PTY: add kernel parameter to overwrite legacy pty count

Signed-off-by: NKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Documentation/kernel-parameters.txt

@@ -1430,6 +1430,10 @@ and is between 256 and 4096 characters. It is defined in the file
 	pt.		[PARIDE]
 			See Documentation/paride.txt.
 
+	pty.legacy_count=
+			[KNL] Number of legacy pty's. Overwrites compiled-in
+			default number.
+
 	quiet		[KNL] Disable most log messages
 
 	r128=		[HW,DRM]

drivers/char/pty.c

@@ -248,14 +248,19 @@ static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
 	return -ENOIOCTLCMD;
 }
 
+static int legacy_count = CONFIG_LEGACY_PTY_COUNT;
+module_param(legacy_count, int, 0);
+
 static void __init legacy_pty_init(void)
 {
+	if (legacy_count <= 0)
+		return;
 
-	pty_driver = alloc_tty_driver(NR_PTYS);
+	pty_driver = alloc_tty_driver(legacy_count);
 	if (!pty_driver)
 		panic("Couldn't allocate pty driver");
 
-	pty_slave_driver = alloc_tty_driver(NR_PTYS);
+	pty_slave_driver = alloc_tty_driver(legacy_count);
 	if (!pty_slave_driver)
 		panic("Couldn't allocate pty slave driver");
 

include/linux/tty.h

@@ -21,7 +21,6 @@
  * (Note: the *_driver.minor_start values 1, 64, 128, 192 are
  * hardcoded at present.)
  */
-#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		17