[patch v2 1/3] tty: add function to convert device name to number

[Okash Khawaja <okash.khawaja@gmail.com>]

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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>

---
 drivers/tty/tty_io.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/tty.h  |    4 ++++
 2 files changed, 49 insertions(+)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -325,6 +325,51 @@ static struct tty_driver *get_tty_driver
 	return NULL;
 }
 
+/**
+ *	tty_dev_name_to_number	-	return dev_t for device name
+ *	@device_name: user space name of device under /dev
+ *	@dev_no: 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
+ */
+int tty_dev_name_to_number(char *dev_name, dev_t *dev_no)
+{
+	struct tty_driver *p;
+	int rv, index, prefix_length = 0;
+
+	while (!isdigit(*(dev_name + prefix_length)) && prefix_length <
+			strlen(dev_name) )
+		prefix_length++;
+
+	if (prefix_length == strlen(dev_name))
+		return -EINVAL;
+
+	mutex_lock(&tty_mutex);
+
+	list_for_each_entry(p, &tty_drivers, tty_drivers)
+		if (prefix_length == strlen(p->name) && strncmp(dev_name,
+					p->name, prefix_length) == 0) {
+			rv = kstrtoint(dev_name + prefix_length, 10, &index);
+			if (rv) {
+				mutex_unlock(&tty_mutex);
+				return rv;
+			}
+			if (index < p->num) {
+				*dev_no = MKDEV(p->major, p->minor_start + index);
+				mutex_unlock(&tty_mutex);
+				return 0;
+			}
+		}
+
+	mutex_unlock(&tty_mutex);
+	return -ENODEV;
+}
+EXPORT_SYMBOL_GPL(tty_dev_name_to_number);
+
 #ifdef CONFIG_CONSOLE_POLL
 
 /**
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -401,6 +401,7 @@ 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(char *dev_name, dev_t *dev_no);
 #else
 static inline void tty_kref_put(struct tty_struct *tty)
 { }
@@ -424,6 +425,9 @@ static inline const char *tty_name(const
 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(char *dev_name, dev_t *dev_no)
+{ return -ENOTSUPP; }
+
 #endif
 
 extern struct ktermios tty_std_termios;