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linux-next/drivers/char/pty.c
Alan Cox 33f0f88f1c [PATCH] TTY layer buffering revamp 
The API and code have been through various bits of initial review by
serial driver people but they definitely need to live somewhere for a
while so the unconverted drivers can get knocked into shape, existing
drivers that have been updated can be better tuned and bugs whacked out.

This replaces the tty flip buffers with kmalloc objects in rings. In the
normal situation for an IRQ driven serial port at typical speeds the
behaviour is pretty much the same, two buffers end up allocated and the
kernel cycles between them as before.

When there are delays or at high speed we now behave far better as the
buffer pool can grow a bit rather than lose characters. This also means
that we can operate at higher speeds reliably.

For drivers that receive characters in blocks (DMA based, USB and
especially virtualisation) the layer allows a lot of driver specific
code that works around the tty layer with private secondary queues to be
removed. The IBM folks need this sort of layer, the smart serial port
people do, the virtualisers do (because a virtualised tty typically
operates at infinite speed rather than emulating 9600 baud).

Finally many drivers had invalid and unsafe attempts to avoid buffer
overflows by directly invoking tty methods extracted out of the innards
of work queue structs. These are no longer needed and all go away. That
fixes various random hangs with serial ports on overflow.

The other change in here is to optimise the receive_room path that is
used by some callers. It turns out that only one ldisc uses receive room
except asa constant and it updates it far far less than the value is
read. We thus make it a variable not a function call.

I expect the code to contain bugs due to the size alone but I'll be
watching and squashing them and feeding out new patches as it goes.

Because the buffers now dynamically expand you should only run out of
buffering when the kernel runs out of memory for real.  That means a lot of
the horrible hacks high performance drivers used to do just aren't needed any
more.

Description:

tty_insert_flip_char is an old API and continues to work as before, as does
tty_flip_buffer_push() [this is why many drivers dont need modification].  It
does now also return the number of chars inserted

There are also

tty_buffer_request_room(tty, len)

which asks for a buffer block of the length requested and returns the space
found.  This improves efficiency with hardware that knows how much to
transfer.

and tty_insert_flip_string_flags(tty, str, flags, len)

to insert a string of characters and flags

For a smart interface the usual code is

    len = tty_request_buffer_room(tty, amount_hardware_says);
    tty_insert_flip_string(tty, buffer_from_card, len);

More description!

At the moment tty buffers are attached directly to the tty.  This is causing a
lot of the problems related to tty layer locking, also problems at high speed
and also with bursty data (such as occurs in virtualised environments)

I'm working on ripping out the flip buffers and replacing them with a pool of
dynamically allocated buffers.  This allows both for old style "byte I/O"
devices and also helps virtualisation and smart devices where large blocks of
data suddenely materialise and need storing.

So far so good.  Lots of drivers reference tty->flip.*.  Several of them also
call directly and unsafely into function pointers it provides.  This will all
break.  Most drivers can use tty_insert_flip_char which can be kept as an API
but others need more.

At the moment I've added the following interfaces, if people think more will
be needed now is a good time to say

 int tty_buffer_request_room(tty, size)

Try and ensure at least size bytes are available, returns actual room (may be
zero).  At the moment it just uses the flipbuf space but that will change.
Repeated calls without characters being added are not cumulative.  (ie if you
call it with 1, 1, 1, and then 4 you'll have four characters of space.  The
other functions will also try and grow buffers in future but this will be a
more efficient way when you know block sizes.

 int tty_insert_flip_char(tty, ch, flag)

As before insert a character if there is room.  Now returns 1 for success, 0
for failure.

 int tty_insert_flip_string(tty, str, len)

Insert a block of non error characters.  Returns the number inserted.

 int tty_prepare_flip_string(tty, strptr, len)

Adjust the buffer to allow len characters to be added.  Returns a buffer
pointer in strptr and the length available.  This allows for hardware that
needs to use functions like insl or mencpy_fromio.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: John Hawkes <hawkes@sgi.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-10 08:01:59 -08:00

