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linux-next/include/linux/tty_driver.h
Alan Cox 38db89799b tty: throttling race fix 
The tty throttling code can race due to the lock drops. It takes very high
loads but this has been observed and verified by Rob Duncan.

The basic problem is that on an SMP box we can go

	CPU #1				CPU #2
	need to throttle ?
	suppose we should		buffer space cleared
					are we throttled
					yes ? - unthrottle
	call throttle method

This changeet take the termios lock to protect against this. The termios
lock isn't the initial obvious candidate but many implementations of throttle
methods already need to poke around their own termios structures (and nobody
really locks them against a racing change of flow control).

This does mean that anyone who is setting tty->low_latency = 1 and then
calling tty_flip_buffer_push from their unthrottle method is going to end up
collapsing in a pile of locks. However we've removed all the known bogus
users of low_latency = 1 and such use isn't safe anyway for other reasons so
catching it would be an improvement.

Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-06-11 08:50:59 -07:00

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#ifndef _LINUX_TTY_DRIVER_H
#define _LINUX_TTY_DRIVER_H
/*
* This structure defines the interface between the low-level tty
* driver and the tty routines. The following routines can be
* defined; unless noted otherwise, they are optional, and can be
* filled in with a null pointer.
*
* struct tty_struct * (*lookup)(struct tty_driver *self, int idx)
*
* Return the tty device corresponding to idx, NULL if there is not
* one currently in use and an ERR_PTR value on error. Called under
* tty_mutex (for now!)
*
* Optional method. Default behaviour is to use the ttys array
*
* int (*install)(struct tty_driver *self, struct tty_struct *tty)
*
* Install a new tty into the tty driver internal tables. Used in
* conjunction with lookup and remove methods.
*
* Optional method. Default behaviour is to use the ttys array
*
* void (*remove)(struct tty_driver *self, struct tty_struct *tty)
*
* Remove a closed tty from the tty driver internal tables. Used in
* conjunction with lookup and remove methods.
*
* Optional method. Default behaviour is to use the ttys array
*
* int (*open)(struct tty_struct * tty, struct file * filp);
*
* This routine is called when a particular tty device is opened.
* This routine is mandatory; if this routine is not filled in,
* the attempted open will fail with ENODEV.
*
* Required method.
*
* void (*close)(struct tty_struct * tty, struct file * filp);
*
* This routine is called when a particular tty device is closed.
*
* Required method.
*
* void (*shutdown)(struct tty_struct * tty);
*
* This routine is called when a particular tty device is closed for
* the last time freeing up the resources.
*
* int (*write)(struct tty_struct * tty,
* const unsigned char *buf, int count);
*
* This routine is called by the kernel to write a series of
* characters to the tty device. The characters may come from
* user space or kernel space. This routine will return the
* number of characters actually accepted for writing.
*
* Optional: Required for writable devices.
*
* int (*put_char)(struct tty_struct *tty, unsigned char ch);
*
* This routine is called by the kernel to write a single
* character to the tty device. If the kernel uses this routine,
* it must call the flush_chars() routine (if defined) when it is
* done stuffing characters into the driver. If there is no room
* in the queue, the character is ignored.
*
* Optional: Kernel will use the write method if not provided.
*
* Note: Do not call this function directly, call tty_put_char
*
* void (*flush_chars)(struct tty_struct *tty);
*
* This routine is called by the kernel after it has written a
* series of characters to the tty device using put_char().
*
* Optional:
*
* Note: Do not call this function directly, call tty_driver_flush_chars
*
* int (*write_room)(struct tty_struct *tty);
*
* This routine returns the numbers of characters the tty driver
* will accept for queuing to be written. This number is subject
* to change as output buffers get emptied, or if the output flow
* control is acted.
*
* Required if write method is provided else not needed.
*
* Note: Do not call this function directly, call tty_write_room
*
* int (*ioctl)(struct tty_struct *tty, struct file * file,
* unsigned int cmd, unsigned long arg);
*
* This routine allows the tty driver to implement
* device-specific ioctl's. If the ioctl number passed in cmd
* is not recognized by the driver, it should return ENOIOCTLCMD.
*
* Optional
*
* long (*compat_ioctl)(struct tty_struct *tty, struct file * file,
