- 根目录:
- drivers
- tty
- tty_ldisc.c
#include <linux/types.h>
#include <linux/major.h>
#include <linux/errno.h>
#include <linux/signal.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/devpts_fs.h>
#include <linux/file.h>
#include <linux/console.h>
#include <linux/timer.h>
#include <linux/ctype.h>
#include <linux/kd.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/proc_fs.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/seq_file.h>
#include <linux/uaccess.h>
#include <asm/system.h>
#include <linux/kbd_kern.h>
#include <linux/vt_kern.h>
#include <linux/selection.h>
#include <linux/kmod.h>
#include <linux/nsproxy.h>
/*
* This guards the refcounted line discipline lists. The lock
* must be taken with irqs off because there are hangup path
* callers who will do ldisc lookups and cannot sleep.
*/
static DEFINE_SPINLOCK(tty_ldisc_lock);
static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
/* Line disc dispatch table */
static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
{
if (ld)
atomic_inc(&ld->users);
return ld;
}
static void put_ldisc(struct tty_ldisc *ld)
{
unsigned long flags;
if (WARN_ON_ONCE(!ld))
return;
/*
* If this is the last user, free the ldisc, and
* release the ldisc ops.
*
* We really want an "atomic_dec_and_lock_irqsave()",
* but we don't have it, so this does it by hand.
*/
local_irq_save(flags);
if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
struct tty_ldisc_ops *ldo = ld->ops;
ldo->refcount--;
module_put(ldo->owner);
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
kfree(ld);
return;
}
local_irq_restore(flags);
wake_up(&tty_ldisc_idle);
}
/**
* tty_register_ldisc - install a line discipline
* @disc: ldisc number
* @new_ldisc: pointer to the ldisc object
*
* Installs a new line discipline into the kernel. The discipline
* is set up as unreferenced and then made available to the kernel
* from this point onwards.
*
* Locking:
* takes tty_ldisc_lock to guard against ldisc races
*/
int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
{
unsigned long flags;
int ret = 0;
if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags);
tty_ldiscs[disc] = new_ldisc;
new_ldisc->num = disc;
new_ldisc->refcount = 0;
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
EXPORT_SYMBOL(tty_register_ldisc);
/**
* tty_unregister_ldisc - unload a line discipline
* @disc: ldisc number
* @new_ldisc: pointer to the ldisc object
*
* Remove a line discipline from the kernel providing it is not
* currently in use.
*
* Locking:
* takes tty_ldisc_lock to guard against ldisc races
*/
int tty_unregister_ldisc(int disc)
{
unsigned long flags;
int ret = 0;
if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags);
if (tty_ldiscs[disc]->refcount)
ret = -EBUSY;
else
tty_ldiscs[disc] = NULL;
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
EXPORT_SYMBOL(tty_unregister_ldisc);
static struct tty_ldisc_ops *get_ldops(int disc)
{
unsigned long flags;
struct tty_ldisc_ops *ldops, *ret;
spin_lock_irqsave(&tty_ldisc_lock, flags);
ret = ERR_PTR(-EINVAL);
ldops = tty_ldiscs[disc];
if (ldops) {
ret = ERR_PTR(-EAGAIN);
if (try_module_get(ldops->owner)) {
ldops->refcount++;
ret = ldops;
}
}
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
}
static void put_ldops(struct tty_ldisc_ops *ldops)
{
unsigned long flags;
spin_lock_irqsave(&tty_ldisc_lock, flags);
ldops->refcount--;
module_put(ldops->owner);
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
}
/**
* tty_ldisc_get - take a reference to an ldisc
* @disc: ldisc number
*
* Takes a reference to a line discipline. Deals with refcounts and
* module locking counts. Returns NULL if the discipline is not available.
