tty: Split ldisc code into its own file

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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);
+}