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[PATCH 0/7][v2] Cloning PTS namespace [message #28596] Tue, 25 March 2008 03:59 Go to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Devpts namespace patchset

In continuation of the implementation of containers in mainline, we need to
support multiple PTY namespaces so that the PTY index (ie the tty names) in
one container is independent of the PTY indices of other containers.  For
instance this would allow each container to have a '/dev/pts/0' PTY and
refer to different terminals.

	[PATCH 1/7]: Propagate error code from devpts_pty_new
	[PATCH 2/7]: Factor out PTY index allocation
	[PATCH 3/7]: Enable multiple mounts of /dev/pts
	[PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
	[PATCH 5/7]: Determine pts_ns from a pty's inode.
	[PATCH 6/7]: Check for user-space mount of /dev/pts
	[PATCH 7/7]: Enable cloning PTY namespaces

Todo:
	- This patchset depends on availability of additional clone flags.
	  and relies on on Cedric's clone64 patchset.

	- Needs more testing.

Changelog[v1]:
	- Fixed circular reference by not caching the pts_ns in sb->s_fs_info
	  (without incrementing reference count) and clearing the sb->s_fs_info
	  when destroying the pts_ns (See patch 3/7 for details).

	- To allow access to a child container's ptys from parent container,
	  determine the 'pts_ns' of a 'pty' from its inode (See patch 5/7
	  for details.

	- Added a check (hack) to ensure user-space mount of /dev/pts is
	  done before creating PTYs in a new pts-ns (see patch 6/7 for
	  details).

	- Reorganized the patchset and removed redundant changes.
	
	- Ported to work wih Cedric Le Goater's clone64() system call now
	  that we are out of clone_flags.

Changelog[v0]:

	This patchset is based on earlier versions developed by Serge Hallyn
	and Matt Helsley.
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[PATCH 1/7] Propagate error code from devpts_pty_new [message #28597 is a reply to message #28596] Tue, 25 March 2008 04:22 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 1/7]: Propagate error code from devpts_pty_new

Have ptmx_open() propagate any error code returned by devpts_pty_new().

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: containers@lists.osdl.org
---
 drivers/char/tty_io.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: 2.6.25-rc5-mm1/drivers/char/tty_io.c
===================================================================
--- 2.6.25-rc5-mm1.orig/drivers/char/tty_io.c	2008-03-21 20:13:38.000000000 -0700
+++ 2.6.25-rc5-mm1/drivers/char/tty_io.c	2008-03-24 20:04:07.000000000 -0700
@@ -2835,8 +2835,8 @@ static int ptmx_open(struct inode *inode
 	filp->private_data = tty;
 	file_move(filp, &tty->tty_files);
 
-	retval = -ENOMEM;
-	if (devpts_pty_new(tty->link))
+	retval = devpts_pty_new(tty->link);
+	if (retval)
 		goto out1;
 
 	check_tty_count(tty, "tty_open");
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[PATCH 2/7]: Factor out PTY index allocation [message #28598 is a reply to message #28596] Tue, 25 March 2008 04:23 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 2/7]: Factor out PTY index allocation

Factor out the code used to allocate/free a pts index into new interfaces,
devpts_new_index() and devpts_kill_index().  This localizes the external
data structures used in managing the pts indices.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn<serue@us.ibm.com>
Signed-off-by: Matt Helsley<matthltc@us.ibm.com>

---
 drivers/char/tty_io.c     |   40 ++++++----------------------------------
 fs/devpts/inode.c         |   42 +++++++++++++++++++++++++++++++++++++++++-
 include/linux/devpts_fs.h |    4 ++++
 3 files changed, 51 insertions(+), 35 deletions(-)

Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:07.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:04:26.000000000 -0700
@@ -17,6 +17,8 @@
 
 #ifdef CONFIG_UNIX98_PTYS
 
+int devpts_new_index(void);
+void devpts_kill_index(int idx);
 int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
 struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
 void devpts_pty_kill(int number);		 /* unlink */
@@ -24,6 +26,8 @@ void devpts_pty_kill(int number);		 /* u
 #else
 
 /* Dummy stubs in the no-pty case */
+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; }
 static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
 static inline void devpts_pty_kill(int number) { }
Index: 2.6.25-rc5-mm1/drivers/char/tty_io.c
===================================================================
--- 2.6.25-rc5-mm1.orig/drivers/char/tty_io.c	2008-03-24 20:04:07.000000000 -0700
+++ 2.6.25-rc5-mm1/drivers/char/tty_io.c	2008-03-24 20:04:26.000000000 -0700
@@ -91,7 +91,6 @@
 #include <linux/module.h>
 #include <linux/smp_lock.h>
 #include <linux/device.h>
-#include <linux/idr.h>
 #include <linux/wait.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
@@ -137,9 +136,6 @@ EXPORT_SYMBOL(tty_mutex);
 
 #ifdef CONFIG_UNIX98_PTYS
 extern struct tty_driver *ptm_driver;	/* Unix98 pty masters; for /dev/ptmx */
-extern int pty_limit;			/* Config limit on Unix98 ptys */
-static DEFINE_IDR(allocated_ptys);
-static DEFINE_MUTEX(allocated_ptys_lock);
 static int ptmx_open(struct inode *, struct file *);
 #endif
 
@@ -2636,15 +2632,9 @@ static void release_dev(struct file *fil
 	 */
 	release_tty(tty, idx);
 
-#ifdef CONFIG_UNIX98_PTYS
 	/* Make this pty number available for reallocation */
-	if (devpts) {
-		mutex_lock(&allocated_ptys_lock);
-		idr_remove(&allocated_ptys, idx);
-		mutex_unlock(&allocated_ptys_lock);
-	}
-#endif
-
+	if (devpts)
+		devpts_kill_index(idx);
 }
 
 /**
@@ -2800,29 +2790,13 @@ static int ptmx_open(struct inode *inode
 	struct tty_struct *tty;
 	int retval;
 	int index;
-	int idr_ret;
 
 	nonseekable_open(inode, filp);
 
 	/* find a device that is not in use. */
-	mutex_lock(&allocated_ptys_lock);
-	if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
-		mutex_unlock(&allocated_ptys_lock);
-		return -ENOMEM;
-	}
-	idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
-	if (idr_ret < 0) {
-		mutex_unlock(&allocated_ptys_lock);
-		if (idr_ret == -EAGAIN)
-			return -ENOMEM;
-		return -EIO;
-	}
-	if (index >= pty_limit) {
-		idr_remove(&allocated_ptys, index);
-		mutex_unlock(&allocated_ptys_lock);
-		return -EIO;
-	}
-	mutex_unlock(&allocated_ptys_lock);
+	index = devpts_new_index();
+	if (index < 0)
+		return index;
 
 	mutex_lock(&tty_mutex);
 	retval = init_dev(ptm_driver, index, &tty);
@@ -2847,9 +2821,7 @@ out1:
 	release_dev(filp);
 	return retval;
 out:
-	mutex_lock(&allocated_ptys_lock);
-	idr_remove(&allocated_ptys, index);
-	mutex_unlock(&allocated_ptys_lock);
+	devpts_kill_index(index);
 	return retval;
 }
 #endif
Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:04:07.000000000 -0700
+++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:04:26.000000000 -0700
@@ -17,6 +17,7 @@
 #include <linux/namei.h>
 #include <linux/mount.h>
 #include <linux/tty.h>
+#include <linux/idr.h>
 #include <linux/devpts_fs.h>
 #include <linux/parser.h>
 #include <linux/fsnotify.h>
@@ -26,6 +27,10 @@
 
 #define DEVPTS_DEFAULT_MODE 0600
 
+extern int pty_limit;			/* Config limit on Unix98 ptys */
+static DEFINE_IDR(allocated_ptys);
+static DECLARE_MUTEX(allocated_ptys_lock);
+
 static struct vfsmount *devpts_mnt;
 static struct dentry *devpts_root;
 
@@ -171,9 +176,44 @@ static struct dentry *get_node(int num)
 	return lookup_one_len(s, root, sprintf(s, "%d", num));
 }
 
+int devpts_new_index(void)
+{
+	int index;
+	int idr_ret;
+
+retry:
+	if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
+		return -ENOMEM;
+	}
+
+	down(&allocated_ptys_lock);
+	idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
+	if (idr_ret < 0) {
+		up(&allocated_ptys_lock);
+		if (idr_ret == -EAGAIN)
+			goto retry;
+		return -EIO;
+	}
+
+	if (index >= pty_limit) {
+		idr_remove(&allocated_ptys, index);
+		up(&allocated_ptys_lock);
+		return -EIO;
+	}
+	up(&allocated_ptys_lock);
+	return index;
+}
+
+void devpts_kill_index(int idx)
+{
+	down(&allocated_ptys_lock);
+	idr_remove(&allocated_ptys, idx);
+	up(&allocated_ptys_lock);
+}
+
 int devpts_pty_new(struct tty_struct *tty)
 {
-	int number = tty->index;
+	int number = tty->index; /* tty layer puts index from devpts_new_index() in here */
 	struct tty_driver *driver = tty->driver;
 	dev_t device = MKDEV(driver->major, driver->minor_start+number);
 	struct dentry *dentry;
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[PATCH 3/7]: Enable multiple mounts of /dev/pts [message #28599 is a reply to message #28596] Tue, 25 March 2008 04:24 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 3/7]: Enable multiple mounts of /dev/pts

To support multiple PTY namespaces, we should be allow multiple
mounts of /dev/pts, once within each PTY namespace.

This patch removes the get_sb_single() in devpts_get_sb() and
uses test and set sb interfaces to allow remounting /dev/pts.
The patch also removes the globals, 'devpts_mnt', 'devpts_root'
and uses a skeletal 'init_pts_ns' to store the vfsmount.

Changelog [v2]:

	- (Pavel Emelianov/Serge Hallyn) Remove reference to pts_ns from
	  sb->s_fs_info to fix the circular reference (/dev/pts is not
	  unmounted unless the pts_ns is destroyed, so we don't need a
	  reference to the pts_ns).

