TTY: extract driver lookup from tty_open

The error handling in tty_open became unbearable. There were many
errors fixed recently. Extract the tty driver lookup from tty_open to
a separate function. This reduces the fail paths significantly and
makes tty_open more readable.

In the next patch we will move the fail path handling to the end of
the function.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 55 insertions, 38 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1b90c986b1bf..00b84984308d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1824,6 +1824,53 @@ static struct tty_struct *tty_open_current_tty(dev_t device, struct file *filp)
 }
 
 /**
+ *      tty_lookup_driver - lookup a tty driver for a given device file
+ *      @device: device number
+ *      @filp: file pointer to tty
+ *      @noctty: set if the device should not become a controlling tty
+ *      @index: index for the device in the @return driver
+ *      @return: driver for this inode (with increased refcount)
+ *
+ *      If @return is not erroneous, the caller is responsible to decrement the
+ *      refcount by tty_driver_kref_put.
+ *
+ *      Locking: tty_mutex protects get_tty_driver
+ */
+static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
+                int *noctty, int *index)
+{
+        struct tty_driver *driver;
+
+#ifdef CONFIG_VT
+        if (device == MKDEV(TTY_MAJOR, 0)) {
+                extern struct tty_driver *console_driver;
+                driver = tty_driver_kref_get(console_driver);
+                *index = fg_console;
+                *noctty = 1;
+                return driver;
+        }
+#endif
+        if (device == MKDEV(TTYAUX_MAJOR, 1)) {
+                struct tty_driver *console_driver = console_device(index);
+                if (console_driver) {
+                        driver = tty_driver_kref_get(console_driver);
+                        if (driver) {
+                                /* Don't let /dev/console block */
+                                filp->f_flags |= O_NONBLOCK;
+                                *noctty = 1;
+                                return driver;
+                        }
+                }
+                return ERR_PTR(-ENODEV);
+        }
+
+        driver = get_tty_driver(device, index);
+        if (!driver)
+                return ERR_PTR(-ENODEV);
+        return driver;
+}
+
+/**
  *      tty_open                -       open a tty device
  *      @inode: inode of device file
  *      @filp: file pointer to tty
@@ -1839,7 +1886,7 @@ static struct tty_struct *tty_open_current_tty(dev_t device, struct file *filp)
  *      The termios state of a pty is reset on first open so that
  *      settings don't persist across reuse.
  *
- *      Locking: tty_mutex protects tty, get_tty_driver and tty_init_dev work.
+ *      Locking: tty_mutex protects tty, tty_lookup_driver and tty_init_dev.
  *               tty->count should protect the rest.
  *               ->siglock protects ->signal/->sighand
  */
@@ -1873,47 +1920,17 @@ retry_open:
                 mutex_unlock(&tty_mutex);
                 tty_free_file(filp);
                 return PTR_ERR(tty);
-        } else if (tty)
-                goto got_driver;
-
-#ifdef CONFIG_VT
-        if (device == MKDEV(TTY_MAJOR, 0)) {
-                extern struct tty_driver *console_driver;
-                driver = tty_driver_kref_get(console_driver);
-                index = fg_console;
-                noctty = 1;
-                goto got_driver;
-        }
-#endif
-        if (device == MKDEV(TTYAUX_MAJOR, 1)) {
-                struct tty_driver *console_driver = console_device(&index);
-                if (console_driver) {
-                        driver = tty_driver_kref_get(console_driver);
-                        if (driver) {
-                                /* Don't let /dev/console block */
-                                filp->f_flags |= O_NONBLOCK;
-                                noctty = 1;
-                                goto got_driver;
-                        }
+        } else if (!tty) {
+                driver = tty_lookup_driver(device, filp, &noctty, &index);
+                if (IS_ERR(driver)) {
+                        tty_unlock();
+                        mutex_unlock(&tty_mutex);
+                        tty_free_file(filp);
+                        return PTR_ERR(driver);
                 }
-                tty_unlock();
-                mutex_unlock(&tty_mutex);
-                tty_free_file(filp);
-                return -ENODEV;
-        }
 
-        driver = get_tty_driver(device, &index);
-        if (!driver) {
-                tty_unlock();
-                mutex_unlock(&tty_mutex);
-                tty_free_file(filp);
-                return -ENODEV;
-        }
-got_driver:
-        if (!tty) {
                 /* check whether we're reopening an existing tty */
                 tty = tty_driver_lookup_tty(driver, inode, index);
-
                 if (IS_ERR(tty)) {
                         tty_unlock();
                         mutex_unlock(&tty_mutex);