diff options
Diffstat (limited to 'drivers/tty/tty_ldisc.c')
| -rw-r--r-- | drivers/tty/tty_ldisc.c | 915 |
1 files changed, 915 insertions, 0 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c new file mode 100644 index 000000000000..412f9775d19c --- /dev/null +++ b/drivers/tty/tty_ldisc.c @@ -0,0 +1,915 @@ +#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/smp_lock.h> /* For the moment */ + +#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); +/* 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); +} + +/** + * 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); + 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_delayed_work_sync(&tty->buf.work); +} + +/** + * 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); + + flush_scheduled_work(); + + tty_lock(); + mutex_lock(&tty->ldisc_mutex); + 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); + + /* + * 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_delayed_work(&tty->buf.work, 1); + if (o_work) + schedule_delayed_work(&o_tty->buf.work, 1); + 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 void tty_ldisc_reinit(struct tty_struct *tty, int ldisc) +{ + struct tty_ldisc *ld; + + tty_ldisc_close(tty, tty->ldisc); + tty_ldisc_put(tty->ldisc); + tty->ldisc = NULL; + /* + * Switch the line discipline back + */ + ld = tty_ldisc_get(ldisc); + BUG_ON(IS_ERR(ld)); + tty_ldisc_assign(tty, ld); + tty_set_termios_ldisc(tty, ldisc); +} + +/** + * 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_delayed_work_sync, + * which may need to wait for another function taking the BTM + */ + clear_bit(TTY_LDISC, &tty->flags); + tty_unlock(); + cancel_delayed_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) { + tty_ldisc_reinit(tty, tty->termios->c_line); + err = tty_ldisc_open(tty, tty->ldisc); + } + /* If the re-open fails or we reset then go to N_TTY. The + N_TTY open cannot fail */ + if (reset || err) { + 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); + flush_scheduled_work(); + 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); +} |