[RFC] checkpoint/restart of PTYs

[RFC] checkpoint/restart of PTYs

[Oren Laadan]

This short series adds support for checkpoint and restart of PTYs. It
is mildly tested on top of ckpt-v17-dev (with test/pty from user-cr).

I'm not an expert on PTYs, TTYs, line disciplines and the like,
comments are mostly welcome:

* Only handles PTYs related to open files (no signal->...)

* What (additional) values we need to sanitize on restart ?

* What additional locking should be in place ? (especially checkpoint)

* Need to save/restore echo buffer (and position) ?

* /dev/ptmx and /dev/pts/... paths are currently hardcoded

* For restart without restoring PIDs, need to ensure the session and
  pgrp are either -1 (none) or limited to a PID value that belongs to
  the restarted subtree.

* For restart with restoring PIDs, need to create on-the-fly session
  and/or pgrp PIDs that do not exist (e.g. of a dead process). This is
  also necessary to correctly restore pgrp, regardless of PTYs.

* Other security concerns ? ...

* and probably more :p

Oren.

[RFC][PATCH 1/3] c/r: [objhash] add ckpt_obj_reserve()

[Oren Laadan]

Use ckpt_obj_reserve() during checkpoint to reserve an objref that
will not be otherwise used for any other object in checkpoint. Such an
objref can be useful for restart to add objects that were not there at
checkpoint.

One use case for this is ptys (subsequent patches): when restoring a
master pty, we create a file pointer, which must be kept somewhere and
later cleaned up. The hash is a good place to store it.

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 checkpoint/objhash.c       |   20 +++++++++++++++++++-
 include/linux/checkpoint.h |    1 +
 2 files changed, 20 insertions(+), 1 deletions(-)

diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
index dc0a10a..2ea71bd 100644
--- a/checkpoint/objhash.c
+++ b/checkpoint/objhash.c
@@ -465,6 +465,11 @@ static struct ckpt_obj *obj_find_by_objref(struct ckpt_ctx *ctx, int objref)
 	return NULL;
 }
 
+static inline int obj_alloc_objref(struct ckpt_ctx *ctx)
+{
+	return ctx->obj_hash->next_free_objref++;
+}
+
 /**
  * ckpt_obj_new - add an object to the obj_hash
  * @ctx: checkpoint context
@@ -498,7 +503,7 @@ static struct ckpt_obj *obj_new(struct ckpt_ctx *ctx, void *ptr,
 
 	if (!objref) {
 		/* use @obj->ptr to index, assign objref (checkpoint) */
-		obj->objref = ctx->obj_hash->next_free_objref++;;
+		obj->objref = obj_alloc_objref(ctx);
 		i = hash_long((unsigned long) ptr, CKPT_OBJ_HASH_NBITS);
 	} else {
 		/* use @obj->objref to index (restart) */
@@ -637,6 +642,19 @@ int ckpt_obj_lookup_add(struct ckpt_ctx *ctx, void *ptr,
 }
 
 /**
+ * ckpt_obj_reserve - reserve an objref
+ * @ctx: checkpoint context
+ *
+ * The reserved objref will not be used for subsequent objects. This
+ * gives an objref that can be safely used during restart without a
+ * matching object in checkpoint.  [used during checkpoint].
+ */
+int ckpt_obj_reserve(struct ckpt_ctx *ctx)
+{
+	return obj_alloc_objref(ctx);
+}
+
+/**
  * checkpoint_obj - if not already in hash, add object and checkpoint
  * @ctx: checkpoint context
  * @ptr: pointer to object
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 761cad5..1d050f8 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -121,6 +121,7 @@ extern void *ckpt_obj_fetch(struct ckpt_ctx *ctx, int objref,
 			    enum obj_type type);
 extern int ckpt_obj_insert(struct ckpt_ctx *ctx, void *ptr, int objref,
 			   enum obj_type type);
+extern int ckpt_obj_reserve(struct ckpt_ctx *ctx);
 
 extern void ckpt_ctx_get(struct ckpt_ctx *ctx);
 extern void ckpt_ctx_put(struct ckpt_ctx *ctx);
-- 
1.6.0.4

[RFC][PATCH 2/3] c/r: [pty 1/2] allow allocation of desired pty slave

[Oren Laadan]

During restart, we need to allocate pty slaves with the same
identifiers as recorded during checkpoint. Modify the allocation code
to allow an in-kernel caller to request a specific slave identifier.

For this, add a new field to task_struct - 'required_id'. It will
hold the desired identifier when restoring a (master) pty.

The code in ptmx_open() will use this value only for tasks that try to
open /dev/ptmx that are restarting (PF_RESTARTING), and if the value
isn't CKPT_REQUIRED_NONE (-1).

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 checkpoint/sys.c           |    7 +++++++
 drivers/char/pty.c         |    9 +++++++--
 fs/devpts/inode.c          |   10 ++++++++--
 include/linux/checkpoint.h |    2 ++
 include/linux/devpts_fs.h  |    2 +-
 include/linux/sched.h      |    1 +
 6 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/checkpoint/sys.c b/checkpoint/sys.c
index 525182a..3db18f7 100644
--- a/checkpoint/sys.c
+++ b/checkpoint/sys.c
@@ -339,6 +339,13 @@ SYSCALL_DEFINE3(restart, pid_t, pid, int, fd, unsigned long, flags)
 	return ret;
 }
 
+static int __init checkpoint_init(void)
+{
+	init_task.required_id = CKPT_REQUIRED_NONE;
+	return 0;
+}
+__initcall(checkpoint_init);
+
 
 /* 'ckpt_debug_level' controls the verbosity level of c/r code */
 #ifdef CONFIG_CHECKPOINT_DEBUG
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 6e6942c..326c2e9 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -633,12 +633,17 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
 {
 	struct tty_struct *tty;
 	int retval;
-	int index;
+	int index = 0;
 
 	nonseekable_open(inode, filp);
 
+#ifdef CONFIG_CHECKPOINT
+	/* when restarting, request specific index */
+	if (current->flags & PF_RESTARTING)
+		index = (int) current->required_id;
+#endif
 	/* find a device that is not in use. */
-	index = devpts_new_index(inode);
+	index = devpts_new_index(inode, index);
 	if (index < 0)
 		return index;
 
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 75efb02..8921726 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -433,7 +433,7 @@ static struct file_system_type devpts_fs_type = {
  * to the System V naming convention
  */
 
-int devpts_new_index(struct inode *ptmx_inode)
+int devpts_new_index(struct inode *ptmx_inode, int req_idx)
 {
 	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
@@ -445,7 +445,8 @@ retry:
 		return -ENOMEM;
 
 	mutex_lock(&allocated_ptys_lock);
-	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
+	index = (req_idx >= 0 ? req_idx : 0);
+	ida_ret = ida_get_new_above(&fsi->allocated_ptys, index, &index);
 	if (ida_ret < 0) {
 		mutex_unlock(&allocated_ptys_lock);
 		if (ida_ret == -EAGAIN)
@@ -453,6 +454,11 @@ retry:
 		return -EIO;
 	}
 
