net/usb/usbnet.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * USB Network driver infrastructure
 * Copyright (C) 2000-2005 by David Brownell
 * Copyright (C) 2003-2005 David Hollis <dhollis@davehollis.com>
 */

/*
 * This is a generic "USB networking" framework that works with several
 * kinds of full and high speed networking devices:  host-to-host cables,
 * smart usb peripherals, and actual Ethernet adapters.
 *
 * These devices usually differ in terms of control protocols (if they
 * even have one!) and sometimes they define new framing to wrap or batch
 * Ethernet packets.  Otherwise, they talk to USB pretty much the same,
 * so interface (un)binding, endpoint I/O queues, fault handling, and other
 * issues can usefully be addressed by this framework.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ctype.h>
#include <linux/ethtool.h>
#include <linux/workqueue.h>
#include <linux/mii.h>
#include <linux/usb.h>
#include <linux/usb/usbnet.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/pm_runtime.h>

/*-------------------------------------------------------------------------*/

/*
 * Nineteen USB 1.1 max size bulk transactions per frame (ms), max.
 * Several dozen bytes of IPv4 data can fit in two such transactions.
 * One maximum size Ethernet packet takes twenty four of them.
 * For high speed, each frame comfortably fits almost 36 max size
 * Ethernet packets (so queues should be bigger).
 *
 * The goal is to let the USB host controller be busy for 5msec or
 * more before an irq is required, under load.  Jumbograms change
 * the equation.
 */
#define	MAX_QUEUE_MEMORY	(60 * 1518)
#define	RX_QLEN(dev)		((dev)->rx_qlen)
#define	TX_QLEN(dev)		((dev)->tx_qlen)

// reawaken network queue this soon after stopping; else watchdog barks
#define TX_TIMEOUT_JIFFIES	(5*HZ)

/* throttle rx/tx briefly after some faults, so hub_wq might disconnect()
 * us (it polls at HZ/4 usually) before we report too many false errors.
 */
#define THROTTLE_JIFFIES	(HZ/8)

// between wakeups
#define UNLINK_TIMEOUT_MS	3

/*-------------------------------------------------------------------------*/

/* use ethtool to change the level for any given device */
static int msg_level = -1;
module_param (msg_level, int, 0);
MODULE_PARM_DESC (msg_level, "Override default message level");

/*-------------------------------------------------------------------------*/

static const char * const usbnet_event_names[] = {
	[EVENT_TX_HALT]		   = "EVENT_TX_HALT",
	[EVENT_RX_HALT]		   = "EVENT_RX_HALT",
	[EVENT_RX_MEMORY]	   = "EVENT_RX_MEMORY",
	[EVENT_STS_SPLIT]	   = "EVENT_STS_SPLIT",
	[EVENT_LINK_RESET]	   = "EVENT_LINK_RESET",
	[EVENT_RX_PAUSED]	   = "EVENT_RX_PAUSED",
	[EVENT_DEV_ASLEEP]	   = "EVENT_DEV_ASLEEP",
	[EVENT_DEV_OPEN]	   = "EVENT_DEV_OPEN",
	[EVENT_DEVICE_REPORT_IDLE] = "EVENT_DEVICE_REPORT_IDLE",
	[EVENT_NO_RUNTIME_PM]	   = "EVENT_NO_RUNTIME_PM",
	[EVENT_RX_KILL]		   = "EVENT_RX_KILL",
	[EVENT_LINK_CHANGE]	   = "EVENT_LINK_CHANGE",
	[EVENT_SET_RX_MODE]	   = "EVENT_SET_RX_MODE",
	[EVENT_NO_IP_ALIGN]	   = "EVENT_NO_IP_ALIGN",
};

/* handles CDC Ethernet and many other network "bulk data" interfaces */
int usbnet_get_endpoints(struct usbnet *dev, struct usb_interface *intf)
{
	int				tmp;
	struct usb_host_interface	*alt = NULL;
	struct usb_host_endpoint	*in = NULL, *out = NULL;
	struct usb_host_endpoint	*status = NULL;

	for (tmp = 0; tmp < intf->num_altsetting; tmp++) {
		unsigned	ep;

		in = out = status = NULL;
		alt = intf->altsetting + tmp;

		/* take the first altsetting with in-bulk + out-bulk;
		 * remember any status endpoint, just in case;
		 * ignore other endpoints and altsettings.
		 */
		for (ep = 0; ep < alt->desc.bNumEndpoints; ep++) {
			struct usb_host_endpoint	*e;
			int				intr = 0;

			e = alt->endpoint + ep;

			/* ignore endpoints which cannot transfer data */
			if (!usb_endpoint_maxp(&e->desc))
				continue;

			switch (e->desc.bmAttributes) {
			case USB_ENDPOINT_XFER_INT:
				if (!usb_endpoint_dir_in(&e->desc))
					continue;
				intr = 1;
				fallthrough;
			case USB_ENDPOINT_XFER_BULK:
				break;
			default:
				continue;
			}
			if (usb_endpoint_dir_in(&e->desc)) {
				if (!intr && !in)
					in = e;
				else if (intr && !status)
					status = e;
			} else {
				if (!out)
					out = e;
			}
		}
		if (in && out)
			break;
	}
	if (!alt || !in || !out)
		return -EINVAL;

	if (alt->desc.bAlternateSetting != 0 ||
	    !(dev->driver_info->flags & FLAG_NO_SETINT)) {
		tmp = usb_set_interface (dev->udev, alt->desc.bInterfaceNumber,
				alt->desc.bAlternateSetting);
		if (tmp < 0)
			return tmp;
	}

