linux-kernel - [PATCH v2 4/9] misc: c2port: Calculate bin

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Message-Id: <20241221-sysfs-const-bin_attr-misc-drivers-v2-4-ba5e79fe8771@weissschuh.net>
Date: Sat, 21 Dec 2024 15:48:10 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Frederic Barrat <fbarrat@...ux.ibm.com>, 
 Andrew Donnellan <ajd@...ux.ibm.com>, Arnd Bergmann <arnd@...db.de>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v2 4/9] misc: c2port: Calculate bin_attribute size through
 group callback

Modifying the size of the global bin_attribute instance can be racy.
Instead use the new .bin_size callback to do so safely.

For this to work move the initialization of c2dev->ops before the call
to device_create() as the size callback will need access to it.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 drivers/misc/c2port/core.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/c2port/core.c b/drivers/misc/c2port/core.c
index 2bb1dd2511f9dd178b8c06baa460bb609f7f8fd7..f455d702b9cd4999648a57985e305aac5301403f 100644
--- a/drivers/misc/c2port/core.c
+++ b/drivers/misc/c2port/core.c
@@ -874,9 +874,22 @@ static struct bin_attribute *c2port_bin_attrs[] = {
 	NULL,
 };
 
+static size_t c2port_bin_attr_size(struct kobject *kobj,
+				   const struct bin_attribute *attr,
+				   int i)
+{
+	struct c2port_device *c2dev = dev_get_drvdata(kobj_to_dev(kobj));
+
+	if (attr == &bin_attr_flash_data)
+		return c2dev->ops->blocks_num * c2dev->ops->block_size;
+
+	return attr->size;
+}
+
 static const struct attribute_group c2port_group = {
 	.attrs = c2port_attrs,
 	.bin_attrs = c2port_bin_attrs,
+	.bin_size = c2port_bin_attr_size,
 };
 
 static const struct attribute_group *c2port_groups[] = {
@@ -912,8 +925,7 @@ struct c2port_device *c2port_device_register(char *name,
 	if (ret < 0)
 		goto error_idr_alloc;
 	c2dev->id = ret;
-
-	bin_attr_flash_data.size = ops->blocks_num * ops->block_size;
+	c2dev->ops = ops;
 
 	c2dev->dev = device_create(c2port_class, NULL, 0, c2dev,
 				   "c2port%d", c2dev->id);
@@ -924,7 +936,6 @@ struct c2port_device *c2port_device_register(char *name,
 	dev_set_drvdata(c2dev->dev, c2dev);
 
 	strscpy(c2dev->name, name, sizeof(c2dev->name));
-	c2dev->ops = ops;
 	mutex_init(&c2dev->mutex);
 
 	/* By default C2 port access is off */

-- 
2.47.1