[PATCH v2 1/3] tty: new helper function tty_kopen_shared

[Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>]

This function gives a struct tty_struct for a given device number.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
---
 drivers/tty/tty_io.c | 27 +++++++++++++++++++++++++++
 include/linux/tty.h  |  1 +
 2 files changed, 28 insertions(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index d9f54c7d94f2..584025117cd3 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1925,6 +1925,33 @@ struct tty_struct *tty_kopen(dev_t device)
 }
 EXPORT_SYMBOL_GPL(tty_kopen);
 
+/*
+ * Caller gets a reference on (non-error) ttys, that must be disposed using
+ * tty_kref_put().
+ */
+struct tty_struct *tty_kopen_shared(dev_t device)
+{
+	struct tty_struct *tty;
+	struct tty_driver *driver;
+	int index = -1;
+
+	mutex_lock(&tty_mutex);
+	driver = tty_lookup_driver(device, NULL, &index);
+	if (IS_ERR(driver)) {
+		tty = ERR_CAST(driver);
+		goto err_lookup_driver;
+	}
+
+	tty = tty_driver_lookup_tty(driver, NULL, index);
+
+	tty_driver_kref_put(driver);
+err_lookup_driver:
+
+	mutex_unlock(&tty_mutex);
+	return tty;
+}
+EXPORT_SYMBOL(tty_kopen_shared);
+
 /**
  *	tty_open_by_driver	-	open a tty device
  *	@device: dev_t of device to open
diff --git a/include/linux/tty.h b/include/linux/tty.h
index bfa4e2ee94a9..616268eb1613 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -412,6 +412,7 @@ extern struct tty_struct *get_current_tty(void);
 extern int __init tty_init(void);
 extern const char *tty_name(const struct tty_struct *tty);
 extern struct tty_struct *tty_kopen(dev_t device);
+extern struct tty_struct *tty_kopen_shared(dev_t device);
 extern void tty_kclose(struct tty_struct *tty);
 extern int tty_dev_name_to_number(const char *name, dev_t *number);
 extern int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout);
-- 
2.24.0