	dev->in = usb_rcvbulkpipe (dev->udev,
			in->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
	dev->out = usb_sndbulkpipe (dev->udev,
			out->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
	dev->status = status;
	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_endpoints);

int usbnet_get_ethernet_addr(struct usbnet *dev, int iMACAddress)
{
	u8		addr[ETH_ALEN];
	int 		tmp = -1, ret;
	unsigned char	buf [13];

	ret = usb_string(dev->udev, iMACAddress, buf, sizeof buf);
	if (ret == 12)
		tmp = hex2bin(addr, buf, 6);
	if (tmp < 0) {
		dev_dbg(&dev->udev->dev,
			"bad MAC string %d fetch, %d\n", iMACAddress, tmp);
		if (ret >= 0)
			ret = -EINVAL;
		return ret;
	}
	eth_hw_addr_set(dev->net, addr);
	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_ethernet_addr);

static bool usbnet_needs_usb_name_format(struct usbnet *dev, struct net_device *net)
{
	/* Point to point devices which don't have a real MAC address
	 * (or report a fake local one) have historically used the usb%d
	 * naming. Preserve this..
	 */
	return (dev->driver_info->flags & FLAG_POINTTOPOINT) != 0 &&
		(is_zero_ether_addr(net->dev_addr) ||
		 is_local_ether_addr(net->dev_addr));
}

static void intr_complete(struct urb *urb)
{
	struct usbnet	*dev = urb->context;
	int		status = urb->status;

	switch (status) {
	/* success */
	case 0:
		dev->driver_info->status(dev, urb);
		break;

	/* software-driven interface shutdown */
	case -ENOENT:		/* urb killed */
	case -ESHUTDOWN:	/* hardware gone */
		netif_dbg(dev, ifdown, dev->net,
			  "intr shutdown, code %d\n", status);
		return;

	/* NOTE:  not throttling like RX/TX, since this endpoint
	 * already polls infrequently
	 */
	default:
		netdev_dbg(dev->net, "intr status %d\n", status);
		break;
	}

	status = usb_submit_urb (urb, GFP_ATOMIC);
	if (status != 0)
		netif_err(dev, timer, dev->net,
			  "intr resubmit --> %d\n", status);
}

static int init_status(struct usbnet *dev, struct usb_interface *intf)
{
	char		*buf = NULL;
	unsigned	pipe = 0;
	unsigned	maxp;
	unsigned	period;

	if (!dev->driver_info->status)
		return 0;

	pipe = usb_rcvintpipe (dev->udev,
			dev->status->desc.bEndpointAddress
				& USB_ENDPOINT_NUMBER_MASK);
	maxp = usb_maxpacket(dev->udev, pipe);

	/* avoid 1 msec chatter:  min 8 msec poll rate */
	period = max ((int) dev->status->desc.bInterval,
		(dev->udev->speed == USB_SPEED_HIGH) ? 7 : 3);

	buf = kmalloc (maxp, GFP_KERNEL);
	if (buf) {
		dev->interrupt = usb_alloc_urb (0, GFP_KERNEL);
		if (!dev->interrupt) {
			kfree (buf);
			return -ENOMEM;
		} else {
			usb_fill_int_urb(dev->interrupt, dev->udev, pipe,
				buf, maxp, intr_complete, dev, period);
			dev->interrupt->transfer_flags |= URB_FREE_BUFFER;
			dev_dbg(&intf->dev,
				"status ep%din, %d bytes period %d\n",
				usb_pipeendpoint(pipe), maxp, period);
		}
	}
	return 0;
}

/* Submit the interrupt URB if not previously submitted, increasing refcount */
int usbnet_status_start(struct usbnet *dev, gfp_t mem_flags)
{
	int ret = 0;

	WARN_ON_ONCE(dev->interrupt == NULL);
	if (dev->interrupt) {
		mutex_lock(&dev->interrupt_mutex);

		if (++dev->interrupt_count == 1)
			ret = usb_submit_urb(dev->interrupt, mem_flags);

		dev_dbg(&dev->udev->dev, "incremented interrupt URB count to %d\n",
			dev->interrupt_count);
		mutex_unlock(&dev->interrupt_mutex);
	}
	return ret;
}
EXPORT_SYMBOL_GPL(usbnet_status_start);

/* For resume; submit interrupt URB if previously submitted */
static int __usbnet_status_start_force(struct usbnet *dev, gfp_t mem_flags)
{
	int ret = 0;

	mutex_lock(&dev->interrupt_mutex);
	if (dev->interrupt_count) {
		ret = usb_submit_urb(dev->interrupt, mem_flags);
		dev_dbg(&dev->udev->dev,
			"submitted interrupt URB for resume\n");
	}
	mutex_unlock(&dev->interrupt_mutex);
	return ret;
}

/* Kill the interrupt URB if all submitters want it killed */
void usbnet_status_stop(struct usbnet *dev)
{
	if (dev->interrupt) {
		mutex_lock(&dev->interrupt_mutex);
		WARN_ON(dev->interrupt_count == 0);

		if (dev->interrupt_count && --dev->interrupt_count == 0)
			usb_kill_urb(dev->interrupt);

		dev_dbg(&dev->udev->dev,
			"decremented interrupt URB count to %d\n",
			dev->interrupt_count);
		mutex_unlock(&dev->interrupt_mutex);
	}
}
EXPORT_SYMBOL_GPL(usbnet_status_stop);