412 lines
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/*
* linux/drivers/char/pty.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
* Added support for a Unix98-style ptmx device.
* -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
* Added TTY_DO_WRITE_WAKEUP to enable n_tty to send POLL_OUT to
* waiting writers -- Sapan Bhatia <sapan@corewars.org>
*
*
*/
#include <linux/config.h>
#include <linux/module.h> /* For EXPORT_SYMBOL */
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/fcntl.h>
#include <linux/string.h>
#include <linux/major.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/sysctl.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <linux/bitops.h>
#include <linux/devpts_fs.h>
/* These are global because they are accessed in tty_io.c */
#ifdef CONFIG_UNIX98_PTYS
struct tty_driver *ptm_driver;
static struct tty_driver *pts_driver;
#endif
static void pty_close(struct tty_struct * tty, struct file * filp)
{
if (!tty)
return;
if (tty->driver->subtype == PTY_TYPE_MASTER) {
if (tty->count > 1)
printk("master pty_close: count = %d!!\n", tty->count);
} else {
if (tty->count > 2)
return;
}
wake_up_interruptible(&tty->read_wait);
wake_up_interruptible(&tty->write_wait);
tty->packet = 0;
if (!tty->link)
return;
tty->link->packet = 0;
set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
wake_up_interruptible(&tty->link->read_wait);
wake_up_interruptible(&tty->link->write_wait);
if (tty->driver->subtype == PTY_TYPE_MASTER) {
set_bit(TTY_OTHER_CLOSED, &tty->flags);
#ifdef CONFIG_UNIX98_PTYS
if (tty->driver == ptm_driver)
devpts_pty_kill(tty->index);
#endif
tty_vhangup(tty->link);
}
}
/*
* The unthrottle routine is called by the line discipline to signal
* that it can receive more characters. For PTY's, the TTY_THROTTLED
* flag is always set, to force the line discipline to always call the
* unthrottle routine when there are fewer than TTY_THRESHOLD_UNTHROTTLE
* characters in the queue. This is necessary since each time this
* happens, we need to wake up any sleeping processes that could be
* (1) trying to send data to the pty, or (2) waiting in wait_until_sent()
* for the pty buffer to be drained.
*/
static void pty_unthrottle(struct tty_struct * tty)
{
struct tty_struct *o_tty = tty->link;
if (!o_tty)
return;
tty_wakeup(o_tty);
set_bit(TTY_THROTTLED, &tty->flags);
}
/*
* WSH 05/24/97: modified to
* (1) use space in tty->flip instead of a shared temp buffer
* The flip buffers aren't being used for a pty, so there's lots
* of space available. The buffer is protected by a per-pty
* semaphore that should almost never come under contention.
* (2) avoid redundant copying for cases where count >> receive_room
* N.B. Calls from user space may now return an error code instead of
* a count.
*
* FIXME: Our pty_write method is called with our ldisc lock held but
* not our partners. We can't just take the other one blindly without
* risking deadlocks. There is also the small matter of TTY_DONT_FLIP
*/
static int pty_write(struct tty_struct * tty, const unsigned char *buf, int count)
{
struct tty_struct *to = tty->link;
int c;
if (!to || tty->stopped)
return 0;
c = to->receive_room;
if (c > count)
c = count;
to->ldisc.receive_buf(to, buf, NULL, c);
return c;
}
static int pty_write_room(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
if (!to || tty->stopped)
return 0;
return to->receive_room;
}
/*
* WSH 05/24/97: Modified for asymmetric MASTER/SLAVE behavior
* The chars_in_buffer() value is used by the ldisc select() function
* to hold off writing when chars_in_buffer > WAKEUP_CHARS (== 256).
* The pty driver chars_in_buffer() Master/Slave must behave differently:
*
* The Master side needs to allow typed-ahead commands to accumulate
* while being canonicalized, so we report "our buffer" as empty until
