[PATCH] cr: pts (v2): detect use of multiple devpts mounts in container

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

We don't support multiple devpts mounts in a container.  So
bail on checkpoint if a container has them.  This will cause
checkpoint to fail of a container which still has a pty from
parent container in use.

Since I don't actually need any methods in the ckpt_ops for
ptsns, I just register the ckpt_ops in tty_io.c which is never
a module.  We will presumably have to deal with modular ckpt_ops
after the next submission, and we've talked about how to do it,
but it's kind of late in this cycle to do that now.

checkpointing a task with open fd to pty from parent ns results
in a message like:

[err -16][pos 3382][E @ tty_file_checkpoint:2760]Open pty from alien ptsns

Signed-off-by: Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
---
 drivers/char/tty_io.c            |   32 ++++++++++++++++++++++++++++++++
 include/linux/checkpoint_hdr.h   |   18 ++++++++++++++++++
 include/linux/checkpoint_types.h |    2 ++
 3 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index d264000..999317c 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -96,6 +96,7 @@
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/seq_file.h>
+#include <linux/mount.h>
 
 #include <linux/uaccess.h>
 #include <asm/system.h>
@@ -2687,6 +2688,27 @@ static int tty_can_checkpoint(struct ckpt_ctx *ctx, struct tty_struct *tty)
 	return 1;
 }
 
+/*
+ * If tty_file_checkpoint() ever supports more than unix98 ptys we'll have
+ * to check for that
+ */
+static int detect_multiple_ptsns(struct ckpt_ctx *ctx, struct file *file)
+{
+	int objref;
+	int new;
+
+	objref = ckpt_obj_lookup_add(ctx, file->f_path.mnt->mnt_sb,
+				  CKPT_OBJ_PTS_NS, &new);
+	if (objref < 0)
+		return objref;
+	if (new && ctx->num_devpts_ns)
+		return -EBUSY;
+	if (file->f_path.mnt->mnt_ns != ctx->root_nsproxy->mnt_ns)
+		return -EBUSY;
+	ctx->num_devpts_ns++;
+	return 0;
+}
+
 static int tty_file_checkpoint(struct ckpt_ctx *ctx, struct file *file)
 {
 	struct ckpt_hdr_file_tty *h;
@@ -2732,6 +2754,11 @@ static int tty_file_checkpoint(struct ckpt_ctx *ctx, struct file *file)
 		ret = ckpt_write_obj(ctx, &h->common.h);
 
 	ckpt_hdr_put(ctx, h);
+
+	ret = detect_multiple_ptsns(ctx, file);
+	if (ret)
+		ckpt_err(ctx, ret, "Open pty from alien ptsns\n");
+
 	return ret;
 }
 
@@ -3680,6 +3707,8 @@ static struct cdev tty_cdev, console_cdev;
  */
 static int __init tty_init(void)
 {
+	int err;
+
 	cdev_init(&tty_cdev, &tty_fops);
 	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
@@ -3698,6 +3727,9 @@ static int __init tty_init(void)
 	vty_init(&console_fops);
 #endif
 #ifdef CONFIG_CHECKPOINT
+	err = register_checkpoint_obj(&ckpt_obj_ptsns_ops);
+	if (err)
+		return err;
 	return checkpoint_register_tty();
 #else
 	return 0;
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index eb5e1b4..27113ca 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -271,6 +271,8 @@ enum obj_type {
 #define CKPT_OBJ_NET_NS CKPT_OBJ_NET_NS
 	CKPT_OBJ_NETDEV,
 #define CKPT_OBJ_NETDEV CKPT_OBJ_NETDEV
+	CKPT_OBJ_PTS_NS,
+#define CKPT_OBJ_PTS_NS CKPT_OBJ_PTS_NS
 	CKPT_OBJ_MAX
 #define CKPT_OBJ_MAX CKPT_OBJ_MAX
 };
@@ -1142,5 +1144,21 @@ struct ckpt_hdr_ldisc_n_tty {
 #define CKPT_TST_OVERFLOW_64(a, b) \
 	((sizeof(a) > sizeof(b)) && ((a) > LONG_MAX))
 
+#if defined(CONFIG_UNIX98_PTYS) || defined(CONFIG_UNIX98_PTYS_MODULE)
+/*
+ * We don't yet support multiple pts mounts in a container, so
+ * all we're doing here is detecting pty's in >1 ptsns.  We'll
+ * actually stick the sb on the objhash because that's all there
+ * is.  Note that means that when we start checkpointing mounts
+ * and filesystems we'll need to change this.
+ *
+ * We don't need to pin these bc they are pinned by the pty,
+ * which we do have pinned.
+ */
+static const struct ckpt_obj_ops ckpt_obj_ptsns_ops = {
+	.obj_name = "PTS NS",
+	.obj_type = CKPT_OBJ_PTS_NS,
+};
+#endif /* CONFIG_UNIX98_PTYS */
 
 #endif /* _CHECKPOINT_CKPT_HDR_H_ */
diff --git a/include/linux/checkpoint_types.h b/include/linux/checkpoint_types.h
index eb3fdac..84782b0 100644
--- a/include/linux/checkpoint_types.h
+++ b/include/linux/checkpoint_types.h
@@ -86,6 +86,8 @@ struct ckpt_ctx {
 	struct cred *realcred, *ecred;	/* tmp storage for cred at restart */
 	struct list_head listen_sockets;/* listening parent sockets */
 
+	int num_devpts_ns;		/* must not become > 1 at the moment */
+
 	struct ckpt_stats stats;	/* statistics */
 
 #define CKPT_MSG_LEN 1024
-- 
1.7.0.4