/* For suspend; always kill interrupt URB */
static void __usbnet_status_stop_force(struct usbnet *dev)
{
	if (dev->interrupt) {
		mutex_lock(&dev->interrupt_mutex);
		usb_kill_urb(dev->interrupt);
		dev_dbg(&dev->udev->dev, "killed interrupt URB for suspend\n");
		mutex_unlock(&dev->interrupt_mutex);
	}
}

/* Passes this packet up the stack, updating its accounting.
 * Some link protocols batch packets, so their rx_fixup paths
 * can return clones as well as just modify the original skb.
 */
void usbnet_skb_return(struct usbnet *dev, struct sk_buff *skb)
{
	struct pcpu_sw_netstats *stats64 = this_cpu_ptr(dev->net->tstats);
	unsigned long flags;
	int	status;

	if (test_bit(EVENT_RX_PAUSED, &dev->flags)) {
		skb_queue_tail(&dev->rxq_pause, skb);
		return;
	}

	/* only update if unset to allow minidriver rx_fixup override */
	if (skb->protocol == 0)
		skb->protocol = eth_type_trans (skb, dev->net);

	flags = u64_stats_update_begin_irqsave(&stats64->syncp);
	u64_stats_inc(&stats64->rx_packets);
	u64_stats_add(&stats64->rx_bytes, skb->len);
	u64_stats_update_end_irqrestore(&stats64->syncp, flags);

	netif_dbg(dev, rx_status, dev->net, "< rx, len %zu, type 0x%x\n",
		  skb->len + sizeof (struct ethhdr), skb->protocol);
	memset (skb->cb, 0, sizeof (struct skb_data));

	if (skb_defer_rx_timestamp(skb))
		return;

	status = netif_rx (skb);
	if (status != NET_RX_SUCCESS)
		netif_dbg(dev, rx_err, dev->net,
			  "netif_rx status %d\n", status);
}
EXPORT_SYMBOL_GPL(usbnet_skb_return);

/* must be called if hard_mtu or rx_urb_size changed */
void usbnet_update_max_qlen(struct usbnet *dev)
{
	enum usb_device_speed speed = dev->udev->speed;

	if (!dev->rx_urb_size || !dev->hard_mtu)
		goto insanity;
	switch (speed) {
	case USB_SPEED_HIGH:
		dev->rx_qlen = MAX_QUEUE_MEMORY / dev->rx_urb_size;
		dev->tx_qlen = MAX_QUEUE_MEMORY / dev->hard_mtu;
		break;
	case USB_SPEED_SUPER:
	case USB_SPEED_SUPER_PLUS:
		/*
		 * Not take default 5ms qlen for super speed HC to
		 * save memory, and iperf tests show 2.5ms qlen can
		 * work well
		 */
		dev->rx_qlen = 5 * MAX_QUEUE_MEMORY / dev->rx_urb_size;
		dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;
		break;
	default:
insanity:
		dev->rx_qlen = dev->tx_qlen = 4;
	}
}
EXPORT_SYMBOL_GPL(usbnet_update_max_qlen);


/*-------------------------------------------------------------------------
 *
 * Network Device Driver (peer link to "Host Device", from USB host)
 *
 *-------------------------------------------------------------------------*/

int usbnet_change_mtu(struct net_device *net, int new_mtu)
{
	struct usbnet	*dev = netdev_priv(net);
	int		ll_mtu = new_mtu + net->hard_header_len;
	int		old_hard_mtu = dev->hard_mtu;
	int		old_rx_urb_size = dev->rx_urb_size;

	// no second zero-length packet read wanted after mtu-sized packets
	if ((ll_mtu % dev->maxpacket) == 0)
		return -EDOM;
	WRITE_ONCE(net->mtu, new_mtu);

	dev->hard_mtu = net->mtu + net->hard_header_len;
	if (dev->rx_urb_size == old_hard_mtu) {
		dev->rx_urb_size = dev->hard_mtu;
		if (dev->rx_urb_size > old_rx_urb_size) {
			usbnet_pause_rx(dev);
			usbnet_unlink_rx_urbs(dev);
			usbnet_resume_rx(dev);
		}
	}

	/* max qlen depend on hard_mtu and rx_urb_size */
	usbnet_update_max_qlen(dev);

	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_change_mtu);

/* The caller must hold list->lock */
static void __usbnet_queue_skb(struct sk_buff_head *list,
			struct sk_buff *newsk, enum skb_state state)
{
	struct skb_data *entry = (struct skb_data *) newsk->cb;

	__skb_queue_tail(list, newsk);
	entry->state = state;
}

/*-------------------------------------------------------------------------*/

/* some LK 2.4 HCDs oopsed if we freed or resubmitted urbs from
 * completion callbacks.  2.5 should have fixed those bugs...
 */

static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb,
		struct sk_buff_head *list, enum skb_state state)
{
	unsigned long		flags;
	enum skb_state 		old_state;
	struct skb_data *entry = (struct skb_data *) skb->cb;

	spin_lock_irqsave(&list->lock, flags);
	old_state = entry->state;
	entry->state = state;
	__skb_unlink(skb, list);

	/* defer_bh() is never called with list == &dev->done.
	 * spin_lock_nested() tells lockdep that it is OK to take
	 * dev->done.lock here with list->lock held.
	 */
	spin_lock_nested(&dev->done.lock, SINGLE_DEPTH_NESTING);

	__skb_queue_tail(&dev->done, skb);
	if (dev->done.qlen == 1)
		queue_work(system_bh_wq, &dev->bh_work);
	spin_unlock(&dev->done.lock);
	spin_unlock_irqrestore(&list->lock, flags);
	return old_state;
}

