diff options
Diffstat (limited to 'drivers/char/tty_ldisc.c')
| -rw-r--r-- | drivers/char/tty_ldisc.c | 714 |
1 files changed, 714 insertions, 0 deletions
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c new file mode 100644 index 000000000000..241cbdea65ab --- /dev/null +++ b/drivers/char/tty_ldisc.c @@ -0,0 +1,714 @@ +#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/fdtable.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/smp_lock.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); +/* 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_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); + + +/** + * tty_ldisc_try_get - try and reference an ldisc + * @disc: ldisc number + * @ld: tty ldisc structure to complete + * + * Attempt to open and lock a line discipline into place. Return + * the line discipline refcounted and assigned in ld. On an error + * report the error code back + */ + +static int tty_ldisc_try_get(int disc, struct tty_ldisc *ld) +{ + unsigned long flags; + struct tty_ldisc_ops *ldops; + int err = -EINVAL; + + spin_lock_irqsave(&tty_ldisc_lock, flags); + ld->ops = NULL; + ldops = tty_ldiscs[disc]; + /* Check the entry is defined */ + if (ldops) { + /* If the module is being unloaded we can't use it */ + if (!try_module_get(ldops->owner)) + err = -EAGAIN; + else { + /* lock it */ + ldops->refcount++; + ld->ops = ldops; + err = 0; + } + } + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + return err; +} + +/** + * tty_ldisc_get - take a reference to an ldisc + * @disc: ldisc number + * @ld: tty line discipline structure to use + * + * 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 int tty_ldisc_get(int disc, struct tty_ldisc *ld) +{ + int err; + + if (disc < N_TTY || disc >= NR_LDISCS) + return -EINVAL; + err = tty_ldisc_try_get(disc, ld); + if (err == -EAGAIN) { + request_module("tty-ldisc-%d", disc); + err = tty_ldisc_try_get(disc, ld); + } + return err; +} + +/** + * tty_ldisc_put - drop ldisc reference + * @disc: ldisc number + * + * Drop a reference to a line discipline. Manage refcounts and + * module usage counts + * + * Locking: + * takes tty_ldisc_lock to guard against ldisc races + */ + +static void tty_ldisc_put(struct tty_ldisc_ops *ld) +{ + unsigned long flags; + int disc = ld->num; + + BUG_ON(disc < N_TTY || disc >= NR_LDISCS); + + spin_lock_irqsave(&tty_ldisc_lock, flags); + ld = tty_ldiscs[disc]; + BUG_ON(ld->refcount == 0); + ld->refcount--; + module_put(ld->owner); + spin_unlock_irqrestore(&tty_ldisc_lock, flags); +} + +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 ld; + + if (tty_ldisc_get(i, &ld) < 0) + return 0; + seq_printf(m, "%-10s %2d\n", ld.ops->name ? ld.ops->name : "???", i); + tty_ldisc_put(ld.ops); + 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) +{ + ld->refcount = 0; + 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 int tty_ldisc_try(struct tty_struct *tty) +{ + unsigned long flags; + struct tty_ldisc *ld; + int ret = 0; + + spin_lock_irqsave(&tty_ldisc_lock, flags); + ld = &tty->ldisc; + if (test_bit(TTY_LDISC, &tty->flags)) { + ld->refcount++; + ret = 1; + } + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + return ret; +} + +/** + * 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) +{ + /* wait_event is a macro */ + wait_event(tty_ldisc_wait, tty_ldisc_try(tty)); + if (tty->ldisc.refcount == 0) + printk(KERN_ERR "tty_ldisc_ref_wait\n"); + 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. + * + * Locking: called functions take tty_ldisc_lock + */ + +struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) +{ + if (tty_ldisc_try(tty)) + return &tty->ldisc; + return NULL; +} + +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) +{ + unsigned long flags; + + BUG_ON(ld == NULL); + + spin_lock_irqsave(&tty_ldisc_lock, flags); + if (ld->refcount == 0) + printk(KERN_ERR "tty_ldisc_deref: no references.\n"); + else + ld->refcount--; + if (ld->refcount == 0) + wake_up(&tty_ldisc_wait); + spin_unlock_irqrestore(&tty_ldisc_lock, flags); +} + +EXPORT_SYMBOL_GPL(tty_ldisc_deref); + +/** + * 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. + * + * Note: nobody should set this bit except via this function. Clearing + * directly is allowed. + */ + +void tty_ldisc_enable(struct tty_struct *tty) +{ + set_bit(TTY_LDISC, &tty->flags); + wake_up(&tty_ldisc_wait); +} + +/** + * 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_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; + + /* There is an outstanding reference here so this is safe */ + tty_ldisc_get(old->ops->num, old); + tty_ldisc_assign(tty, old); + tty_set_termios_ldisc(tty, old->ops->num); + if (old->ops->open && (old->ops->open(tty) < 0)) { + tty_ldisc_put(old->ops); + /* This driver is always present */ + if (tty_ldisc_get(N_TTY, &new_ldisc) < 0) + panic("n_tty: get"); + tty_ldisc_assign(tty, &new_ldisc); + tty_set_termios_ldisc(tty, N_TTY); + if (new_ldisc.ops->open) { + int r = new_ldisc.ops->open(tty); + 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. + * + * Locking: takes tty_ldisc_lock. + * called functions take termios_mutex + */ + +int tty_set_ldisc(struct tty_struct *tty, int ldisc) +{ + int retval; + struct tty_ldisc o_ldisc, new_ldisc; + int