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
---
 fs/devpts/inode.c         |  160 +++++++++++++++++++++++++++++++++++++---------
 include/linux/devpts_fs.h |   11 +++
 2 files changed, 143 insertions(+), 28 deletions(-)

Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:26.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:04:31.000000000 -0700
@@ -14,6 +14,17 @@
 #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
 
Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:04:26.000000000 -0700
+++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:04:31.000000000 -0700
@@ -28,12 +28,8 @@
 #define DEVPTS_DEFAULT_MODE 0600
 
 extern int pty_limit;			/* Config limit on Unix98 ptys */
-static DEFINE_IDR(allocated_ptys);
 static DECLARE_MUTEX(allocated_ptys_lock);
 
-static struct vfsmount *devpts_mnt;
-static struct dentry *devpts_root;
-
 static struct {
 	int setuid;
 	int setgid;
@@ -54,6 +50,15 @@ static match_table_t tokens = {
 	{Opt_err, NULL}
 };
 
+struct pts_namespace init_pts_ns = {
+	.kref = {
+		.refcount = ATOMIC_INIT(2),
+	},
+	.allocated_ptys = IDR_INIT(init_pts_ns.allocated_ptys),
+	.mnt = NULL,
+};
+
+
 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 {
 	char *p;
@@ -140,7 +145,7 @@ devpts_fill_super(struct super_block *s,
 	inode->i_fop = &simple_dir_operations;
 	inode->i_nlink = 2;
 
-	devpts_root = s->s_root = d_alloc_root(inode);
+	s->s_root = d_alloc_root(inode);
 	if (s->s_root)
 		return 0;
 	
@@ -150,17 +155,82 @@ fail:
 	return -ENOMEM;
 }
 
+/*
+ * We use test and set super-block operations to help determine whether we
+ * need a new super-block for this namespace. get_sb() walks the list of
+ * existing devpts supers, comparing them with the @data ptr. Since we
+ * passed 'current's namespace as the @data pointer we can compare the
+ * namespace pointer in the super-block's 's_fs_info'.  If the test is
+ * TRUE then get_sb() returns a new active reference to the super block.
+ * Otherwise, it helps us build an active reference to a new one.
+ */
+
+static int devpts_test_sb(struct super_block *sb, void *data)
+{
+	return sb->s_fs_info == data;
+}
+
+static int devpts_set_sb(struct super_block *sb, void *data)
+{
+	/*
+	 * new_pts_ns() mounts the pts namespace and free_pts_ns()
+	 * drops the reference to the mount. i.e the s_fs_inf is
+	 * cleared and vfsmnt is releasand _before_ pts_namespace
+	 * is freed.
+	 *
+	 * So we don't need a reference to the pts_namespace here
+	 * (Getting a reference here will also cause circular reference).
+	 */
+	sb->s_fs_info = data;
+	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)
 {
-	return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
+	struct super_block *sb;
+	struct pts_namespace *ns;
+	int err;
+
+	/* hereafter we're very similar to proc_get_sb */
+	if (flags & MS_KERNMOUNT)
+		ns = data;
+	else
+		ns = &init_pts_ns;
+
+	/* hereafter we're very simlar to get_sb_nodev */
+	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns);
+	if (IS_ERR(sb))
+		return PTR_ERR(sb);
+
+	if (sb->s_root)
+		return simple_set_mnt(mnt, sb);
+
+	sb->s_flags = flags;
+	err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
+	if (err) {
+		up_write(&sb->s_umount);
+		deactivate_super(sb);
+		return err;
+	}
+
+	sb->s_flags |= MS_ACTIVE;
+	ns->mnt = mnt;
+
+	return simple_set_mnt(mnt, sb);
+}
+
+static void devpts_kill_sb(struct super_block *sb)
+{
+	sb->s_fs_info = NULL;
+	kill_anon_super(sb);
 }
 
 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,
 };
 
 /*
@@ -168,10 +238,9 @@ static struct file_system_type devpts_fs
  * to the System V naming convention
  */
 
-static struct dentry *get_node(int num)
+static struct dentry *get_node(struct dentry *root, int num)
 {
 	char s[12];
-	struct dentry *root = devpts_root;
 	mutex_lock(&root->d_inode->i_mutex);
 	return lookup_one_len(s, root, sprintf(s, "%d", num));
 }
@@ -180,14 +249,15 @@ int devpts_new_index(void)
 {
 	int index;
 	int idr_ret;
+	struct pts_namespace *pts_ns = &init_pts_ns;
 
 retry:
-	if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
+	if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) {
 		return -ENOMEM;
 	}
 
 	down(&allocated_ptys_lock);
-	idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
+	idr_ret = idr_get_new(&pts_ns->allocated_ptys, NULL, &index);
 	if (idr_ret < 0) {
 		up(&allocated_ptys_lock);
 		if (idr_ret == -EAGAIN)
@@ -196,7 +266,7 @@ retry:
 	}
 
 	if (index >= pty_limit) {
-		idr_remove(&allocated_ptys, index);
+		idr_remove(&pts_ns->allocated_ptys, index);
 		up(&allocated_ptys_lock);
 		return -EIO;
 	}
@@ -206,8 +276,10 @@ retry:
 
 void devpts_kill_index(int idx)
 {
+	struct pts_namespace *pts_ns = &init_pts_ns;
+
 	down(&allocated_ptys_lock);
-	idr_remove(&allocated_ptys, idx);
+	idr_remove(&pts_ns->allocated_ptys, idx);
 	up(&allocated_ptys_lock);
 }
 
@@ -217,12 +289,26 @@ int devpts_pty_new(struct tty_struct *tt
 	struct tty_driver *driver = tty->driver;
 	dev_t device = MKDEV(driver->major, driver->minor_start+number);
 	struct dentry *dentry;
-	struct inode *inode = new_inode(devpts_mnt->mnt_sb);
+	struct dentry *root;
+	struct vfsmount *mnt;
+	struct inode *inode;
+	struct pts_namespace *pts_ns = &init_pts_ns;
 
 	/* We're supposed to be given the slave end of a pty */
 	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
 	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
 
+	mnt = pts_ns->mnt;
+	root = mnt->mnt_root;
+
+	mutex_lock(&root->d_inode->i_mutex);
+	inode = idr_find(&pts_ns->allocated_ptys, number);
+	mutex_unlock(&root->d_inode->i_mutex);
+
+	if (inode && !IS_ERR(inode))
+		return -EEXIST;
+
+	inode = new_inode(mnt->mnt_sb);
 	if (!inode)
 		return -ENOMEM;
 
@@ -232,23 +318,29 @@ int devpts_pty_new(struct tty_struct *tt
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	init_special_inode(inode, S_IFCHR|config.mode, device);
 	inode->i_private = tty;
+	idr_replace(&pts_ns->allocated_ptys, inode, number);
 
-	dentry = get_node(number);
+	dentry = get_node(root, number);
 	if (!IS_ERR(dentry) && !dentry->d_inode) {
 		d_instantiate(dentry, inode);
-		fsnotify_create(devpts_root->d_inode, dentry);
+		fsnotify_create(root->d_inode, dentry);
 	}
 
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&root->d_inode->i_mutex);
 
 	return 0;
 }
 
 struct tty_struct *devpts_get_tty(int number)
 {
-	struct dentry *dentry = get_node(number);
+	struct vfsmount *mnt;
+	struct dentry *dentry;
 	struct tty_struct *tty;
 
+	mnt = init_pts_ns.mnt;
+
+	dentry = get_node(mnt->mnt_root, number);
+
 	tty = NULL;
 	if (!IS_ERR(dentry)) {
 		if (dentry->d_inode)
@@ -256,14 +348,19 @@ struct tty_struct *devpts_get_tty(int nu
 		dput(dentry);
 	}
 
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&mnt->mnt_root->d_inode->i_mutex);
 
 	return tty;
 }
 
 void devpts_pty_kill(int number)
 {
-	struct dentry *dentry = get_node(number);
+	struct dentry *dentry;
+	struct dentry *root;
+
+	root = init_pts_ns.mnt->mnt_root;
+
+	dentry = get_node(root, number);
 
 	if (!IS_ERR(dentry)) {
 		struct inode *inode = dentry->d_inode;
@@ -274,24 +371,31 @@ void devpts_pty_kill(int number)
 		}
 		dput(dentry);
 	}
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&root->d_inode->i_mutex);
 }
 
 static int __init init_devpts_fs(void)
 {
-	int err = register_filesystem(&devpts_fs_type);
-	if (!err) {
-		devpts_mnt = kern_mount(&devpts_fs_type);
-		if (IS_ERR(devpts_mnt))
-			err = PTR_ERR(devpts_mnt);
-	}
+	struct vfsmount *mnt;
+	int err;
+
+	err = register_filesystem(&devpts_fs_type);
+	if (err)
+		return err;
+
+	mnt = kern_mount_data(&devpts_fs_type, &init_pts_ns);
+	if (IS_ERR(mnt))
+		err = PTR_ERR(mnt);
+	else
+		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)
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[PATCH 4/7] Implement get_pts_ns() and put_pts_ns() [message #28600 is a reply to message #28596] Tue, 25 March 2008 04:25 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()

Implement get_pts_ns() and put_pts_ns() interfaces.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
 include/linux/devpts_fs.h |   21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:31.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
@@ -27,13 +27,26 @@ struct pts_namespace {
 extern struct pts_namespace init_pts_ns;
 
 #ifdef CONFIG_UNIX98_PTYS
-
 int devpts_new_index(void);
 void devpts_kill_index(int idx);
 int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
 struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
 void devpts_pty_kill(int number);		 /* unlink */
 
+static inline void free_pts_ns(struct kref *ns_kref) { }
+
+static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
+{
+	if (ns && (ns != &init_pts_ns))
+		kref_get(&ns->kref);
+	return ns;
+}
+static inline void put_pts_ns(struct pts_namespace *ns)
+{
+	if (ns && (ns != &init_pts_ns))
+		kref_put(&ns->kref, free_pts_ns);
+}
+
 #else
 
 /* Dummy stubs in the no-pty case */
@@ -43,6 +56,12 @@ static inline int devpts_pty_new(struct 
 static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
 static inline void devpts_pty_kill(int number) { }
 
+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) { }
 #endif
 
 
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[PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28601 is a reply to message #28596] Tue, 25 March 2008 04:25 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 5/7]: Determine pts_ns from a pty's inode.

The devpts interfaces currently operate on a specific pts namespace
which they get from the 'current' task.

With implementation of containers and cloning of PTS namespaces, we want
to be able to access PTYs in a child-pts-ns from a parent-pts-ns. For
instance we could bind-mount and pivot-root the child container on
'/vserver/vserver1' and then access the "pts/0" of 'vserver1' using 

	$ echo foo > /vserver/vserver1/dev/pts/0
	
The task doing the above 'echo' could be in parent-pts-ns. So we find
the 'pts-ns' of the above file from the inode representing the above
file rather than from the 'current' task.

Note that we need to find and hold a reference to the pts_ns to prevent
the pts_ns from being freed while it is being accessed from 'outside'.

This patch implements, 'pts_ns_from_inode()' which returns the pts_ns
using 'inode->i_sb->s_fs_info'.

Since, the 'inode' information is not visible inside devpts code itself,
this patch modifies the tty driver code to determine the pts_ns and passes
it into devpts.

