tty: add function to convert device name to number

The function converts strings like ttyS0 and ttyUSB0 to dev_t like
(4, 64) and (188, 0). It does this by scanning tty_drivers list for
corresponding device name and index. If the driver is not registered,
this function returns -ENODEV. It also acquires tty_mutex.

Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 49abf04c90b2ac7db35756d5fb45634f0ee98e4e..974b13d244010de234d0350b9c45425251ff99c6 100644 (file)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -325,6 +325,56 @@ static struct tty_driver *get_tty_driver(dev_t device, int *index)
        return NULL;
 }
 
+/**
+ *     tty_dev_name_to_number  -       return dev_t for device name
+ *     @name: user space name of device under /dev
+ *     @number: pointer to dev_t that this function will populate
+ *
+ *     This function converts device names like ttyS0 or ttyUSB1 into dev_t
+ *     like (4, 64) or (188, 1). If no corresponding driver is registered then
+ *     the function returns -ENODEV.
+ *
+ *     Locking: this acquires tty_mutex to protect the tty_drivers list from
+ *             being modified while we are traversing it, and makes sure to
+ *             release it before exiting.
+ */
+int tty_dev_name_to_number(const char *name, dev_t *number)
+{
+       struct tty_driver *p;
+       int ret;
+       int index, prefix_length = 0;
+       const char *str;
+
+       for (str = name; *str && !isdigit(*str); str++)
+               ;
+
+       if (!*str)
+               return -EINVAL;
+
+       ret = kstrtoint(str, 10, &index);
+       if (ret)
+               return ret;
+
+       prefix_length = str - name;
+       mutex_lock(&tty_mutex);
+
+       list_for_each_entry(p, &tty_drivers, tty_drivers)
+               if (prefix_length == strlen(p->name) && strncmp(name,
+                                       p->name, prefix_length) == 0) {
+                       if (index < p->num) {
+                               *number = MKDEV(p->major, p->minor_start + index);
+                               goto out;
+                       }
+               }
+
+       /* if here then driver wasn't found */
+       ret = -ENODEV;
+out:
+       mutex_unlock(&tty_mutex);
+       return ret;
+}
+EXPORT_SYMBOL_GPL(tty_dev_name_to_number);
+
 #ifdef CONFIG_CONSOLE_POLL
 
 /**

diff --git a/include/linux/tty.h b/include/linux/tty.h
index b75b2d51ba2b5b574b382f7e8df3169cb81a705a..8156a9ee6fe6a3ba989525d2a5bf38fdaa9954fb 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -402,6 +402,7 @@ extern int __init tty_init(void);
 extern const char *tty_name(const struct tty_struct *tty);
 extern struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
                struct file *filp);
+extern int tty_dev_name_to_number(const char *name, dev_t *number);
 #else
 static inline void tty_kref_put(struct tty_struct *tty)
 { }
@@ -425,6 +426,8 @@ static inline const char *tty_name(const struct tty_struct *tty)
 static inline struct tty_struct *tty_open_by_driver(dev_t device,
                struct inode *inode, struct file *filp)
 { return NULL; }
+static inline int tty_dev_name_to_number(const char *name, dev_t *number)
+{ return -ENOTSUPP; }
 #endif
 
 extern struct ktermios tty_std_termios;