work; + unsigned long flags; + struct tty_struct *o_tty; + +restart: + /* This is a bit ugly for now but means we can break the 'ldisc + is part of the tty struct' assumption later */ + retval = tty_ldisc_get(ldisc, &new_ldisc); + if (retval) + return retval; + + /* + * Problem: What do we do if this blocks ? + */ + + tty_wait_until_sent(tty, 0); + + if (tty->ldisc.ops->num == ldisc) { + tty_ldisc_put(new_ldisc.ops); + return 0; + } + + /* + * 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; + o_tty = tty->link; + + /* + * 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. + */ + + spin_lock_irqsave(&tty_ldisc_lock, flags); + if (tty->ldisc.refcount || (o_tty && o_tty->ldisc.refcount)) { + if (tty->ldisc.refcount) { + /* Free the new ldisc we grabbed. Must drop the lock + first. */ + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + tty_ldisc_put(o_ldisc.ops); + /* + * There are several reasons we may be busy, including + * random momentary I/O traffic. We must therefore + * retry. We could distinguish between blocking ops + * and retries if we made tty_ldisc_wait() smarter. + * That is up for discussion. + */ + if (wait_event_interruptible(tty_ldisc_wait, tty->ldisc.refcount == 0) < 0) + return -ERESTARTSYS; + goto restart; + } + if (o_tty && o_tty->ldisc.refcount) { + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + tty_ldisc_put(o_tty->ldisc.ops); + if (wait_event_interruptible(tty_ldisc_wait, o_tty->ldisc.refcount == 0) < 0) + return -ERESTARTSYS; + goto restart; + } + } + /* + * If the TTY_LDISC bit is set, then we are racing against + * another ldisc change + */ + if (!test_bit(TTY_LDISC, &tty->flags)) { + struct tty_ldisc *ld; + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + tty_ldisc_put(new_ldisc.ops); + ld = tty_ldisc_ref_wait(tty); + tty_ldisc_deref(ld); + goto restart; + } + + clear_bit(TTY_LDISC, &tty->flags); + if (o_tty) + clear_bit(TTY_LDISC, &o_tty->flags); + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + + /* + * From this point on we know nobody has an ldisc + * usage reference, nor can they obtain one until + * we say so later on. + */ + + work = cancel_delayed_work(&tty->buf.work); + /* + * Wait for ->hangup_work and ->buf.work handlers to terminate + * MUST NOT hold locks here. + */ + flush_scheduled_work(); + /* Shutdown the current discipline. */ + if (o_ldisc.ops->close) + (o_ldisc.ops->close)(tty); + + /* Now set up the new line discipline. */ + tty_ldisc_assign(tty, &new_ldisc); + tty_set_termios_ldisc(tty, ldisc); + if (new_ldisc.ops->open) + retval = (new_ldisc.ops->open)(tty); + if (retval < 0) { + tty_ldisc_put(new_ldisc.ops); + 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.ops); + + /* + * Allow ldisc referencing to occur as soon as the driver + * ldisc callback completes. + */ + + tty_ldisc_enable(tty); + if (o_tty) + tty_ldisc_enable(o_tty); + + /* Restart it in case no characters kick it off. Safe if + already running */ + if (work) + schedule_delayed_work(&tty->buf.work, 1); + return retval; +} + + +/** + * 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 discplines and bind them to the tty. + */ + +int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty) +{ + struct tty_ldisc *ld = &tty->ldisc; + int retval; + + if (ld->ops->open) { + retval = (ld->ops->open)(tty); + if (retval) + return retval; + } + if (o_tty && o_tty->ldisc.ops->open) { + retval = (o_tty->ldisc.ops->open)(o_tty); + if (retval) { + if (ld->ops->close) + (ld->ops->close)(tty); + 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. + */ + +void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) +{ + unsigned long flags; + struct tty_ldisc ld; + /* + * 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. + */ + clear_bit(TTY_LDISC, &tty->flags); + cancel_delayed_work(&tty->buf.work); + + /* + * Wait for ->hangup_work and ->buf.work handlers to terminate + */ + + flush_scheduled_work(); + + /* + * Wait for any short term users (we know they are just driver + * side waiters as the file is closing so user count on the file + * side is zero. + */ + spin_lock_irqsave(&tty_ldisc_lock, flags); + while (tty->ldisc.refcount) { + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + wait_event(tty_ldisc_wait, tty->ldisc.refcount == 0); + spin_lock_irqsave(&tty_ldisc_lock, flags); + } + spin_unlock_irqrestore(&tty_ldisc_lock, flags); + /* + * Shutdown the current line discipline, and reset it to N_TTY. + * + * FIXME: this MUST get fixed for the new reflocking + */ + if (tty->ldisc.ops->close) + (tty->ldisc.ops->close)(tty); + tty_ldisc_put(tty->ldisc.ops); + + /* + * Switch the line discipline back + */ + WARN_ON(tty_ldisc_get(N_TTY, &ld)); + tty_ldisc_assign(tty, &ld); + tty_set_termios_ldisc(tty, N_TTY); + if (o_tty) { + /* FIXME: could o_tty be in setldisc here ? */ + clear_bit(TTY_LDISC, &o_tty->flags); + if (o_tty->ldisc.ops->close) + (o_tty->ldisc.ops->close)(o_tty); + tty_ldisc_put(o_tty->ldisc.ops); + WARN_ON(tty_ldisc_get(N_TTY, &ld)); + tty_ldisc_assign(o_tty, &ld); + tty_set_termios_ldisc(o_tty, N_TTY); + } +} + +/** + * 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; + if (tty_ldisc_get(N_TTY, &ld) < 0) + 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); +} |