/* some work can't be done in tasklets, so we use keventd
 *
 * NOTE:  annoying asymmetry:  if it's active, schedule_work() fails,
 * but tasklet_schedule() doesn't.  hope the failure is rare.
 */
void usbnet_defer_kevent(struct usbnet *dev, int work)
{
	set_bit (work, &dev->flags);
	if (!usbnet_going_away(dev)) {
		if (!schedule_work(&dev->kevent))
			netdev_dbg(dev->net,
				   "kevent %s may have been dropped\n",
				   usbnet_event_names[work]);
		else
			netdev_dbg(dev->net,
				   "kevent %s scheduled\n", usbnet_event_names[work]);
	}
}
EXPORT_SYMBOL_GPL(usbnet_defer_kevent);

/*-------------------------------------------------------------------------*/

static void rx_complete(struct urb *urb);

static int rx_submit(struct usbnet *dev, struct urb *urb, gfp_t flags)
{
	struct sk_buff		*skb;
	struct skb_data		*entry;
	int			retval = 0;
	unsigned long		lockflags;
	size_t			size = dev->rx_urb_size;

	/* prevent rx skb allocation when error ratio is high */
	if (test_bit(EVENT_RX_KILL, &dev->flags)) {
		usb_free_urb(urb);
		return -ENOLINK;
	}

	if (test_bit(EVENT_NO_IP_ALIGN, &dev->flags))
		skb = __netdev_alloc_skb(dev->net, size, flags);
	else
		skb = __netdev_alloc_skb_ip_align(dev->net, size, flags);
	if (!skb) {
		netif_dbg(dev, rx_err, dev->net, "no rx skb\n");
		usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
		usb_free_urb (urb);
		return -ENOMEM;
	}

	entry = (struct skb_data *) skb->cb;
	entry->urb = urb;
	entry->dev = dev;
	entry->length = 0;

	usb_fill_bulk_urb (urb, dev->udev, dev->in,
		skb->data, size, rx_complete, skb);

	spin_lock_irqsave (&dev->rxq.lock, lockflags);

	if (netif_running (dev->net) &&
	    netif_device_present (dev->net) &&
	    test_bit(EVENT_DEV_OPEN, &dev->flags) &&
	    !test_bit (EVENT_RX_HALT, &dev->flags) &&
	    !test_bit (EVENT_DEV_ASLEEP, &dev->flags) &&
	    !usbnet_going_away(dev)) {
		switch (retval = usb_submit_urb (urb, GFP_ATOMIC)) {
		case -EPIPE:
			usbnet_defer_kevent (dev, EVENT_RX_HALT);
			break;
		case -ENOMEM:
			usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
			break;
		case -ENODEV:
			netif_dbg(dev, ifdown, dev->net, "device gone\n");
			netif_device_detach (dev->net);
			break;
		case -EHOSTUNREACH:
			retval = -ENOLINK;
			break;
		default:
			netif_dbg(dev, rx_err, dev->net,
				  "rx submit, %d\n", retval);
			queue_work(system_bh_wq, &dev->bh_work);
			break;
		case 0:
			__usbnet_queue_skb(&dev->rxq, skb, rx_start);
		}
	} else {
		netif_dbg(dev, ifdown, dev->net, "rx: stopped\n");
		retval = -ENOLINK;
	}
	spin_unlock_irqrestore (&dev->rxq.lock, lockflags);
	if (retval) {
		dev_kfree_skb_any (skb);
		usb_free_urb (urb);
	}
	return retval;
}


/*-------------------------------------------------------------------------*/

static inline int rx_process(struct usbnet *dev, struct sk_buff *skb)
{
	if (dev->driver_info->rx_fixup &&
	    !dev->driver_info->rx_fixup (dev, skb)) {
		/* With RX_ASSEMBLE, rx_fixup() must update counters */
		if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
			dev->net->stats.rx_errors++;
		return -EPROTO;
	}
	// else network stack removes extra byte if we forced a short packet

	/* all data was already cloned from skb inside the driver */
	if (dev->driver_info->flags & FLAG_MULTI_PACKET)
		return -EALREADY;

	if (skb->len < ETH_HLEN) {
		dev->net->stats.rx_errors++;
		dev->net->stats.rx_length_errors++;
		netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);
		return -EPROTO;
	}

	usbnet_skb_return(dev, skb);
	return 0;
}

/*-------------------------------------------------------------------------*/

static void rx_complete(struct urb *urb)
{
	struct sk_buff		*skb = (struct sk_buff *) urb->context;
	struct skb_data		*entry = (struct skb_data *) skb->cb;
	struct usbnet		*dev = entry->dev;
	int			urb_status = urb->status;
	enum skb_state		state;

	skb_put (skb, urb->actual_length);
	state = rx_done;
	entry->urb = NULL;

	switch (urb_status) {
	/* success */
	case 0:
		break;

	/* stalls need manual reset. this is rare ... except that
	 * when going through USB 2.0 TTs, unplug appears this way.
	 * we avoid the highspeed version of the ETIMEDOUT/EILSEQ
	 * storm, recovering as needed.
	 */
	case -EPIPE:
		dev->net->stats.rx_errors++;
		usbnet_defer_kevent (dev, EVENT_RX_HALT);
		fallthrough;

	/* software-driven interface shutdown */
	case -ECONNRESET:		/* async unlink */
	case -ESHUTDOWN:		/* hardware gone */
		netif_dbg(dev, ifdown, dev->net,
			  "rx shutdown, code %d\n", urb_status);
		goto block;