* Returns a pointer to the discipline and bumps the ref count if it is
* available
*
* Locking:
* takes tty_ldisc_lock to guard against ldisc races
*/
static struct tty_ldisc *tty_ldisc_get(int disc)
{
struct tty_ldisc *ld;
struct tty_ldisc_ops *ldops;
if (disc < N_TTY || disc >= NR_LDISCS)
return ERR_PTR(-EINVAL);
/*
* Get the ldisc ops - we may need to request them to be loaded
* dynamically and try again.
*/
ldops = get_ldops(disc);
if (IS_ERR(ldops)) {
request_module("tty-ldisc-%d", disc);
ldops = get_ldops(disc);
if (IS_ERR(ldops))
return ERR_CAST(ldops);
}
ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
if (ld == NULL) {
put_ldops(ldops);
return ERR_PTR(-ENOMEM);
}
ld->ops = ldops;
atomic_set(&ld->users, 1);
return ld;
}
static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
{
return (*pos < NR_LDISCS) ? pos : NULL;
}
static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
(*pos)++;
return (*pos < NR_LDISCS) ? pos : NULL;
}
static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
{
}
static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
{
int i = *(loff_t *)v;
struct tty_ldisc_ops *ldops;
ldops = get_ldops(i);
if (IS_ERR(ldops))
return 0;
seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
put_ldops(ldops);
return 0;
}
static const struct seq_operations tty_ldiscs_seq_ops = {
.start = tty_ldiscs_seq_start,
.next = tty_ldiscs_seq_next,
.stop = tty_ldiscs_seq_stop,
.show = tty_ldiscs_seq_show,
};
static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
{
return seq_open(file, &tty_ldiscs_seq_ops);
}
const struct file_operations tty_ldiscs_proc_fops = {
.owner = THIS_MODULE,
.open = proc_tty_ldiscs_open,
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
};
/**
* tty_ldisc_assign - set ldisc on a tty
* @tty: tty to assign
* @ld: line discipline
*
* Install an instance of a line discipline into a tty structure. The
* ldisc must have a reference count above zero to ensure it remains.
* The tty instance refcount starts at zero.
*
* Locking:
* Caller must hold references
*/
static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
{
tty->ldisc = ld;
}
/**
* tty_ldisc_try - internal helper
* @tty: the tty
*
* Make a single attempt to grab and bump the refcount on
* the tty ldisc. Return 0 on failure or 1 on success. This is
* used to implement both the waiting and non waiting versions
* of tty_ldisc_ref
*
* Locking: takes tty_ldisc_lock
*/
static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
{
unsigned long flags;
struct tty_ldisc *ld;
spin_lock_irqsave(&tty_ldisc_lock, flags);
ld = NULL;
if (test_bit(TTY_LDISC, &tty->flags))
ld = get_ldisc(tty->ldisc);
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ld;
}
/**
* tty_ldisc_ref_wait - wait for the tty ldisc
* @tty: tty device
*
* Dereference the line discipline for the terminal and take a
* reference to it. If the line discipline is in flux then
* wait patiently until it changes.
*
* Note: Must not be called from an IRQ/timer context. The caller
* must also be careful not to hold other locks that will deadlock
* against a discipline change, such as an existing ldisc reference
* (which we check for)
*
* Locking: call functions take tty_ldisc_lock
*/
struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
{
struct tty_ldisc *ld;
/* wait_event is a macro */
wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
return ld;
}
EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
/**
* tty_ldisc_ref - get the tty ldisc
* @tty: tty device
*
* Dereference the line discipline for the terminal and take a
* reference to it. If the line discipline is in flux then
* return NULL. Can be called from IRQ and timer functions.
*
* Locking: called functions take tty_ldisc_lock
*/
struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
{
return tty_ldisc_try(tty);
}
EXPORT_SYMBOL_GPL(tty_ldisc_ref);
/**
* tty_ldisc_deref - free a tty ldisc reference
* @ld: reference to free up
*
* Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
* be called in IRQ context.