* some threshold is reached, and then report the count. (Any count >
* WAKEUP_CHARS is regarded by select() as "full".) To avoid deadlock
* the count returned must be 0 if no canonical data is available to be
* read. (The N_TTY ldisc.chars_in_buffer now knows this.)
*
* The Slave side passes all characters in raw mode to the Master side's
* buffer where they can be read immediately, so in this case we can
* return the true count in the buffer.
*/
static int pty_chars_in_buffer(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
int count;
/* We should get the line discipline lock for "tty->link" */
if (!to || !to->ldisc.chars_in_buffer)
return 0;
/* The ldisc must report 0 if no characters available to be read */
count = to->ldisc.chars_in_buffer(to);
if (tty->driver->subtype == PTY_TYPE_SLAVE) return count;
/* Master side driver ... if the other side's read buffer is less than
* half full, return 0 to allow writers to proceed; otherwise return
* the count. This leaves a comfortable margin to avoid overflow,
* and still allows half a buffer's worth of typed-ahead commands.
*/
return ((count < N_TTY_BUF_SIZE/2) ? 0 : count);
}
/* Set the lock flag on a pty */
static int pty_set_lock(struct tty_struct *tty, int __user * arg)
{
int val;
if (get_user(val,arg))
return -EFAULT;
if (val)
set_bit(TTY_PTY_LOCK, &tty->flags);
else
clear_bit(TTY_PTY_LOCK, &tty->flags);
return 0;
}
static void pty_flush_buffer(struct tty_struct *tty)
{
struct tty_struct *to = tty->link;
if (!to)
return;
if (to->ldisc.flush_buffer)
to->ldisc.flush_buffer(to);
if (to->packet) {
tty->ctrl_status |= TIOCPKT_FLUSHWRITE;
wake_up_interruptible(&to->read_wait);
}
}
static int pty_open(struct tty_struct *tty, struct file * filp)
{
int retval = -ENODEV;
if (!tty || !tty->link)
goto out;
retval = -EIO;
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
goto out;
if (test_bit(TTY_PTY_LOCK, &tty->link->flags))
goto out;
if (tty->link->count != 1)
goto out;
clear_bit(TTY_OTHER_CLOSED, &tty->link->flags);
set_bit(TTY_THROTTLED, &tty->flags);
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
retval = 0;
out:
return retval;
}
static void pty_set_termios(struct tty_struct *tty, struct termios *old_termios)
{
tty->termios->c_cflag &= ~(CSIZE | PARENB);
tty->termios->c_cflag |= (CS8 | CREAD);
}
static struct tty_operations pty_ops = {
.open = pty_open,
.close = pty_close,
.write = pty_write,
.write_room = pty_write_room,
.flush_buffer = pty_flush_buffer,
.chars_in_buffer = pty_chars_in_buffer,
.unthrottle = pty_unthrottle,
.set_termios = pty_set_termios,
};
/* Traditional BSD devices */
#ifdef CONFIG_LEGACY_PTYS
static struct tty_driver *pty_driver, *pty_slave_driver;
static int pty_bsd_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
switch (cmd) {
case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
return pty_set_lock(tty, (int __user *) arg);
}
return -ENOIOCTLCMD;
}
static void __init legacy_pty_init(void)
{
pty_driver = alloc_tty_driver(NR_PTYS);
if (!pty_driver)
panic("Couldn't allocate pty driver");
pty_slave_driver = alloc_tty_driver(NR_PTYS);
if (!pty_slave_driver)
panic("Couldn't allocate pty slave driver");
pty_driver->owner = THIS_MODULE;
pty_driver->driver_name = "pty_master";
pty_driver->name = "pty";
pty_driver->devfs_name = "pty/m";
pty_driver->major = PTY_MASTER_MAJOR;
pty_driver->minor_start = 0;
pty_driver->type = TTY_DRIVER_TYPE_PTY;
pty_driver->subtype = PTY_TYPE_MASTER;
pty_driver->init_termios = tty_std_termios;
pty_driver->init_termios.c_iflag = 0;
pty_driver->init_termios.c_oflag = 0;
pty_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pty_driver->init_termios.c_lflag = 0;
pty_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW;
pty_driver->other = pty_slave_driver;
