linux-kernel - [PATCH v2 RFC] char/tty_io: fix legacy pty name when more than 256 pty devices are requested

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Message-ID: <20090908155906.0d30f4bc@caramujo.chehab.org>
Date:	Tue, 8 Sep 2009 15:59:06 -0300
From:	Mauro Carvalho Chehab <mchehab@...radead.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH v2 RFC] char/tty_io: fix legacy pty name when more than 256
 pty devices are requested

With kernel 2.6, the number of minors is not 255 anymore. So, it is
possible to have more than 255 pty devices.

However, the pty_line_name() only provides device names for the first
256 tty/pty devices.

This is a bug, since there's no limits for the maximum number of legacy
pty devices at Kconfig or at pty.legacy_count.

This patch preserves the old nomenclature for tty/pty devices for the
first 256 devices. After that, it names the next devices as:
	ttyf0000-ttfpffff	(pty slave)
	ptyf0000-ttyfffff	(pty master)

This way, the existing udev rules for legacy pty devices to not
break. Only after minor 255, it will start to use the new nomenclature.

Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>

---

Version 2: devices.txt namespace doc were updated accordingly.

diff --git a/Documentation/devices.txt b/Documentation/devices.txt
index 53d64d3..cfd3e20 100644
--- a/Documentation/devices.txt
+++ b/Documentation/devices.txt
@@ -114,18 +114,27 @@ Your cooperation is appreciated.
 		the initrd.
 
   2 char	Pseudo-TTY masters
-		  0 = /dev/ptyp0	First PTY master
-		  1 = /dev/ptyp1	Second PTY master
+		    0 = /dev/ptyp0	First PTY master
+		    1 = /dev/ptyp1	Second PTY master
 		    ...
-		255 = /dev/ptyef	256th PTY master
+		  255 = /dev/ptyef	256th PTY master
+		  256 = /dev/ptyf0000	257th PTY slave
+		  257 = /dev/ptyf0001	258th PTY slave
+		   ...
+		65791 = /dev/ptyfffff	65791 PTY slave
 
-		Pseudo-tty's are named as follows:
+		Pseudo-tty's up to 256 are named as follows:
 		* Masters are "pty", slaves are "tty";
 		* the fourth letter is one of pqrstuvwxyzabcde indicating
 		  the 1st through 16th series of 16 pseudo-ttys each, and
 		* the fifth letter is one of 0123456789abcdef indicating
 		  the position within the series.
 
+		Pseudo-tty's above 256 are named as follows:
+		* Masters are "ptyf", slaves are "ttyf";
+		* the fifth to eighth letters are hexadecimal digits
+		  indicating the position within the series.
+
 		These are the old-style (BSD) PTY devices; Unix98
 		devices are on major 128 and above and use the PTY
 		master multiplex (/dev/ptmx) to acquire a PTY on
@@ -189,10 +198,14 @@ Your cooperation is appreciated.
 		the drive type is insignificant for these devices.
 
   3 char	Pseudo-TTY slaves
-		  0 = /dev/ttyp0	First PTY slave
-		  1 = /dev/ttyp1	Second PTY slave
-		    ...
-		255 = /dev/ttyef	256th PTY slave
+		    0 = /dev/ttyp0	First PTY slave
+		    1 = /dev/ttyp1	Second PTY slave
+		  ...
+		  255 = /dev/ttyef	256th PTY slave
+		  256 = /dev/ttyf0000	257th PTY slave
+		  257 = /dev/ttyf0001	258th PTY slave
+		   ...
+		65791 = /dev/ttyfffff	65791 PTY slave
 
 		These are the old-style (BSD) PTY devices; Unix98
 		devices are on major 136 and above.
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index a3afa0c..fdea89b 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1110,9 +1110,15 @@ static void pty_line_name(struct tty_driver *driver, int index, char *p)
 {
 	int i = index + driver->name_base;
 	/* ->name is initialized to "ttyp", but "tty" is expected */
-	sprintf(p, "%s%c%x",
-		driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
-		ptychar[i >> 4 & 0xf], i & 0xf);
+	if (i < 256) {
+		sprintf(p, "%s%c%x",
+				driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
+				ptychar[i >> 4 & 0xf], i & 0xf);
+	} else {	/* Up to 4096 */
+		sprintf(p, "%sf%04x",
+				driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
+				i - 256);
+	}
 }
 
 /**







Cheers,
Mauro
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