usb: gadget: u_ether: add gether_opts for config caching

Currently, the net_device is allocated when the function instance is
created (e.g., in ncm_alloc_inst()). While this allows userspace to
configure the device early, it decouples the net_device lifecycle from
the actual USB connection state (bind/unbind). The goal is to defer
net_device creation to the bind callback to properly align the lifecycle
with its parent gadget device.

However, deferring net_device allocation would prevent userspace from
configuring parameters (like interface name or MAC address) before the
net_device exists.

Introduce a new structure, struct gether_opts, associated with the
usb_function_instance, to cache settings independently of the
net_device. These settings include the interface name pattern, MAC
addresses (device and host), queue multiplier, and address assignment
type.

New helper functions are added:
- gether_setup_opts_default(): Initializes struct gether_opts with
  defaults, including random MAC addresses.
- gether_apply_opts(): Applies the cached options from a struct
  gether_opts to a valid net_device.

To expose these options to userspace, new configfs macros
(USB_ETHER_OPTS_ITEM and USB_ETHER_OPTS_ATTR_*) are defined in
u_ether_configfs.h. These attributes are part of the function
instance's configfs group.

This refactoring is a preparatory step. It allows the subsequent patch
to safely move the net_device allocation from the instance creation
phase to the bind phase without losing the ability to pre-configure
the interface via configfs.

Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20251230-ncm-refactor-v1-1-793e347bc7a7@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_ether.c

@@ -1039,6 +1039,36 @@ int gether_set_ifname(struct net_device *net, const char *name, int len)
 }
 EXPORT_SYMBOL_GPL(gether_set_ifname);
 
+void gether_setup_opts_default(struct gether_opts *opts, const char *name)
+{
+	opts->qmult = QMULT_DEFAULT;
+	snprintf(opts->name, sizeof(opts->name), "%s%%d", name);
+	eth_random_addr(opts->dev_mac);
+	opts->addr_assign_type = NET_ADDR_RANDOM;
+	eth_random_addr(opts->host_mac);
+}
+EXPORT_SYMBOL_GPL(gether_setup_opts_default);
+
+void gether_apply_opts(struct net_device *net, struct gether_opts *opts)
+{
+	struct eth_dev *dev = netdev_priv(net);
+
+	dev->qmult = opts->qmult;
+
+	if (opts->ifname_set) {
+		strscpy(net->name, opts->name, sizeof(net->name));
+		dev->ifname_set = true;
+	}
+
+	memcpy(dev->host_mac, opts->host_mac, sizeof(dev->host_mac));
+
+	if (opts->addr_assign_type == NET_ADDR_SET) {
+		memcpy(dev->dev_mac, opts->dev_mac, sizeof(dev->dev_mac));
+		net->addr_assign_type = opts->addr_assign_type;
+	}
+}
+EXPORT_SYMBOL_GPL(gether_apply_opts);
+
 void gether_suspend(struct gether *link)
 {
 	struct eth_dev *dev = link->ioport;

drivers/usb/gadget/function/u_ether.h

@@ -38,6 +38,31 @@
 
 struct eth_dev;
 
+/**
+ * struct gether_opts - Options for Ethernet gadget function instances
+ * @name: Pattern for the network interface name (e.g., "usb%d").
+ *        Used to generate the net device name.
+ * @qmult: Queue length multiplier for high/super speed.
+ * @host_mac: The MAC address to be used by the host side.
+ * @dev_mac: The MAC address to be used by the device side.
+ * @ifname_set: True if the interface name pattern has been set by userspace.
+ * @addr_assign_type: The method used for assigning the device MAC address
+ *                    (e.g., NET_ADDR_RANDOM, NET_ADDR_SET).
+ *
+ * This structure caches network-related settings provided through configfs
+ * before the net_device is fully instantiated. This allows for early
+ * configuration while deferring net_device allocation until the function
+ * is bound.
+ */
+struct gether_opts {
+	char			name[IFNAMSIZ];
+	unsigned int		qmult;
+	u8			host_mac[ETH_ALEN];
+	u8			dev_mac[ETH_ALEN];
+	bool			ifname_set;
+	unsigned char		addr_assign_type;
+};
+
 /*
  * This represents the USB side of an "ethernet" link, managed by a USB
  * function which provides control and (maybe) framing.  Two functions
@@ -259,6 +284,9 @@ int gether_set_ifname(struct net_device *net, const char *name, int len);
 
