[RFC][PATCH 4/4]: Enable cloning PTY namespaces

[sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org]

From: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Subject: [RFC][PATCH 4/4]: Enable cloning PTY namespaces

Enable cloning PTY namespaces.

TODO:
	This version temporarily uses the clone flag '0x80000000' which
	is unused in mainline atm, but used for CLONE_IO in -mm. 
	While we must extend clone() (urgently) to solve this, it hopefully
	does not affect review of the rest of this patchset.

Changelog:
	- Version 0: Based on earlier versions from Serge Hallyn and
	  Matt Helsley.

Signed-off-by: Sukadev Bhattiprolu <sukadev-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 fs/devpts/inode.c         |   84 +++++++++++++++++++++++++++++++++++++++-------
 include/linux/devpts_fs.h |   52 ++++++++++++++++++++++++++++
 include/linux/init_task.h |    1 
 include/linux/nsproxy.h   |    2 +
 include/linux/sched.h     |    2 +
 kernel/fork.c             |    2 -
 kernel/nsproxy.c          |   17 ++++++++-
 7 files changed, 146 insertions(+), 14 deletions(-)

Index: linux-2.6.24/fs/devpts/inode.c
===================================================================
--- linux-2.6.24.orig/fs/devpts/inode.c	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/fs/devpts/inode.c	2008-02-05 20:27:41.000000000 -0800
@@ -25,18 +25,25 @@
 #define DEVPTS_SUPER_MAGIC 0x1cd1
 
 extern int pty_limit;		/* Config limit on Unix98 ptys */
-static DEFINE_IDR(allocated_ptys);
 static DECLARE_MUTEX(allocated_ptys_lock);
+static struct file_system_type devpts_fs_type;
+
+struct pts_namespace init_pts_ns = {
+	.kref = {
+		.refcount = ATOMIC_INIT(2),
+	},
+	.allocated_ptys = IDR_INIT(init_pts_ns.allocated_ptys),
+	.mnt = NULL,
+};
 
 static inline struct idr *current_pts_ns_allocated_ptys(void)
 {
-	return &allocated_ptys;
+	return &current->nsproxy->pts_ns->allocated_ptys;
 }
 
-static struct vfsmount *devpts_mnt;
 static inline struct vfsmount *current_pts_ns_mnt(void)
 {
-	return devpts_mnt;
+	return current->nsproxy->pts_ns->mnt;
 }
 
 static struct {
@@ -59,6 +66,42 @@ static match_table_t tokens = {
 	{Opt_err, NULL}
 };
 
+struct pts_namespace *new_pts_ns(void)
+{
+	struct pts_namespace *ns;
+
+	ns = kmalloc(sizeof(*ns), GFP_KERNEL);
+	if (!ns)
+		return ERR_PTR(-ENOMEM);
+
+	ns->mnt = kern_mount_data(&devpts_fs_type, ns);
+	if (IS_ERR(ns->mnt)) {
+		kfree(ns);
+		return ERR_PTR(PTR_ERR(ns->mnt));
+	}
+
+	idr_init(&ns->allocated_ptys);
+	kref_init(&ns->kref);
+
+	return ns;
+}
+
+void free_pts_ns(struct kref *ns_kref)
+{
+	struct pts_namespace *ns;
+
+	ns = container_of(ns_kref, struct pts_namespace, kref);
+	BUG_ON(ns == &init_pts_ns);
+
+	mntput(ns->mnt);
+	/*
+	 * TODO:
+	 *      idr_remove_all(&ns->allocated_ptys); introduced in 2.6.23
+	 */
+	idr_destroy(&ns->allocated_ptys);
+	kfree(ns);
+}
+
 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 {
 	char *p;
@@ -160,18 +203,27 @@ static int devpts_test_sb(struct super_b
 
 static int devpts_set_sb(struct super_block *sb, void *data)
 {
-	sb->s_fs_info = data;
+	struct pts_namespace *ns = data;
+
+	sb->s_fs_info = get_pts_ns(ns);
 	return set_anon_super(sb, NULL);
 }
 
 static int devpts_get_sb(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
 {
+	struct pts_namespace *ns;
 	struct super_block *sb;
 	int err;
 
+	/* hereafter we're very similar to proc_get_sb */
+	if (flags & MS_KERNMOUNT)
+		ns = data;
+	else
+		ns = current->nsproxy->pts_ns;
+
 	/* hereafter we're very simlar to get_sb_nodev */
-	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, data);
+	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns);
 	if (IS_ERR(sb))
 		return PTR_ERR(sb);
 