+	if (req_idx >= 0 && index != req_idx) {
+		ida_remove(&fsi->allocated_ptys, index);
+		mutex_unlock(&allocated_ptys_lock);
+		return -EBUSY;
+	}
 	if (index >= pty_limit) {
 		ida_remove(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 1d050f8..473164e 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -46,6 +46,8 @@
 #define CHECKPOINT_USER_FLAGS		CHECKPOINT_SUBTREE
 #define RESTART_USER_FLAGS		(RESTART_TASKSELF | RESTART_FROZEN)
 
+#define CKPT_REQUIRED_NONE  ((unsigned long) -1L)
+
 extern void exit_checkpoint(struct task_struct *tsk);
 
 extern int ckpt_kwrite(struct ckpt_ctx *ctx, void *buf, int count);
diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 5ce0e5f..14948ee 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -17,7 +17,7 @@
 
 #ifdef CONFIG_UNIX98_PTYS
 
-int devpts_new_index(struct inode *ptmx_inode);
+int devpts_new_index(struct inode *ptmx_inode, int req_idx);
 void devpts_kill_index(struct inode *ptmx_inode, int idx);
 /* mknod in devpts */
 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0e67de7..f6f1350 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1481,6 +1481,7 @@ struct task_struct {
 #endif /* CONFIG_TRACING */
 #ifdef CONFIG_CHECKPOINT
 	struct ckpt_ctx *checkpoint_ctx;
+	unsigned long required_id;
 #endif
 };
 
-- 
1.6.0.4

Re: [RFC][PATCH 2/3] c/r: [pty 1/2] allow allocation of desired pty slave

[Serge E. Hallyn]

Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> During restart, we need to allocate pty slaves with the same
> identifiers as recorded during checkpoint. Modify the allocation code
> to allow an in-kernel caller to request a specific slave identifier.
> 
> For this, add a new field to task_struct - 'required_id'. It will
> hold the desired identifier when restoring a (master) pty.

This is really unfortunate.

I assume you left the rather generic name 'required_id' because
you intend to use it for other calls as well?  Which is even
more unfortunate...

I know I'm generally the one who pushes for re-using existing
helpers as much as possible, both to avoid missing existing
security checks, and to prevent future code changes which forget
to update the c/r code.

But in this case I don't think re-using fopen to ask the kernel
to create a new device with more info than fopen usually gets is
right.  Unfortunately, actually coming up with 'the right way' is
escaping me at the moment :)

Though... then again...  your code is hardcoded for devpts and
opening /dev/ptmx anyway, so surely we can create a new helper
which takes a devpts_ns and index and returns the new devpts
tty_struct without using the current->required_id?

Then, if we ever want to support a tty type other than unix98,
maybe we can more generally split up more like:

	1. add 'struct tty_struct *make_tty(struct tty_driver *driver,
			void *data) to tty_operations.  It is
			undefined for all but devpts.
	2. for devpts, the void *data includes an int devpts_ns_id
			and index
	3. the container-level checkpoint stores a relation between
		pathnames and devpts_ns_id.  devpts_ns_id is valid
		only for one checkpoint image.  The pathname is
		where that devpts_ns is mounted.  If we ever start
		checkpointing and restoring fs mounts from kernel,
		then we can tweak this treatment.  For now it is
		assumed (and verified) that at restart, pathname is
		in fact where a devpts instance is mounted.
	4. the tty_struct itself is checkpointed and restored.  It
		is restored using make_tty() in tty_operations,
		and for devpts the void *data  is a struct storing
		the devpts_ns_id and index.
	5. when a struct file for a devpts is restored, the tty_struct
		will already have been re-created.  The  tty_struct's objref
		is stored in the file struct checkpoint data.

It requires more finagling of the file/inode/tty_struct relationship
though...  But I don't see required_id being acceptable upstream.

Of course I've been wrong about such things before.

-serge

Re: [RFC][PATCH 2/3] c/r: [pty 1/2] allow allocation of desired pty slave

[Oren Laadan]

Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
>> During restart, we need to allocate pty slaves with the same
>> identifiers as recorded during checkpoint. Modify the allocation code
>> to allow an in-kernel caller to request a specific slave identifier.
>>
>> For this, add a new field to task_struct - 'required_id'. It will
>> hold the desired identifier when restoring a (master) pty.
> 
> This is really unfortunate.

:(

> 
> I assume you left the rather generic name 'required_id' because
> you intend to use it for other calls as well?  Which is even
> more unfortunate...

:'(

> 
> I know I'm generally the one who pushes for re-using existing
> helpers as much as possible, both to avoid missing existing
> security checks, and to prevent future code changes which forget
> to update the c/r code.
> 
> But in this case I don't think re-using fopen to ask the kernel
> to create a new device with more info than fopen usually gets is
> right.  Unfortunately, actually coming up with 'the right way' is
> escaping me at the moment :)
> 
> Though... then again...  your code is hardcoded for devpts and
> opening /dev/ptmx anyway, so surely we can create a new helper
> which takes a devpts_ns and index and returns the new devpts
> tty_struct without using the current->required_id?

The problem is that the way pty works: the index allocation takes
place inside ptmx_open(). As it is, I can't find of a way to
directly transfer a piece of data to it, because all we do is
call filp_open().

For this, we need add new functionality for pty code to

a) Allocate a master PTY without the corresponding file; this
function will be called from ptmx_open() and from restart code,
and will accept the "desired index" variable.

b) Attach an existing (master) PTY to a file pointer. This
will also be called from ptmx_open() and from restart code.

and

c) For restart only, manually do the work of filp_open() to
create a file, dentry, inode etc. This is what I really wanted
to avoid.

> 
> Then, if we ever want to support a tty type other than unix98,
> maybe we can more generally split up more like:

Other tty types have index that is indicated by the device minor
number (e.g. old style PTYs) or no index considerations :)

Oren.

> 
> 	1. add 'struct tty_struct *make_tty(struct tty_driver *driver,
> 			void *data) to tty_operations.  It is
> 			undefined for all but devpts.
> 	2. for devpts, the void *data includes an int devpts_ns_id
> 			and index
> 	3. the container-level checkpoint stores a relation between
> 		pathnames and devpts_ns_id.  devpts_ns_id is valid
> 		only for one checkpoint image.  The pathname is
> 		where that devpts_ns is mounted.  If we ever start
> 		checkpointing and restoring fs mounts from kernel,
> 		then we can tweak this treatment.  For now it is
> 		assumed (and verified) that at restart, pathname is
> 		in fact where a devpts instance is mounted.
> 	4. the tty_struct itself is checkpointed and restored.  It
> 		is restored using make_tty() in tty_operations,
> 		and for devpts the void *data  is a struct storing
> 		the devpts_ns_id and index.
> 	5. when a struct file for a devpts is restored, the tty_struct
> 		will already have been re-created.  The  tty_struct's objref
> 		is stored in the file struct checkpoint data.
> 
> It requires more finagling of the file/inode/tty_struct relationship
> though...  But I don't see required_id being acceptable upstream.
> 
> Of course I've been wrong about such things before.
> 
> -serge

[RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Oren Laadan]

This patch adds support for checkpoint and restart of pseudo terminals
(PTYs). Since PTYs are shared (pointed to by file, and signal), they
are managed via objhash.

PTYs are master/slave pairs; The code arranges for the master to
always be checkpointed first, followed by the slave. This is important
since during restart both ends are created when restoring the master.

In this patch only UNIX98 style PTYs are supported.