tty_set_operations(pty_driver, &pty_ops);
pty_driver->ioctl = pty_bsd_ioctl;
pty_slave_driver->owner = THIS_MODULE;
pty_slave_driver->driver_name = "pty_slave";
pty_slave_driver->name = "ttyp";
pty_slave_driver->devfs_name = "pty/s";
pty_slave_driver->major = PTY_SLAVE_MAJOR;
pty_slave_driver->minor_start = 0;
pty_slave_driver->type = TTY_DRIVER_TYPE_PTY;
pty_slave_driver->subtype = PTY_TYPE_SLAVE;
pty_slave_driver->init_termios = tty_std_termios;
pty_slave_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pty_slave_driver->flags = TTY_DRIVER_RESET_TERMIOS |
TTY_DRIVER_REAL_RAW;
pty_slave_driver->other = pty_driver;
tty_set_operations(pty_slave_driver, &pty_ops);
if (tty_register_driver(pty_driver))
panic("Couldn't register pty driver");
if (tty_register_driver(pty_slave_driver))
panic("Couldn't register pty slave driver");
}
#else
static inline void legacy_pty_init(void) { }
#endif
/* Unix98 devices */
#ifdef CONFIG_UNIX98_PTYS
/*
* sysctl support for setting limits on the number of Unix98 ptys allocated.
* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
*/
int pty_limit = NR_UNIX98_PTY_DEFAULT;
static int pty_limit_min = 0;
static int pty_limit_max = NR_UNIX98_PTY_MAX;
ctl_table pty_table[] = {
{
.ctl_name = PTY_MAX,
.procname = "max",
.maxlen = sizeof(int),
.mode = 0644,
.data = &pty_limit,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &pty_limit_min,
.extra2 = &pty_limit_max,
}, {
.ctl_name = PTY_NR,
.procname = "nr",
.maxlen = sizeof(int),
.mode = 0444,
.proc_handler = &proc_dointvec,
}, {
.ctl_name = 0
}
};
static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg)
{
switch (cmd) {
case TIOCSPTLCK: /* Set PT Lock (disallow slave open) */
return pty_set_lock(tty, (int __user *)arg);
case TIOCGPTN: /* Get PT Number */
return put_user(tty->index, (unsigned int __user *)arg);
}
return -ENOIOCTLCMD;
}
static void __init unix98_pty_init(void)
{
devfs_mk_dir("pts");
ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
if (!ptm_driver)
panic("Couldn't allocate Unix98 ptm driver");
pts_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
if (!pts_driver)
panic("Couldn't allocate Unix98 pts driver");
ptm_driver->owner = THIS_MODULE;
ptm_driver->driver_name = "pty_master";
ptm_driver->name = "ptm";
ptm_driver->major = UNIX98_PTY_MASTER_MAJOR;
ptm_driver->minor_start = 0;
ptm_driver->type = TTY_DRIVER_TYPE_PTY;
ptm_driver->subtype = PTY_TYPE_MASTER;
ptm_driver->init_termios = tty_std_termios;
ptm_driver->init_termios.c_iflag = 0;
ptm_driver->init_termios.c_oflag = 0;
ptm_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
ptm_driver->init_termios.c_lflag = 0;
ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
TTY_DRIVER_NO_DEVFS | TTY_DRIVER_DEVPTS_MEM;
ptm_driver->other = pts_driver;
tty_set_operations(ptm_driver, &pty_ops);
ptm_driver->ioctl = pty_unix98_ioctl;
pts_driver->owner = THIS_MODULE;
pts_driver->driver_name = "pty_slave";
pts_driver->name = "pts";
pts_driver->major = UNIX98_PTY_SLAVE_MAJOR;
pts_driver->minor_start = 0;
pts_driver->type = TTY_DRIVER_TYPE_PTY;
pts_driver->subtype = PTY_TYPE_SLAVE;
pts_driver->init_termios = tty_std_termios;
pts_driver->init_termios.c_cflag = B38400 | CS8 | CREAD;
pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
TTY_DRIVER_NO_DEVFS | TTY_DRIVER_DEVPTS_MEM;
pts_driver->other = ptm_driver;
tty_set_operations(pts_driver, &pty_ops);
if (tty_register_driver(ptm_driver))
panic("Couldn't register Unix98 ptm driver");
if (tty_register_driver(pts_driver))
panic("Couldn't register Unix98 pts driver");
pty_table[1].data = &ptm_driver->refcount;
}
#else
static inline void unix98_pty_init(void) { }
#endif
static int __init pty_init(void)
{
legacy_pty_init();
unix98_pty_init();
return 0;
}
module_init(pty_init);
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