@@ -187,16 +239,25 @@ static int devpts_get_sb(struct file_sys
 	}
 
 	sb->s_flags |= MS_ACTIVE;
-	devpts_mnt = mnt;
+	ns->mnt = mnt;
 
 	return simple_set_mnt(mnt, sb);
 }
 
+static void devpts_kill_sb(struct super_block *sb)
+{
+       struct pts_namespace *ns;
+
+       ns = sb->s_fs_info;
+       kill_anon_super(sb);
+       put_pts_ns(ns);
+}
+
 static struct file_system_type devpts_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "devpts",
 	.get_sb		= devpts_get_sb,
-	.kill_sb	= kill_anon_super,
+	.kill_sb	= devpts_kill_sb,
 };
 
 /*
@@ -352,18 +413,19 @@ static int __init init_devpts_fs(void)
 	if (err)
 		return err;
 
-	mnt = kern_mount_data(&devpts_fs_type, NULL);
+	mnt = kern_mount_data(&devpts_fs_type, &init_pts_ns);
 	if (IS_ERR(mnt))
 		err = PTR_ERR(mnt);
 	else
-		devpts_mnt = mnt;
+		init_pts_ns.mnt = mnt;
 	return err;
 }
 
 static void __exit exit_devpts_fs(void)
 {
 	unregister_filesystem(&devpts_fs_type);
-	mntput(devpts_mnt);
+	mntput(init_pts_ns.mnt);
+	init_pts_ns.mnt = NULL;
 }
 
 module_init(init_devpts_fs)
Index: linux-2.6.24/include/linux/devpts_fs.h
===================================================================
--- linux-2.6.24.orig/include/linux/devpts_fs.h	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/include/linux/devpts_fs.h	2008-02-05 20:21:08.000000000 -0800
@@ -14,9 +14,45 @@
 #define _LINUX_DEVPTS_FS_H
 
 #include <linux/errno.h>
+#include <linux/nsproxy.h>
+#include <linux/kref.h>
+#include <linux/idr.h>
+
+struct pts_namespace {
+	struct kref kref;
+	struct idr allocated_ptys;
+	struct vfsmount *mnt;
+};
+
+extern struct pts_namespace init_pts_ns;
 
 #ifdef CONFIG_UNIX98_PTYS
 
+extern struct pts_namespace *new_pts_ns(void);
+extern void free_pts_ns(struct kref *kref);
+
+static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
+{
+	if (ns)
+		kref_get(&ns->kref);
+	return ns;
+}
+
+static inline void put_pts_ns(struct pts_namespace *ns)
+{
+	if (ns)
+		kref_put(&ns->kref, free_pts_ns);
+}
+
+static inline struct pts_namespace *copy_pts_ns(unsigned long flags,
+		struct pts_namespace *old_ns)
+{
+	if (flags & CLONE_NEWPTS)
+		return new_pts_ns();
+	else
+		return get_pts_ns(old_ns);
+}
+
 int devpts_new_index(void);
 void devpts_kill_index(int idx);
 int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
@@ -26,6 +62,22 @@ void devpts_pty_kill(int number);		 /* u
 #else
 
 /* Dummy stubs in the no-pty case */
+
+static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
+{
+	return &init_pts_ns;
+}
+
+static inline void put_pts_ns(struct pts_namespace *ns) { }
+
+static inline struct pts_namespace *copy_pts_ns(unsigned long flags,
+		struct pts_namespace *old_ns)
+{
+	if (flags & CLONE_NEWPTS)
+		return ERR_PTR(-EINVAL);
+	return old_ns;
+}
+
 static inline int devpts_new_index(void) { return -EINVAL; }
 static inline void devpts_kill_index(int idx) { }
 static inline int devpts_pty_new(struct tty_struct *tty) { return -EINVAL; }
Index: linux-2.6.24/include/linux/init_task.h
===================================================================
--- linux-2.6.24.orig/include/linux/init_task.h	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/include/linux/init_task.h	2008-02-05 19:18:00.000000000 -0800
@@ -77,6 +77,7 @@ extern struct nsproxy init_nsproxy;
 	.mnt_ns		= NULL,						\
 	INIT_NET_NS(net_ns)                                             \
 	INIT_IPC_NS(ipc_ns)						\
+	.pts_ns		= &init_pts_ns,					\
 	.user_ns	= &init_user_ns,				\
 }
 