Currently only PTYs that are referenced by open files are handled.
Thus PTYs checkpoint starts with a file in tty_file_checkpoint(). It
will first checkpoint the master and slave PTYs via tty_checkpoint(),
and then complete the saving of the file descriptor. This means that
in the image file, the order of objects is: master-tty, slave-tty,
file-desc.

During restart, to restore the master side, we open the /dev/ptmx
device and get a file handle. But at this point we don't know the
designated objref for this file, because the file is due later on in
the image stream. On the other hand, we can't just fput() the file
because it will close the PTY too.

Instead, when we checkpoint the master PTY, we _reserve_ an objref
for the file (which won't be further used in checkpoint). Then at
restart, use it to insert the file to objhash.

TODO:

* Better sanitize input from checkpoint image on restore
* Check the locking when saving/restoring tty_struct state
* Echo position/buffer isn't saved (is it needed ?)
* Handle multiple devpts mounts (namespaces)
* Handle case where session/pgrp do not exist on restart
* Paths of ptmx and slaves are hard coded (/dev/ptmx, /dev/pts/...)

Signed-off-by: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
---
 arch/x86/include/asm/checkpoint_hdr.h |    9 +
 checkpoint/files.c                    |    6 +
 checkpoint/objhash.c                  |   26 ++
 drivers/char/pty.c                    |    2 +-
 drivers/char/tty_io.c                 |  511 ++++++++++++++++++++++++++++++++-
 include/linux/checkpoint.h            |    5 +
 include/linux/checkpoint_hdr.h        |   76 +++++
 include/linux/tty.h                   |    6 +
 8 files changed, 639 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h
index 1228d1b..13634fd 100644
--- a/arch/x86/include/asm/checkpoint_hdr.h
+++ b/arch/x86/include/asm/checkpoint_hdr.h
@@ -56,6 +56,15 @@ enum {
 #endif
 #endif
 
+#define CKPT_TTY_NCC  8
+#ifdef __KERNEL__
+#include <linux/tty.h>
+#if CKPT_TTY_NCC != NCC
+#error CKPT_TTY_NCC size is wrong per asm-generic/termios.h
+#endif
+#endif
+
+
 struct ckpt_hdr_header_arch {
 	struct ckpt_hdr h;
 	/* FIXME: add HAVE_HWFP */
diff --git a/checkpoint/files.c b/checkpoint/files.c
index 204055b..b51324a 100644
--- a/checkpoint/files.c
+++ b/checkpoint/files.c
@@ -572,6 +572,12 @@ static struct restore_file_ops restore_file_ops[] = {
 		.file_type = CKPT_FILE_SOCKET,
 		.restore = sock_file_restore,
 	},
+	/* tty */
+	{
+		.file_name = "TTY",
+		.file_type = CKPT_FILE_TTY,
+		.restore = tty_file_restore,
+	},
 };
 
 static struct file *do_restore_file(struct ckpt_ctx *ctx)
diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
index 2ea71bd..10d5c02 100644
--- a/checkpoint/objhash.c
+++ b/checkpoint/objhash.c
@@ -246,6 +246,22 @@ static void obj_sock_drop(void *ptr)
 	sock_put((struct sock *) ptr);
 }
 
+static int obj_tty_grab(void *ptr)
+{
+	tty_kref_get((struct tty_struct *) ptr);
+	return 0;
+}
+
+static void obj_tty_drop(void *ptr)
+{
+	tty_kref_put((struct tty_struct *) ptr);
+}
+
+static int obj_tty_users(void *ptr)
+{
+	return atomic_read(&((struct tty_struct *) ptr)->kref.refcount);
+}
+
 static struct ckpt_obj_ops ckpt_obj_ops[] = {
 	/* ignored object */
 	{
@@ -382,6 +398,16 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
 		.ref_drop = obj_sock_drop,
 		.ref_grab = obj_sock_grab,
 	},
+	/* struct tty_struct */
+	{
+		.obj_name = "TTY",
+		.obj_type = CKPT_OBJ_TTY,
+		.ref_drop = obj_tty_drop,
+		.ref_grab = obj_tty_grab,
+		.ref_users = obj_tty_users,
+		.checkpoint = checkpoint_tty,
+		.restore = restore_tty,
+	},
 };
 
 
diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 326c2e9..afdab5e 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -633,7 +633,7 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
 {
 	struct tty_struct *tty;
 	int retval;
-	int index = 0;
+	int index = -1;
 
 	nonseekable_open(inode, filp);
 
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index a3afa0c..9d98bb8 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -106,6 +106,7 @@
 
 #include <linux/kmod.h>
 #include <linux/nsproxy.h>
+#include <linux/checkpoint.h>
 
 #undef TTY_DEBUG_HANGUP
 
@@ -151,6 +152,13 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 #define tty_compat_ioctl NULL
 #endif
 static int tty_fasync(int fd, struct file *filp, int on);
+#ifdef CONFIG_CHECKPOINT
+static int tty_file_checkpoint(struct ckpt_ctx *ctx, struct file *file);
+static int tty_file_collect(struct ckpt_ctx *ctx, struct file *file);
+#else
+#define tty_file_checkpoint NULL
+#define tty_file_collect NULL
+#endif /* CONFIG_CHECKPOINT */
 static void release_tty(struct tty_struct *tty, int idx);
 static void __proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
 static void proc_set_tty(struct task_struct *tsk, struct tty_struct *tty);
@@ -417,6 +425,8 @@ static const struct file_operations tty_fops = {
 	.open		= tty_open,
 	.release	= tty_release,
 	.fasync		= tty_fasync,
+	.checkpoint	= tty_file_checkpoint,
+	.collect	= tty_file_collect,
 };
 
 static const struct file_operations console_fops = {
@@ -439,6 +449,8 @@ static const struct file_operations hung_up_tty_fops = {
 	.unlocked_ioctl	= hung_up_tty_ioctl,
 	.compat_ioctl	= hung_up_tty_compat_ioctl,
 	.release	= tty_release,
+	.checkpoint	= tty_file_checkpoint,
+	.collect	= tty_file_collect,
 };
 
 static DEFINE_SPINLOCK(redirect_lock);
@@ -570,7 +582,9 @@ static void do_tty_hangup(struct work_struct *work)
 	set_bit(TTY_HUPPED, &tty->flags);
 	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 
-	/* Account for the p->signal references we killed */
+	/* Account
+
+	   for the p->signal references we killed */
 	while (refs--)
 		tty_kref_put(tty);
 
@@ -2586,6 +2600,501 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,
 }
 #endif
 
