nscommon: simplify initialization

There's a lot of information that namespace implementers don't need to
know about at all. Encapsulate this all in the initialization helper.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

kernel/cgroup/namespace.c

@@ -27,7 +27,7 @@ static struct cgroup_namespace *alloc_cgroup_ns(void)
 	new_ns = kzalloc(sizeof(struct cgroup_namespace), GFP_KERNEL_ACCOUNT);
 	if (!new_ns)
 		return ERR_PTR(-ENOMEM);
-	ret = ns_common_init(&new_ns->ns, &cgroupns_operations, true);
+	ret = ns_common_init(new_ns, &cgroupns_operations);
 	if (ret)
 		return ERR_PTR(ret);
 	ns_tree_add(new_ns);

kernel/nscommon.c

@@ -1,21 +1,20 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
 #include <linux/ns_common.h>
+#include <linux/proc_ns.h>
 
-int ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops,
-		   bool alloc_inum)
+int __ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops, int inum)
 {
-	if (alloc_inum && !ns->inum) {
-		int ret;
-		ret = proc_alloc_inum(&ns->inum);
-		if (ret)
-			return ret;
-	}
 	refcount_set(&ns->count, 1);
 	ns->stashed = NULL;
 	ns->ops = ops;
 	ns->ns_id = 0;
 	RB_CLEAR_NODE(&ns->ns_tree_node);
 	INIT_LIST_HEAD(&ns->ns_list_node);
-	return 0;
+
+	if (inum) {
+		ns->inum = inum;
+		return 0;
+	}
+	return proc_alloc_inum(&ns->inum);
 }

kernel/pid_namespace.c

@@ -103,7 +103,7 @@ static struct pid_namespace *create_pid_namespace(struct user_namespace *user_ns
 	if (ns->pid_cachep == NULL)
 		goto out_free_idr;
 
-	err = ns_common_init(&ns->ns, &pidns_operations, true);
+	err = ns_common_init(ns, &pidns_operations);
 	if (err)
 		goto out_free_idr;
 

kernel/time/namespace.c

@@ -97,7 +97,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 	if (!ns->vvar_page)
 		goto fail_free;
 
-	err = ns_common_init(&ns->ns, &timens_operations, true);
+	err = ns_common_init(ns, &timens_operations);
 	if (err)
 		goto fail_free_page;
 

kernel/user_namespace.c

@@ -126,7 +126,7 @@ int create_user_ns(struct cred *new)
 
 	ns->parent_could_setfcap = cap_raised(new->cap_effective, CAP_SETFCAP);
 
-	ret = ns_common_init(&ns->ns, &userns_operations, true);
+	ret = ns_common_init(ns, &userns_operations);
 	if (ret)
 		goto fail_free;
 

kernel/utsname.c

@@ -50,7 +50,7 @@ static struct uts_namespace *clone_uts_ns(struct user_namespace *user_ns,
 	if (!ns)
 		goto fail_dec;
 
-	err = ns_common_init(&ns->ns, &utsns_operations, true);
+	err = ns_common_init(ns, &utsns_operations);
 	if (err)
 		goto fail_free;