 void gether_cleanup(struct eth_dev *dev);
 
+void gether_setup_opts_default(struct gether_opts *opts, const char *name);
+void gether_apply_opts(struct net_device *net, struct gether_opts *opts);
+
 void gether_suspend(struct gether *link);
 void gether_resume(struct gether *link);
 

drivers/usb/gadget/function/u_ether_configfs.h

@@ -13,6 +13,12 @@
 #ifndef __U_ETHER_CONFIGFS_H
 #define __U_ETHER_CONFIGFS_H
 
+#include <linux/cleanup.h>
+#include <linux/if_ether.h>
+#include <linux/mutex.h>
+#include <linux/netdevice.h>
+#include <linux/rtnetlink.h>
+
 #define USB_ETHERNET_CONFIGFS_ITEM(_f_)					\
 	static void _f_##_attr_release(struct config_item *item)	\
 	{								\
@@ -197,4 +203,174 @@ out:									\
 									\
 	CONFIGFS_ATTR(_f_##_opts_, _n_)
 
+#define USB_ETHER_OPTS_ITEM(_f_)						\
+	static void _f_##_attr_release(struct config_item *item)		\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+										\
+		usb_put_function_instance(&opts->func_inst);			\
+	}									\
+										\
+	static struct configfs_item_operations _f_##_item_ops = {		\
+		.release	= _f_##_attr_release,				\
+	}
+
+#define USB_ETHER_OPTS_ATTR_DEV_ADDR(_f_)					\
+	static ssize_t _f_##_opts_dev_addr_show(struct config_item *item,	\
+						char *page)			\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+										\
+		guard(mutex)(&opts->lock);					\
+		return sysfs_emit(page, "%pM\n", opts->net_opts.dev_mac);	\
+	}									\
+										\
+	static ssize_t _f_##_opts_dev_addr_store(struct config_item *item,	\
+						 const char *page, size_t len)	\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+		u8 new_addr[ETH_ALEN];						\
+		const char *p = page;						\
+										\
+		guard(mutex)(&opts->lock);					\
+		if (opts->refcnt)						\
+			return -EBUSY;						\
+										\
+		for (int i = 0; i < ETH_ALEN; i++) {				\
+			unsigned char num;					\
+			if ((*p == '.') || (*p == ':'))				\
+				p++;						\
+			num = hex_to_bin(*p++) << 4;				\
+			num |= hex_to_bin(*p++);				\
+			new_addr[i] = num;					\
+		}								\
+		if (!is_valid_ether_addr(new_addr))				\
+			return -EINVAL;						\
+		memcpy(opts->net_opts.dev_mac, new_addr, ETH_ALEN);		\
+		opts->net_opts.addr_assign_type = NET_ADDR_SET;			\
+		return len;							\
+	}									\
+										\
+	CONFIGFS_ATTR(_f_##_opts_, dev_addr)
+
+#define USB_ETHER_OPTS_ATTR_HOST_ADDR(_f_)					\
+	static ssize_t _f_##_opts_host_addr_show(struct config_item *item,	\
+						 char *page)			\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+										\
+		guard(mutex)(&opts->lock);					\
+		return sysfs_emit(page, "%pM\n", opts->net_opts.host_mac);	\
+	}									\
+										\
+	static ssize_t _f_##_opts_host_addr_store(struct config_item *item,	\
+						  const char *page, size_t len)	\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+		u8 new_addr[ETH_ALEN];						\
+		const char *p = page;						\
+										\
+		guard(mutex)(&opts->lock);					\
+		if (opts->refcnt)						\
+			return -EBUSY;						\
