css_set(
+ struct css_set *oldcg, struct cgroup *cgrp)
+{
+ struct css_set *res;
+ struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+ int i;
+
+ struct list_head tmp_cg_links;
+ struct cg_cgroup_link *link;
+
+ /* First see if we already have a cgroup group that matches
+ * the desired set */
+ write_lock(&css_set_lock);
+ res = find_existing_css_set(oldcg, cgrp, template);
+ if (res)
+ get_css_set(res);
+ write_unlock(&css_set_lock);
+
+ if (res)
+ return res;
+
+ res = kmalloc(sizeof(*res), GFP_KERNEL);
+ if (!res)
+ return NULL;
+
+ /* Allocate all the cg_cgroup_link objects that we'll need */
+ if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
+ kfree(res);
+ return NULL;
+ }
+
+ kref_init(&res->ref);
+ INIT_LIST_HEAD(&res->cg_links);
+ INIT_LIST_HEAD(&res->tasks);
+
+ /* Copy the set of subsystem state objects generated in
+ * find_existing_css_set() */
+ memcpy(res->subsys, template, sizeof(res->subsys));
+
+ write_lock(&css_set_lock);
+ /* Add reference counts and links from the new css_set. */
+ for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+ struct cgroup *cgrp = res->subsys[i]->cgroup;
+ struct cgroup_subsys *ss = subsys[i];
+ atomic_inc(&cgrp->count);
+ /*
+ * We want to add a link once per cgroup, so we
+ * only do it for the first subsystem in each
+ * hierarchy
+ */
+ if (ss->root->subsys_list.next == &ss->sibling) {
+ BUG_ON(list_empty(&tmp_cg_links));
+ link = list_entry(tmp_cg_links.next,
+ struct cg_cgroup_link,
+ cgrp_link_list);
+ list_del(&link->cgrp_link_list);
+ list_add(&link->cgrp_link_list, &cgrp->css_sets);
+ link->cg = res;
+ list_add(&link->cg_link_list, &res->cg_links);
+ }
+ }
+ if (list_empty(&rootnode.subsys_list)) {
+ link = list_entry(tmp_cg_links.next,
+ struct cg_cgroup_link,
+ cgrp_link_list);
+ list_del(&link->cgrp_link_list);
+ list_add(&link->cgrp_link_list, &dummytop->css_sets);
+ link->cg = res;
+ list_add(&link->cg_link_list, &res->cg_links);
+ }
+
+ BUG_ON(!list_empty(&tmp_cg_links));
+
+ /* Link this cgroup group into the list */
+ list_add(&res->list, &init_css_set.list);
+ css_set_count++;
+ INIT_LIST_HEAD(&res->tasks);
+ write_unlock(&css_set_lock);
+
+ return res;