*
* Locking: takes tty_ldisc_lock
*/
void tty_ldisc_deref(struct tty_ldisc *ld)
{
put_ldisc(ld);
}
EXPORT_SYMBOL_GPL(tty_ldisc_deref);
static inline void tty_ldisc_put(struct tty_ldisc *ld)
{
put_ldisc(ld);
}
/**
* tty_ldisc_enable - allow ldisc use
* @tty: terminal to activate ldisc on
*
* Set the TTY_LDISC flag when the line discipline can be called
* again. Do necessary wakeups for existing sleepers. Clear the LDISC
* changing flag to indicate any ldisc change is now over.
*
* Note: nobody should set the TTY_LDISC bit except via this function.
* Clearing directly is allowed.
*/
void tty_ldisc_enable(struct tty_struct *tty)
{
set_bit(TTY_LDISC, &tty->flags);
clear_bit(TTY_LDISC_CHANGING, &tty->flags);
wake_up(&tty_ldisc_wait);
}
/**
* tty_ldisc_flush - flush line discipline queue
* @tty: tty
*
* Flush the line discipline queue (if any) for this tty. If there
* is no line discipline active this is a no-op.
*/
void tty_ldisc_flush(struct tty_struct *tty)
{
struct tty_ldisc *ld = tty_ldisc_ref(tty);
if (ld) {
if (ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
tty_ldisc_deref(ld);
}
tty_buffer_flush(tty);
}
EXPORT_SYMBOL_GPL(tty_ldisc_flush);
/**
* tty_set_termios_ldisc - set ldisc field
* @tty: tty structure
* @num: line discipline number
*
* This is probably overkill for real world processors but
* they are not on hot paths so a little discipline won't do
* any harm.
*
* Locking: takes termios_mutex
*/
static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
{
mutex_lock(&tty->termios_mutex);
tty->termios->c_line = num;
mutex_unlock(&tty->termios_mutex);
}
/**
* tty_ldisc_open - open a line discipline
* @tty: tty we are opening the ldisc on
* @ld: discipline to open
*
* A helper opening method. Also a convenient debugging and check
* point.
*
* Locking: always called with BTM already held.
*/
static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
{
WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
if (ld->ops->open) {
int ret;
/* BTM here locks versus a hangup event */
WARN_ON(!tty_locked());
ret = ld->ops->open(tty);
if (ret)
clear_bit(TTY_LDISC_OPEN, &tty->flags);
return ret;
}
return 0;
}
/**
* tty_ldisc_close - close a line discipline
* @tty: tty we are opening the ldisc on
* @ld: discipline to close
*
* A helper close method. Also a convenient debugging and check
* point.
*/
static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
{
WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
clear_bit(TTY_LDISC_OPEN, &tty->flags);
if (ld->ops->close)
ld->ops->close(tty);
}
/**
* tty_ldisc_restore - helper for tty ldisc change
* @tty: tty to recover
* @old: previous ldisc
*
* Restore the previous line discipline or N_TTY when a line discipline
* change fails due to an open error
*/
static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
{
char buf[64];
struct tty_ldisc *new_ldisc;
int r;
/* There is an outstanding reference here so this is safe */
old = tty_ldisc_get(old->ops->num);
WARN_ON(IS_ERR(old));
tty_ldisc_assign(tty, old);
tty_set_termios_ldisc(tty, old->ops->num);
if (tty_ldisc_open(tty, old) < 0) {
tty_ldisc_put(old);
/* This driver is always present */
new_ldisc = tty_ldisc_get(N_TTY);
if (IS_ERR(new_ldisc))
panic("n_tty: get");
tty_ldisc_assign(tty, new_ldisc);
tty_set_termios_ldisc(tty, N_TTY);
r = tty_ldisc_open(tty, new_ldisc);
if (r < 0)
panic("Couldn't open N_TTY ldisc for "
"%s --- error %d.",
tty_name(tty, buf), r);
}
}
/**
* tty_ldisc_halt - shut down the line discipline
* @tty: tty device
*
* Shut down the line discipline and work queue for this tty device.
