cgroup: introduce cgroup_subsys->legacy_name

This allows cgroup subsystems to use a different name on the unified
hierarchy.  cgroup_subsys->name is used on the unified hierarchy,
->legacy_name elsewhere.  If ->legacy_name is not explicitly set, it's
automatically set to ->name and the userland visible behavior remains
unchanged.

v2: Make parse_cgroupfs_options() only consider ->legacy_name as mount
    options are used only on legacy hierarchies.  Suggested by Li
    Zefan.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: cgroups@vger.kernel.org

2 files changed, 21 insertions, 11 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 8f5770a7d85a..7d0bb53e4553 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -434,6 +434,9 @@ struct cgroup_subsys {
         int id;
         const char *name;
 
+        /* optional, initialized automatically during boot if not set */
+        const char *legacy_name;
+
         /* link to parent, protected by cgroup_lock() */
         struct cgroup_root *root;
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d9f854defa78..9c8eb17d593a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1028,10 +1028,13 @@ static const struct file_operations proc_cgroupstats_operations;
 static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft,
                               char *buf)
 {
+        struct cgroup_subsys *ss = cft->ss;
+
         if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
             !(cgrp->root->flags & CGRP_ROOT_NOPREFIX))
                 snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s",
-                         cft->ss->name, cft->name);
+                         cgroup_on_dfl(cgrp) ? ss->name : ss->legacy_name,
+                         cft->name);
         else
                 strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
         return buf;
@@ -1336,7 +1339,7 @@ static int cgroup_show_options(struct seq_file *seq,
         if (root != &cgrp_dfl_root)
                 for_each_subsys(ss, ssid)
                         if (root->subsys_mask & (1 << ssid))
-                                seq_printf(seq, ",%s", ss->name);
+                                seq_printf(seq, ",%s", ss->legacy_name);
         if (root->flags & CGRP_ROOT_NOPREFIX)
                 seq_puts(seq, ",noprefix");
         if (root->flags & CGRP_ROOT_XATTR)
@@ -1449,7 +1452,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts)
                 }
 
                 for_each_subsys(ss, i) {
-                        if (strcmp(token, ss->name))
+                        if (strcmp(token, ss->legacy_name))
                                 continue;
                         if (ss->disabled)
                                 continue;
@@ -4995,6 +4998,8 @@ int __init cgroup_init_early(void)
 
                 ss->id = i;
                 ss->name = cgroup_subsys_name[i];
+                if (!ss->legacy_name)
+                        ss->legacy_name = cgroup_subsys_name[i];
 
                 if (ss->early_init)
                         cgroup_init_subsys(ss, true);
@@ -5142,7 +5147,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                         for_each_subsys(ss, ssid)
                                 if (root->subsys_mask & (1 << ssid))
                                         seq_printf(m, "%s%s", count++ ? "," : "",
-                                                   ss->name);
+                                                   ss->legacy_name);
                 if (strlen(root->name))
                         seq_printf(m, "%sname=%s", count ? "," : "",
                                    root->name);
@@ -5182,7 +5187,7 @@ static int proc_cgroupstats_show(struct seq_file *m, void *v)
 
         for_each_subsys(ss, i)
                 seq_printf(m, "%s\t%d\t%d\t%d\n",
-                           ss->name, ss->root->hierarchy_id,
+                           ss->legacy_name, ss->root->hierarchy_id,
                            atomic_read(&ss->root->nr_cgrps), !ss->disabled);
 
         mutex_unlock(&cgroup_mutex);
@@ -5404,12 +5409,14 @@ static int __init cgroup_disable(char *str)
                         continue;
 
                 for_each_subsys(ss, i) {
-                        if (!strcmp(token, ss->name)) {
-                                ss->disabled = 1;
-                                printk(KERN_INFO "Disabling %s control group"
-                                        " subsystem\n", ss->name);
-                                break;
-                        }
+                        if (strcmp(token, ss->name) &&
+                            strcmp(token, ss->legacy_name))
+                                continue;
+
+                        ss->disabled = 1;
+                        printk(KERN_INFO "Disabling %s control group subsystem\n",
+                               ss->name);
+                        break;
                 }
         }
         return 1;