[PATCH] dynamic pty allocation

From: "H. Peter Anvin" <hpa@transmeta.com>

Remove the limit of 2048 pty's - allocate them on demand up to the 12:20
dev_t limit: a million.

4 files changed, 32 insertions, 34 deletions

diff --git a/include/linux/devpts_fs.h b/include/linux/devpts_fs.h
index 4def3512b355..734f7ea9e835 100644
--- a/include/linux/devpts_fs.h
+++ b/include/linux/devpts_fs.h
@@ -2,7 +2,7 @@
  *
  * linux/include/linux/devpts_fs.h
  *
- *  Copyright 1998 H. Peter Anvin -- All Rights Reserved
+ *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
  *
  * This file is part of the Linux kernel and is made available under
  * the terms of the GNU General Public License, version 2, or at your
@@ -13,21 +13,22 @@
 #ifndef _LINUX_DEVPTS_FS_H
 #define _LINUX_DEVPTS_FS_H 1
 
-#ifdef CONFIG_DEVPTS_FS
+#include <linux/errno.h>
 
-void devpts_pty_new(int, dev_t);	/* mknod in devpts */
-void devpts_pty_kill(int);		/* unlink */
+#if CONFIG_UNIX98_PTYS
 
-#else
+int devpts_pty_new(struct tty_struct *); /* mknod in devpts */
+struct tty_struct *devpts_get_tty(int);	 /* get tty structure */
+void devpts_pty_kill(int);		 /* unlink */
 
-static inline void devpts_pty_new(int line, dev_t device)
-{
-}
+#else
 
-static inline void devpts_pty_kill(int line)
-{
-}
+/* Dummy stubs in the no-pty case */
+static inline int devpts_pty_new(struct tty_struct *) { return -EINVAL; }
+static inline struct tty_struct *devpts_get_tty(int)  { return NULL; }
+static inline void devpts_pty_kill(int) { }
 
 #endif
 
+
 #endif /* _LINUX_DEVPTS_FS_H */
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index f800e292d8a1..6819132d40d4 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -129,6 +129,7 @@ enum
 	KERN_HPPA_UNALIGNED=59,	/* int: hppa unaligned-trap enable */
 	KERN_PRINTK_RATELIMIT=60, /* int: tune printk ratelimiting */
 	KERN_PRINTK_RATELIMIT_BURST=61,	/* int: tune printk ratelimiting */
+	KERN_PTY=62,		/* dir: pty driver */
 };
 
 
@@ -192,6 +193,13 @@ enum
 	RANDOM_UUID=6
 };
 
+/* /proc/sys/kernel/pty */
+enum
+{
+	PTY_MAX=1,
+	PTY_NR=2
+};
+
 /* /proc/sys/bus/isa */
 enum
 {
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 0626d1b321aa..ca1f1ccf6c49 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -28,29 +28,13 @@
 
 
 /*
- * Note: don't mess with NR_PTYS until you understand the tty minor 
- * number allocation game...
  * (Note: the *_driver.minor_start values 1, 64, 128, 192 are
  * hardcoded at present.)
  */
-#define NR_PTYS		256	/* ptys/major */
-#define NR_LDISCS	16
-
-/*
- * Unix98 PTY's can be defined as any multiple of NR_PTYS up to
- * UNIX98_PTY_MAJOR_COUNT; this section defines what we need from the
- * config options
- */
-#ifdef CONFIG_UNIX98_PTYS
-# define UNIX98_NR_MAJORS ((CONFIG_UNIX98_PTY_COUNT+NR_PTYS-1)/NR_PTYS)
-# if UNIX98_NR_MAJORS <= 0
-#  undef CONFIG_UNIX98_PTYS
-# elif UNIX98_NR_MAJORS > UNIX98_PTY_MAJOR_COUNT
-#  error  Too many Unix98 ptys defined
-#  undef  UNIX98_NR_MAJORS
-#  define UNIX98_NR_MAJORS UNIX98_PTY_MAJOR_COUNT
-# endif
-#endif
+#define NR_PTYS	CONFIG_LEGACY_PTY_COUNT   /* Number of legacy ptys */
+#define NR_UNIX98_PTY_DEFAULT	4096      /* Default maximum for Unix98 ptys */
+#define NR_UNIX98_PTY_MAX	(1 << MINORBITS) /* Absolute limit */
+#define NR_LDISCS		16
 
 /*
  * These are set up by the setup-routine at boot-time:
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 63051af4d8ac..f0b98e5a5473 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -160,9 +160,10 @@ struct tty_driver {
 	const char	*devfs_name;
 	const char	*name;
 	int	name_base;	/* offset of printed name */
-	short	major;		/* major device number */
-	short	minor_start;	/* start of minor device number*/
-	short	num;		/* number of devices */
+	int	major;		/* major device number */
+	int	minor_start;	/* start of minor device number */
+	int	minor_num;	/* number of *possible* devices */
+	int	num;		/* number of devices allocated */
 	short	type;		/* type of tty driver */
 	short	subtype;	/* subtype of tty driver */
 	struct termios init_termios; /* Initial termios */
@@ -244,11 +245,15 @@ void tty_set_operations(struct tty_driver *driver, struct tty_operations *op);
  * TTY_DRIVER_NO_DEVFS --- if set, do not create devfs entries. This
  *	is only used by tty_register_driver().
  *
+ * TTY_DRIVER_DEVPTS_MEM -- don't use the standard arrays, instead
+ *	use dynamic memory keyed through the devpts filesystem.  This
+ *	is only applicable to the pty driver.
  */
 #define TTY_DRIVER_INSTALLED		0x0001
 #define TTY_DRIVER_RESET_TERMIOS	0x0002
 #define TTY_DRIVER_REAL_RAW		0x0004
 #define TTY_DRIVER_NO_DEVFS		0x0008
+#define TTY_DRIVER_DEVPTS_MEM		0x0010
 
 /* tty driver types */
 #define TTY_DRIVER_TYPE_SYSTEM		0x0001