Index: linux-2.6.24/include/linux/nsproxy.h
===================================================================
--- linux-2.6.24.orig/include/linux/nsproxy.h	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/include/linux/nsproxy.h	2008-02-05 19:18:00.000000000 -0800
@@ -8,6 +8,7 @@ struct mnt_namespace;
 struct uts_namespace;
 struct ipc_namespace;
 struct pid_namespace;
+struct pts_namespace;
 
 /*
  * A structure to contain pointers to all per-process
@@ -29,6 +30,7 @@ struct nsproxy {
 	struct pid_namespace *pid_ns;
 	struct user_namespace *user_ns;
 	struct net 	     *net_ns;
+	struct pts_namespace *pts_ns;
 };
 extern struct nsproxy init_nsproxy;
 
Index: linux-2.6.24/include/linux/sched.h
===================================================================
--- linux-2.6.24.orig/include/linux/sched.h	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/include/linux/sched.h	2008-02-05 19:54:05.000000000 -0800
@@ -27,6 +27,8 @@
 #define CLONE_NEWUSER		0x10000000	/* New user namespace */
 #define CLONE_NEWPID		0x20000000	/* New pid namespace */
 #define CLONE_NEWNET		0x40000000	/* New network namespace */
+#define CLONE_NEWPTS    	(CLONE_NEWNS|0x80000000) /* Temporary - only for patch review */
+							 /* Badly need to /extend clone() !!! */
 
 /*
  * Scheduling policies
Index: linux-2.6.24/kernel/fork.c
===================================================================
--- linux-2.6.24.orig/kernel/fork.c	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/kernel/fork.c	2008-02-05 19:18:00.000000000 -0800
@@ -1655,7 +1655,7 @@ asmlinkage long sys_unshare(unsigned lon
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
 				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|
-				CLONE_NEWNET))
+				CLONE_NEWNET|CLONE_NEWPTS))
 		goto bad_unshare_out;
 
 	if ((err = unshare_thread(unshare_flags)))
Index: linux-2.6.24/kernel/nsproxy.c
===================================================================
--- linux-2.6.24.orig/kernel/nsproxy.c	2008-02-05 19:16:39.000000000 -0800
+++ linux-2.6.24/kernel/nsproxy.c	2008-02-05 19:18:00.000000000 -0800
@@ -21,6 +21,7 @@
 #include <linux/utsname.h>
 #include <linux/pid_namespace.h>
 #include <net/net_namespace.h>
+#include <linux/devpts_fs.h>
 
 static struct kmem_cache *nsproxy_cachep;
 
@@ -92,8 +93,17 @@ static struct nsproxy *create_new_namesp
 		goto out_net;
 	}
 
+	new_nsp->pts_ns = copy_pts_ns(flags, tsk->nsproxy->pts_ns);
+	if (IS_ERR(new_nsp->pts_ns)) {
+		err = PTR_ERR(new_nsp->pts_ns);
+		goto out_pts;
+	}
+
 	return new_nsp;
 
+out_pts:
+	if (new_nsp->net_ns)
+		put_net(new_nsp->net_ns);
 out_net:
 	if (new_nsp->user_ns)
 		put_user_ns(new_nsp->user_ns);
@@ -130,7 +140,8 @@ int copy_namespaces(unsigned long flags,
 	get_nsproxy(old_ns);
 
 	if (!(flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET)))
+				CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET |
+				CLONE_NEWPTS)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN)) {
@@ -169,6 +180,8 @@ void free_nsproxy(struct nsproxy *ns)
 		put_pid_ns(ns->pid_ns);
 	if (ns->user_ns)
 		put_user_ns(ns->user_ns);
+	if (ns->pts_ns)
+		put_pts_ns(ns->pts_ns);
 	put_net(ns->net_ns);
 	kmem_cache_free(nsproxy_cachep, ns);
 }
@@ -183,7 +196,7 @@ int unshare_nsproxy_namespaces(unsigned 
 	int err = 0;
 
 	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
-			       CLONE_NEWUSER | CLONE_NEWNET)))
+			       CLONE_NEWUSER | CLONE_NEWNET | CLONE_NEWPTS)))
 		return 0;
 
 	if (!capable(CAP_SYS_ADMIN))