TODO:
	What is the expected behavior when '/dev/tty' or '/dev/ptmx' are
	accessed from parent-pts-ns. i.e:

		$ echo "foobar" > /vserver/vserver1/dev/tty)
		
	This patch currently ignores the '/vserver/vserver1' part (that
	seemed to be the easiest to do :-). So opening /dev/ptmx from
	even the child pts-ns will create a pty in the _PARENT_ pts-ns.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
 drivers/char/pty.c        |    2 -
 drivers/char/tty_io.c     |   86 +++++++++++++++++++++++++++++++++++++++-------
 fs/devpts/inode.c         |   19 +++-------
 include/linux/devpts_fs.h |   42 +++++++++++++++++++---
 4 files changed, 119 insertions(+), 30 deletions(-)

Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:08:33.000000000 -0700
@@ -17,6 +17,7 @@
 #include <linux/nsproxy.h>
 #include <linux/kref.h>
 #include <linux/idr.h>
+#include <linux/fs.h>
 
 struct pts_namespace {
 	struct kref kref;
@@ -26,12 +27,43 @@ struct pts_namespace {
 
 extern struct pts_namespace init_pts_ns;
 
+#define DEVPTS_SUPER_MAGIC 	0x1cd1
+static inline struct pts_namespace *pts_ns_from_inode(struct inode *inode)
+{
+	/*
+	 * Need this bug-on for now to catch any cases in tty_open()
+	 * or release_dev() I may have missed.
+	 */
+	BUG_ON(inode->i_sb->s_magic != DEVPTS_SUPER_MAGIC);
+
+	/*
+	 * If we have a valid inode, we already have a reference to
+	 * mount-point. Since there is a single super-block for the
+	 * devpts mount, i_sb->s_fs_info cannot go to NULL. So we
+	 * should not need a lock here.
+	 */
+
+	return (struct pts_namespace *)inode->i_sb->s_fs_info;
+}
+
+static inline struct pts_namespace *current_pts_ns(void)
+{
+	return &init_pts_ns;
+}
+
+
 #ifdef CONFIG_UNIX98_PTYS
-int devpts_new_index(void);
-void devpts_kill_index(int idx);
-int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
-struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
-void devpts_pty_kill(int number);		 /* unlink */
+int devpts_new_index(struct pts_namespace *pts_ns);
+void devpts_kill_index(struct pts_namespace *pts_ns, int idx);
+
+/* mknod in devpts */
+int devpts_pty_new(struct pts_namespace *pts_ns, struct tty_struct *tty);
+
+/* get tty structure */
+struct tty_struct *devpts_get_tty(struct pts_namespace *pts_ns, int number);
+
+/* unlink */
+void devpts_pty_kill(struct pts_namespace *pts_ns, int number);
 
 static inline void free_pts_ns(struct kref *ns_kref) { }
 
Index: 2.6.25-rc5-mm1/drivers/char/tty_io.c
===================================================================
--- 2.6.25-rc5-mm1.orig/drivers/char/tty_io.c	2008-03-24 20:04:26.000000000 -0700
+++ 2.6.25-rc5-mm1/drivers/char/tty_io.c	2008-03-24 20:08:15.000000000 -0700
@@ -2064,8 +2064,8 @@ static void tty_line_name(struct tty_dri
  * relaxed for the (most common) case of reopening a tty.
  */
 
-static int init_dev(struct tty_driver *driver, int idx,
-	struct tty_struct **ret_tty)
+static int init_dev(struct tty_driver *driver, struct pts_namespace *pts_ns,
+		int idx, struct tty_struct **ret_tty)
 {
 	struct tty_struct *tty, *o_tty;
 	struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
@@ -2074,7 +2074,7 @@ static int init_dev(struct tty_driver *d
 
 	/* check whether we're reopening an existing tty */
 	if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
-		tty = devpts_get_tty(idx);
+		tty = devpts_get_tty(pts_ns, idx);
 		/*
 		 * If we don't have a tty here on a slave open, it's because
 		 * the master already started the close process and there's
@@ -2361,6 +2361,43 @@ static void release_tty(struct tty_struc
 }
 
 /*
+ * When opening /dev/tty and /dev/ptmx, use the pts-ns of the calling
+ * process. For any other pts device, use the pts-ns, in which the
+ * device was created. This latter case is needed when the pty is
+ * being accessed from a parent container.
+ *
+ * Eg: 	Suppose the user used bind-mount and pivot-root to mount a
+ * 	child- container's root on /vs/vs1. Then "/vs/vs1/dev/pts/0"
+ * 	in parent container and "/dev/pts/0" in child container would
+ * 	refer to the same device.
+ *
+ * 	When parent-container opens, "/vs/vs1/dev/pts/0" we find and
+ * 	grab/drop reference to child container's pts-ns (using @filp).
+ */
+struct pts_namespace *pty_pts_ns(struct tty_driver *driver, struct inode *inode)
+{
+
+	int devpts;
+	int pty_master;
+	dev_t dev;
+	struct pts_namespace *pts_ns;
+
+	devpts = (driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
+	pty_master = (driver->type == TTY_DRIVER_TYPE_PTY &&
+		      driver->subtype == PTY_TYPE_MASTER);
+
+	pts_ns = NULL;
+	if (devpts) {
+		dev = inode->i_rdev;
+		if (pty_master || dev == MKDEV(TTYAUX_MAJOR, 0))
+			pts_ns = current_pts_ns();
+		else
+			pts_ns = pts_ns_from_inode(inode);
+	}
+	return pts_ns;
+}
+
+/*
  * Even releasing the tty structures is a tricky business.. We have
  * to be very careful that the structures are all released at the
  * same time, as interrupts might otherwise get the wrong pointers.
@@ -2376,10 +2413,12 @@ static void release_dev(struct file *fil
 	int	idx;
 	char	buf[64];
 	unsigned long flags;
+	struct pts_namespace *pts_ns;
+	struct inode *inode;
 
+	inode = filp->f_path.dentry->d_inode;
 	tty = (struct tty_struct *)filp->private_data;
-	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode,
-							"release_dev"))
+	if (tty_paranoia_check(tty, inode, "release_dev"))
 		return;
 
 	check_tty_count(tty, "release_dev");
@@ -2391,6 +2430,7 @@ static void release_dev(struct file *fil
 		      tty->driver->subtype == PTY_TYPE_MASTER);
 	devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
 	o_tty = tty->link;
+	pts_ns = pty_pts_ns(tty->driver, inode);
 
 #ifdef TTY_PARANOIA_CHECK
 	if (idx < 0 || idx >= tty->driver->num) {
@@ -2633,8 +2673,13 @@ static void release_dev(struct file *fil
 	release_tty(tty, idx);
 
 	/* Make this pty number available for reallocation */
-	if (devpts)
-		devpts_kill_index(idx);
+	if (devpts) {
+		devpts_kill_index(pts_ns, idx);
+		/*
+		 * Drop reference got in init_dev()
+		 */
+		put_pts_ns(pts_ns);
+	}
 }
 
 /**
@@ -2666,6 +2711,7 @@ static int tty_open(struct inode *inode,
 	int index;
 	dev_t device = inode->i_rdev;
 	unsigned short saved_flags = filp->f_flags;
+	struct pts_namespace *pts_ns;
 
 	nonseekable_open(inode, filp);
 
@@ -2715,7 +2761,20 @@ retry_open:
 		return -ENODEV;
 	}
 got_driver:
-	retval = init_dev(driver, index, &tty);
+
+	/*
+	 * What pts-ns do we want to use when opening "/dev/tty" ?
+	 * Sounds like current_pts_ns(), but what should happen
+	 * if parent pts ns does:
+	 *
+	 * 	echo foo > /vs/vs1/dev/tty
+	 *
+	 * (See Serge's setupvs1 script for the /vs/vs1...)
+	 */
+	pts_ns = pty_pts_ns(driver, inode);
+	get_pts_ns(pts_ns);
+
+	retval = init_dev(driver, pts_ns, index, &tty);
 	mutex_unlock(&tty_mutex);
 	if (retval)
 		return retval;
@@ -2790,16 +2849,19 @@ static int ptmx_open(struct inode *inode
 	struct tty_struct *tty;
 	int retval;
 	int index;
+	struct pts_namespace *pts_ns;
 
 	nonseekable_open(inode, filp);
 
+	pts_ns = current_pts_ns();
+
 	/* find a device that is not in use. */
-	index = devpts_new_index();
+	index = devpts_new_index(pts_ns);
 	if (index < 0)
 		return index;
 
 	mutex_lock(&tty_mutex);
-	retval = init_dev(ptm_driver, index, &tty);
+	retval = init_dev(ptm_driver, pts_ns, index, &tty);
 	mutex_unlock(&tty_mutex);
 
 	if (retval)
@@ -2809,7 +2871,7 @@ static int ptmx_open(struct inode *inode
 	filp->private_data = tty;
 	file_move(filp, &tty->tty_files);
 
-	retval = devpts_pty_new(tty->link);
+	retval = devpts_pty_new(pts_ns, tty->link);
 	if (retval)
 		goto out1;
 
@@ -2821,7 +2883,7 @@ out1:
 	release_dev(filp);
 	return retval;
 out:
-	devpts_kill_index(index);
+	devpts_kill_index(pts_ns, index);
 	return retval;
 }
 #endif
Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:04:31.000000000 -0700
+++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:08:33.000000000 -0700
@@ -23,8 +23,6 @@
 #include <linux/fsnotify.h>
 #include <linux/seq_file.h>
 
-#define DEVPTS_SUPER_MAGIC 0x1cd1
-
 #define DEVPTS_DEFAULT_MODE 0600
 
 extern int pty_limit;			/* Config limit on Unix98 ptys */
@@ -245,11 +243,10 @@ static struct dentry *get_node(struct de
 	return lookup_one_len(s, root, sprintf(s, "%d", num));
 }
 
-int dev
...

[PATCH 6/7]: Check for user-space mount of /dev/pts [message #28602 is a reply to message #28596] Tue, 25 March 2008 04:26 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts

When the pts namespace is cloned, the /dev/pts is not useful unless it
is remounted from the user space.

If user-space clones pts namespace but does not remount /dev/pts, it
would end up using the /dev/pts mount from parent-pts-ns but allocate
the pts indices from current pts ns.

This patch (hack ?) prevents creation of PTYs in user space unless
user-space mounts /dev/pts.

