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>

fs/namespace.c

@@ -4104,8 +4104,9 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool a
 	}
 
 	if (anon)
-		new_ns->ns.inum = MNT_NS_ANON_INO;
+		ret = ns_common_init_inum(new_ns, &mntns_operations, MNT_NS_ANON_INO);
-	ret = ns_common_init(&new_ns->ns, &mntns_operations, !anon);
+	else
+		ret = ns_common_init(new_ns, &mntns_operations);
 	if (ret) {
 		kfree(new_ns);
 		dec_mnt_namespaces(ucounts);

include/linux/ns_common.h

@@ -16,6 +16,15 @@ struct time_namespace;
 struct user_namespace;
 struct uts_namespace;
 
+extern struct cgroup_namespace init_cgroup_ns;
+extern struct ipc_namespace init_ipc_ns;
+extern struct mnt_namespace init_mnt_ns;
+extern struct net init_net;
+extern struct pid_namespace init_pid_ns;
+extern struct time_namespace init_time_ns;
+extern struct user_namespace init_user_ns;
+extern struct uts_namespace init_uts_ns;
+
 struct ns_common {
 	struct dentry *stashed;
 	const struct proc_ns_operations *ops;
@@ -31,8 +40,7 @@ struct ns_common {
 	};
 };
 
-int ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops,
+int __ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops, int inum);
-		   bool alloc_inum);
 
 #define to_ns_common(__ns)                              \
 	_Generic((__ns),                                \
@@ -45,4 +53,31 @@ int ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops,
 		struct user_namespace *:   &(__ns)->ns, \
 		struct uts_namespace *:    &(__ns)->ns)
 
+#define ns_init_inum(__ns)                                     \
+	_Generic((__ns),                                       \
+		struct cgroup_namespace *: CGROUP_NS_INIT_INO, \
+		struct ipc_namespace *:    IPC_NS_INIT_INO,    \
+		struct mnt_namespace *:    MNT_NS_INIT_INO,    \
+		struct net *:              NET_NS_INIT_INO,    \
+		struct pid_namespace *:    PID_NS_INIT_INO,    \
+		struct time_namespace *:   TIME_NS_INIT_INO,   \
+		struct user_namespace *:   USER_NS_INIT_INO,   \
+		struct uts_namespace *:    UTS_NS_INIT_INO)
+
+#define ns_init_ns(__ns)                                    \
+	_Generic((__ns),                                    \
+		struct cgroup_namespace *: &init_cgroup_ns, \
+		struct ipc_namespace *:    &init_ipc_ns,    \
+		struct mnt_namespace *:    &init_mnt_ns,     \
+		struct net *:              &init_net,       \
+		struct pid_namespace *:    &init_pid_ns,    \
+		struct time_namespace *:   &init_time_ns,   \
+		struct user_namespace *:   &init_user_ns,   \
+		struct uts_namespace *:    &init_uts_ns)
+
+#define ns_common_init(__ns, __ops) \
+	__ns_common_init(to_ns_common(__ns), __ops, (((__ns) == ns_init_ns(__ns)) ? ns_init_inum(__ns) : 0))
+
+#define ns_common_init_inum(__ns, __ops, __inum) __ns_common_init(to_ns_common(__ns), __ops, __inum)
+
 #endif

ipc/namespace.c

@@ -62,7 +62,7 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
 	if (ns == NULL)
 		goto fail_dec;
 
-	err = ns_common_init(&ns->ns, &ipcns_operations, true);
+	err = ns_common_init(ns, &ipcns_operations);
 	if (err)
 		goto fail_free;
 

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,
+int __ns_common_init(struct ns_common *ns, const struct proc_ns_operations *ops, int inum)
-		   bool alloc_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);
+
+	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;
 

net/core/net_namespace.c

@@ -409,7 +409,7 @@ static __net_init int preinit_net(struct net *net, struct user_namespace *user_n
 	ns_ops = NULL;
 #endif
 
-	ret = ns_common_init(&net->ns, ns_ops, true);
+	ret = ns_common_init(net, ns_ops);
 	if (ret)
 		return ret;