	/* we get controller i/o faults during hub_wq disconnect() delays.
	 * throttle down resubmits, to avoid log floods; just temporarily,
	 * so we still recover when the fault isn't a hub_wq delay.
	 */
	case -EPROTO:
	case -ETIME:
	case -EILSEQ:
		dev->net->stats.rx_errors++;
		if (!timer_pending (&dev->delay)) {
			mod_timer (&dev->delay, jiffies + THROTTLE_JIFFIES);
			netif_dbg(dev, link, dev->net,
				  "rx throttle %d\n", urb_status);
		}
block:
		state = rx_cleanup;
		entry->urb = urb;
		urb = NULL;
		break;

	/* data overrun ... flush fifo? */
	case -EOVERFLOW:
		dev->net->stats.rx_over_errors++;
		fallthrough;

	default:
		state = rx_cleanup;
		dev->net->stats.rx_errors++;
		netif_dbg(dev, rx_err, dev->net, "rx status %d\n", urb_status);
		break;
	}

	/* stop rx if packet error rate is high */
	if (++dev->pkt_cnt > 30) {
		dev->pkt_cnt = 0;
		dev->pkt_err = 0;
	} else {
		if (state == rx_cleanup)
			dev->pkt_err++;
		if (dev->pkt_err > 20)
			set_bit(EVENT_RX_KILL, &dev->flags);
	}

	state = defer_bh(dev, skb, &dev->rxq, state);

	if (urb) {
		if (netif_running (dev->net) &&
		    !test_bit (EVENT_RX_HALT, &dev->flags) &&
		    state != unlink_start) {
			rx_submit (dev, urb, GFP_ATOMIC);
			usb_mark_last_busy(dev->udev);
			return;
		}
		usb_free_urb (urb);
	}
	netif_dbg(dev, rx_err, dev->net, "no read resubmitted\n");
}

/*-------------------------------------------------------------------------*/
void usbnet_pause_rx(struct usbnet *dev)
{
	set_bit(EVENT_RX_PAUSED, &dev->flags);

	netif_dbg(dev, rx_status, dev->net, "paused rx queue enabled\n");
}
EXPORT_SYMBOL_GPL(usbnet_pause_rx);

void usbnet_resume_rx(struct usbnet *dev)
{
	struct sk_buff *skb;
	int num = 0;

	local_bh_disable();
	clear_bit(EVENT_RX_PAUSED, &dev->flags);

	while ((skb = skb_dequeue(&dev->rxq_pause)) != NULL) {
		usbnet_skb_return(dev, skb);
		num++;
	}

	queue_work(system_bh_wq, &dev->bh_work);
	local_bh_enable();

	netif_dbg(dev, rx_status, dev->net,
		  "paused rx queue disabled, %d skbs requeued\n", num);
}
EXPORT_SYMBOL_GPL(usbnet_resume_rx);

void usbnet_purge_paused_rxq(struct usbnet *dev)
{
	skb_queue_purge(&dev->rxq_pause);
}
EXPORT_SYMBOL_GPL(usbnet_purge_paused_rxq);

/*-------------------------------------------------------------------------*/

// unlink pending rx/tx; completion handlers do all other cleanup

static int unlink_urbs(struct usbnet *dev, struct sk_buff_head *q)
{
	unsigned long		flags;
	struct sk_buff		*skb;
	int			count = 0;

	spin_lock_irqsave (&q->lock, flags);
	while (!skb_queue_empty(q)) {
		struct skb_data		*entry;
		struct urb		*urb;
		int			retval;

		skb_queue_walk(q, skb) {
			entry = (struct skb_data *) skb->cb;
			if (entry->state != unlink_start)
				goto found;
		}
		break;
found:
		entry->state = unlink_start;
		urb = entry->urb;

		/*
		 * Get reference count of the URB to avoid it to be
		 * freed during usb_unlink_urb, which may trigger
		 * use-after-free problem inside usb_unlink_urb since
		 * usb_unlink_urb is always racing with .complete
		 * handler(include defer_bh).
		 */
		usb_get_urb(urb);
		spin_unlock_irqrestore(&q->lock, flags);
		// during some PM-driven resume scenarios,
		// these (async) unlinks complete immediately
		retval = usb_unlink_urb (urb);
		if (retval != -EINPROGRESS && retval != 0)
			netdev_dbg(dev->net, "unlink urb err, %d\n", retval);
		else
			count++;
		usb_put_urb(urb);
		spin_lock_irqsave(&q->lock, flags);
	}
	spin_unlock_irqrestore (&q->lock, flags);
	return count;
}

// Flush all pending rx urbs
// minidrivers may need to do this when the MTU changes

void usbnet_unlink_rx_urbs(struct usbnet *dev)
{
	if (netif_running(dev->net)) {
		(void) unlink_urbs (dev, &dev->rxq);
		queue_work(system_bh_wq, &dev->bh_work);
	}
}
EXPORT_SYMBOL_GPL(usbnet_unlink_rx_urbs);

/*-------------------------------------------------------------------------*/

static void wait_skb_queue_empty(struct sk_buff_head *q)
{
	unsigned long flags;

	spin_lock_irqsave(&q->lock, flags);
	while (!skb_queue_empty(q)) {
		spin_unlock_irqrestore(&q->lock, flags);
		schedule_timeout(msecs_to_jiffies(UNLINK_TIMEOUT_MS));
		set_current_state(TASK_UNINTERRUPTIBLE);
		spin_lock_irqsave(&q->lock, flags);
	}
	spin_unlock_irqrestore(&q->lock, flags);
}

// precondition: never called in_interrupt
static void usbnet_terminate_urbs(struct usbnet *dev)
{
	DECLARE_WAITQUEUE(wait, current);
	int temp;