* The TTY_LDISC flag being cleared ensures no further references can
* be obtained while the delayed work queue halt ensures that no more
* data is fed to the ldisc.
*
* You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
* in order to make sure any currently executing ldisc work is also
* flushed.
*/
static int tty_ldisc_halt(struct tty_struct *tty)
{
clear_bit(TTY_LDISC, &tty->flags);
return cancel_work_sync(&tty->buf.work);
}
/**
* tty_ldisc_flush_works - flush all works of a tty
* @tty: tty device to flush works for
*
* Sync flush all works belonging to @tty.
*/
static void tty_ldisc_flush_works(struct tty_struct *tty)
{
flush_work_sync(&tty->hangup_work);
flush_work_sync(&tty->SAK_work);
flush_work_sync(&tty->buf.work);
}
/**
* tty_ldisc_wait_idle - wait for the ldisc to become idle
* @tty: tty to wait for
*
* Wait for the line discipline to become idle. The discipline must
* have been halted for this to guarantee it remains idle.
*/
static int tty_ldisc_wait_idle(struct tty_struct *tty)
{
int ret;
ret = wait_event_timeout(tty_ldisc_idle,
atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
if (ret < 0)
return ret;
return ret > 0 ? 0 : -EBUSY;
}
/**
* tty_set_ldisc - set line discipline
* @tty: the terminal to set
* @ldisc: the line discipline
*
* Set the discipline of a tty line. Must be called from a process
* context. The ldisc change logic has to protect itself against any
* overlapping ldisc change (including on the other end of pty pairs),
* the close of one side of a tty/pty pair, and eventually hangup.
*
* Locking: takes tty_ldisc_lock, termios_mutex
*/
int tty_set_ldisc(struct tty_struct *tty, int ldisc)
{
int retval;
struct tty_ldisc *o_ldisc, *new_ldisc;
int work, o_work = 0;
struct tty_struct *o_tty;
new_ldisc = tty_ldisc_get(ldisc);
if (IS_ERR(new_ldisc))
return PTR_ERR(new_ldisc);
tty_lock();
/*
* We need to look at the tty locking here for pty/tty pairs
* when both sides try to change in parallel.
*/
o_tty = tty->link; /* o_tty is the pty side or NULL */
/*
* Check the no-op case
*/
if (tty->ldisc->ops->num == ldisc) {
tty_unlock();
tty_ldisc_put(new_ldisc);
return 0;
}
tty_unlock();
/*
* Problem: What do we do if this blocks ?
* We could deadlock here
*/
tty_wait_until_sent(tty, 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
* We could be midstream of another ldisc change which has
* dropped the lock during processing. If so we need to wait.
*/
while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
mutex_unlock(&tty->ldisc_mutex);
tty_unlock();
wait_event(tty_ldisc_wait,
test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
}
set_bit(TTY_LDISC_CHANGING, &tty->flags);
/*
* No more input please, we are switching. The new ldisc
* will update this value in the ldisc open function
*/
tty->receive_room = 0;
o_ldisc = tty->ldisc;
tty_unlock();
/*
* Make sure we don't change while someone holds a
* reference to the line discipline. The TTY_LDISC bit
* prevents anyone taking a reference once it is clear.
* We need the lock to avoid racing reference takers.
*
* We must clear the TTY_LDISC bit here to avoid a livelock
* with a userspace app continually trying to use the tty in
* parallel to the change and re-referencing the tty.
*/
work = tty_ldisc_halt(tty);
if (o_tty)
o_work = tty_ldisc_halt(o_tty);
/*
* Wait for ->hangup_work and ->buf.work handlers to terminate.
* We must drop the mutex here in case a hangup is also in process.