+										\
+		for (int i = 0; i < ETH_ALEN; i++) {				\
+			unsigned char num;					\
+			if ((*p == '.') || (*p == ':'))				\
+				p++;						\
+			num = hex_to_bin(*p++) << 4;				\
+			num |= hex_to_bin(*p++);				\
+			new_addr[i] = num;					\
+		}								\
+		if (!is_valid_ether_addr(new_addr))				\
+			return -EINVAL;						\
+		memcpy(opts->net_opts.host_mac, new_addr, ETH_ALEN);		\
+		return len;							\
+	}									\
+										\
+	CONFIGFS_ATTR(_f_##_opts_, host_addr)
+
+#define USB_ETHER_OPTS_ATTR_QMULT(_f_)						\
+	static ssize_t _f_##_opts_qmult_show(struct config_item *item,		\
+					     char *page)			\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+										\
+		guard(mutex)(&opts->lock);					\
+		return sysfs_emit(page, "%u\n", opts->net_opts.qmult);		\
+	}									\
+										\
+	static ssize_t _f_##_opts_qmult_store(struct config_item *item,		\
+					      const char *page, size_t len)	\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+		u32 val;							\
+		int ret;							\
+										\
+		guard(mutex)(&opts->lock);					\
+		if (opts->refcnt)						\
+			return -EBUSY;						\
+										\
+		ret = kstrtou32(page, 0, &val);					\
+		if (ret)							\
+			return ret;						\
+										\
+		opts->net_opts.qmult = val;					\
+		return len;							\
+	}									\
+										\
+	CONFIGFS_ATTR(_f_##_opts_, qmult)
+
+#define USB_ETHER_OPTS_ATTR_IFNAME(_f_)						\
+	static ssize_t _f_##_opts_ifname_show(struct config_item *item,		\
+					      char *page)			\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+		const char *name;						\
+										\
+		guard(mutex)(&opts->lock);					\
+		rtnl_lock();							\
+		if (opts->net_opts.ifname_set)					\
+			name = opts->net_opts.name;				\
+		else if (opts->net)						\
+			name = netdev_name(opts->net);				\
+		else								\
+			name = "(inactive net_device)";				\
+		rtnl_unlock();							\
+		return sysfs_emit(page, "%s\n", name);				\
+	}									\
+										\
+	static ssize_t _f_##_opts_ifname_store(struct config_item *item,	\
+					       const char *page, size_t len)	\
+	{									\
+		struct f_##_f_##_opts *opts = to_f_##_f_##_opts(item);		\
+		char tmp[IFNAMSIZ];						\
+		const char *p;							\
+		size_t c_len = len;						\
+										\
+		if (c_len > 0 && page[c_len - 1] == '\n')			\
+			c_len--;						\
+										\
+		if (c_len >= sizeof(tmp))					\
+			return -E2BIG;						\
+										\
+		strscpy(tmp, page, c_len + 1);					\
+		if (!dev_valid_name(tmp))					\
+			return -EINVAL;						\
+										\
+		/* Require exactly one %d */					\
+		p = strchr(tmp, '%');						\
+		if (!p || p[1] != 'd' || strchr(p + 2, '%'))			\
+			return -EINVAL;						\
+										\
+		guard(mutex)(&opts->lock);					\
+		if (opts->refcnt)						\
+			return -EBUSY;						\
+		strscpy(opts->net_opts.name, tmp, sizeof(opts->net_opts.name));	\
+		opts->net_opts.ifname_set = true;				\
+		return len;							\
+	}									\
+										\
+	CONFIGFS_ATTR(_f_##_opts_, ifname)
+
 #endif /* __U_ETHER_CONFIGFS_H */