	/* ensure there are no more active urbs */
	add_wait_queue(&dev->wait, &wait);
	set_current_state(TASK_UNINTERRUPTIBLE);
	temp = unlink_urbs(dev, &dev->txq) +
		unlink_urbs(dev, &dev->rxq);

	/* maybe wait for deletions to finish. */
	wait_skb_queue_empty(&dev->rxq);
	wait_skb_queue_empty(&dev->txq);
	wait_skb_queue_empty(&dev->done);
	netif_dbg(dev, ifdown, dev->net,
		  "waited for %d urb completions\n", temp);
	set_current_state(TASK_RUNNING);
	remove_wait_queue(&dev->wait, &wait);
}

int usbnet_stop(struct net_device *net)
{
	struct usbnet		*dev = netdev_priv(net);
	const struct driver_info *info = dev->driver_info;
	int			retval, pm, mpn;

	clear_bit(EVENT_DEV_OPEN, &dev->flags);
	netif_stop_queue (net);
	netdev_reset_queue(net);

	netif_info(dev, ifdown, dev->net,
		   "stop stats: rx/tx %lu/%lu, errs %lu/%lu\n",
		   net->stats.rx_packets, net->stats.tx_packets,
		   net->stats.rx_errors, net->stats.tx_errors);

	/* to not race resume */
	pm = usb_autopm_get_interface(dev->intf);
	/* allow minidriver to stop correctly (wireless devices to turn off
	 * radio etc) */
	if (info->stop) {
		retval = info->stop(dev);
		if (retval < 0)
			netif_info(dev, ifdown, dev->net,
				   "stop fail (%d) usbnet usb-%s-%s, %s\n",
				   retval,
				   dev->udev->bus->bus_name, dev->udev->devpath,
				   info->description);
	}

	if (!(info->flags & FLAG_AVOID_UNLINK_URBS))
		usbnet_terminate_urbs(dev);

	usbnet_status_stop(dev);

	usbnet_purge_paused_rxq(dev);

	mpn = !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags);

	/* deferred work (timer, softirq, task) must also stop */
	dev->flags = 0;
	timer_delete_sync(&dev->delay);
	cancel_work_sync(&dev->bh_work);
	cancel_work_sync(&dev->kevent);

	/* We have cyclic dependencies. Those calls are needed
	 * to break a cycle. We cannot fall into the gaps because
	 * we have a flag
	 */
	cancel_work_sync(&dev->bh_work);
	timer_delete_sync(&dev->delay);
	cancel_work_sync(&dev->kevent);

	if (!pm)
		usb_autopm_put_interface(dev->intf);

	if (info->manage_power && mpn)
		info->manage_power(dev, 0);
	else
		usb_autopm_put_interface(dev->intf);

	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_stop);

/*-------------------------------------------------------------------------*/

// posts reads, and enables write queuing

// precondition: never called in_interrupt

int usbnet_open(struct net_device *net)
{
	struct usbnet		*dev = netdev_priv(net);
	int			retval;
	const struct driver_info *info = dev->driver_info;

	if ((retval = usb_autopm_get_interface(dev->intf)) < 0) {
		netif_info(dev, ifup, dev->net,
			   "resumption fail (%d) usbnet usb-%s-%s, %s\n",
			   retval,
			   dev->udev->bus->bus_name,
			   dev->udev->devpath,
			   info->description);
		goto done_nopm;
	}

	// put into "known safe" state
	if (info->reset && (retval = info->reset (dev)) < 0) {
		netif_info(dev, ifup, dev->net,
			   "open reset fail (%d) usbnet usb-%s-%s, %s\n",
			   retval,
			   dev->udev->bus->bus_name,
			   dev->udev->devpath,
			   info->description);
		goto done;
	}

	/* hard_mtu or rx_urb_size may change in reset() */
	usbnet_update_max_qlen(dev);

	// insist peer be connected
	if (info->check_connect && (retval = info->check_connect (dev)) < 0) {
		netif_err(dev, ifup, dev->net, "can't open; %d\n", retval);
		goto done;
	}

	/* start any status interrupt transfer */
	if (dev->interrupt) {
		retval = usbnet_status_start(dev, GFP_KERNEL);
		if (retval < 0) {
			netif_err(dev, ifup, dev->net,
				  "intr submit %d\n", retval);
			goto done;
		}
	}

	set_bit(EVENT_DEV_OPEN, &dev->flags);
	netdev_reset_queue(net);
	netif_start_queue (net);
	netif_info(dev, ifup, dev->net,
		   "open: enable queueing (rx %d, tx %d) mtu %d %s framing\n",
		   (int)RX_QLEN(dev), (int)TX_QLEN(dev),
		   dev->net->mtu,
		   (dev->driver_info->flags & FLAG_FRAMING_NC) ? "NetChip" :
		   (dev->driver_info->flags & FLAG_FRAMING_GL) ? "GeneSys" :
		   (dev->driver_info->flags & FLAG_FRAMING_Z) ? "Zaurus" :
		   (dev->driver_info->flags & FLAG_FRAMING_RN) ? "RNDIS" :
		   (dev->driver_info->flags & FLAG_FRAMING_AX) ? "ASIX" :
		   "simple");

	/* reset rx error state */
	dev->pkt_cnt = 0;
	dev->pkt_err = 0;
	clear_bit(EVENT_RX_KILL, &dev->flags);

	// delay posting reads until we're fully open
	queue_work(system_bh_wq, &dev->bh_work);
	if (info->manage_power) {
		retval = info->manage_power(dev, 1);
		if (retval < 0) {
			retval = 0;
			set_bit(EVENT_NO_RUNTIME_PM, &dev->flags);
		} else {
			usb_autopm_put_interface(dev->intf);
		}
	}
	return retval;
done:
	usb_autopm_put_interface(dev->intf);
done_nopm:
	return retval;
}
EXPORT_SYMBOL_GPL(usbnet_open);