+#ifdef CONFIG_CHECKPOINT
+static int tty_can_checkpoint(struct ckpt_ctx *ctx, struct tty_struct *tty)
+{
+	/* only support pty driver */
+	if (tty->driver->type != TTY_DRIVER_TYPE_PTY) {
+		ckpt_write_err(ctx, "unsupported tty type %d",
+			       tty->driver->type);
+		return 0;
+	}
+	/* only support unix98 style */
+	if (tty->driver->major != UNIX98_PTY_MASTER_MAJOR &&
+	    tty->driver->major != UNIX98_PTY_SLAVE_MAJOR) {
+		ckpt_write_err(ctx, "unsupported legacy pty");
+		return 0;
+	}
+	/* only support n_tty ldisc */
+	if (tty->ldisc->ops->num != N_TTY) {
+		ckpt_write_err(ctx, "unsupported ldisc %d",
+			       tty->ldisc->ops->num);
+		return 0;
+	}
+
+	return 1;
+}
+
+static int tty_file_checkpoint(struct ckpt_ctx *ctx, struct file *file)
+{
+	struct ckpt_hdr_file_tty *h;
+	struct tty_struct *tty, *real_tty;
+	struct inode *inode;
+	int master_objref, slave_objref;
+	int ret;
+
+	tty = (struct tty_struct *)file->private_data;
+	inode = file->f_path.dentry->d_inode;
+	if (tty_paranoia_check(tty, inode, "tty_file_checkpoint"))
+		return -EIO;
+
+	if (!tty_can_checkpoint(ctx, tty))
+		return -ENOSYS;
+
+	/*
+	 * If we ever support more than PTYs, this would be tty-type
+	 * specific (and probably called via tty_operations).
+	 */
+
+	real_tty = tty_pair_get_tty(tty);
+	ckpt_debug("tty: %p, real_tty: %p\n", tty, real_tty);
+
+	master_objref = checkpoint_obj(ctx, real_tty->link, CKPT_OBJ_TTY);
+	if (master_objref < 0)
+		return master_objref;
+	slave_objref = checkpoint_obj(ctx, real_tty, CKPT_OBJ_TTY);
+	if (slave_objref < 0)
+		return slave_objref;
+	ckpt_debug("master %p %d, slave %p %d\n",
+		   real_tty->link, master_objref, real_tty, slave_objref);
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_FILE);
+	if (!h)
+		return -ENOMEM;
+
+	h->common.f_type = CKPT_FILE_TTY;
+	h->tty_objref = (tty == real_tty ? slave_objref : master_objref);
+
+	ret = checkpoint_file_common(ctx, file, &h->common);
+	if (!ret)
+		ret = ckpt_write_obj(ctx, &h->common.h);
+
+	ckpt_hdr_put(ctx, h);
+	return ret;
+}
+
+static int tty_file_collect(struct ckpt_ctx *ctx, struct file *file)
+{
+	struct tty_struct *tty;
+	struct inode *inode;
+	int ret;
+
+	tty = (struct tty_struct *)file->private_data;
+	inode = file->f_path.dentry->d_inode;
+	if (tty_paranoia_check(tty, inode, "tty_collect"))
+		return -EIO;
+
+	if (!tty_can_checkpoint(ctx, tty))
+		return -ENOSYS;
+
+	ckpt_debug("collecting tty: %p\n", tty);
+	ret = ckpt_obj_collect(ctx, tty, CKPT_OBJ_TTY);
+	if (ret < 0)
+		return ret;
+
+	if (tty->driver->subtype == PTY_TYPE_MASTER) {
+		if (!tty->link) {
+			ckpt_write_err(ctx, "missing tty->link\n");
+			return -EIO;
+		}
+		ckpt_debug("collecting slave tty: %p\n", tty->link);
+		ret = ckpt_obj_collect(ctx, tty->link, CKPT_OBJ_TTY);
+	}
+
+	return ret;
+}
+
+#define CKPT_LDISC_BAD   (1 << TTY_LDISC_CHANGING)
+#define CKPT_LDISC_GOOD  ((1 << TTY_LDISC_OPEN) | (1 << TTY_LDISC))
+#define CKPT_LDISC_FLAGS (CKPT_LDISC_GOOD | CKPT_LDISC_BAD)
+
+static int checkpoint_tty_ldisc(struct ckpt_ctx *ctx, struct tty_struct *tty)
+{
+	struct ckpt_hdr_ldisc_n_tty *h;
+	int datalen, read_tail;
+	int n, ret;
+
+	/* shouldn't reach here unless ldisc is n_tty */
+	BUG_ON(tty->ldisc->ops->num != N_TTY);
+
+	if ((tty->flags & CKPT_LDISC_FLAGS) != CKPT_LDISC_GOOD) {
+		ckpt_write_err(ctx, "bad ldisc flags $#lx\n", tty->flags);
+		return -EBUSY;
+	}
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TTY_LDISC);
+	if (!h)
+		return -ENOMEM;
+
+	spin_lock_irq(&tty->read_lock);
+	h->column = tty->column;
+	h->datalen = tty->read_cnt;
+	h->canon_column = tty->canon_column;
+	h->canon_datalen = tty->canon_head - tty->read_tail;
+	h->canon_data = tty->canon_data;
+
+	datalen = tty->read_cnt;
+	read_tail = tty->read_tail;
+	spin_unlock_irq(&tty->read_lock);
+
+	h->minimum_to_wake = tty->minimum_to_wake;
+
+	h->stopped = tty->stopped;
+	h->hw_stopped = tty->hw_stopped;
+	h->flow_stopped = tty->flow_stopped;
+	h->packet = tty->packet;
+	h->ctrl_status = tty->ctrl_status;
+	h->lnext = tty->lnext;
+	h->erasing = tty->erasing;
+	h->raw = tty->raw;
+	h->real_raw = tty->real_raw;
+	h->icanon = tty->icanon;
+	h->closing = tty->closing;
+
+	BUILD_BUG_ON(sizeof(h->read_flags) != sizeof(tty->read_flags));
+	memcpy(h->read_flags, tty->read_flags, sizeof(tty->read_flags));
+
+	ret = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	if (ret < 0)
+		return ret;
+
+	ckpt_debug("datalen %d\n", datalen);
+	if (datalen) {
+		ret = ckpt_write_buffer(ctx, NULL, datalen);
+		if (ret < 0)
+			return ret;
+		n = min(datalen, N_TTY_BUF_SIZE - read_tail);
+		ret = ckpt_kwrite(ctx, &tty->read_buf[read_tail], n);
+		if (ret < 0)
+			return ret;
+		n = datalen - n;
+		ret = ckpt_kwrite(ctx, tty->read_buf, n);
+	}
+
+	return ret;
+}
+
+#define CKPT_TTY_BAD   ((1 << TTY_CLOSING) | (1 << TTY_FLUSHING))
+#define CKPT_TTY_GOOD  0
+
+static int do_checkpoint_tty(struct ckpt_ctx *ctx, struct tty_struct *tty)
+{
+	struct ckpt_hdr_tty *h;
+	int link_objref;
+	int master = 0;
+	int ret;
+
+	if ((tty->flags & (CKPT_TTY_BAD | CKPT_TTY_GOOD)) != CKPT_TTY_GOOD) {
+		ckpt_write_err(ctx, "bad tty flags %#lx\n", tty->flags);
+		return -EBUSY;
+	}
+
+	/*
+	 * If we ever support more than PTYs, this would be tty-type
+	 * specific (and probably called via tty_operations).
+	 */
+	link_objref = ckpt_obj_lookup(ctx, tty->link, CKPT_OBJ_TTY);
+
+	if (tty->driver->subtype == PTY_TYPE_MASTER)
+		master = 1;
+
+	/* tty is master if-and-only-if link_objref is zero */
+	BUG_ON(master ^ !link_objref);
+
+	h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TTY);
+	if (!h)
+		return -ENOMEM;
+
+	h->driver_type = tty->driver->type;
+	h->driver_subtype = tty->driver->subtype;
+
+	h->link_objref = link_objref;
+
+	/* if master, reserve an objref (see do_restore_tty) */
+	h->file_objref = (master ? ckpt_obj_reserve(ctx) : 0);
+	ckpt_debug("link %d file %d\n", h->link_objref, h->file_objref);
+
+	h->index = tty->index;
+	h->ldisc = tty->ldisc->ops->num;
+	h->flags = tty->flags;
+
+	spin_lock_irq(&tty->ctrl_lock);
+	if (tty->session)
+		h->session = pid_vnr(tty->session);
+	if (tty->pgrp)
+		h->pgrp = pid_vnr(tty->pgrp);
+	spin_unlock_irq(&tty->ctrl_lock);
+	BUG_ON(h->session < 0);
+	BUG_ON(h->pgrp < 0);
+
+	mutex_lock(&tty->termios_mutex);
+	h->termios.c_line = tty->termios->c_line;
+	h->termios.c_iflag = tty->termios->c_iflag;
+	h->termios.c_oflag = tty->termios->c_oflag;
+	h->termios.c_cflag = tty->termios->c_cflag;
+	h->termios.c_lflag = tty->termios->c_lflag;
+	memcpy(h->termios.c_cc, tty->termios->c_cc, NCC);
+	h->winsize.ws_row = tty->winsize.ws_row;
+	h->winsize.ws_col = tty->winsize.ws_col;
+	h->winsize.ws_ypixel = tty->winsize.ws_ypixel;
+	h->winsize.ws_xpixel = tty->winsize.ws_xpixel;
+	mutex_unlock(&tty->termios_mutex);
+
+	ret  = ckpt_write_obj(ctx, &h->h);
+	ckpt_hdr_put(ctx, h);
+	if (ret < 0)
+		return ret;
+
+	/* save line discipline data (also writes buffer) */
+	if (!test_bit(TTY_HUPPED, &tty->flags))
+		ret = checkpoint_tty_ldisc(ctx, tty);
+
+	return ret;
+}
+
+int checkpoint_tty(struct ckpt_ctx *ctx, void *ptr)
+{
+	return do_checkpoint_tty(ctx, (struct tty_struct *) ptr);
