tty: Introduce a tty_port generic block_til_ready

Start sucking more commonality out of the drivers into a single piece of
core code.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 105 insertions, 0 deletions

diff --git a/drivers/char/tty_port.c b/drivers/char/tty_port.c
index 9f418bca4a22..ff94182b3813 100644
--- a/drivers/char/tty_port.c
+++ b/drivers/char/tty_port.c
@@ -151,3 +151,108 @@ void tty_port_raise_dtr_rts(struct tty_port *port)
                 port->ops->raise_dtr_rts(port);
 }
 EXPORT_SYMBOL(tty_port_raise_dtr_rts);
+
+/**
+ *      tty_port_block_til_ready        -       Waiting logic for tty open
+ *      @port: the tty port being opened
+ *      @tty: the tty device being bound
+ *      @filp: the file pointer of the opener
+ *
+ *      Implement the core POSIX/SuS tty behaviour when opening a tty device.
+ *      Handles:
+ *              - hangup (both before and during)
+ *              - non blocking open
+ *              - rts/dtr/dcd
+ *              - signals
+ *              - port flags and counts
+ *
+ *      The passed tty_port must implement the carrier_raised method if it can
+ *      do carrier detect and the raise_dtr_rts method if it supports software
+ *      management of these lines. Note that the dtr/rts raise is done each
+ *      iteration as a hangup may have previously dropped them while we wait.
+ */
+ 
+int tty_port_block_til_ready(struct tty_port *port,
+                                struct tty_struct *tty, struct file *filp)
+{
+        int do_clocal = 0, retval;
+        unsigned long flags;
+        DECLARE_WAITQUEUE(wait, current);
+        int cd;
+
+        /* block if port is in the process of being closed */
+        if (tty_hung_up_p(filp) || port->flags & ASYNC_CLOSING) {
+                interruptible_sleep_on(&port->close_wait);
+                if (port->flags & ASYNC_HUP_NOTIFY)
+                        return -EAGAIN;
+                else
+                        return -ERESTARTSYS;
+        }
+
+        /* if non-blocking mode is set we can pass directly to open unless
+           the port has just hung up or is in another error state */
+        if ((filp->f_flags & O_NONBLOCK) ||
+                        (tty->flags & (1 << TTY_IO_ERROR))) {
+                port->flags |= ASYNC_NORMAL_ACTIVE;
+                return 0;
+        }
+
+        if (C_CLOCAL(tty))
+                do_clocal = 1;
+
+        /* Block waiting until we can proceed. We may need to wait for the
+           carrier, but we must also wait for any close that is in progress
+           before the next open may complete */
+
+        retval = 0;
+        add_wait_queue(&port->open_wait, &wait);
+
+        /* The port lock protects the port counts */
+        spin_lock_irqsave(&port->lock, flags);
+        if (!tty_hung_up_p(filp))
+                port->count--;
+        port->blocked_open++;
+        spin_unlock_irqrestore(&port->lock, flags);
+
+        while (1) {
+                /* Indicate we are open */
+                tty_port_raise_dtr_rts(port);
+
+                set_current_state(TASK_INTERRUPTIBLE);
+                /* Check for a hangup or uninitialised port. Return accordingly */
+                if (tty_hung_up_p(filp) || !(port->flags & ASYNC_INITIALIZED)) {
+                        if (port->flags & ASYNC_HUP_NOTIFY)
+                                retval = -EAGAIN;
+                        else
+                                retval = -ERESTARTSYS;
+                        break;
+                }
+                /* Probe the carrier. For devices with no carrier detect this
+                   will always return true */
+                cd = tty_port_carrier_raised(port);
+                if (!(port->flags & ASYNC_CLOSING) &&
+                                (do_clocal || cd))
+                        break;
+                if (signal_pending(current)) {
+                        retval = -ERESTARTSYS;
+                        break;
+                }
+                schedule();
+        }
+        set_current_state(TASK_RUNNING);
+        remove_wait_queue(&port->open_wait, &wait);
+
+        /* Update counts. A parallel hangup will have set count to zero and
+           we must not mess that up further */
+        spin_lock_irqsave(&port->lock, flags);
+        if (!tty_hung_up_p(filp))
+                port->count++;
+        port->blocked_open--;
+        if (retval == 0)
+                port->flags |= ASYNC_NORMAL_ACTIVE;
+        spin_unlock_irqrestore(&port->lock, flags);
+        return 0;
+        
+}
+EXPORT_SYMBOL(tty_port_block_til_ready);
+