/*-------------------------------------------------------------------------*/

/* ethtool methods; minidrivers may need to add some more, but
 * they'll probably want to use this base set.
 */

/* These methods are written on the assumption that the device
 * uses MII
 */
int usbnet_get_link_ksettings_mii(struct net_device *net,
			      struct ethtool_link_ksettings *cmd)
{
	struct usbnet *dev = netdev_priv(net);

	if (!dev->mii.mdio_read)
		return -EOPNOTSUPP;

	mii_ethtool_get_link_ksettings(&dev->mii, cmd);

	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_link_ksettings_mii);

int usbnet_get_link_ksettings_internal(struct net_device *net,
					struct ethtool_link_ksettings *cmd)
{
	struct usbnet *dev = netdev_priv(net);

	/* the assumption that speed is equal on tx and rx
	 * is deeply engrained into the networking layer.
	 * For wireless stuff it is not true.
	 * We assume that rx_speed matters more.
	 */
	if (dev->rx_speed != SPEED_UNSET)
		cmd->base.speed = dev->rx_speed / 1000000;
	else if (dev->tx_speed != SPEED_UNSET)
		cmd->base.speed = dev->tx_speed / 1000000;
	else
		cmd->base.speed = SPEED_UNKNOWN;

	/* The standard "Universal Serial Bus Class Definitions
	 * for Communications Devices v1.2" does not specify
	 * anything about duplex status.
	 * So set it DUPLEX_UNKNOWN instead of default DUPLEX_HALF.
	 */
	cmd->base.duplex = DUPLEX_UNKNOWN;

	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_link_ksettings_internal);

int usbnet_set_link_ksettings_mii(struct net_device *net,
			      const struct ethtool_link_ksettings *cmd)
{
	struct usbnet *dev = netdev_priv(net);
	int retval;

	if (!dev->mii.mdio_write)
		return -EOPNOTSUPP;

	retval = mii_ethtool_set_link_ksettings(&dev->mii, cmd);

	/* link speed/duplex might have changed */
	if (dev->driver_info->link_reset)
		dev->driver_info->link_reset(dev);

	/* hard_mtu or rx_urb_size may change in link_reset() */
	usbnet_update_max_qlen(dev);

	return retval;
}
EXPORT_SYMBOL_GPL(usbnet_set_link_ksettings_mii);

u32 usbnet_get_link(struct net_device *net)
{
	struct usbnet *dev = netdev_priv(net);

	/* If a check_connect is defined, return its result */
	if (dev->driver_info->check_connect)
		return dev->driver_info->check_connect (dev) == 0;

	/* if the device has mii operations, use those */
	if (dev->mii.mdio_read)
		return mii_link_ok(&dev->mii);

	/* Otherwise, dtrt for drivers calling netif_carrier_{on,off} */
	return ethtool_op_get_link(net);
}
EXPORT_SYMBOL_GPL(usbnet_get_link);

int usbnet_nway_reset(struct net_device *net)
{
	struct usbnet *dev = netdev_priv(net);

	if (!dev->mii.mdio_write)
		return -EOPNOTSUPP;

	return mii_nway_restart(&dev->mii);
}
EXPORT_SYMBOL_GPL(usbnet_nway_reset);

void usbnet_get_drvinfo(struct net_device *net, struct ethtool_drvinfo *info)
{
	struct usbnet *dev = netdev_priv(net);

	strscpy(info->driver, dev->driver_name, sizeof(info->driver));
	strscpy(info->fw_version, dev->driver_info->description,
		sizeof(info->fw_version));
	usb_make_path (dev->udev, info->bus_info, sizeof info->bus_info);
}
EXPORT_SYMBOL_GPL(usbnet_get_drvinfo);

u32 usbnet_get_msglevel(struct net_device *net)
{
	struct usbnet *dev = netdev_priv(net);

	return dev->msg_enable;
}
EXPORT_SYMBOL_GPL(usbnet_get_msglevel);

void usbnet_set_msglevel(struct net_device *net, u32 level)
{
	struct usbnet *dev = netdev_priv(net);

	dev->msg_enable = level;
}
EXPORT_SYMBOL_GPL(usbnet_set_msglevel);

/* drivers may override default ethtool_ops in their bind() routine */
static const struct ethtool_ops usbnet_ethtool_ops = {
	.get_link		= usbnet_get_link,
	.nway_reset		= usbnet_nway_reset,
	.get_drvinfo		= usbnet_get_drvinfo,
	.get_msglevel		= usbnet_get_msglevel,
	.set_msglevel		= usbnet_set_msglevel,
	.get_ts_info		= ethtool_op_get_ts_info,
	.get_link_ksettings	= usbnet_get_link_ksettings_mii,
	.set_link_ksettings	= usbnet_set_link_ksettings_mii,
};

/*-------------------------------------------------------------------------*/

static void __handle_link_change(struct usbnet *dev)
{
	if (!test_bit(EVENT_DEV_OPEN, &dev->flags))
		return;

	if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
		netif_carrier_on(dev->net);

	if (!netif_carrier_ok(dev->net)) {
		/* kill URBs for reading packets to save bus bandwidth */
		unlink_urbs(dev, &dev->rxq);

		/*
		 * tx_timeout will unlink URBs for sending packets and
		 * tx queue is stopped by netcore after link becomes off
		 */
	} else {
		/* submitting URBs for reading packets */
		queue_work(system_bh_wq, &dev->bh_work);
	}