(While this patch can be folded into others, keeping this separate
for now for easier review (and to highlight the hack :-)

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
 fs/devpts/inode.c         |   25 +++++++++++++++++++++++--
 include/linux/devpts_fs.h |   20 +++++++++++++++++++-
 2 files changed, 42 insertions(+), 3 deletions(-)

Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:08:33.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:08:57.000000000 -0700
@@ -23,6 +23,7 @@ struct pts_namespace {
 	struct kref kref;
 	struct idr allocated_ptys;
 	struct vfsmount *mnt;
+	int user_mounted;
 };
 
 extern struct pts_namespace init_pts_ns;
@@ -30,6 +31,8 @@ extern struct pts_namespace init_pts_ns;
 #define DEVPTS_SUPER_MAGIC 	0x1cd1
 static inline struct pts_namespace *pts_ns_from_inode(struct inode *inode)
 {
+	struct pts_namespace *ns;
+
 	/*
 	 * Need this bug-on for now to catch any cases in tty_open()
 	 * or release_dev() I may have missed.
@@ -43,7 +46,22 @@ static inline struct pts_namespace *pts_
 	 * should not need a lock here.
 	 */
 
-	return (struct pts_namespace *)inode->i_sb->s_fs_info;
+	ns = (struct pts_namespace *)inode->i_sb->s_fs_info;
+
+	/*
+	 * If user-space did not mount pts ns after cloning pts namespace,
+	 * the child process would end up accessing devpts mount of the
+	 * parent but use allocated_ptys from the cloned pts ns.
+	 *
+	 * This check prevents creating ptys unless user-space mounts
+	 * devpts  in the new pts namespace.
+	 *
+	 * Is there a cleaner way to prevent this ?
+	 */
+	if (!ns->user_mounted)
+		return NULL;
+
+	return ns;
 }
 
 static inline struct pts_namespace *current_pts_ns(void)
Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:08:33.000000000 -0700
+++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:08:57.000000000 -0700
@@ -201,8 +201,11 @@ static int devpts_get_sb(struct file_sys
 	if (IS_ERR(sb))
 		return PTR_ERR(sb);
 
-	if (sb->s_root)
+	if (sb->s_root) {
+		if (!(flags & MS_KERNMOUNT))
+			ns->user_mounted = 1;
 		return simple_set_mnt(mnt, sb);
+	}
 
 	sb->s_flags = flags;
 	err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
@@ -248,6 +251,10 @@ int devpts_new_index(struct pts_namespac
 	int index;
 	int idr_ret;
 
+	if (!pts_ns || !pts_ns->user_mounted) {
+		printk(KERN_ERR "devpts_new_index() without user_mount\n");
+		return -ENOSYS;
+	}
 retry:
 	if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) {
 		return -ENOMEM;
@@ -273,7 +280,7 @@ retry:
 
 void devpts_kill_index(struct pts_namespace *pts_ns, int idx)
 {
-
+	BUG_ON(!pts_ns->user_mounted);
 	down(&allocated_ptys_lock);
 	idr_remove(&pts_ns->allocated_ptys, idx);
 	up(&allocated_ptys_lock);
@@ -293,6 +300,11 @@ int devpts_pty_new( struct pts_namespace
 	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
 	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
 
+	if (!pts_ns || !pts_ns->user_mounted) {
+		printk(KERN_ERR "devpts_pty_new() without user_mount\n");
+		return -ENOSYS;
+	}
+
 	mnt = pts_ns->mnt;
 	root = mnt->mnt_root;
 
@@ -332,6 +344,11 @@ struct tty_struct *devpts_get_tty(struct
 	struct dentry *dentry;
 	struct tty_struct *tty;
 
+	if (!pts_ns || !pts_ns->user_mounted) {
+		printk(KERN_ERR "devpts_get_tty() without user_mount\n");
+		return ERR_PTR(-ENOSYS);
+	}
+
 	mnt = pts_ns->mnt;
 
 	dentry = get_node(mnt->mnt_root, number);
@@ -353,6 +370,10 @@ void devpts_pty_kill(struct pts_namespac
 	struct dentry *dentry;
 	struct dentry *root;
 
+	if (!pts_ns || !pts_ns->user_mounted) {
+		printk(KERN_ERR "devpts_pty_kill() without user_mount\n");
+		BUG_ON(1);
+	}
 	root = pts_ns->mnt->mnt_root;
 
 	dentry = get_node(root, number);
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[PATCH 7/7]: Enable cloning PTY namespaces [message #28604 is a reply to message #28596] Tue, 25 March 2008 04:27 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 7/7]: Enable cloning PTY namespaces

Enable cloning PTY namespaces.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>

---
 fs/devpts/inode.c         |   40 +++++++++++++++++++++++++++++++++++++++-
 include/linux/devpts_fs.h |   22 ++++++++++++++++++++--
 include/linux/init_task.h |    1 +
 include/linux/nsproxy.h   |    2 ++
 include/linux/sched.h     |    1 +
 kernel/fork.c             |    2 +-
 kernel/nsproxy.c          |   17 +++++++++++++++--
 7 files changed, 79 insertions(+), 6 deletions(-)

Index: 2.6.25-rc5-mm1/include/linux/sched.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/sched.h	2008-03-24 20:02:57.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/sched.h	2008-03-24 20:12:56.000000000 -0700
@@ -28,6 +28,7 @@
 #define CLONE_NEWPID		0x20000000	/* New pid namespace */
 #define CLONE_NEWNET		0x40000000	/* New network namespace */
 #define CLONE_IO		0x80000000	/* Clone io context */
+#define CLONE_NEWPTS		0x0000000200000000ULL	/* Clone pts ns */
 
 /*
  * Scheduling policies
Index: 2.6.25-rc5-mm1/include/linux/nsproxy.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/nsproxy.h	2008-03-24 20:02:57.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/nsproxy.h	2008-03-24 20:12:56.000000000 -0700
@@ -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: 2.6.25-rc5-mm1/include/linux/init_task.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/init_task.h	2008-03-24 20:02:57.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/init_task.h	2008-03-24 20:12:56.000000000 -0700
@@ -78,6 +78,7 @@ 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: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:08:57.000000000 -0700
+++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:12:56.000000000 -0700
@@ -66,7 +66,7 @@ static inline struct pts_namespace *pts_
 
 static inline struct pts_namespace *current_pts_ns(void)
 {
-	return &init_pts_ns;
+	return current->nsproxy->pts_ns;
 }
 
 
@@ -83,7 +83,8 @@ struct tty_struct *devpts_get_tty(struct
 /* unlink */
 void devpts_pty_kill(struct pts_namespace *pts_ns, int number);
 
-static inline void free_pts_ns(struct kref *ns_kref) { }
+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)
 {
@@ -97,6 +98,15 @@ static inline void put_pts_ns(struct pts
 		kref_put(&ns->kref, free_pts_ns);
 }
 
+static inline struct pts_namespace *copy_pts_ns(u64 flags,
+              struct pts_namespace *old_ns)
+{
+      if (flags & CLONE_NEWPTS)
+              return new_pts_ns();
+      else
+              return get_pts_ns(old_ns);
+}
+
 #else
 
 /* Dummy stubs in the no-pty case */
@@ -112,6 +122,14 @@ static inline struct pts_namespace *get_
 }
 
 static inline void put_pts_ns(struct pts_namespace *ns) { }
+
+static inline struct pts_namespace *copy_pts_ns(u64 flags,
+              struct pts_namespace *old_ns)
+{
+      if (flags & CLONE_NEWPTS)
+              return ERR_PTR(-EINVAL);
+      return old_ns;
+}
 #endif
 
 
Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:08:57.000000000 -0700
+++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:14:20.000000000 -0700
@@ -27,6 +27,7 @@
 
 extern int pty_limit;			/* Config limit on Unix98 ptys */
 static DECLARE_MUTEX(allocated_ptys_lock);
+static struct file_system_type devpts_fs_type;
 
 static struct {
 	int setuid;
@@ -56,6 +57,43 @@ struct pts_namespace init_pts_ns = {
 	.mnt = NULL,
 };
 
+struct pts_namespace *new_pts_ns(void)
+{
+	struct pts_namespace *ns;
+
+	ns = kmalloc(sizeof(*ns), GFP_KERNEL);
+	if (!ns)
+		return ERR_PTR(-ENOMEM);
+
+	kref_init(&ns->kref);
+
+	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);
+	ns->user_mounted = 0;
+
+	return ns;
+}
+
+void free_pts_ns(struct kref *ns_kref)
+{
+	struct pts_namespace *ns;
+
+	ns = container_of(ns_kref, struct pts_namespace, kref);
+	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)
 {
@@ -194,7 +232,7 @@ static int devpts_get_sb(struct file_sys
 	if (flags & MS_KERNMOUNT)
 		ns = data;
 	else
-		ns = &init_pts_ns;
+		ns = current_pts_ns();
 
 	/* hereafter we're very simlar to get_sb_nodev */
 	sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns);
Index: 2.6.25-rc5-mm1/kernel/fork.c
===================================================================
--- 2.6.25-rc5-mm1.orig/kernel/fork.c	2008-03-24 20:02:57.000000000 -0700
+++ 2.6.25-rc5-mm1/kernel/fork.c	2008-03-24 20:12:56.000000000 -0700
@@ -1713,7 +1713,7 @@ static long do_unshare(u64 unshare_flags
 	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: 2.6.25-rc5-mm1/kernel/nsproxy.c
===================================================================
--- 2.6.25-rc5-mm1.orig/kernel/nsproxy.c	2008-03-24 20:02:57.000000000 -0700
+++ 2.6.25-rc5-mm1/kernel/nsproxy.c	2008-03-24 20:12:56.000000000 -0700
@@ -21,6 +21,7 @@
 #include <linux/utsname.h>
 #include <linux/pid_namespace.h>
 #include <net/net_namespace.h>
+#include <linux/devpts_fs.h>
 #include <linux/ipc_namespace.h>
 
 static struct kmem_cache *nsproxy_cachep;
@@ -93,8 +94,17 @@ 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);
@@ -131,7 +141,8 @@ int copy_namespaces(u64 flags, struct ta
 	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)) {
@@ -170,6 +181,8 @@ 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);
 }
@@ -184,7 +197,7 @@ int unshare_nsproxy_namespaces(u64 unsha
 	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))
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Re: [PATCH 6/7]: Check for user-space mount of /dev/pts [message #28613 is a reply to message #28602] Tue, 25 March 2008 07:46 Go to previous messageGo to next message
Pavel Emelianov is currently offline  Pavel Emelianov
Messages: 1149
Registered: September 2006
Senior Member
sukadev@us.ibm.com wrote:
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts
> 
> When the pts namespace is cloned, the /dev/pts is not useful unless it
> is remounted from the user space.
> 
> If user-space clones pts namespace but does not remount /dev/pts, it
> would end up using the /dev/pts mount from parent-pts-ns but allocate
> the pts indices from current pts ns.
> 
> This patch (hack ?) prevents creation of PTYs in user space unless
> user-space mounts /dev/pts.
> 
> (While this patch can be folded into others, keeping this separate
> for now for easier review (and to highlight the hack :-)
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
>  fs/devpts/inode.c         |   25 +++++++++++++++++++++++--
>  include/linux/devpts_fs.h |   20 +++++++++++++++++++-
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================

[snip]

> ===================================================================
> --- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:08:33.000000000 -0700
> +++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:08:57.000000000 -0700
> @@ -201,8 +201,11 @@ static int devpts_get_sb(struct file_sys
>  	if (IS_ERR(sb))
>  		return PTR_ERR(sb);
>  
> -	if (sb->s_root)
> +	if (sb->s_root) {
> +		if (!(flags & MS_KERNMOUNT))
> +			ns->user_mounted = 1;

What if user space umounts this back? Won't this break?

