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Message-ID: <20090910093301.4ccfd786@caramujo.chehab.org>
Date: Thu, 10 Sep 2009 09:33:01 -0300
From: Mauro Carvalho Chehab <mchehab@...radead.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Alan Cox <alan@...ux.intel.com>,
LKML <linux-kernel@...r.kernel.org>,
Kay Sievers <kay.sievers@...y.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH] char/tty_io: fix legacy pty name when more than 256 pty
devices are requested
char/tty_io: fix pty name convention
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.
To preserve backward compatibility, the device index is broken into
nibbles, each nibble generating a letter, at the following order:
* The second nibble of the index is represented by one of pqrstuvwxyzabcde
letters, indicating the 1st through 16th nibble value;
* The remaining nibbles are represented by one of 0123456789abcdef letters,
indicating the 1st through 16th nibble value, starting from the most
significative nibble to the least significative nibble, excluding the
second nibble (that were already represented).
So, device numbers will be:
0 = ptyp0
1 = ptyp1
...
255 = ptyef
256 = ptyp10
...
4095 = ptyeff
4096 = ptyp100
...
65535 = ptyefff
65536 = ptyp1000
...
Thanks to H. Peter Anvin <hpa@...or.com> for proposing this algorithm.
Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>
diff --git a/Documentation/devices.txt b/Documentation/devices.txt
index 53d64d3..6a74635 100644
--- a/Documentation/devices.txt
+++ b/Documentation/devices.txt
@@ -114,17 +114,30 @@ 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/ptyp10 257th PTY master
+ 257 = /dev/ptyp11 258th PTY master
+ ...
+ 4095 = /dev/ptyeff 4095th PTY master
+ 4096 = /dev/ptyp100 4096th PTY master
+ ...
Pseudo-tty's 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.
+ Masters are "pty", slaves are "tty";
+
+ The device index is broken into nibbles, each nibble
+ generating a letter, at the following order:
+ * The second nibble of the index is represented by one
+ of pqrstuvwxyzabcde letters, indicating the 1st
+ through 16th nibble value;
+ * The remaining nibbles are represented by one of
+ 0123456789abcdef letters, indicating the 1st through
+ 16th nibble value, starting from the most
+ significative nibble to the least significative nibble,
+ excluding the second nibble.
These are the old-style (BSD) PTY devices; Unix98
devices are on major 128 and above and use the PTY
@@ -189,10 +202,18 @@ 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/ttyp10 257th PTY slave
+ 257 = /dev/ttyp11 258th PTY slave
+ ...
+ 4095 = /dev/ttyeff 4095th PTY slave
+ 4096 = /dev/ttyp100 4096th PTY slave
+ ...
+
+ See char major number 2 for the used rules to name them.
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..de6d617 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1093,8 +1093,6 @@ ssize_t redirected_tty_write(struct file *file, const char __user *buf,
return tty_write(file, buf, count, ppos);
}
-static char ptychar[] = "pqrstuvwxyzabcde";
-
/**
* pty_line_name - generate name for a pty
* @driver: the tty driver in use
@@ -1108,11 +1106,23 @@ static char ptychar[] = "pqrstuvwxyzabcde";
*/
static void pty_line_name(struct tty_driver *driver, int index, char *p)
{
+ static const char ptychar[] = "pqrstuvwxyzabcde";
+
int i = index + driver->name_base;
- /* ->name is initialized to "ttyp", but "tty" is expected */
+ /*
+ * On slave, driver->name is initialized to "ttyp",
+ * but "tty" is expected.
+ * The index part of the name is broken into nibbles, following
+ * this sequence:
+ * The second nibble encoded with ptychar;
+ * The other nibbles, printed in hexadecimal, from most to
+ * the least significant nibble.
+ * This is done to preserve backward compatibility with the older
+ * naming conventions.
+ */
sprintf(p, "%s%c%x",
driver->subtype == PTY_TYPE_SLAVE ? "tty" : driver->name,
- ptychar[i >> 4 & 0xf], i & 0xf);
+ ptychar[(i >> 4) & 0xf], (i & 0xf) | ((i >> 4) & ~0xf));
}
/**
Cheers,
Mauro
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