Re: [patch 1/2] staging: speakup: add function to convert dev name to number

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

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Hi,

On Thu, Jun 15, 2017 at 07:52:51AM +0100, Okash Khawaja wrote:
> On Wed, Jun 14, 2017 at 03:04:18PM +0200, Greg Kroah-Hartman wrote: 
> > The console stuff is odd though, but that is each driver defining the
> > name for itself, major/minor does not apply.  Also, a separate driver is
> > not having to figure this all out.  I wonder if we could just add a tty
> > core function for this as it does know the name of everything that has
> > been registered with it, right?
> 
> I can start working on a patch for this. I'm still new to the tty code
> so will follow up with any questions I might have.

I've put together this function for converting device name to number.
It traverses tty_drivers list looking for corresponding dev name and
index. Is this the right approach?

Thanks,
Okash

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---
 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
@@ -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(char *dev_name, dev_t *dev_no);
 #else
 static inline void tty_kref_put(struct tty_struct *tty)
 { }
@@ -422,6 +423,9 @@ static inline int __init tty_init(void)
 { return 0; }
 static inline const char *tty_name(const struct tty_struct *tty)
 { return "(none)"; }
+extern int tty_dev_name_to_number(char *dev_name, dev_t *dev_no)
+{ return -ENOTSUPP; }
+
 #endif
 
 extern struct ktermios tty_std_termios;