+}
+
+struct file *tty_file_restore(struct ckpt_ctx *ctx, struct ckpt_hdr_file *ptr)
+{
+	struct ckpt_hdr_file_tty *h = (struct ckpt_hdr_file_tty *) ptr;
+	struct tty_struct *tty;
+	struct file *file;
+	char slavepath[16];	/* "/dev/pts/###" */
+	int slavelock;
+	int ret;
+
+	if (ptr->h.type != CKPT_HDR_FILE ||
+	    ptr->h.len != sizeof(*h) || ptr->f_type != CKPT_FILE_TTY)
+		return ERR_PTR(-EINVAL);
+
+	if (h->tty_objref <= 0)
+		return ERR_PTR(-EINVAL);
+
+	tty = ckpt_obj_fetch(ctx, h->tty_objref, CKPT_OBJ_TTY);
+	ckpt_debug("tty %p objref %d\n", tty, h->tty_objref);
+
+	/* at this point the tty should have been restore already */
+	if (IS_ERR(tty))
+		return (struct file *) tty;
+
+	/*
+	 * If we ever support more than PTYs, this would be tty-type
+	 * specific (and probably called via tty_operations).
+	 */
+
+	/*
+	 * If this tty is master, get the corresponding file from
+	 * tty->tty_file. Otherwise, open the slave device.
+	 */
+	if (tty->driver->subtype == PTY_TYPE_MASTER) {
+		file_list_lock();
+		file = list_first_entry(&tty->tty_files,
+					typeof(*file), f_u.fu_list);
+		file_list_unlock();
+		ckpt_debug("master file %p\n", file);
+		get_file(file);
+	} else {
+		sprintf(slavepath, "/dev/pts/%d", tty->index);
+		slavelock = test_bit(TTY_PTY_LOCK, &tty->link->flags);
+		clear_bit(TTY_PTY_LOCK, &tty->link->flags);
+		file = filp_open(slavepath, O_RDWR | O_NOCTTY, 0);
+		ckpt_debug("slave file %p (idnex %d)\n", file, tty->index);
+		if (IS_ERR(file))
+			return file;
+		if (slavelock)
+			set_bit(TTY_PTY_LOCK, &tty->link->flags);
+	}
+
+	ret = restore_file_common(ctx, file, ptr);
+	if (ret < 0) {
+		fput(file);
+		file = ERR_PTR(ret);
+	}
+
+	return file;
+}
+
+static int restore_tty_ldisc(struct ckpt_ctx *ctx,
+			     struct tty_struct *tty,
+			     struct ckpt_hdr_tty *hh)
+{
+	struct ckpt_hdr_ldisc_n_tty *h;
+	int ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TTY_LDISC);
+	if (IS_ERR(h))
+		return PTR_ERR(h);
+
+	/* this is unfair shortcut, because we know ldisc is n_tty */
+	if (hh->ldisc != N_TTY)
+		return -EINVAL;
+	if ((hh->flags & CKPT_LDISC_FLAGS) != CKPT_LDISC_GOOD)
+		return -EINVAL;
+
+	if (h->datalen > N_TTY_BUF_SIZE)
+		return -EINVAL;
+	if (h->canon_datalen > N_TTY_BUF_SIZE)
+		return -EINVAL;
+
+	if (h->datalen) {
+		ret = _ckpt_read_buffer(ctx, tty->read_buf, h->datalen);
+		if (ret < 0)
+			return ret;
+	}
+
+	/* TODO: sanitize all these values ? */
+
+	spin_lock_irq(&tty->read_lock);
+	tty->column = h->column;
+	tty->read_cnt = h->datalen;
+	tty->read_head = h->datalen;
+	tty->read_tail = 0;
+	tty->canon_column = h->canon_column;
+	tty->canon_head = h->canon_datalen;
+	tty->canon_data = h->canon_data;
+	spin_unlock_irq(&tty->read_lock);
+
+	tty->minimum_to_wake = h->minimum_to_wake;
+
+	tty->stopped = h->stopped;
+	tty->hw_stopped = h->hw_stopped;
+	tty->flow_stopped = h->flow_stopped;
+	tty->packet = h->packet;
+	tty->ctrl_status = h->ctrl_status;
+	tty->lnext = h->lnext;
+	tty->erasing = h->erasing;
+	tty->raw = h->raw;
+	tty->real_raw = h->real_raw;
+	tty->icanon = h->icanon;
+	tty->closing = h->closing;
+
+	BUILD_BUG_ON(sizeof(h->read_flags) != sizeof(tty->read_flags));
+	memcpy(tty->read_flags, h->read_flags, sizeof(tty->read_flags));
+
+	return 0;
+}
+
+#define CKPT_PTMX_PATH  "/dev/ptmx"
+
+static struct tty_struct *do_restore_tty(struct ckpt_ctx *ctx)
+{
+	struct ckpt_hdr_tty *h;
+	struct tty_struct *tty = ERR_PTR(-EINVAL);
+	struct file *file = NULL;
+	int master, ret;
+
+	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TTY);
+	if (IS_ERR(h))
+		return (struct tty_struct *) h;
+
+	if (h->driver_type != TTY_DRIVER_TYPE_PTY)
+		goto out;
+	if (h->driver_subtype == PTY_TYPE_MASTER)
+		master = 1;
+	else if (h->driver_subtype == PTY_TYPE_SLAVE)
+		master = 0;
+	else
+		goto out;
+	/* @link_object is positive if-and-only-if tty is not master */
+	if (h->link_objref < 0 || (master ^ !h->link_objref))
+		goto out;
+	/* @file_object is positive if-and-only-if tty is master */
+	if (h->file_objref < 0 || (master ^ !!h->file_objref))
+		goto out;
+	if (h->session < 0 || h->pgrp < 0)
+		goto out;
+	if (h->flags & CKPT_TTY_BAD)
+		goto out;
+	/* hung-up tty cannot be master, or have session or pgrp */
+	if (test_bit(TTY_HUPPED, (unsigned long *) &h->flags) &&
+	    (master || h->session || h->pgrp))
+		goto out;
+
+	ckpt_debug("sanity checks passed, link %d\n", h->link_objref);
+
+	/*
+	 * If we ever support more than PTYs, this would be tty-type
+	 * specific (and probably called via tty_operations).
+	 */
+	if (master) {
+		current->required_id = h->index;
+		file = filp_open(CKPT_PTMX_PATH, O_RDWR | O_NOCTTY, 0);
+		current->required_id = CKPT_REQUIRED_NONE;
+		ckpt_debug("master file %p (obj %d)\n", file, h->file_objref);
+		if (IS_ERR(file)) {
+			tty = (struct tty_struct *) file;
+			goto out;
+		}
+
+		/*
+		 * Add file to objhash to ensure proper cleanup later
+		 * (it isn't referenced elsewhere). Use h->file_objref
+		 * which was explicitly during checkpoint for this.
+		 */
+		ret = ckpt_obj_insert(ctx, file, h->file_objref, CKPT_OBJ_FILE);
+		if (ret < 0) {
+			tty = ERR_PTR(ret);
+			fput(file);
+			goto out;
+		}
+
+		tty = file->private_data;
+	} else {
+		tty = ckpt_obj_fetch(ctx, h->link_objref, CKPT_OBJ_TTY);
+		if (IS_ERR(tty))
+			goto out;
+		tty = tty->link;
+	}
+
+	ckpt_debug("tty %p (hup %d)\n",
+		   tty, test_bit(TTY_HUPPED, (unsigned long *) &h->flags));
+
+	/* we now have the desired tty: restore its state as per @h */
+
+	spin_lock_irq(&tty->ctrl_lock);
+	tty->session = find_get_pid(h->session);
+	tty->pgrp = find_get_pid(h->pgrp);
+	spin_unlock_irq(&tty->ctrl_lock);
+
+	mutex_lock(&tty->termios_mutex);
+	tty->termios->c_line = h->termios.c_line;
+	tty->termios->c_iflag = h->termios.c_iflag;
+	tty->termios->c_oflag = h->termios.c_oflag;
+	tty->termios->c_cflag = h->termios.c_cflag;
+	tty->termios->c_lflag = h->termios.c_lflag;
+	memcpy(tty->termios->c_cc, h->termios.c_cc, NCC);
+	tty->winsize.ws_row = h->winsize.ws_row;
+	tty->winsize.ws_col = h->winsize.ws_col;
+	tty->winsize.ws_ypixel = h->winsize.ws_ypixel;
+	tty->winsize.ws_xpixel = h->winsize.ws_xpixel;
+	mutex_unlock(&tty->termios_mutex);
+
+	if (test_bit(TTY_HUPPED, (unsigned long *) &h->flags))
+		tty_vhangup(tty);
+	else {
+		ret = restore_tty_ldisc(ctx, tty, h);
+		if (ret < 0) {
+			tty = ERR_PTR(ret);
+			goto out;
+		}
+	}
+
+	tty_kref_get(tty);
+ out:
+	ckpt_hdr_put(ctx, h);
+	return tty;
+}
+
+void *restore_tty(struct ckpt_ctx *ctx)
+{
+	return (void *) do_restore_tty(ctx);
+}
+#endif /* COFNIG_CHECKPOINT */
+
 /*
  * This implements the "Secure Attention Key" ---  the idea is to
  * prevent trojan horses by killing all processes associated with this
diff --git a/include/linux/checkpoint.h b/include/linux/checkpoint.h
index 473164e..5e90ef9 100644
--- a/include/linux/checkpoint.h
+++ b/include/linux/checkpoint.h
@@ -265,6 +265,11 @@ extern int restore_obj_signal(struct ckpt_ctx *ctx, int signal_objref);
 extern int checkpoint_task_signal(struct ckpt_ctx *ctx, struct task_struct *t);
 extern int restore_task_signal(struct ckpt_ctx *ctx);
 
