From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: André Fabian Silva Delgado Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- drivers/tty/tty_ldisc.c | 828 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 828 insertions(+) create mode 100644 drivers/tty/tty_ldisc.c (limited to 'drivers/tty/tty_ldisc.c') diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c new file mode 100644 index 000000000..3737f5527 --- /dev/null +++ b/drivers/tty/tty_ldisc.c @@ -0,0 +1,828 @@ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#undef LDISC_DEBUG_HANGUP + +#ifdef LDISC_DEBUG_HANGUP +#define tty_ldisc_debug(tty, f, args...) ({ \ + char __b[64]; \ + printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \ +}) +#else +#define tty_ldisc_debug(tty, f, args...) +#endif + +/* lockdep nested classes for tty->ldisc_sem */ +enum { + LDISC_SEM_NORMAL, + LDISC_SEM_OTHER, +}; + + +/* + * 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_RAW_SPINLOCK(tty_ldiscs_lock); +/* Line disc dispatch table */ +static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS]; + +/** + * 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_ldiscs_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; + + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); + tty_ldiscs[disc] = new_ldisc; + new_ldisc->num = disc; + new_ldisc->refcount = 0; + raw_spin_unlock_irqrestore(&tty_ldiscs_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_ldiscs_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; + + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); + if (tty_ldiscs[disc]->refcount) + ret = -EBUSY; + else + tty_ldiscs[disc] = NULL; + raw_spin_unlock_irqrestore(&tty_ldiscs_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; + + raw_spin_lock_irqsave(&tty_ldiscs_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; + } + } + raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags); + return ret; +} + +static void put_ldops(struct tty_ldisc_ops *ldops) +{ + unsigned long flags; + + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); + ldops->refcount--; + module_put(ldops->owner); + raw_spin_unlock_irqrestore(&tty_ldiscs_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_ldiscs_lock to guard against ldisc races + */ + +static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, 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; + ld->tty = tty; + + return ld; +} + +/** + * tty_ldisc_put - release the ldisc + * + * Complement of tty_ldisc_get(). + */ +static inline void tty_ldisc_put(struct tty_ldisc *ld) +{ + if (WARN_ON_ONCE(!ld)) + return; + + put_ldops(ld->ops); + kfree(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_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) + * + * Note: only callable from a file_operations routine (which + * guarantees tty->ldisc != NULL when the lock is acquired). + */ + +struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty) +{ + ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT); + WARN_ON(!tty->ldisc); + return tty->ldisc; +} +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. + */ + +struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) +{ + struct tty_ldisc *ld = NULL; + + if (ldsem_down_read_trylock(&tty->ldisc_sem)) { + ld = tty->ldisc; + if (!ld) + ldsem_up_read(&tty->ldisc_sem); + } + return ld; +} +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. + */ + +void tty_ldisc_deref(struct tty_ldisc *ld) +{ + ldsem_up_read(&ld->tty->ldisc_sem); +} +EXPORT_SYMBOL_GPL(tty_ldisc_deref); + + +static inline int __lockfunc +__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) +{ + return ldsem_down_write(&tty->ldisc_sem, timeout); +} + +static inline int __lockfunc +__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout) +{ + return ldsem_down_write_nested(&tty->ldisc_sem, + LDISC_SEM_OTHER, timeout); +} + +static inline void __tty_ldisc_unlock(struct tty_struct *tty) +{ + return ldsem_up_write(&tty->ldisc_sem); +} + +static int __lockfunc +tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) +{ + int ret; + + ret = __tty_ldisc_lock(tty, timeout); + if (!ret) + return -EBUSY; + set_bit(TTY_LDISC_HALTED, &tty->flags); + return 0; +} + +static void tty_ldisc_unlock(struct tty_struct *tty) +{ + clear_bit(TTY_LDISC_HALTED, &tty->flags); + __tty_ldisc_unlock(tty); +} + +static int __lockfunc +tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2, + unsigned long timeout) +{ + int ret; + + if (tty < tty2) { + ret = __tty_ldisc_lock(tty, timeout); + if (ret) { + ret = __tty_ldisc_lock_nested(tty2, timeout); + if (!ret) + __tty_ldisc_unlock(tty); + } + } else { + /* if this is possible, it has lots of implications */ + WARN_ON_ONCE(tty == tty2); + if (tty2 && tty != tty2) { + ret = __tty_ldisc_lock(tty2, timeout); + if (ret) { + ret = __tty_ldisc_lock_nested(tty, timeout); + if (!ret) + __tty_ldisc_unlock(tty2); + } + } else + ret = __tty_ldisc_lock(tty, timeout); + } + + if (!ret) + return -EBUSY; + + set_bit(TTY_LDISC_HALTED, &tty->flags); + if (tty2) + set_bit(TTY_LDISC_HALTED, &tty2->flags); + return 0; +} + +static void __lockfunc +tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2) +{ + tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT); +} + +static void __lockfunc tty_ldisc_unlock_pair(struct tty_struct *tty, + struct tty_struct *tty2) +{ + __tty_ldisc_unlock(tty); + if (tty2) + __tty_ldisc_unlock(tty2); +} + +/** + * tty_ldisc_flush - flush line discipline