*/
mutex_unlock(&tty->ldisc_mutex);
tty_ldisc_flush_works(tty);
retval = tty_ldisc_wait_idle(tty);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/* handle wait idle failure locked */
if (retval) {
tty_ldisc_put(new_ldisc);
goto enable;
}
if (test_bit(TTY_HUPPED, &tty->flags)) {
/* We were raced by the hangup method. It will have stomped
the ldisc data and closed the ldisc down */
clear_bit(TTY_LDISC_CHANGING, &tty->flags);
mutex_unlock(&tty->ldisc_mutex);
tty_ldisc_put(new_ldisc);
tty_unlock();
return -EIO;
}
/* Shutdown the current discipline. */
tty_ldisc_close(tty, o_ldisc);
/* Now set up the new line discipline. */
tty_ldisc_assign(tty, new_ldisc);
tty_set_termios_ldisc(tty, ldisc);
retval = tty_ldisc_open(tty, new_ldisc);
if (retval < 0) {
/* Back to the old one or N_TTY if we can't */
tty_ldisc_put(new_ldisc);
tty_ldisc_restore(tty, o_ldisc);
}
/* At this point we hold a reference to the new ldisc and a
a reference to the old ldisc. If we ended up flipping back
to the existing ldisc we have two references to it */
if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
tty->ops->set_ldisc(tty);
tty_ldisc_put(o_ldisc);
enable:
/*
* Allow ldisc referencing to occur again
*/
tty_ldisc_enable(tty);
if (o_tty)
tty_ldisc_enable(o_tty);
/* Restart the work queue in case no characters kick it off. Safe if
already running */
if (work)
schedule_work(&tty->buf.work);
if (o_work)
schedule_work(&o_tty->buf.work);
mutex_unlock(&tty->ldisc_mutex);
tty_unlock();
return retval;
}
/**
* tty_reset_termios - reset terminal state
* @tty: tty to reset
*
* Restore a terminal to the driver default state.
*/
static void tty_reset_termios(struct tty_struct *tty)
{
mutex_lock(&tty->termios_mutex);
*tty->termios = tty->driver->init_termios;
tty->termios->c_ispeed = tty_termios_input_baud_rate(tty->termios);
tty->termios->c_ospeed = tty_termios_baud_rate(tty->termios);
mutex_unlock(&tty->termios_mutex);
}
/**
* tty_ldisc_reinit - reinitialise the tty ldisc
* @tty: tty to reinit
* @ldisc: line discipline to reinitialize
*
* Switch the tty to a line discipline and leave the ldisc
* state closed
*/
static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
{
struct tty_ldisc *ld = tty_ldisc_get(ldisc);
if (IS_ERR(ld))
return -1;
WARN_ON_ONCE(tty_ldisc_wait_idle(tty));
tty_ldisc_close(tty, tty->ldisc);
tty_ldisc_put(tty->ldisc);
tty->ldisc = NULL;
/*
* Switch the line discipline back
*/
tty_ldisc_assign(tty, ld);
tty_set_termios_ldisc(tty, ldisc);
return 0;
}
/**
* tty_ldisc_hangup - hangup ldisc reset
* @tty: tty being hung up
*
* Some tty devices reset their termios when they receive a hangup
* event. In that situation we must also switch back to N_TTY properly
* before we reset the termios data.
*
* Locking: We can take the ldisc mutex as the rest of the code is
* careful to allow for this.
*
* In the pty pair case this occurs in the close() path of the
* tty itself so we must be careful about locking rules.
*/
void tty_ldisc_hangup(struct tty_struct *tty)
{
struct tty_ldisc *ld;
int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
int err = 0;
/*
* FIXME! What are the locking issues here? This may me overdoing
* things... This question is especially important now that we've
* removed the irqlock.
*/
ld = tty_ldisc_ref(tty);
if (ld != NULL) {
/* We may have no line discipline at this point */
if (ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
tty_driver_flush_buffer(tty);
if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
ld->ops->write_wakeup)
ld->ops->write_wakeup(tty);
if (ld->ops->hangup)
ld->ops->hangup(tty);
tty_ldisc_deref(ld);
}
/*
* FIXME: Once we trust the LDISC code better we can wait here for
* ldisc completion and fix the driver call race
*/
wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
wake_up_interruptible_poll(&tty->read_wait, POLLIN);
/*
* Shutdown the current line discipline, and reset it to
* N_TTY if need be.