+/* ttys */
+extern int checkpoint_tty(struct ckpt_ctx *ctx, void *ptr);
+extern void *restore_tty(struct ckpt_ctx *ctx);
+
+
 /* useful macros to copy fields and buffers to/from ckpt_hdr_xxx structures */
 #define CKPT_CPT 1
 #define CKPT_RST 2
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 4d5c22a..7c7b993 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -76,6 +76,8 @@ enum {
 	CKPT_HDR_FILE_NAME,
 	CKPT_HDR_FILE,
 	CKPT_HDR_PIPE_BUF,
+	CKPT_HDR_TTY,
+	CKPT_HDR_TTY_LDISC,
 
 	CKPT_HDR_MM = 401,
 	CKPT_HDR_VMA,
@@ -134,6 +136,7 @@ enum obj_type {
 	CKPT_OBJ_USER,
 	CKPT_OBJ_GROUPINFO,
 	CKPT_OBJ_SOCK,
+	CKPT_OBJ_TTY,
 	CKPT_OBJ_MAX
 };
 
@@ -342,6 +345,7 @@ enum file_type {
 	CKPT_FILE_PIPE,
 	CKPT_FILE_FIFO,
 	CKPT_FILE_SOCKET,
+	CKPT_FILE_TTY,
 	CKPT_FILE_MAX
 };
 
@@ -633,6 +637,78 @@ struct ckpt_hdr_ipc_sem {
 } __attribute__((aligned(8)));
 
 
+/* devices */
+struct ckpt_hdr_file_tty {
+	struct ckpt_hdr_file common;
+	__s32 tty_objref;
+};
+
+struct ckpt_hdr_tty {
+	struct ckpt_hdr h;
+
+	__u16 driver_type;
+	__u16 driver_subtype;
+
+	__s32 link_objref;
+	__s32 file_objref;
+	__u32 _padding;
+
+	__u32 index;
+	__u32 ldisc;
+	__u64 flags;
+
+	__s32 session;
+	__s32 pgrp;
+
+	/* termios */
+	struct {
+		__u16 c_iflag;
+		__u16 c_oflag;
+		__u16 c_cflag;
+		__u16 c_lflag;
+		__u8 c_line;
+		__u8 c_cc[CKPT_TTY_NCC];
+	} __attribute__((aligned(8))) termios;
+
+	/* winsize */
+	struct {
+		__u16 ws_row;
+		__u16 ws_col;
+		__u16 ws_xpixel;
+		__u16 ws_ypixel;
+	} __attribute__((aligned(8))) winsize;
+} __attribute__((aligned(8)));
+
+struct ckpt_hdr_ldisc_n_tty {
+	struct ckpt_hdr h;
+
+	__u32 column;
+	__u32 datalen;
+	__u32 canon_column;
+	__u32 canon_datalen;
+	__u32 canon_data;
+
+	__u16 minimum_to_wake;
+
+	__u8 stopped;
+	__u8 hw_stopped;
+	__u8 flow_stopped;
+	__u8 packet;
+	__u8 ctrl_status;
+	__u8 lnext;
+	__u8 erasing;
+	__u8 raw;
+	__u8 real_raw;
+	__u8 icanon;
+	__u8 closing;
+	__u8 padding[3];
+
+	__u8 read_flags[N_TTY_BUF_SIZE / 8];
+
+	/* if @datalen > 0, buffer contents follow (next object) */
+} __attribute__((aligned(8)));
+
+
 #define CKPT_TST_OVERFLOW_16(a, b) \
 	((sizeof(a) > sizeof(b)) && ((a) > SHORT_MAX))
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1488d8c..fd77894 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -467,6 +467,12 @@ extern void tty_ldisc_begin(void);
 /* This last one is just for the tty layer internals and shouldn't be used elsewhere */
 extern void tty_ldisc_enable(struct tty_struct *tty);
 
