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tty: add function to convert device name to number

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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 <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Okash Khawaja 2017-06-25 19:40:00 +01:00 • committed by Greg Kroah-Hartman
commit fc61ed5127
2 changed files with 53 additions and 0 deletions
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50
drivers/tty/tty_io.c
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@ -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
/**