queue + * @tty: tty + * + * Flush the line discipline queue (if any) and the tty flip buffers + * for this tty. + */ + +void tty_ldisc_flush(struct tty_struct *tty) +{ + struct tty_ldisc *ld = tty_ldisc_ref(tty); + + tty_buffer_flush(tty, ld); + if (ld) + tty_ldisc_deref(ld); +} +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_rwsem + */ + +static void tty_set_termios_ldisc(struct tty_struct *tty, int num) +{ + down_write(&tty->termios_rwsem); + tty->termios.c_line = num; + up_write(&tty->termios_rwsem); +} + +/** + * 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 */ + 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(tty, old->ops->num); + WARN_ON(IS_ERR(old)); + tty->ldisc = 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(tty, N_TTY); + if (IS_ERR(new_ldisc)) + panic("n_tty: get"); + tty->ldisc = 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_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. + */ + +int tty_set_ldisc(struct tty_struct *tty, int ldisc) +{ + int retval; + struct tty_ldisc *old_ldisc, *new_ldisc; + + new_ldisc = tty_ldisc_get(tty, ldisc); + if (IS_ERR(new_ldisc)) + return PTR_ERR(new_ldisc); + + tty_lock(tty); + retval = tty_ldisc_lock(tty, 5 * HZ); + if (retval) { + tty_ldisc_put(new_ldisc); + tty_unlock(tty); + return retval; + } + + /* + * Check the no-op case + */ + + if (tty->ldisc->ops->num == ldisc) { + tty_ldisc_unlock(tty); + tty_ldisc_put(new_ldisc); + tty_unlock(tty); + return 0; + } + + old_ldisc = tty->ldisc; + + 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 */ + tty_ldisc_unlock(tty); + tty_ldisc_put(new_ldisc); + tty_unlock(tty); + return -EIO; + } + + /* Shutdown the old discipline. */ + tty_ldisc_close(tty, old_ldisc); + + /* Now set up the new line discipline. */ + tty->ldisc = 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, old_ldisc); + } + + if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) { + down_read(&tty->termios_rwsem); + tty->ops->set_ldisc(tty); + up_read(&tty->termios_rwsem); + } + + /* At this point we hold a reference to the new ldisc and a + reference to the old ldisc, or we hold two references to + the old ldisc (if it was restored as part of error cleanup + above). In either case, releasing a single reference from + the old ldisc is correct. */ + + tty_ldisc_put(old_ldisc); + + /* + * Allow ldisc referencing to occur again + */ + tty_ldisc_unlock(tty); + + /* Restart the work queue in case no characters kick it off. Safe if + already running */ + schedule_work(&tty->port->buf.work); + + tty_unlock(tty); + 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) +{ + down_write(&tty->termios_rwsem); + 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); + up_write(&tty->termios_rwsem); +} + + +/** + * 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(tty, ldisc); + + if (IS_ERR(ld)) + return -1; + + tty_ldisc_close(tty, tty->ldisc); + tty_ldisc_put(tty->ldisc); + /* + * Switch the line discipline back + */ + tty->ldisc = 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; + + tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc); + + ld = tty_ldisc_ref(tty); + if (ld != NULL) { + 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); + } + + 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 + */ + tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT); + + if (tty->ldisc) { + + /* At this point we have a halted ldisc; we want to close it and + reopen a new ldisc. We could defer the reopen to the next + open but it means auditing a lot of other paths so this is + a FIXME */ + 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_unlock(tty); + if (reset) + tty_reset_termios(tty); + + tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc); +} + +/** + * 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; + } + } + return 0; +} + +static void tty_ldisc_kill(struct tty_struct *tty) +{ + /* + * 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); +} + +/** + * tty_ldisc_release - release line discipline + * @tty: tty being shut down (or one end of pty pair) + * + * Called during the final close of a tty or a pty pair in order to shut + * down the line discpline layer. On exit, each ldisc assigned is N_TTY and + * each ldisc has not been opened. + */ + +void tty_ldisc_release(struct tty_struct *tty) +{ + struct tty_struct *o_tty = tty->link; + + /* + * Shutdown this line discipline. As this is the final close, + * it does not race with the set_ldisc code path. + */ + + tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc); + + tty_ldisc_lock_pair(tty, o_tty); + tty_ldisc_kill(tty); + if (o_tty) + tty_ldisc_kill(o_tty); + tty_ldisc_unlock_pair(tty, o_tty); + + /* And the memory resources remaining (buffers, termios) will be + disposed of when the kref hits zero */ + + tty_ldisc_debug(tty, "ldisc closed\n"); +} + +/** + * 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(tty, N_TTY); + if (IS_ERR(ld)) + panic("n_tty: init_tty"); + tty->ldisc = ld; +} + +/** + * tty_ldisc_init - ldisc cleanup for new tty + * @tty: tty that was allocated recently + * + * The tty structure must not becompletely set up (tty_ldisc_setup) when + * this call is made. + */ +void tty_ldisc_deinit(struct tty_struct *tty) +{ + tty_ldisc_put(tty->ldisc); + tty->ldisc = NULL; +} + +void tty_ldisc_begin(void) +{ + /* Setup the default TTY line discipline. */ + (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY); +} -- cgit v1.2.3-54-g00ecf