net: dsa: strip sysfs "tagging" string of trailing newline

Currently, dsa_find_tagger_by_name() uses sysfs_streq() which works both
with strings that contain \n at the end (echo ocelot > .../dsa/tagging)
and with strings that don't (printf ocelot > .../dsa/tagging).

There will be a problem once we'll want to construct the modalias string
based on which we auto-load the protocol kernel module. If the sysfs
buffer ends in a newline, we need to strip it first. This is a
preparatory patch specifically for that.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Michael Walle <michael@walle.cc>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/dsa.c

@@ -79,7 +79,7 @@ const char *dsa_tag_protocol_to_str(const struct dsa_device_ops *ops)
 /* Function takes a reference on the module owning the tagger,
  * so dsa_tag_driver_put must be called afterwards.
  */
-const struct dsa_device_ops *dsa_find_tagger_by_name(const char *buf)
+const struct dsa_device_ops *dsa_find_tagger_by_name(const char *name)
 {
 	const struct dsa_device_ops *ops = ERR_PTR(-ENOPROTOOPT);
 	struct dsa_tag_driver *dsa_tag_driver;
@@ -88,7 +88,7 @@ const struct dsa_device_ops *dsa_find_tagger_by_name(const char *buf)
 	list_for_each_entry(dsa_tag_driver, &dsa_tag_drivers_list, list) {
 		const struct dsa_device_ops *tmp = dsa_tag_driver->ops;
 
-		if (!sysfs_streq(buf, tmp->name))
+		if (strcmp(name, tmp->name))
 			continue;
 
 		if (!try_module_get(dsa_tag_driver->owner))

net/dsa/dsa_priv.h

@@ -245,7 +245,7 @@ struct dsa_slave_priv {
 /* dsa.c */
 const struct dsa_device_ops *dsa_tag_driver_get(int tag_protocol);
 void dsa_tag_driver_put(const struct dsa_device_ops *ops);
-const struct dsa_device_ops *dsa_find_tagger_by_name(const char *buf);
+const struct dsa_device_ops *dsa_find_tagger_by_name(const char *name);
 
 bool dsa_db_equal(const struct dsa_db *a, const struct dsa_db *b);
 

net/dsa/master.c

@@ -299,12 +299,23 @@ static ssize_t tagging_store(struct device *d, struct device_attribute *attr,
 			     const char *buf, size_t count)
 {
 	const struct dsa_device_ops *new_tag_ops, *old_tag_ops;
+	const char *end = strchrnul(buf, '\n'), *name;
 	struct net_device *dev = to_net_dev(d);
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
+	size_t len = end - buf;
 	int err;
 
+	/* Empty string passed */
+	if (!len)
+		return -ENOPROTOOPT;
+
+	name = kstrndup(buf, len, GFP_KERNEL);
+	if (!name)
+		return -ENOMEM;
+
 	old_tag_ops = cpu_dp->tag_ops;
-	new_tag_ops = dsa_find_tagger_by_name(buf);
+	new_tag_ops = dsa_find_tagger_by_name(name);
+	kfree(name);
 	/* Bad tagger name, or module is not loaded? */
 	if (IS_ERR(new_tag_ops))
 		return PTR_ERR(new_tag_ops);