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Date:   Fri, 18 Dec 2020 11:42:44 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     linux-serial@...r.kernel.org, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Johan Hovold <johan@...nel.org>
Subject: [PATCH v10 1/3] tty: rename tty_kopen() and add new function tty_kopen_shared()

Introduce a new function tty_kopen_shared() that yields a struct
tty_struct. The semantic difference to tty_kopen() is that the tty is
expected to be used already. So rename tty_kopen() to
tty_kopen_exclusive() for clearness, adapt the single user and put the
common code in a new static helper function.

tty_kopen_shared is to be used to implement an LED trigger for tty
devices in one of the next patches.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
 drivers/accessibility/speakup/spk_ttyio.c |  2 +-
 drivers/tty/tty_io.c                      | 56 +++++++++++++++--------
 include/linux/tty.h                       |  5 +-
 3 files changed, 42 insertions(+), 21 deletions(-)

diff --git a/drivers/accessibility/speakup/spk_ttyio.c b/drivers/accessibility/speakup/spk_ttyio.c
index 6284aff434a1..835d17455fcd 100644
--- a/drivers/accessibility/speakup/spk_ttyio.c
+++ b/drivers/accessibility/speakup/spk_ttyio.c
@@ -152,7 +152,7 @@ static int spk_ttyio_initialise_ldisc(struct spk_synth *synth)
 	if (ret)
 		return ret;
 
-	tty = tty_kopen(dev);
+	tty = tty_kopen_exclusive(dev);
 	if (IS_ERR(tty))
 		return PTR_ERR(tty);
 
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 56ade99ef99f..d0c1f97adc17 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1873,22 +1873,7 @@ static struct tty_driver *tty_lookup_driver(dev_t device, struct file *filp,
 	return driver;
 }
 
-/**
- *	tty_kopen	-	open a tty device for kernel
- *	@device: dev_t of device to open
- *
- *	Opens tty exclusively for kernel. Performs the driver lookup,
- *	makes sure it's not already opened and performs the first-time
- *	tty initialization.
- *
- *	Returns the locked initialized &tty_struct
- *
- *	Claims the global tty_mutex to serialize:
- *	  - concurrent first-time tty initialization
- *	  - concurrent tty driver removal w/ lookup
- *	  - concurrent tty removal from driver table
- */
-struct tty_struct *tty_kopen(dev_t device)
+static struct tty_struct *tty_kopen(dev_t device, int shared)
 {
 	struct tty_struct *tty;
 	struct tty_driver *driver;
@@ -1903,7 +1888,7 @@ struct tty_struct *tty_kopen(dev_t device)
 
 	/* check whether we're reopening an existing tty */
 	tty = tty_driver_lookup_tty(driver, NULL, index);
-	if (IS_ERR(tty))
+	if (IS_ERR(tty) || shared)
 		goto out;
 
 	if (tty) {
@@ -1921,7 +1906,42 @@ struct tty_struct *tty_kopen(dev_t device)
 	tty_driver_kref_put(driver);
 	return tty;
 }
-EXPORT_SYMBOL_GPL(tty_kopen);
+
+/**
+ *	tty_kopen_exclusive	-	open a tty device for kernel
+ *	@device: dev_t of device to open
+ *
+ *	Opens tty exclusively for kernel. Performs the driver lookup,
+ *	makes sure it's not already opened and performs the first-time
+ *	tty initialization.
+ *
+ *	Returns the locked initialized &tty_struct
+ *
+ *	Claims the global tty_mutex to serialize:
+ *	  - concurrent first-time tty initialization
+ *	  - concurrent tty driver removal w/ lookup
+ *	  - concurrent tty removal from driver table
+ */
+struct tty_struct *tty_kopen_exclusive(dev_t device)
+{
+	return tty_kopen(device, 0);
+}
+EXPORT_SYMBOL_GPL(tty_kopen_exclusive);
+
+/**
+ *	tty_kopen_shared	-	open a tty device for shared in-kernel use
+ *	@device: dev_t of device to open
+ *
+ *	Opens an already existing tty for in-kernel use. Compared to
+ *	tty_kopen_exclusive() above it doesn't ensure to be the only user.
+ *
+ *	Locking is identical to tty_kopen() above.
+ */
+struct tty_struct *tty_kopen_shared(dev_t device)
+{
+	return tty_kopen(device, 1);
+}
+EXPORT_SYMBOL_GPL(tty_kopen_shared);
 
 /**
  *	tty_open_by_driver	-	open a tty device
diff --git a/include/linux/tty.h b/include/linux/tty.h
index eb33d948788c..7c3b5f156f03 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -417,7 +417,8 @@ extern struct tty_struct *get_current_tty(void);
 /* tty_io.c */
 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_exclusive(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);
@@ -442,7 +443,7 @@ static inline int __init tty_init(void)
 { return 0; }
 static inline const char *tty_name(const struct tty_struct *tty)
 { return "(none)"; }
-static inline struct tty_struct *tty_kopen(dev_t device)
+static inline struct tty_struct *tty_kopen_exclusive(dev_t device)
 { return ERR_PTR(-ENODEV); }
 static inline void tty_kclose(struct tty_struct *tty)
 { }
-- 
2.29.2

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