*
* Avoid racing set_ldisc or tty_ldisc_release
*/
mutex_lock(&tty->ldisc_mutex);
/*
* this is like tty_ldisc_halt, but we need to give up
* the BTM before calling cancel_work_sync, which may
* need to wait for another function taking the BTM
*/
clear_bit(TTY_LDISC, &tty->flags);
tty_unlock();
cancel_work_sync(&tty->buf.work);
mutex_unlock(&tty->ldisc_mutex);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/* At this point we have a closed ldisc and we want to
reopen it. We could defer this to the next open but
it means auditing a lot of other paths so this is
a FIXME */
if (tty->ldisc) { /* Not yet closed */
if (reset == 0) {
if (!tty_ldisc_reinit(tty, tty->termios->c_line))
err = tty_ldisc_open(tty, tty->ldisc);
else
err = 1;
}
/* If the re-open fails or we reset then go to N_TTY. The
N_TTY open cannot fail */
if (reset || err) {
BUG_ON(tty_ldisc_reinit(tty, N_TTY));
WARN_ON(tty_ldisc_open(tty, tty->ldisc));
}
tty_ldisc_enable(tty);
}
mutex_unlock(&tty->ldisc_mutex);
if (reset)
tty_reset_termios(tty);
}
/**
* tty_ldisc_setup - open line discipline
* @tty: tty being shut down
* @o_tty: pair tty for pty/tty pairs
*
* Called during the initial open of a tty/pty pair in order to set up the
* line disciplines and bind them to the tty. This has no locking issues
* as the device isn't yet active.
*/
int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
{
struct tty_ldisc *ld = tty->ldisc;
int retval;
retval = tty_ldisc_open(tty, ld);
if (retval)
return retval;
if (o_tty) {
retval = tty_ldisc_open(o_tty, o_tty->ldisc);
if (retval) {
tty_ldisc_close(tty, ld);
return retval;
}
tty_ldisc_enable(o_tty);
}
tty_ldisc_enable(tty);
return 0;
}
/**
* tty_ldisc_release - release line discipline
* @tty: tty being shut down
* @o_tty: pair tty for pty/tty pairs
*
* Called during the final close of a tty/pty pair in order to shut down
* the line discpline layer. On exit the ldisc assigned is N_TTY and the
* ldisc has not been opened.
*/
void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
{
/*
* Prevent flush_to_ldisc() from rescheduling the work for later. Then
* kill any delayed work. As this is the final close it does not
* race with the set_ldisc code path.
*/
tty_unlock();
tty_ldisc_halt(tty);
tty_ldisc_flush_works(tty);
tty_lock();
mutex_lock(&tty->ldisc_mutex);
/*
* Now kill off the ldisc
*/
tty_ldisc_close(tty, tty->ldisc);
tty_ldisc_put(tty->ldisc);
/* Force an oops if we mess this up */
tty->ldisc = NULL;
/* Ensure the next open requests the N_TTY ldisc */
tty_set_termios_ldisc(tty, N_TTY);
mutex_unlock(&tty->ldisc_mutex);
/* This will need doing differently if we need to lock */
if (o_tty)
tty_ldisc_release(o_tty, NULL);
/* And the memory resources remaining (buffers, termios) will be
disposed of when the kref hits zero */
}
/**
* tty_ldisc_init - ldisc setup for new tty
* @tty: tty being allocated
*
* Set up the line discipline objects for a newly allocated tty. Note that
* the tty structure is not completely set up when this call is made.
*/
void tty_ldisc_init(struct tty_struct *tty)
{
struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
if (IS_ERR(ld))
panic("n_tty: init_tty");
tty_ldisc_assign(tty, ld);
}
void tty_ldisc_begin(void)
{
/* Setup the default TTY line discipline. */
(void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
}