+#ifdef CONFIG_CHECKPOINT
+struct ckpt_ctx;
+struct ckpt_hdr_file;
+extern struct file *tty_file_restore(struct ckpt_ctx *ctx,
+				     struct ckpt_hdr_file *ptr);
+#endif
 
 /* n_tty.c */
 extern struct tty_ldisc_ops tty_ldisc_N_TTY;
-- 
1.6.0.4

Re: [RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Serge E. Hallyn]

[-- Attachment #1: Type: text/plain, Size: 1286 bytes --]

All right, I'm not sure how to go about this - i want to have a conversation
involving patches without making it seem like I want any of the patches
pushed yet :)  To get this working on s390, I needed the two attached
patches.  Then the testcase under git://git.sr71.net/~hallyn/cr_tests.git
under cr_tests/pty/ passes with your code.

I'd still like to get a more invasive approach working where we directly
ask the pty code to create the pty with the right index.  I'm playing with
it right now, but of course having some trouble figuring out what to do
for the master end and how best to construct a filp to pass to
the main pty_create function.  I'll take a few more stabs and send out
what I have later (or announce defeat).

There is certainly something to be said for the un-invasiveness of
your approach (and that it works).

In either case, we will need to figure out how to deal with devpts
namespaces.  Perhaps we separately checkpoint a 'devpts_mnt'.  It
just stores the mountpoint of the mount.  At restart, we don't
recreate those, we just confirm that the mountpoints still exist.
Then, each pty entry has a ref to its devpts mount, and we use the
mountpoint to construct ${mountpoint}/ptmx and pass that to
filp_open() or ptmx_create)( to create the pty entry.

-serge

[-- Attachment #2: 0001-pty-cr-s390-define-CKPT_TTY_NCC.patch --]
[-- Type: text/x-diff, Size: 942 bytes --]

From 552f3df7802a8833276a0aac69b92c1bce385dbf Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Date: Tue, 1 Sep 2009 12:36:28 -0400
Subject: [PATCH 1/2] pty cr: s390: define CKPT_TTY_NCC

Signed-off-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 arch/s390/include/asm/checkpoint_hdr.h |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/s390/include/asm/checkpoint_hdr.h b/arch/s390/include/asm/checkpoint_hdr.h
index 1976355..609fc4c 100644
--- a/arch/s390/include/asm/checkpoint_hdr.h
+++ b/arch/s390/include/asm/checkpoint_hdr.h
@@ -90,6 +90,14 @@ struct ckpt_hdr_mm_context {
 #endif
 #endif
 
+#define CKPT_TTY_NCC  8
+#ifdef __KERNEL__
+#include <linux/tty.h>
+#if CKPT_TTY_NCC != NCC
+#error CKPT_TTY_NCC size is wrong per asm-generic/termios.h
+#endif
+#endif
+
 struct ckpt_hdr_header_arch {
 	struct ckpt_hdr h;
 };
-- 
1.6.1


[-- Attachment #3: 0002-cr-bugfixes-of-oren-s-code.patch --]
[-- Type: text/x-diff, Size: 1471 bytes --]

From 68b12cb69f2741052eba60658404e4eec221d112 Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Date: Tue, 1 Sep 2009 21:34:12 -0400
Subject: [PATCH 2/2] cr: bugfixes of oren's code

Signed-off-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 drivers/char/tty_io.c          |    6 +++++-
 include/linux/checkpoint_hdr.h |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 9d98bb8..b8f8d79 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -2730,7 +2730,11 @@ static int checkpoint_tty_ldisc(struct ckpt_ctx *ctx, struct tty_struct *tty)
 	h->column = tty->column;
 	h->datalen = tty->read_cnt;
 	h->canon_column = tty->canon_column;
-	h->canon_datalen = tty->canon_head - tty->read_tail;
+	h->canon_datalen = tty->canon_head;
+	if (tty->canon_head > tty->read_tail)
+		h->canon_datalen -= tty->read_tail;
+	else
+		h->canon_datalen += N_TTY_BUF_SIZE - tty->read_tail;
 	h->canon_data = tty->canon_data;
 
 	datalen = tty->read_cnt;
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index 5febdc7..492b4d5 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -688,7 +688,7 @@ struct ckpt_hdr_ldisc_n_tty {
 	struct ckpt_hdr h;
 
 	__u32 column;
-	__u32 datalen;
+	__s32 datalen;
 	__u32 canon_column;
 	__u32 canon_datalen;
 	__u32 canon_data;
-- 
1.6.1


[-- Attachment #4: Type: text/plain, Size: 206 bytes --]

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Re: [RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Oren Laadan]

Thanks for the patches (the first was already in). I'll leave
out the change to signed type, though.


Serge E. Hallyn wrote:
> All right, I'm not sure how to go about this - i want to have a conversation
> involving patches without making it seem like I want any of the patches
> pushed yet :)  To get this working on s390, I needed the two attached
> patches.  Then the testcase under git://git.sr71.net/~hallyn/cr_tests.git
> under cr_tests/pty/ passes with your code.
> 
> I'd still like to get a more invasive approach working where we directly
> ask the pty code to create the pty with the right index.  I'm playing with
> it right now, but of course having some trouble figuring out what to do
> for the master end and how best to construct a filp to pass to
> the main pty_create function.  I'll take a few more stabs and send out
> what I have later (or announce defeat).
> 
> There is certainly something to be said for the un-invasiveness of
> your approach (and that it works).
> 
> In either case, we will need to figure out how to deal with devpts
> namespaces.  Perhaps we separately checkpoint a 'devpts_mnt'.  It
> just stores the mountpoint of the mount.  At restart, we don't
> recreate those, we just confirm that the mountpoints still exist.
> Then, each pty entry has a ref to its devpts mount, and we use the
> mountpoint to construct ${mountpoint}/ptmx and pass that to
> filp_open() or ptmx_create)( to create the pty entry.

Yes, I was thinking along these lines. I think it's very much
related to the whole mount-namespaces issues; I guess it's time
to address both.

Oren.

Re: [RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Serge E. Hallyn]

Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> 
> Thanks for the patches (the first was already in). I'll leave
> out the change to signed type, though.

Yup, "oops".

