cgroup: implement cgroup_rm_cftypes()

Implement cgroup_rm_cftypes() which removes an array of cftypes from a
subsystem.  It can be called whether the target subsys is attached or
not.  cgroup core will remove the specified file from all existing
cgroups.

This will be used to improve sub-subsys modularity and will be helpful
for unified hierarchy.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 44 insertions, 10 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7d5d1c927d9d..21bba7722350 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2690,17 +2690,20 @@ out:
         return error;
 }
 
-static int cgroup_add_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
-                            const struct cftype cfts[])
+static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
+                              const struct cftype cfts[], bool is_add)
 {
         const struct cftype *cft;
         int err, ret = 0;
 
         for (cft = cfts; cft->name[0] != '\0'; cft++) {
-                err = cgroup_add_file(cgrp, subsys, cft);
+                if (is_add)
+                        err = cgroup_add_file(cgrp, subsys, cft);
+                else
+                        err = cgroup_rm_file(cgrp, cft);
                 if (err) {
-                        pr_warning("cgroup_add_files: failed to create %s, err=%d\n",
-                                   cft->name, err);
+                        pr_warning("cgroup_addrm_files: failed to %s %s, err=%d\n",
+                                   is_add ? "add" : "remove", cft->name, err);
                         ret = err;
                 }
         }
@@ -2724,7 +2727,7 @@ static void cgroup_cfts_prepare(void)
 }
 
 static void cgroup_cfts_commit(struct cgroup_subsys *ss,
-                               const struct cftype *cfts)
+                               const struct cftype *cfts, bool is_add)
         __releases(&cgroup_mutex) __releases(&cgroup_cft_mutex)
 {
         LIST_HEAD(pending);
@@ -2750,7 +2753,7 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
                 mutex_lock(&inode->i_mutex);
                 mutex_lock(&cgroup_mutex);
                 if (!cgroup_is_removed(cgrp))
-                        cgroup_add_files(cgrp, ss, cfts);
+                        cgroup_addrm_files(cgrp, ss, cfts, is_add);
                 mutex_unlock(&cgroup_mutex);
                 mutex_unlock(&inode->i_mutex);
 
@@ -2786,13 +2789,44 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
         cgroup_cfts_prepare();
         set->cfts = cfts;
         list_add_tail(&set->node, &ss->cftsets);
-        cgroup_cfts_commit(ss, cfts);
+        cgroup_cfts_commit(ss, cfts, true);
 
         return 0;
 }
 EXPORT_SYMBOL_GPL(cgroup_add_cftypes);
 
 /**
+ * cgroup_rm_cftypes - remove an array of cftypes from a subsystem
+ * @ss: target cgroup subsystem
+ * @cfts: zero-length name terminated array of cftypes
+ *
+ * Unregister @cfts from @ss.  Files described by @cfts are removed from
+ * all existing cgroups to which @ss is attached and all future cgroups
+ * won't have them either.  This function can be called anytime whether @ss
+ * is attached or not.
+ *
+ * Returns 0 on successful unregistration, -ENOENT if @cfts is not
+ * registered with @ss.
+ */
+int cgroup_rm_cftypes(struct cgroup_subsys *ss, const struct cftype *cfts)
+{
+        struct cftype_set *set;
+
+        cgroup_cfts_prepare();
+
+        list_for_each_entry(set, &ss->cftsets, node) {
+                if (set->cfts == cfts) {
+                        list_del_init(&set->node);
+                        cgroup_cfts_commit(ss, cfts, false);
+                        return 0;
+                }
+        }
+
+        cgroup_cfts_commit(ss, NULL, false);
+        return -ENOENT;
+}
+
+/**
  * cgroup_task_count - count the number of tasks in a cgroup.
  * @cgrp: the cgroup in question
  *
@@ -3784,7 +3818,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
         int err;
         struct cgroup_subsys *ss;
 
-        err = cgroup_add_files(cgrp, NULL, files);
+        err = cgroup_addrm_files(cgrp, NULL, files, true);
         if (err < 0)
                 return err;
 
@@ -3796,7 +3830,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
                         return err;
 
                 list_for_each_entry(set, &ss->cftsets, node)
-                        cgroup_add_files(cgrp, ss, set->cfts);
+                        cgroup_addrm_files(cgrp, ss, set->cfts, true);
         }
 
         /* This cgroup is ready now */