Thanks,
Pavel
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Re: [PATCH 0/7][v2] Cloning PTS namespace [message #28614 is a reply to message #28596] Tue, 25 March 2008 07:51 Go to previous messageGo to next message
Pavel Emelianov is currently offline  Pavel Emelianov
Messages: 1149
Registered: September 2006
Senior Member
sukadev@us.ibm.com wrote:
> Devpts namespace patchset
> 
> In continuation of the implementation of containers in mainline, we need to
> support multiple PTY namespaces so that the PTY index (ie the tty names) in
> one container is independent of the PTY indices of other containers.  For
> instance this would allow each container to have a '/dev/pts/0' PTY and
> refer to different terminals.
> 
> 	[PATCH 1/7]: Propagate error code from devpts_pty_new
> 	[PATCH 2/7]: Factor out PTY index allocation
> 	[PATCH 3/7]: Enable multiple mounts of /dev/pts
> 	[PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
> 	[PATCH 5/7]: Determine pts_ns from a pty's inode.
> 	[PATCH 6/7]: Check for user-space mount of /dev/pts
> 	[PATCH 7/7]: Enable cloning PTY namespaces
> 
> Todo:
> 	- This patchset depends on availability of additional clone flags.
> 	  and relies on on Cedric's clone64 patchset.

But this set was not even reviewed, wasn't it? Does anybody
know what are the plans about exhausted flags?

Thanks,
Pavel
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Re: [PATCH 6/7]: Check for user-space mount of /dev/pts [message #28619 is a reply to message #28602] Tue, 25 March 2008 09:40 Go to previous messageGo to next message
Alexey Dobriyan is currently offline  Alexey Dobriyan
Messages: 195
Registered: August 2006
Senior Member
On Tuesday 25 March 2008 07:26:14 sukadev@us.ibm.com wrote:
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts
>
> When the pts namespace is cloned, the /dev/pts is not useful unless it
> is remounted from the user space.
>
> If user-space clones pts namespace but does not remount /dev/pts, it
> would end up using the /dev/pts mount from parent-pts-ns but allocate
> the pts indices from current pts ns.
>
> This patch (hack ?) prevents creation of PTYs in user space unless
> user-space mounts /dev/pts.

This is absolutely horrible and shouldn't go anywhere.
Re: [PATCH 0/7][v2] Cloning PTS namespace [message #28629 is a reply to message #28614] Tue, 25 March 2008 14:42 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting Pavel Emelyanov (xemul@openvz.org):
> sukadev@us.ibm.com wrote:
> > Devpts namespace patchset
> > 
> > In continuation of the implementation of containers in mainline, we need to
> > support multiple PTY namespaces so that the PTY index (ie the tty names) in
> > one container is independent of the PTY indices of other containers.  For
> > instance this would allow each container to have a '/dev/pts/0' PTY and
> > refer to different terminals.
> > 
> > 	[PATCH 1/7]: Propagate error code from devpts_pty_new
> > 	[PATCH 2/7]: Factor out PTY index allocation
> > 	[PATCH 3/7]: Enable multiple mounts of /dev/pts
> > 	[PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
> > 	[PATCH 5/7]: Determine pts_ns from a pty's inode.
> > 	[PATCH 6/7]: Check for user-space mount of /dev/pts
> > 	[PATCH 7/7]: Enable cloning PTY namespaces
> > 
> > Todo:
> > 	- This patchset depends on availability of additional clone flags.
> > 	  and relies on on Cedric's clone64 patchset.
> 
> But this set was not even reviewed, wasn't it?

Well it was sent out!  :)  Last time was Feb 11.  There'd been no
responses so while Cedric has been maintaining it, I suspect he
hasn't wanted to gratuitously spam the list with countless resends.

> Does anybody
> know what are the plans about exhausted flags?

hopefully "go with clone64/unshare64"  :)

-serge
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Re: [PATCH 6/7]: Check for user-space mount of /dev/pts [message #28630 is a reply to message #28602] Tue, 25 March 2008 14:54 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> 
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts
> 
> When the pts namespace is cloned, the /dev/pts is not useful unless it
> is remounted from the user space.
> 
> If user-space clones pts namespace but does not remount /dev/pts, it
> would end up using the /dev/pts mount from parent-pts-ns but allocate
> the pts indices from current pts ns.

So why not use the allocated_ptys from the parent ptsns?  It's what
userspace asked for and it's safe to do.

> This patch (hack ?) prevents creation of PTYs in user space unless
> user-space mounts /dev/pts.
> 
> (While this patch can be folded into others, keeping this separate
> for now for easier review (and to highlight the hack :-)
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
>  fs/devpts/inode.c         |   25 +++++++++++++++++++++++--
>  include/linux/devpts_fs.h |   20 +++++++++++++++++++-
>  2 files changed, 42 insertions(+), 3 deletions(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:08:33.000000000 -0700
> +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:08:57.000000000 -0700
> @@ -23,6 +23,7 @@ struct pts_namespace {
>  	struct kref kref;
>  	struct idr allocated_ptys;
>  	struct vfsmount *mnt;
> +	int user_mounted;
>  };
> 
>  extern struct pts_namespace init_pts_ns;
> @@ -30,6 +31,8 @@ extern struct pts_namespace init_pts_ns;
>  #define DEVPTS_SUPER_MAGIC 	0x1cd1
>  static inline struct pts_namespace *pts_ns_from_inode(struct inode *inode)
>  {
> +	struct pts_namespace *ns;
> +
>  	/*
>  	 * Need this bug-on for now to catch any cases in tty_open()
>  	 * or release_dev() I may have missed.
> @@ -43,7 +46,22 @@ static inline struct pts_namespace *pts_
>  	 * should not need a lock here.
>  	 */
> 
> -	return (struct pts_namespace *)inode->i_sb->s_fs_info;
> +	ns = (struct pts_namespace *)inode->i_sb->s_fs_info;
> +
> +	/*
> +	 * If user-space did not mount pts ns after cloning pts namespace,
> +	 * the child process would end up accessing devpts mount of the
> +	 * parent but use allocated_ptys from the cloned pts ns.
> +	 *
> +	 * This check prevents creating ptys unless user-space mounts
> +	 * devpts  in the new pts namespace.
> +	 *
> +	 * Is there a cleaner way to prevent this ?
> +	 */
> +	if (!ns->user_mounted)
> +		return NULL;
> +
> +	return ns;
>  }
> 
>  static inline struct pts_namespace *current_pts_ns(void)
> Index: 2.6.25-rc5-mm1/fs/devpts/inode.c
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/fs/devpts/inode.c	2008-03-24 20:08:33.000000000 -0700
> +++ 2.6.25-rc5-mm1/fs/devpts/inode.c	2008-03-24 20:08:57.000000000 -0700
> @@ -201,8 +201,11 @@ static int devpts_get_sb(struct file_sys
>  	if (IS_ERR(sb))
>  		return PTR_ERR(sb);
> 
> -	if (sb->s_root)
> +	if (sb->s_root) {
> +		if (!(flags & MS_KERNMOUNT))
> +			ns->user_mounted = 1;
>  		return simple_set_mnt(mnt, sb);
> +	}
> 
>  	sb->s_flags = flags;
>  	err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
> @@ -248,6 +251,10 @@ int devpts_new_index(struct pts_namespac
>  	int index;
>  	int idr_ret;
> 
> +	if (!pts_ns || !pts_ns->user_mounted) {
> +		printk(KERN_ERR "devpts_new_index() without user_mount\n");
> +		return -ENOSYS;
> +	}
>  retry:
>  	if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) {
>  		return -ENOMEM;
> @@ -273,7 +280,7 @@ retry:
> 
>  void devpts_kill_index(struct pts_namespace *pts_ns, int idx)
>  {
> -
> +	BUG_ON(!pts_ns->user_mounted);
>  	down(&allocated_ptys_lock);
>  	idr_remove(&pts_ns->allocated_ptys, idx);
>  	up(&allocated_ptys_lock);
> @@ -293,6 +300,11 @@ int devpts_pty_new( struct pts_namespace
>  	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
>  	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
> 
> +	if (!pts_ns || !pts_ns->user_mounted) {
> +		printk(KERN_ERR "devpts_pty_new() without user_mount\n");
> +		return -ENOSYS;
> +	}
> +
>  	mnt = pts_ns->mnt;
>  	root = mnt->mnt_root;
> 
> @@ -332,6 +344,11 @@ struct tty_struct *devpts_get_tty(struct
>  	struct dentry *dentry;
>  	struct tty_struct *tty;
> 
> +	if (!pts_ns || !pts_ns->user_mounted) {
> +		printk(KERN_ERR "devpts_get_tty() without user_mount\n");
> +		return ERR_PTR(-ENOSYS);
> +	}
> +
>  	mnt = pts_ns->mnt;
> 
>  	dentry = get_node(mnt->mnt_root, number);
> @@ -353,6 +370,10 @@ void devpts_pty_kill(struct pts_namespac
>  	struct dentry *dentry;
>  	struct dentry *root;
> 
> +	if (!pts_ns || !pts_ns->user_mounted) {
> +		printk(KERN_ERR "devpts_pty_kill() without user_mount\n");
> +		BUG_ON(1);
> +	}
>  	root = pts_ns->mnt->mnt_root;
> 
>  	dentry = get_node(root, number);
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Re: [PATCH 4/7] Implement get_pts_ns() and put_pts_ns() [message #28631 is a reply to message #28600] Tue, 25 March 2008 15:06 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> 
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
> 
> Implement get_pts_ns() and put_pts_ns() interfaces.
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
>  include/linux/devpts_fs.h |   21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:31.000000000 -0700
> +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
> @@ -27,13 +27,26 @@ struct pts_namespace {
>  extern struct pts_namespace init_pts_ns;
> 
>  #ifdef CONFIG_UNIX98_PTYS
> -
>  int devpts_new_index(void);
>  void devpts_kill_index(int idx);
>  int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
>  struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
>  void devpts_pty_kill(int number);		 /* unlink */
> 
> +static inline void free_pts_ns(struct kref *ns_kref) { }
> +
> +static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
> +{
> +	if (ns && (ns != &init_pts_ns))

How come you need to this extra check?  No other namespaces special-case
the initial ns this way, do they?