* unsigned int cmd, unsigned long arg);
*
* implement ioctl processing for 32 bit process on 64 bit system
*
* Optional
*
* void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
*
* This routine allows the tty driver to be notified when
* device's termios settings have changed.
*
* Optional: Called under the termios lock
*
*
* void (*set_ldisc)(struct tty_struct *tty);
*
* This routine allows the tty driver to be notified when the
* device's termios settings have changed.
*
* Optional: Called under BKL (currently)
*
* void (*throttle)(struct tty_struct * tty);
*
* This routine notifies the tty driver that input buffers for
* the line discipline are close to full, and it should somehow
* signal that no more characters should be sent to the tty.
*
* Optional: Always invoke via tty_throttle(), called under the
* termios lock.
*
* void (*unthrottle)(struct tty_struct * tty);
*
* This routine notifies the tty drivers that it should signals
* that characters can now be sent to the tty without fear of
* overrunning the input buffers of the line disciplines.
*
* Optional: Always invoke via tty_unthrottle(), called under the
* termios lock.
*
* void (*stop)(struct tty_struct *tty);
*
* This routine notifies the tty driver that it should stop
* outputting characters to the tty device.
*
* Optional:
*
* Note: Call stop_tty not this method.
*
* void (*start)(struct tty_struct *tty);
*
* This routine notifies the tty driver that it resume sending
* characters to the tty device.
*
* Optional:
*
* Note: Call start_tty not this method.
*
* void (*hangup)(struct tty_struct *tty);
*
* This routine notifies the tty driver that it should hangup the
* tty device.
*
* Optional:
*
* int (*break_ctl)(struct tty_stuct *tty, int state);
*
* This optional routine requests the tty driver to turn on or
* off BREAK status on the RS-232 port. If state is -1,
* then the BREAK status should be turned on; if state is 0, then
* BREAK should be turned off.
*
* If this routine is implemented, the high-level tty driver will
* handle the following ioctls: TCSBRK, TCSBRKP, TIOCSBRK,
* TIOCCBRK.
*
* If the driver sets TTY_DRIVER_HARDWARE_BREAK then the interface
* will also be called with actual times and the hardware is expected
* to do the delay work itself. 0 and -1 are still used for on/off.
*
* Optional: Required for TCSBRK/BRKP/etc handling.
*
* void (*wait_until_sent)(struct tty_struct *tty, int timeout);
*
* This routine waits until the device has written out all of the
* characters in its transmitter FIFO.
*
* Optional: If not provided the device is assumed to have no FIFO
*
* Note: Usually correct to call tty_wait_until_sent
*
* void (*send_xchar)(struct tty_struct *tty, char ch);
*
* This routine is used to send a high-priority XON/XOFF
* character to the device.
*
* Optional: If not provided then the write method is called under
* the atomic write lock to keep it serialized with the ldisc.
*
* int (*resize)(struct tty_struct *tty, struct winsize *ws)
*
* Called when a termios request is issued which changes the
* requested terminal geometry.
*
* Optional: the default action is to update the termios structure
* without error. This is usually the correct behaviour. Drivers should
* not force errors here if they are not resizable objects (eg a serial
* line). See tty_do_resize() if you need to wrap the standard method
* in your own logic - the usual case.
*
* void (*set_termiox)(struct tty_struct *tty, struct termiox *new);
*
* Called when the device receives a termiox based ioctl. Passes down
* the requested data from user space. This method will not be invoked
* unless the tty also has a valid tty->termiox pointer.
*
* Optional: Called under the termios lock
*/
#include <linux/fs.h>
#include <linux/list.h>
#include <linux/cdev.h>
struct tty_struct;
struct tty_driver;
struct tty_operations {
struct tty_struct * (*lookup)(struct tty_driver *driver,
struct inode *inode, int idx);
int (*install)(struct tty_driver *driver, struct tty_struct *tty);
void (*remove)(struct tty_driver *driver, struct tty_struct *tty);
int (*open)(struct tty_struct * tty, struct file * filp);
void (*close)(struct tty_struct * tty, struct file * filp);
void (*shutdown)(struct tty_struct *tty);
int (*write)(struct tty_struct * tty,
const unsigned char *buf, int count);
int (*put_char)(struct tty_struct *tty, unsigned char ch);
void (*flush_chars)(struct tty_struct *tty);
int (*write_room)(struct tty_struct *tty);
int (*chars_in_buffer)(struct tty_struct *tty);
int (*ioctl)(struct tty_struct *tty, struct file * file,
unsigned int cmd, unsigned long arg);
long (*compat_ioctl)(struct tty_struct *tty, struct file * file,
unsigned int cmd, unsigned long arg);
