cgroup: bring some sanity to naming around cg_cgroup_link

cgroups and css_sets are mapped M:N and this M:N mapping is
represented by struct cg_cgroup_link which forms linked lists on both
sides.  The naming around this mapping is already confusing and struct
cg_cgroup_link exacerbates the situation quite a bit.

>From cgroup side, it starts off ->css_sets and runs through
->cgrp_link_list.  From css_set side, it starts off ->cg_links and
runs through ->cg_link_list.  This is rather reversed as
cgrp_link_list is used to iterate css_sets and cg_link_list cgroups.
Also, this is the only place which is still using the confusing "cg"
for css_sets.  This patch cleans it up a bit.

* s/cgroup->css_sets/cgroup->cset_links/
  s/css_set->cg_links/css_set->cgrp_links/
  s/cgroup_iter->cg_link/cgroup_iter->cset_link/

* s/cg_cgroup_link/cgrp_cset_link/

* s/cgrp_cset_link->cg/cgrp_cset_link->cset/
  s/cgrp_cset_link->cgrp_link_list/cgrp_cset_link->cset_link/
  s/cgrp_cset_link->cg_link_list/cgrp_cset_link->cgrp_link/

* s/init_css_set_link/init_cgrp_cset_link/
  s/free_cg_links/free_cgrp_cset_links/
  s/allocate_cg_links/allocate_cgrp_cset_links/

* s/cgl[12]/link[12]/ in compare_css_sets()

* s/saved_link/tmp_link/ s/tmp/tmp_links/ and a couple similar
  adustments.

* Comment and whiteline adjustments.

After the changes, we have

	list_for_each_entry(link, &cont->cset_links, cset_link) {
		struct css_set *cset = link->cset;

instead of

	list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
		struct css_set *cset = link->cg;

This patch is purely cosmetic.

v2: Fix broken sentences in the patch description.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

include/linux/cgroup.h

@@ -215,10 +215,10 @@ struct cgroup {
 	struct cgroupfs_root *root;
 
 	/*
-	 * List of cg_cgroup_links pointing at css_sets with
-	 * tasks in this cgroup. Protected by css_set_lock
+	 * List of cgrp_cset_links pointing at css_sets with tasks in this
+	 * cgroup.  Protected by css_set_lock.
 	 */
-	struct list_head css_sets;
+	struct list_head cset_links;
 
 	struct list_head allcg_node;	/* cgroupfs_root->allcg_list */
 	struct list_head cft_q_node;	/* used during cftype add/rm */
@@ -365,11 +365,10 @@ struct css_set {
 	struct list_head tasks;
 
 	/*
-	 * List of cg_cgroup_link objects on link chains from
-	 * cgroups referenced from this css_set. Protected by
-	 * css_set_lock
+	 * List of cgrp_cset_links pointing at cgroups referenced from this
+	 * css_set.  Protected by css_set_lock.
 	 */
-	struct list_head cg_links;
+	struct list_head cgrp_links;
 
 	/*
 	 * Set of subsystem states, one for each subsystem. This array
@@ -792,7 +791,7 @@ struct cgroup *cgroup_next_descendant_post(struct cgroup *pos,
 
 /* A cgroup_iter should be treated as an opaque object */
 struct cgroup_iter {
-	struct list_head *cg_link;
+	struct list_head *cset_link;
 	struct list_head *task;
 };