> +		kref_get(&ns->kref);
> +	return ns;
> +}
> +static inline void put_pts_ns(struct pts_namespace *ns)
> +{
> +	if (ns && (ns != &init_pts_ns))
> +		kref_put(&ns->kref, free_pts_ns);
> +}
> +
>  #else
> 
>  /* Dummy stubs in the no-pty case */
> @@ -43,6 +56,12 @@ static inline int devpts_pty_new(struct 
>  static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
>  static inline void devpts_pty_kill(int number) { }
> 
> +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) { }
>  #endif
> 
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28632 is a reply to message #28601] Tue, 25 March 2008 15:17 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> 
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 5/7]: Determine pts_ns from a pty's inode.
> 
> The devpts interfaces currently operate on a specific pts namespace
> which they get from the 'current' task.
> 
> With implementation of containers and cloning of PTS namespaces, we want
> to be able to access PTYs in a child-pts-ns from a parent-pts-ns. For
> instance we could bind-mount and pivot-root the child container on
> '/vserver/vserver1' and then access the "pts/0" of 'vserver1' using 
> 
> 	$ echo foo > /vserver/vserver1/dev/pts/0
> 	
> The task doing the above 'echo' could be in parent-pts-ns. So we find
> the 'pts-ns' of the above file from the inode representing the above
> file rather than from the 'current' task.
> 
> Note that we need to find and hold a reference to the pts_ns to prevent
> the pts_ns from being freed while it is being accessed from 'outside'.
> 
> This patch implements, 'pts_ns_from_inode()' which returns the pts_ns
> using 'inode->i_sb->s_fs_info'.
> 
> Since, the 'inode' information is not visible inside devpts code itself,
> this patch modifies the tty driver code to determine the pts_ns and passes
> it into devpts.
> 
> TODO:
> 	What is the expected behavior when '/dev/tty' or '/dev/ptmx' are
> 	accessed from parent-pts-ns. i.e:
> 
> 		$ echo "foobar" > /vserver/vserver1/dev/tty)
> 		
> 	This patch currently ignores the '/vserver/vserver1' part (that

The way this is phrased it almost sounds like you're considering using
the pathnames to figure out the ptsns to use :).

It's not clear to me what is the sane thing to do.

what you're doing here - have /dev/ptmx and /dev/tty always use
current->'s ptsns - isn't ideal.

It would be nicer to not have a 'devpts ns', and instead have a
full device namespace.  However, then it still isn't clear how to tie
/vs/vs1/dev/ptmx to vs1's device namespace, since there is no device
fs to which to tie the devns.

We could tie the devns to a device inode on mknod, using the devns of
the creating task.  Then when starting up vs1, you just have to always
let vs1 create /dev/ptmx and /dev/tty.  I can't think of anything
better offhand.

Other ideas?

Or do we just keep what Suka has?

> 	seemed to be the easiest to do :-). So opening /dev/ptmx from
> 	even the child pts-ns will create a pty in the _PARENT_ pts-ns.

> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
>  drivers/char/pty.c        |    2 -
>  drivers/char/tty_io.c     |   86 +++++++++++++++++++++++++++++++++++++++-------
>  fs/devpts/inode.c         |   19 +++-------
>  include/linux/devpts_fs.h |   42 +++++++++++++++++++---
>  4 files changed, 119 insertions(+), 30 deletions(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
> +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:08:33.000000000 -0700
> @@ -17,6 +17,7 @@
>  #include <linux/nsproxy.h>
>  #include <linux/kref.h>
>  #include <linux/idr.h>
> +#include <linux/fs.h>
> 
>  struct pts_namespace {
>  	struct kref kref;
> @@ -26,12 +27,43 @@ struct pts_namespace {
> 
>  extern struct pts_namespace init_pts_ns;
> 
> +#define DEVPTS_SUPER_MAGIC 	0x1cd1
> +static inline struct pts_namespace *pts_ns_from_inode(struct inode *inode)
> +{
> +	/*
> +	 * Need this bug-on for now to catch any cases in tty_open()
> +	 * or release_dev() I may have missed.
> +	 */
> +	BUG_ON(inode->i_sb->s_magic != DEVPTS_SUPER_MAGIC);
> +
> +	/*
> +	 * If we have a valid inode, we already have a reference to
> +	 * mount-point. Since there is a single super-block for the
> +	 * devpts mount, i_sb->s_fs_info cannot go to NULL. So we
> +	 * should not need a lock here.
> +	 */
> +
> +	return (struct pts_namespace *)inode->i_sb->s_fs_info;
> +}
> +
> +static inline struct pts_namespace *current_pts_ns(void)
> +{
> +	return &init_pts_ns;
> +}
> +
> +
>  #ifdef CONFIG_UNIX98_PTYS
> -int devpts_new_index(void);
> -void devpts_kill_index(int idx);
> -int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
> -struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
> -void devpts_pty_kill(int number);		 /* unlink */
> +int devpts_new_index(struct pts_namespace *pts_ns);
> +void devpts_kill_index(struct pts_namespace *pts_ns, int idx);
> +
> +/* mknod in devpts */
> +int devpts_pty_new(struct pts_namespace *pts_ns, struct tty_struct *tty);
> +
> +/* get tty structure */
> +struct tty_struct *devpts_get_tty(struct pts_namespace *pts_ns, int number);
> +
> +/* unlink */
> +void devpts_pty_kill(struct pts_namespace *pts_ns, int number);
> 
>  static inline void free_pts_ns(struct kref *ns_kref) { }
> 
> Index: 2.6.25-rc5-mm1/drivers/char/tty_io.c
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/drivers/char/tty_io.c	2008-03-24 20:04:26.000000000 -0700
> +++ 2.6.25-rc5-mm1/drivers/char/tty_io.c	2008-03-24 20:08:15.000000000 -0700
> @@ -2064,8 +2064,8 @@ static void tty_line_name(struct tty_dri
>   * relaxed for the (most common) case of reopening a tty.
>   */
> 
> -static int init_dev(struct tty_driver *driver, int idx,
> -	struct tty_struct **ret_tty)
> +static int init_dev(struct tty_driver *driver, struct pts_namespace *pts_ns,
> +		int idx, struct tty_struct **ret_tty)
>  {
>  	struct tty_struct *tty, *o_tty;
>  	struct ktermios *tp, **tp_loc, *o_tp, **o_tp_loc;
> @@ -2074,7 +2074,7 @@ static int init_dev(struct tty_driver *d
> 
>  	/* check whether we're reopening an existing tty */
>  	if (driver->flags & TTY_DRIVER_DEVPTS_MEM) {
> -		tty = devpts_get_tty(idx);
> +		tty = devpts_get_tty(pts_ns, idx);
>  		/*
>  		 * If we don't have a tty here on a slave open, it's because
>  		 * the master already started the close process and there's
> @@ -2361,6 +2361,43 @@ static void release_tty(struct tty_struc
>  }
> 
>  /*
> + * When opening /dev/tty and /dev/ptmx, use the pts-ns of the calling
> + * process. For any other pts device, use the pts-ns, in which the
> + * device was created. This latter case is needed when the pty is
> + * being accessed from a parent container.
> + *
> + * Eg: 	Suppose the user used bind-mount and pivot-root to mount a
> + * 	child- container's root on /vs/vs1. Then "/vs/vs1/dev/pts/0"
> + * 	in parent container and "/dev/pts/0" in child container would
> + * 	refer to the same device.
> + *
> + * 	When parent-container opens, "/vs/vs1/dev/pts/0" we find and
> + * 	grab/drop reference to child container's pts-ns (using @filp).
> + */
> +struct pts_namespace *pty_pts_ns(struct tty_driver *driver, struct inode *inode)
> +{
> +
> +	int devpts;
> +	int pty_master;
> +	dev_t dev;
> +	struct pts_namespace *pts_ns;
> +
> +	devpts = (driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
> +	pty_master = (driver->type == TTY_DRIVER_TYPE_PTY &&
> +		      driver->subtype == PTY_TYPE_MASTER);
> +
> +	pts_ns = NULL;
> +	if (devpts) {
> +		dev = inode->i_rdev;
> +		if (pty_master || dev == MKDEV(TTYAUX_MAJOR, 0))
> +			pts_ns = current_pts_ns();
> +		else
> +			pts_ns = pts_ns_from_inode(inode);
> +	}
> +	return pts_ns;
> +}
> +
> +/*
>   * Even releasing the tty structures is a tricky business.. We have
>   * to be very careful that the structures are all released at the
>   * same time, as interrupts might otherwise get the wrong pointers.
> @@ -2376,10 +2413,12 @@ static void release_dev(struct file *fil
>  	int	idx;
>  	char	buf[64];
>  	unsigned long flags;
> +	struct pts_namespace *pts_ns;
> +	struct inode *inode;
> 
> +	inode = filp->f_path.dentry->d_inode;
>  	tty = (struct tty_struct *)filp->private_data;
> -	if (tty_paranoia_check(tty, filp->f_path.dentry->d_inode,
> -							"release_dev"))
> +	if (tty_paranoia_check(tty, inode, "release_dev"))
>  		return;
> 
>  	check_tty_count(tty, "release_dev");
> @@ -2391,6 +2430,7 @@ static void release_dev(struct file *fil
>  		      tty->driver->subtype == PTY_TYPE_MASTER);
>  	devpts = (tty->driver->flags & TTY_DRIVER_DEVPTS_MEM) != 0;
>  	o_tty = tty->link;
> +	pts_ns = pty_pts_ns(tty->driver, inode);
> 
>  #ifdef TTY_PARANOIA_CHECK
>  	if (idx < 0 || idx >= tty->driver->num) {
> @@ -2633,8 +2673,13 @@ static void release_dev(struct file *fil
>  	release_tty(tty, idx);
> 
>  	/* Make this pty number available for reallocation */
> -	if (devpts)
> -		devpts_kill_index(idx);
> +	if (devpts) {
> +		devpts_kill_index(pts_ns, idx);
> +		/*
> +		 * Drop reference got in init_dev()
> +		 */
> +		put_pts_ns(pts_ns);
> +	}
>  }
> 
>  /**
> @@ -2666,6 +2711,7 @@ static int tty_open(struct inode *inode,
>  	int index;
>  	dev_t device = inode->i_rdev;
>  	unsigned short saved_flags = filp->f_flags;
> +	struct pts_namespace *pts_ns;
> 
>  	nonseekable_open(inode, filp);
> 
> @@ -2715,7 +2761,20 @@ retry_open:
>  		return -ENODEV;
>  	}
>  got_driver:
> -	retval = init_dev(driver, index, &tty);
> +
> +	/*
> +	 * What pts-ns do we want to use when opening "/dev/tty" ?
> +	 
...

Re: [PATCH 4/7] Implement get_pts_ns() and put_pts_ns() [message #28633 is a reply to message #28600] Tue, 25 March 2008 15:29 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> 
> From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> Subject: [PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
> 
> Implement get_pts_ns() and put_pts_ns() interfaces.
> 
> Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> ---
>  include/linux/devpts_fs.h |   21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
> ===================================================================
> --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:31.000000000 -0700
> +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
> @@ -27,13 +27,26 @@ struct pts_namespace {
>  extern struct pts_namespace init_pts_ns;
> 
>  #ifdef CONFIG_UNIX98_PTYS
> -
>  int devpts_new_index(void);
>  void devpts_kill_index(int idx);
>  int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
>  struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
>  void devpts_pty_kill(int number);		 /* unlink */
> 
> +static inline void free_pts_ns(struct kref *ns_kref) { }
> +
> +static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
> +{
> +	if (ns && (ns != &init_pts_ns))
> +		kref_get(&ns->kref);
> +	return ns;
> +}
> +static inline void put_pts_ns(struct pts_namespace *ns)
> +{
> +	if (ns && (ns != &init_pts_ns))
> +		kref_put(&ns->kref, free_pts_ns);

This isn't right, or I'm not thinking right.  Don't you somewhere
need to

	1. rcu_assign ns->mnt->mnt_sb->s_fs_info to NULL
	2. wait a grace period
	3. call free_pts_ns and check the refcount on the ns again?

and then do pts_ns_from_inode() under an rcu_read_lock and grab
a ref to the ns?