void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
void (*throttle)(struct tty_struct * tty);
void (*unthrottle)(struct tty_struct * tty);
void (*stop)(struct tty_struct *tty);
void (*start)(struct tty_struct *tty);
void (*hangup)(struct tty_struct *tty);
int (*break_ctl)(struct tty_struct *tty, int state);
void (*flush_buffer)(struct tty_struct *tty);
void (*set_ldisc)(struct tty_struct *tty);
void (*wait_until_sent)(struct tty_struct *tty, int timeout);
void (*send_xchar)(struct tty_struct *tty, char ch);
int (*tiocmget)(struct tty_struct *tty, struct file *file);
int (*tiocmset)(struct tty_struct *tty, struct file *file,
unsigned int set, unsigned int clear);
int (*resize)(struct tty_struct *tty, struct winsize *ws);
int (*set_termiox)(struct tty_struct *tty, struct termiox *tnew);
#ifdef CONFIG_CONSOLE_POLL
int (*poll_init)(struct tty_driver *driver, int line, char *options);
int (*poll_get_char)(struct tty_driver *driver, int line);
void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
#endif
const struct file_operations *proc_fops;
};
struct tty_driver {
int magic; /* magic number for this structure */
struct kref kref; /* Reference management */
struct cdev cdev;
struct module *owner;
const char *driver_name;
const char *name;
int name_base; /* offset of printed name */
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 ktermios init_termios; /* Initial termios */
int flags; /* tty driver flags */
struct proc_dir_entry *proc_entry; /* /proc fs entry */
struct tty_driver *other; /* only used for the PTY driver */
/*
* Pointer to the tty data structures
*/
struct tty_struct **ttys;
struct ktermios **termios;
struct ktermios **termios_locked;
void *driver_state;
/*
* Driver methods
*/
const struct tty_operations *ops;
struct list_head tty_drivers;
};
extern struct list_head tty_drivers;
extern struct tty_driver *alloc_tty_driver(int lines);
extern void put_tty_driver(struct tty_driver *driver);
extern void tty_set_operations(struct tty_driver *driver,
const struct tty_operations *op);
extern struct tty_driver *tty_find_polling_driver(char *name, int *line);
extern void tty_driver_kref_put(struct tty_driver *driver);
static inline struct tty_driver *tty_driver_kref_get(struct tty_driver *d)
{
kref_get(&d->kref);
return d;
}
/* tty driver magic number */
#define TTY_DRIVER_MAGIC 0x5402
/*
* tty driver flags
*
* TTY_DRIVER_RESET_TERMIOS --- requests the tty layer to reset the
* termios setting when the last process has closed the device.
* Used for PTY's, in particular.
*
* TTY_DRIVER_REAL_RAW --- if set, indicates that the driver will
* guarantee never not to set any special character handling
* flags if ((IGNBRK || (!BRKINT && !PARMRK)) && (IGNPAR ||
* !INPCK)). That is, if there is no reason for the driver to
* send notifications of parity and break characters up to the
* line driver, it won't do so. This allows the line driver to
* optimize for this case if this flag is set. (Note that there
* is also a promise, if the above case is true, not to signal
* overruns, either.)
*
* TTY_DRIVER_DYNAMIC_DEV --- if set, the individual tty devices need
* to be registered with a call to tty_register_driver() when the
* device is found in the system and unregistered with a call to
* tty_unregister_device() so the devices will be show up
* properly in sysfs. If not set, driver->num entries will be
* created by the tty core in sysfs when tty_register_driver() is
* called. This is to be used by drivers that have tty devices
* that can appear and disappear while the main tty driver is
* registered with the tty core.
*
* 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.
*
* TTY_DRIVER_HARDWARE_BREAK -- hardware handles break signals. Pass
* the requested timeout to the caller instead of using a simple
* on/off interface.
*
*/
#define TTY_DRIVER_INSTALLED 0x0001
#define TTY_DRIVER_RESET_TERMIOS 0x0002
#define TTY_DRIVER_REAL_RAW 0x0004
#define TTY_DRIVER_DYNAMIC_DEV 0x0008
#define TTY_DRIVER_DEVPTS_MEM 0x0010
#define TTY_DRIVER_HARDWARE_BREAK 0x0020
/* tty driver types */
#define TTY_DRIVER_TYPE_SYSTEM 0x0001
#define TTY_DRIVER_TYPE_CONSOLE 0x0002
#define TTY_DRIVER_TYPE_SERIAL 0x0003
#define TTY_DRIVER_TYPE_PTY 0x0004
#define TTY_DRIVER_TYPE_SCC 0x0005 /* scc driver */
#define TTY_DRIVER_TYPE_SYSCONS 0x0006
/* system subtypes (magic, used by tty_io.c) */
#define SYSTEM_TYPE_TTY 0x0001
#define SYSTEM_TYPE_CONSOLE 0x0002
#define SYSTEM_TYPE_SYSCONS 0x0003
#define SYSTEM_TYPE_SYSPTMX 0x0004
/* pty subtypes (magic, used by tty_io.c) */
#define PTY_TYPE_MASTER 0x0001
#define PTY_TYPE_SLAVE 0x0002
/* serial subtype definitions */
#define SERIAL_TYPE_NORMAL 1
#endif /* #ifdef _LINUX_TTY_DRIVER_H */
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