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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     rafael@kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Subject: [PATCH 5/5] tty: make tty_class a static const structure
Date:   Sun,  2 Apr 2023 19:58:50 +0200
Message-Id: <2023040250-landowner-unfitted-11f4@gregkh>
In-Reply-To: <2023040244-duffel-pushpin-f738@gregkh>
References: <2023040244-duffel-pushpin-f738@gregkh>
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Now that the driver core allows for struct class to be in read-only
memory, move the tty_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Jiri and Ilpo, this is part of the larger driver-core changes to make it
possible to move struct class into read-only memory and is used as proof
that this all works properly.  I'll take it throught the driver-core
tree as it shoudn't conflict with any tty.git changes.

 drivers/tty/pty.c    |  2 +-
 drivers/tty/tty_io.c | 24 +++++++++++-------------
 drivers/tty/vt/vt.c  |  2 +-
 include/linux/tty.h  |  2 +-
 4 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 07394fdaf522..2b1c8ab99dba 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -931,7 +931,7 @@ static void __init unix98_pty_init(void)
 	if (cdev_add(&ptmx_cdev, MKDEV(TTYAUX_MAJOR, 2), 1) ||
 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 2), 1, "/dev/ptmx") < 0)
 		panic("Couldn't register /dev/ptmx driver");
-	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
+	device_create(&tty_class, NULL, MKDEV(TTYAUX_MAJOR, 2), NULL, "ptmx");
 }
 
 #else
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1382d9050ce8..44e0d53aa0b8 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3070,7 +3070,7 @@ static struct device *tty_get_device(struct tty_struct *tty)
 {
 	dev_t devt = tty_devnum(tty);
 
-	return class_find_device_by_devt(tty_class, devt);
+	return class_find_device_by_devt(&tty_class, devt);
 }
 
 
@@ -3143,8 +3143,6 @@ int tty_put_char(struct tty_struct *tty, unsigned char ch)
 }
 EXPORT_SYMBOL_GPL(tty_put_char);
 
-struct class *tty_class;
-
 static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
 		unsigned int index, unsigned int count)
 {
@@ -3239,7 +3237,7 @@ struct device *tty_register_device_attr(struct tty_driver *driver,
 		return ERR_PTR(-ENOMEM);
 
 	dev->devt = devt;
-	dev->class = tty_class;
+	dev->class = &tty_class;
 	dev->parent = device;
 	dev->release = tty_device_create_release;
 	dev_set_name(dev, "%s", name);
@@ -3294,8 +3292,7 @@ EXPORT_SYMBOL_GPL(tty_register_device_attr);
  */
 void tty_unregister_device(struct tty_driver *driver, unsigned index)
 {
-	device_destroy(tty_class,
-		MKDEV(driver->major, driver->minor_start) + index);
+	device_destroy(&tty_class, MKDEV(driver->major, driver->minor_start) + index);
 	if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) {
 		cdev_del(driver->cdevs[index]);
 		driver->cdevs[index] = NULL;
@@ -3510,13 +3507,14 @@ static char *tty_devnode(const struct device *dev, umode_t *mode)
 	return NULL;
 }
 
+const struct class tty_class = {
+	.name		= "tty",
+	.devnode	= tty_devnode,
+};
+
 static int __init tty_class_init(void)
 {
-	tty_class = class_create("tty");
-	if (IS_ERR(tty_class))
-		return PTR_ERR(tty_class);
-	tty_class->devnode = tty_devnode;
-	return 0;
+	return class_register(&tty_class);
 }
 
 postcore_initcall(tty_class_init);
@@ -3643,13 +3641,13 @@ int __init tty_init(void)
 	if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
 		panic("Couldn't register /dev/tty driver\n");
-	device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");
+	device_create(&tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");
 
 	cdev_init(&console_cdev, &console_fops);
 	if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
 	    register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
 		panic("Couldn't register /dev/console driver\n");
-	consdev = device_create_with_groups(tty_class, NULL,
+	consdev = device_create_with_groups(&tty_class, NULL,
 					    MKDEV(TTYAUX_MAJOR, 1), NULL,
 					    cons_dev_groups, "console");
 	if (IS_ERR(consdev))
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 5496bf4b76ec..02f4b6be8584 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3539,7 +3539,7 @@ int __init vty_init(const struct file_operations *console_fops)
 	if (cdev_add(&vc0_cdev, MKDEV(TTY_MAJOR, 0), 1) ||
 	    register_chrdev_region(MKDEV(TTY_MAJOR, 0), 1, "/dev/vc/0") < 0)
 		panic("Couldn't register /dev/tty0 driver\n");
-	tty0dev = device_create_with_groups(tty_class, NULL,
+	tty0dev = device_create_with_groups(&tty_class, NULL,
 					    MKDEV(TTY_MAJOR, 0), NULL,
 					    vt_dev_groups, "tty0");
 	if (IS_ERR(tty0dev))
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 093935e97f42..121eb4b0d325 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -387,7 +387,7 @@ extern struct ktermios tty_std_termios;
 
 int vcs_init(void);
 
-extern struct class *tty_class;
+extern const struct class tty_class;
 
 /**
  *	tty_kref_get		-	get a tty reference
-- 
2.40.0