> +}
> +
>  #else
> 
>  /* Dummy stubs in the no-pty case */
> @@ -43,6 +56,12 @@ static inline int devpts_pty_new(struct 
>  static inline struct tty_struct *devpts_get_tty(int number) { return NULL; }
>  static inline void devpts_pty_kill(int number) { }
> 
> +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) { }
>  #endif
> 
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Re: [PATCH 6/7]: Check for user-space mount of /dev/pts [message #28637 is a reply to message #28630] Tue, 25 March 2008 17:25 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Serge E. Hallyn [serue@us.ibm.com] wrote:
| Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
| > 
| > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > Subject: [PATCH 6/7]: Check for user-space mount of /dev/pts
| > 
| > When the pts namespace is cloned, the /dev/pts is not useful unless it
| > is remounted from the user space.
| > 
| > If user-space clones pts namespace but does not remount /dev/pts, it
| > would end up using the /dev/pts mount from parent-pts-ns but allocate
| > the pts indices from current pts ns.
| 
| So why not use the allocated_ptys from the parent ptsns?  It's what
| userspace asked for and it's safe to do.

The problem is when opening /dev/ptmx, we use current_pts_ns() and
when opening slave-pty, we use pts_ns from the inode.

If child-pts-ns opens /dev/ptmx, we use 'allocated-ptys' from
child-pts-ns and we allocate index 0. But when the process opens
the slave pty "/dev/pts/0", we would get the pts_ns from the
inode which would come from parent-pts-ns (and could refer to
an existing pty).

Agree with Alexey and Pavel, its bad. Will think some more, but
appreciate any ideas.

Sukadev
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Re: [PATCH 4/7] Implement get_pts_ns() and put_pts_ns() [message #28642 is a reply to message #28633] Tue, 25 March 2008 18:44 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Serge E. Hallyn [serue@us.ibm.com] wrote:
| Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
| > 
| > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > Subject: [PATCH 4/7]: Implement get_pts_ns() and put_pts_ns()
| > 
| > Implement get_pts_ns() and put_pts_ns() interfaces.
| > 
| > Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > ---
| >  include/linux/devpts_fs.h |   21 ++++++++++++++++++++-
| >  1 file changed, 20 insertions(+), 1 deletion(-)
| > 
| > Index: 2.6.25-rc5-mm1/include/linux/devpts_fs.h
| > ===================================================================
| > --- 2.6.25-rc5-mm1.orig/include/linux/devpts_fs.h	2008-03-24 20:04:31.000000000 -0700
| > +++ 2.6.25-rc5-mm1/include/linux/devpts_fs.h	2008-03-24 20:05:05.000000000 -0700
| > @@ -27,13 +27,26 @@ struct pts_namespace {
| >  extern struct pts_namespace init_pts_ns;
| > 
| >  #ifdef CONFIG_UNIX98_PTYS
| > -
| >  int devpts_new_index(void);
| >  void devpts_kill_index(int idx);
| >  int devpts_pty_new(struct tty_struct *tty);      /* mknod in devpts */
| >  struct tty_struct *devpts_get_tty(int number);	 /* get tty structure */
| >  void devpts_pty_kill(int number);		 /* unlink */
| > 
| > +static inline void free_pts_ns(struct kref *ns_kref) { }
| > +
| > +static inline struct pts_namespace *get_pts_ns(struct pts_namespace *ns)
| > +{
| > +	if (ns && (ns != &init_pts_ns))
| > +		kref_get(&ns->kref);
| > +	return ns;
| > +}
| > +static inline void put_pts_ns(struct pts_namespace *ns)
| > +{
| > +	if (ns && (ns != &init_pts_ns))
| > +		kref_put(&ns->kref, free_pts_ns);
| 
| This isn't right, or I'm not thinking right.  Don't you somewhere
| need to
| 
| 	1. rcu_assign ns->mnt->mnt_sb->s_fs_info to NULL
| 	2. wait a grace period
| 	3. call free_pts_ns and check the refcount on the ns again?
| 
| and then do pts_ns_from_inode() under an rcu_read_lock and grab
| a ref to the ns?

Yes, we need the rcu to grab the reference to pts_ns.
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28645 is a reply to message #28632] Tue, 25 March 2008 21:14 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting Serge E. Hallyn (serue@us.ibm.com):
> Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> > 
> > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> > Subject: [PATCH 5/7]: Determine pts_ns from a pty's inode.
> > 
> > The devpts interfaces currently operate on a specific pts namespace
> > which they get from the 'current' task.
> > 
> > With implementation of containers and cloning of PTS namespaces, we want
> > to be able to access PTYs in a child-pts-ns from a parent-pts-ns. For
> > instance we could bind-mount and pivot-root the child container on
> > '/vserver/vserver1' and then access the "pts/0" of 'vserver1' using 
> > 
> > 	$ echo foo > /vserver/vserver1/dev/pts/0
> > 	
> > The task doing the above 'echo' could be in parent-pts-ns. So we find
> > the 'pts-ns' of the above file from the inode representing the above
> > file rather than from the 'current' task.
> > 
> > Note that we need to find and hold a reference to the pts_ns to prevent
> > the pts_ns from being freed while it is being accessed from 'outside'.
> > 
> > This patch implements, 'pts_ns_from_inode()' which returns the pts_ns
> > using 'inode->i_sb->s_fs_info'.
> > 
> > Since, the 'inode' information is not visible inside devpts code itself,
> > this patch modifies the tty driver code to determine the pts_ns and passes
> > it into devpts.
> > 
> > TODO:
> > 	What is the expected behavior when '/dev/tty' or '/dev/ptmx' are
> > 	accessed from parent-pts-ns. i.e:
> > 
> > 		$ echo "foobar" > /vserver/vserver1/dev/tty)
> > 		
> > 	This patch currently ignores the '/vserver/vserver1' part (that
> 
> The way this is phrased it almost sounds like you're considering using
> the pathnames to figure out the ptsns to use :).
> 
> It's not clear to me what is the sane thing to do.
> 
> what you're doing here - have /dev/ptmx and /dev/tty always use
> current->'s ptsns - isn't ideal.
> 
> It would be nicer to not have a 'devpts ns', and instead have a
> full device namespace.  However, then it still isn't clear how to tie
> /vs/vs1/dev/ptmx to vs1's device namespace, since there is no device
> fs to which to tie the devns.
> 
> We could tie the devns to a device inode on mknod, using the devns of
> the creating task.  Then when starting up vs1, you just have to always
> let vs1 create /dev/ptmx and /dev/tty.  I can't think of anything
> better offhand.
> 
> Other ideas?

I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
Recommend that in containers /dev/ptmx and /dev/tty be symlinks
into /dev/pts.  Applications don't need to change.  If
ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
namespace from the sb.  If not, then it was a device in /dev
and it gets the nmespace from current.

-serge
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28651 is a reply to message #28645] Wed, 26 March 2008 02:03 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Serge E. Hallyn [serue@us.ibm.com] wrote:
| Quoting Serge E. Hallyn (serue@us.ibm.com):
| > Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
| > > 
| > > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| > > Subject: [PATCH 5/7]: Determine pts_ns from a pty's inode.
| > > 
| > > The devpts interfaces currently operate on a specific pts namespace
| > > which they get from the 'current' task.
| > > 
| > > With implementation of containers and cloning of PTS namespaces, we want
| > > to be able to access PTYs in a child-pts-ns from a parent-pts-ns. For
| > > instance we could bind-mount and pivot-root the child container on
| > > '/vserver/vserver1' and then access the "pts/0" of 'vserver1' using 
| > > 
| > > 	$ echo foo > /vserver/vserver1/dev/pts/0
| > > 	
| > > The task doing the above 'echo' could be in parent-pts-ns. So we find
| > > the 'pts-ns' of the above file from the inode representing the above
| > > file rather than from the 'current' task.
| > > 
| > > Note that we need to find and hold a reference to the pts_ns to prevent
| > > the pts_ns from being freed while it is being accessed from 'outside'.
| > > 
| > > This patch implements, 'pts_ns_from_inode()' which returns the pts_ns
| > > using 'inode->i_sb->s_fs_info'.
| > > 
| > > Since, the 'inode' information is not visible inside devpts code itself,
| > > this patch modifies the tty driver code to determine the pts_ns and passes
| > > it into devpts.
| > > 
| > > TODO:
| > > 	What is the expected behavior when '/dev/tty' or '/dev/ptmx' are
| > > 	accessed from parent-pts-ns. i.e:
| > > 
| > > 		$ echo "foobar" > /vserver/vserver1/dev/tty)
| > > 		
| > > 	This patch currently ignores the '/vserver/vserver1' part (that
| > 
| > The way this is phrased it almost sounds like you're considering using
| > the pathnames to figure out the ptsns to use :).
| > 
| > It's not clear to me what is the sane thing to do.
| > 
| > what you're doing here - have /dev/ptmx and /dev/tty always use
| > current->'s ptsns - isn't ideal.
| > 
| > It would be nicer to not have a 'devpts ns', and instead have a
| > full device namespace.  However, then it still isn't clear how to tie
| > /vs/vs1/dev/ptmx to vs1's device namespace, since there is no device
| > fs to which to tie the devns.
| > 
| > We could tie the devns to a device inode on mknod, using the devns of
| > the creating task.  Then when starting up vs1, you just have to always
| > let vs1 create /dev/ptmx and /dev/tty.  I can't think of anything
| > better offhand.
| > 
| > Other ideas?
| 
| I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
| Recommend that in containers /dev/ptmx and /dev/tty be symlinks
| into /dev/pts.  Applications don't need to change.  If
| ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
| namespace from the sb.  If not, then it was a device in /dev
| and it gets the nmespace from current.