> Serge E. Hallyn wrote:
> > All right, I'm not sure how to go about this - i want to have a conversation
> > involving patches without making it seem like I want any of the patches
> > pushed yet :)  To get this working on s390, I needed the two attached
> > patches.  Then the testcase under git://git.sr71.net/~hallyn/cr_tests.git
> > under cr_tests/pty/ passes with your code.
> > 
> > I'd still like to get a more invasive approach working where we directly
> > ask the pty code to create the pty with the right index.  I'm playing with
> > it right now, but of course having some trouble figuring out what to do
> > for the master end and how best to construct a filp to pass to
> > the main pty_create function.  I'll take a few more stabs and send out
> > what I have later (or announce defeat).
> > 
> > There is certainly something to be said for the un-invasiveness of
> > your approach (and that it works).
> > 
> > In either case, we will need to figure out how to deal with devpts
> > namespaces.  Perhaps we separately checkpoint a 'devpts_mnt'.  It
> > just stores the mountpoint of the mount.  At restart, we don't
> > recreate those, we just confirm that the mountpoints still exist.
> > Then, each pty entry has a ref to its devpts mount, and we use the
> > mountpoint to construct ${mountpoint}/ptmx and pass that to
> > filp_open() or ptmx_create)( to create the pty entry.
> 
> Yes, I was thinking along these lines. I think it's very much
> related to the whole mount-namespaces issues; I guess it's time
> to address both.

Ooooh, I'm not sure it is :)  In fact my approach to devpts should
artfully avoid having to address generic mounts namespaces :)

Well, if we *were* to address mountsns now, I'd suggest we simply
store meaningful /proc/pid/mountinfo data for each task in the
checkpoint image, and just verify it at restart, returning error
if they're not the same.  That way we can continue to defer
the decision on whether mktree or the kernel will restore mounts.

-serge

Re: [RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Oren Laadan]

Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
>> Thanks for the patches (the first was already in). I'll leave
>> out the change to signed type, though.
> 
> Yup, "oops".
> 
>> Serge E. Hallyn wrote:
>>> All right, I'm not sure how to go about this - i want to have a conversation
>>> involving patches without making it seem like I want any of the patches
>>> pushed yet :)  To get this working on s390, I needed the two attached
>>> patches.  Then the testcase under git://git.sr71.net/~hallyn/cr_tests.git
>>> under cr_tests/pty/ passes with your code.
>>>
>>> I'd still like to get a more invasive approach working where we directly
>>> ask the pty code to create the pty with the right index.  I'm playing with
>>> it right now, but of course having some trouble figuring out what to do
>>> for the master end and how best to construct a filp to pass to
>>> the main pty_create function.  I'll take a few more stabs and send out
>>> what I have later (or announce defeat).
>>>
>>> There is certainly something to be said for the un-invasiveness of
>>> your approach (and that it works).
>>>
>>> In either case, we will need to figure out how to deal with devpts
>>> namespaces.  Perhaps we separately checkpoint a 'devpts_mnt'.  It
>>> just stores the mountpoint of the mount.  At restart, we don't
>>> recreate those, we just confirm that the mountpoints still exist.
>>> Then, each pty entry has a ref to its devpts mount, and we use the
>>> mountpoint to construct ${mountpoint}/ptmx and pass that to
>>> filp_open() or ptmx_create)( to create the pty entry.
>> Yes, I was thinking along these lines. I think it's very much
>> related to the whole mount-namespaces issues; I guess it's time
>> to address both.
> 
> Ooooh, I'm not sure it is :)  In fact my approach to devpts should
> artfully avoid having to address generic mounts namespaces :)

lol .. I suppose I misinterpreted then. Perhaps you can take a
stab at it ?

> 
> Well, if we *were* to address mountsns now, I'd suggest we simply
> store meaningful /proc/pid/mountinfo data for each task in the
> checkpoint image, and just verify it at restart, returning error
> if they're not the same.  That way we can continue to defer
> the decision on whether mktree or the kernel will restore mounts.

What is "meaningful" data, and how would you "verify" it ?

At restart the mount data may be substantially (and intentionally)
different. For instance, what used to be a local mount at checkpoint
may be an NFS mount at restart....

Oren.

Re: [RFC][PATCH 3/3] c/r: [pty 2/2] support for pseudo terminals

[Serge E. Hallyn]

Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> 
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> >> Thanks for the patches (the first was already in). I'll leave
> >> out the change to signed type, though.
> > 
> > Yup, "oops".
> > 
> >> Serge E. Hallyn wrote:
> >>> All right, I'm not sure how to go about this - i want to have a conversation
> >>> involving patches without making it seem like I want any of the patches
> >>> pushed yet :)  To get this working on s390, I needed the two attached
> >>> patches.  Then the testcase under git://git.sr71.net/~hallyn/cr_tests.git
> >>> under cr_tests/pty/ passes with your code.
> >>>
> >>> I'd still like to get a more invasive approach working where we directly
> >>> ask the pty code to create the pty with the right index.  I'm playing with
> >>> it right now, but of course having some trouble figuring out what to do
> >>> for the master end and how best to construct a filp to pass to
> >>> the main pty_create function.  I'll take a few more stabs and send out
> >>> what I have later (or announce defeat).
> >>>
> >>> There is certainly something to be said for the un-invasiveness of
> >>> your approach (and that it works).
> >>>
> >>> In either case, we will need to figure out how to deal with devpts
> >>> namespaces.  Perhaps we separately checkpoint a 'devpts_mnt'.  It
> >>> just stores the mountpoint of the mount.  At restart, we don't
> >>> recreate those, we just confirm that the mountpoints still exist.
> >>> Then, each pty entry has a ref to its devpts mount, and we use the
> >>> mountpoint to construct ${mountpoint}/ptmx and pass that to
> >>> filp_open() or ptmx_create)( to create the pty entry.
> >> Yes, I was thinking along these lines. I think it's very much
> >> related to the whole mount-namespaces issues; I guess it's time
> >> to address both.
> > 
> > Ooooh, I'm not sure it is :)  In fact my approach to devpts should
> > artfully avoid having to address generic mounts namespaces :)
> 
> lol .. I suppose I misinterpreted then. Perhaps you can take a
> stab at it ?

Sure, should be pretty simple.  May wait until next week though,
if only to wait for comments on the requested_id vs. ptmx_create().

OTOH - if we're going to consider spitting out full mountinfo in
the ckpt image (per below), then I'll wait until we've discussed
that more too.

> > Well, if we *were* to address mountsns now, I'd suggest we simply
> > store meaningful /proc/pid/mountinfo data for each task in the
> > checkpoint image, and just verify it at restart, returning error
> > if they're not the same.  That way we can continue to defer
> > the decision on whether mktree or the kernel will restore mounts.
> 
> What is "meaningful" data, and how would you "verify" it ?

Meaningful data is, for each task,
	mount ns id
	for each mount,
		mount source, targets, types, propagation (peer group
		and relation to it).
Also for the container init, whether its netns is shared with its
parent, and any mounts which are new in it over its parent.

> At restart the mount data may be substantially (and intentionally)
> different. For instance, what used to be a local mount at checkpoint
> may be an NFS mount at restart....

Yup.  OTOH if a task in the container did
	'mount --bind dataset.bak/b dataset/a'
then that should be safe to repeat.

Whereas the nfs mount presumably is for the whole job's fs, which
likely was not mounted by the job itself.

-serge