cpuset: move mount -t cpuset logics into cgroup.c

... and get rid of the weird dances in ->get_tree() - that logics
can be easily handled in ->init_fs_context().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/cgroup/cgroup.c

@@ -2225,6 +2225,50 @@ static struct file_system_type cgroup2_fs_type = {
 	.fs_flags		= FS_USERNS_MOUNT,
 };
 
+#ifdef CONFIG_CPUSETS
+static const struct fs_context_operations cpuset_fs_context_ops = {
+	.get_tree	= cgroup1_get_tree,
+	.free		= cgroup_fs_context_free,
+};
+
+/*
+ * This is ugly, but preserves the userspace API for existing cpuset
+ * users. If someone tries to mount the "cpuset" filesystem, we
+ * silently switch it to mount "cgroup" instead
+ */
+static int cpuset_init_fs_context(struct fs_context *fc)
+{
+	char *agent = kstrdup("/sbin/cpuset_release_agent", GFP_USER);
+	struct cgroup_fs_context *ctx;
+	int err;
+
+	err = cgroup_init_fs_context(fc);
+	if (err) {
+		kfree(agent);
+		return err;
+	}
+
+	fc->ops = &cpuset_fs_context_ops;
+
+	ctx = cgroup_fc2context(fc);
+	ctx->subsys_mask = 1 << cpuset_cgrp_id;
+	ctx->flags |= CGRP_ROOT_NOPREFIX;
+	ctx->release_agent = agent;
+
+	get_filesystem(&cgroup_fs_type);
+	put_filesystem(fc->fs_type);
+	fc->fs_type = &cgroup_fs_type;
+
+	return 0;
+}
+
+static struct file_system_type cpuset_fs_type = {
+	.name			= "cpuset",
+	.init_fs_context	= cpuset_init_fs_context,
+	.fs_flags		= FS_USERNS_MOUNT,
+};
+#endif
+
 int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
 			  struct cgroup_namespace *ns)
 {
@@ -5710,6 +5754,9 @@ int __init cgroup_init(void)
 	WARN_ON(register_filesystem(&cgroup_fs_type));
 	WARN_ON(register_filesystem(&cgroup2_fs_type));
 	WARN_ON(!proc_create_single("cgroups", 0, NULL, proc_cgroupstats_show));
+#ifdef CONFIG_CPUSETS
+	WARN_ON(register_filesystem(&cpuset_fs_type));
+#endif
 
 	return 0;
 }

kernel/cgroup/cpuset.c

@@ -355,59 +355,6 @@ static inline bool is_in_v2_mode(void)
 	      (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
 }
 
-/*
- * This is ugly, but preserves the userspace API for existing cpuset
- * users. If someone tries to mount the "cpuset" filesystem, we
- * silently switch it to mount "cgroup" instead
- */
-static int cpuset_get_tree(struct fs_context *fc)
-{
-	struct file_system_type *cgroup_fs;
-	struct fs_context *new_fc;
-	int ret;
-
-	cgroup_fs = get_fs_type("cgroup");
-	if (!cgroup_fs)
-		return -ENODEV;
-
-	new_fc = fs_context_for_mount(cgroup_fs, fc->sb_flags);
-	if (IS_ERR(new_fc)) {
-		ret = PTR_ERR(new_fc);
-	} else {
-		static const char agent_path[] = "/sbin/cpuset_release_agent";
-		ret = vfs_parse_fs_string(new_fc, "cpuset", NULL, 0);
-		if (!ret)
-			ret = vfs_parse_fs_string(new_fc, "noprefix", NULL, 0);
-		if (!ret)
-			ret = vfs_parse_fs_string(new_fc, "release_agent",
-					agent_path, sizeof(agent_path) - 1);
-		if (!ret)
-			ret = vfs_get_tree(new_fc);
-		if (!ret) {	/* steal the result */
-			fc->root = new_fc->root;
-			new_fc->root = NULL;
-		}
-		put_fs_context(new_fc);
-	}
-	put_filesystem(cgroup_fs);
-	return ret;
-}
-
-static const struct fs_context_operations cpuset_fs_context_ops = {
-	.get_tree	= cpuset_get_tree,
-};
-
-static int cpuset_init_fs_context(struct fs_context *fc)
-{
-	fc->ops = &cpuset_fs_context_ops;
-	return 0;
-}
-
-static struct file_system_type cpuset_fs_type = {
-	.name			= "cpuset",
-	.init_fs_context	= cpuset_init_fs_context,
-};
-
 /*
  * Return in pmask the portion of a cpusets's cpus_allowed that
  * are online.  If none are online, walk up the cpuset hierarchy
@@ -2853,13 +2800,11 @@ struct cgroup_subsys cpuset_cgrp_subsys = {
 /**
  * cpuset_init - initialize cpusets at system boot
  *
- * Description: Initialize top_cpuset and the cpuset internal file system,
+ * Description: Initialize top_cpuset
  **/
 
 int __init cpuset_init(void)
 {
-	int err = 0;
-
 	BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
 	BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
 	BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_cpus, GFP_KERNEL));
@@ -2873,10 +2818,6 @@ int __init cpuset_init(void)
 	set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
 	top_cpuset.relax_domain_level = -1;
 
-	err = register_filesystem(&cpuset_fs_type);
-	if (err < 0)
-		return err;
-
 	BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));
 
 	return 0;