But we would still depend on user-space remounting /dev/pts after
the clone right ? Until they do that we would access the parent
container's /dev/pts/ptmx ?
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28652 is a reply to message #28651] Wed, 26 March 2008 02:50 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> Serge E. Hallyn [serue@us.ibm.com] wrote:
> | Quoting Serge E. Hallyn (serue@us.ibm.com):
> | > Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> | > > 
> | > > From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
> | > > Subject: [PATCH 5/7]: Determine pts_ns from a pty's inode.
> | > > 
> | > > The devpts interfaces currently operate on a specific pts namespace
> | > > which they get from the 'current' task.
> | > > 
> | > > With implementation of containers and cloning of PTS namespaces, we want
> | > > to be able to access PTYs in a child-pts-ns from a parent-pts-ns. For
> | > > instance we could bind-mount and pivot-root the child container on
> | > > '/vserver/vserver1' and then access the "pts/0" of 'vserver1' using 
> | > > 
> | > > 	$ echo foo > /vserver/vserver1/dev/pts/0
> | > > 	
> | > > The task doing the above 'echo' could be in parent-pts-ns. So we find
> | > > the 'pts-ns' of the above file from the inode representing the above
> | > > file rather than from the 'current' task.
> | > > 
> | > > Note that we need to find and hold a reference to the pts_ns to prevent
> | > > the pts_ns from being freed while it is being accessed from 'outside'.
> | > > 
> | > > This patch implements, 'pts_ns_from_inode()' which returns the pts_ns
> | > > using 'inode->i_sb->s_fs_info'.
> | > > 
> | > > Since, the 'inode' information is not visible inside devpts code itself,
> | > > this patch modifies the tty driver code to determine the pts_ns and passes
> | > > it into devpts.
> | > > 
> | > > TODO:
> | > > 	What is the expected behavior when '/dev/tty' or '/dev/ptmx' are
> | > > 	accessed from parent-pts-ns. i.e:
> | > > 
> | > > 		$ echo "foobar" > /vserver/vserver1/dev/tty)
> | > > 		
> | > > 	This patch currently ignores the '/vserver/vserver1' part (that
> | > 
> | > The way this is phrased it almost sounds like you're considering using
> | > the pathnames to figure out the ptsns to use :).
> | > 
> | > It's not clear to me what is the sane thing to do.
> | > 
> | > what you're doing here - have /dev/ptmx and /dev/tty always use
> | > current->'s ptsns - isn't ideal.
> | > 
> | > It would be nicer to not have a 'devpts ns', and instead have a
> | > full device namespace.  However, then it still isn't clear how to tie
> | > /vs/vs1/dev/ptmx to vs1's device namespace, since there is no device
> | > fs to which to tie the devns.
> | > 
> | > We could tie the devns to a device inode on mknod, using the devns of
> | > the creating task.  Then when starting up vs1, you just have to always
> | > let vs1 create /dev/ptmx and /dev/tty.  I can't think of anything
> | > better offhand.
> | > 
> | > Other ideas?
> | 
> | I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
> | Recommend that in containers /dev/ptmx and /dev/tty be symlinks
> | into /dev/pts.  Applications don't need to change.  If
> | ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
> | namespace from the sb.  If not, then it was a device in /dev
> | and it gets the nmespace from current.
> 
> But we would still depend on user-space remounting /dev/pts after
> the clone right ? Until they do that we would access the parent
> container's /dev/pts/ptmx ?

Yes.  Which is the right thing to do imo.

-serge
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28695 is a reply to message #28652] Wed, 26 March 2008 14:55 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Serge E. Hallyn [serue@us.ibm.com] wrote:
| > | I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
| > | Recommend that in containers /dev/ptmx and /dev/tty be symlinks
| > | into /dev/pts.  Applications don't need to change.  If
| > | ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
| > | namespace from the sb.  If not, then it was a device in /dev
| > | and it gets the nmespace from current.
| > 
| > But we would still depend on user-space remounting /dev/pts after
| > the clone right ? Until they do that we would access the parent
| > container's /dev/pts/ptmx ?
| 
| Yes.  Which is the right thing to do imo.

Hmm, that sounds reasonable, although slightly inconsistent with pid-ns,
where pid starts at 1 regardless of whether /proc is remounted.

But even so, if user fails to establish the symlink, clones the pts ns
and tries to create a pty, we would end up with different pts nses again ?

i.e
	/dev/ptmx is still a char dev in root fs
	clone(pts_ns)
		( In child, (before remount /dev/pts))
		open("/dev/ptmx")
		open("/dev/pts/0")

Since ptmx is not in devpts, we use current_pts_ns() or child-pts-ns
Since /dev/pts is not remounted in child, we get the parent pts-ns from

If we can somehow detect the incorrect configuration and fail either
open, we should be ok :-)
inode.

Suka
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28696 is a reply to message #28695] Wed, 26 March 2008 15:12 Go to previous messageGo to next message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> Serge E. Hallyn [serue@us.ibm.com] wrote:
> | > | I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
> | > | Recommend that in containers /dev/ptmx and /dev/tty be symlinks
> | > | into /dev/pts.  Applications don't need to change.  If
> | > | ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
> | > | namespace from the sb.  If not, then it was a device in /dev
> | > | and it gets the nmespace from current.
> | > 
> | > But we would still depend on user-space remounting /dev/pts after
> | > the clone right ? Until they do that we would access the parent
> | > container's /dev/pts/ptmx ?
> | 
> | Yes.  Which is the right thing to do imo.
> 
> Hmm, that sounds reasonable, although slightly inconsistent with pid-ns,
> where pid starts at 1 regardless of whether /proc is remounted.

Very different cases.  The pid is the task's pid in the new pidns.
The task ALSO has a different pid in the parent pidns.

The pts only has an identity in one ptsns.

> But even so, if user fails to establish the symlink, clones the pts ns
> and tries to create a pty, we would end up with different pts nses again ?

Yes.  So what?

> i.e
> 	/dev/ptmx is still a char dev in root fs
> 	clone(pts_ns)
> 		( In child, (before remount /dev/pts))
> 		open("/dev/ptmx")
> 		open("/dev/pts/0")
> 
> Since ptmx is not in devpts, we use current_pts_ns() or child-pts-ns
> Since /dev/pts is not remounted in child, we get the parent pts-ns from
> 
> If we can somehow detect the incorrect configuration and fail either
> open, we should be ok :-)

I completely disagree with this sentiment.  The kernel doesn't need
to detect an "incorrect configuration" if it isn't dangerous.  One
man's "incorrect configuration" is another man's useful trick.

-serge
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28697 is a reply to message #28696] Wed, 26 March 2008 15:18 Go to previous messageGo to next message
Sukadev Bhattiprolu is currently offline  Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
Senior Member
Serge E. Hallyn [serue@us.ibm.com] wrote:
| Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
| > Serge E. Hallyn [serue@us.ibm.com] wrote:
| > | > | I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
| > | > | Recommend that in containers /dev/ptmx and /dev/tty be symlinks
| > | > | into /dev/pts.  Applications don't need to change.  If
| > | > | ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
| > | > | namespace from the sb.  If not, then it was a device in /dev
| > | > | and it gets the nmespace from current.
| > | > 
| > | > But we would still depend on user-space remounting /dev/pts after
| > | > the clone right ? Until they do that we would access the parent
| > | > container's /dev/pts/ptmx ?
| > | 
| > | Yes.  Which is the right thing to do imo.
| > 
| > Hmm, that sounds reasonable, although slightly inconsistent with pid-ns,
| > where pid starts at 1 regardless of whether /proc is remounted.
| 
| Very different cases.  The pid is the task's pid in the new pidns.
| The task ALSO has a different pid in the parent pidns.
| 
| The pts only has an identity in one ptsns.
| 
| > But even so, if user fails to establish the symlink, clones the pts ns
| > and tries to create a pty, we would end up with different pts nses again ?
| 
| Yes.  So what?

We would end up allocating a pts index from child-pts-ns (i.e index 0)
and attempt to open /dev/pts/0 which could be an existing pty in the
parent pts ns ?
| 
| > i.e
| > 	/dev/ptmx is still a char dev in root fs
| > 	clone(pts_ns)
| > 		( In child, (before remount /dev/pts))
| > 		open("/dev/ptmx")
| > 		open("/dev/pts/0")
| > 
| > Since ptmx is not in devpts, we use current_pts_ns() or child-pts-ns
| > Since /dev/pts is not remounted in child, we get the parent pts-ns from
| > 
| > If we can somehow detect the incorrect configuration and fail either
| > open, we should be ok :-)
| 
| I completely disagree with this sentiment.  The kernel doesn't need
| to detect an "incorrect configuration" if it isn't dangerous.  One
| man's "incorrect configuration" is another man's useful trick.

Myabe configuration is the wrong word, but unless I am missing something
above, spanning two pts-nses is an error condition ?
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Re: [PATCH 5/7]: Determine pts_ns from a pty's inode. [message #28700 is a reply to message #28697] Wed, 26 March 2008 15:43 Go to previous message
serue is currently offline  serue
Messages: 750
Registered: February 2006
Senior Member
Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> Serge E. Hallyn [serue@us.ibm.com] wrote:
> | Quoting sukadev@us.ibm.com (sukadev@us.ibm.com):
> | > Serge E. Hallyn [serue@us.ibm.com] wrote:
> | > | > | I suppose you could just create /dev/pts/ptmx and /dev/pts/tty.
> | > | > | Recommend that in containers /dev/ptmx and /dev/tty be symlinks
> | > | > | into /dev/pts.  Applications don't need to change.  If
> | > | > | ptmx_open() sees that inode->i_sb is a devptsfs, it gets the
> | > | > | namespace from the sb.  If not, then it was a device in /dev
> | > | > | and it gets the nmespace from current.
> | > | > 
> | > | > But we would still depend on user-space remounting /dev/pts after
> | > | > the clone right ? Until they do that we would access the parent
> | > | > container's /dev/pts/ptmx ?
> | > | 
> | > | Yes.  Which is the right thing to do imo.
> | > 
> | > Hmm, that sounds reasonable, although slightly inconsistent with pid-ns,
> | > where pid starts at 1 regardless of whether /proc is remounted.
> | 
> | Very different cases.  The pid is the task's pid in the new pidns.
> | The task ALSO has a different pid in the parent pidns.
> | 
> | The pts only has an identity in one ptsns.
> | 
> | > But even so, if user fails to establish the symlink, clones the pts ns
> | > and tries to create a pty, we would end up with different pts nses again ?
> | 
> | Yes.  So what?
> 
> We would end up allocating a pts index from child-pts-ns (i.e index 0)
> and attempt to open /dev/pts/0 which could be an existing pty in the
> parent pts ns ?

An SELinux policy tagging child devpts entries with vps1_u:vps1_r:vps1_pts_t
and not allowing vps1_t access to host_pts_t entries would forbid it if
you wanted.  But failing that, the kernel doesn't break, so I don't
it's a problem.

> | > i.e
> | > 	/dev/ptmx is still a char dev in root fs
> | > 	clone(pts_ns)
> | > 		( In child, (before remount /dev/pts))
> | > 		open("/dev/ptmx")
> | > 		open("/dev/pts/0")
> | > 
> | > Since ptmx is not in devpts, we use current_pts_ns() or child-pts-ns
> | > Since /dev/pts is not remounted in child, we get the parent pts-ns from
> | > 
> | > If we can somehow detect the incorrect configuration and fail either
> | > open, we should be ok :-)
> | 
> | I completely disagree with this sentiment.  The kernel doesn't need
> | to detect an "incorrect configuration" if it isn't dangerous.  One
> | man's "incorrect configuration" is another man's useful trick.
> 
> Myabe configuration is the wrong word, but unless I am missing something
> above, spanning two pts-nses is an error condition ?

For userspace, but it doesn't crash the kernel.  Userspace didn't set
things up right, so it gets the wrong thing.  If I do a dup2 into fd 3
and then try to read from fd 4, I get the wrong data.  Is that the
kernel's fault?

-serge
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