	/* hard_mtu or rx_urb_size may change during link change */
	usbnet_update_max_qlen(dev);

	clear_bit(EVENT_LINK_CHANGE, &dev->flags);
}

void usbnet_set_rx_mode(struct net_device *net)
{
	struct usbnet		*dev = netdev_priv(net);

	usbnet_defer_kevent(dev, EVENT_SET_RX_MODE);
}
EXPORT_SYMBOL_GPL(usbnet_set_rx_mode);

static void __handle_set_rx_mode(struct usbnet *dev)
{
	if (dev->driver_info->set_rx_mode)
		(dev->driver_info->set_rx_mode)(dev);

	clear_bit(EVENT_SET_RX_MODE, &dev->flags);
}

/* work that cannot be done in interrupt context uses keventd.
 *
 * NOTE:  with 2.5 we could do more of this using completion callbacks,
 * especially now that control transfers can be queued.
 */
static void
usbnet_deferred_kevent(struct work_struct *work)
{
	struct usbnet		*dev =
		container_of(work, struct usbnet, kevent);
	int			status;

	/* usb_clear_halt() needs a thread context */
	if (test_bit (EVENT_TX_HALT, &dev->flags)) {
		unlink_urbs (dev, &dev->txq);
		status = usb_autopm_get_interface(dev->intf);
		if (status < 0)
			goto fail_pipe;
		status = usb_clear_halt (dev->udev, dev->out);
		usb_autopm_put_interface(dev->intf);
		if (status < 0 &&
		    status != -EPIPE &&
		    status != -ESHUTDOWN) {
			if (netif_msg_tx_err (dev))
fail_pipe:
				netdev_err(dev->net, "can't clear tx halt, status %d\n",
					   status);
		} else {
			clear_bit (EVENT_TX_HALT, &dev->flags);
			if (status != -ESHUTDOWN)
				netif_wake_queue (dev->net);
		}
	}
	if (test_bit (EVENT_RX_HALT, &dev->flags)) {
		unlink_urbs (dev, &dev->rxq);
		status = usb_autopm_get_interface(dev->intf);
		if (status < 0)
			goto fail_halt;
		status = usb_clear_halt (dev->udev, dev->in);
		usb_autopm_put_interface(dev->intf);
		if (status < 0 &&
		    status != -EPIPE &&
		    status != -ESHUTDOWN) {
			if (netif_msg_rx_err (dev))
fail_halt:
				netdev_err(dev->net, "can't clear rx halt, status %d\n",
					   status);
		} else {
			clear_bit (EVENT_RX_HALT, &dev->flags);
			if (!usbnet_going_away(dev))
				queue_work(system_bh_wq, &dev->bh_work);
		}
	}

	/* work could resubmit itself forever if memory is tight */
	if (test_bit (EVENT_RX_MEMORY, &dev->flags)) {
		struct urb	*urb = NULL;
		int resched = 1;

		if (netif_running (dev->net))
			urb = usb_alloc_urb (0, GFP_KERNEL);
		else
			clear_bit (EVENT_RX_MEMORY, &dev->flags);
		if (urb != NULL) {
			clear_bit (EVENT_RX_MEMORY, &dev->flags);
			status = usb_autopm_get_interface(dev->intf);
			if (status < 0) {
				usb_free_urb(urb);
				goto fail_lowmem;
			}
			if (rx_submit (dev, urb, GFP_KERNEL) == -ENOLINK)
				resched = 0;
			usb_autopm_put_interface(dev->intf);
fail_lowmem:
			if (resched)
				if (!usbnet_going_away(dev))
					queue_work(system_bh_wq, &dev->bh_work);
		}
	}

	if (test_bit (EVENT_LINK_RESET, &dev->flags)) {
		const struct driver_info *info = dev->driver_info;
		int			retval = 0;

		clear_bit (EVENT_LINK_RESET, &dev->flags);
		status = usb_autopm_get_interface(dev->intf);
		if (status < 0)
			goto skip_reset;
		if(info->link_reset && (retval = info->link_reset(dev)) < 0) {
			usb_autopm_put_interface(dev->intf);
skip_reset:
			netdev_info(dev->net, "link reset failed (%d) usbnet usb-%s-%s, %s\n",
				    retval,
				    dev->udev->bus->bus_name,
				    dev->udev->devpath,
				    info->description);
		} else {
			usb_autopm_put_interface(dev->intf);
		}

		/* handle link change from link resetting */
		__handle_link_change(dev);
	}

	if (test_bit (EVENT_LINK_CHANGE, &dev->flags))
		__handle_link_change(dev);

	if (test_bit (EVENT_SET_RX_MODE, &dev->flags))
		__handle_set_rx_mode(dev);


	if (dev->flags)
		netdev_dbg(dev->net, "kevent done, flags = 0x%lx\n", dev->flags);
}

/*-------------------------------------------------------------------------*/

static void tx_complete(struct urb *urb)
{
	struct sk_buff		*skb = (struct sk_buff *) urb->context;
	struct skb_data		*entry = (struct skb_data *) skb->cb;
	struct usbnet		*dev = entry->dev;

	if (urb->status == 0) {
		struct pcpu_sw_netstats *stats64 = this_cpu_ptr(dev->net->tstats);
		unsigned long flags;

		flags = u64_stats_update_begin_irqsave(&stats64->syncp);
		u64_stats_add(&stats64->tx_packets, entry->packets);
		u64_stats_add(&stats64->tx_bytes, entry->length);
		u64_stats_update_end_irqrestore(&stats64->syncp, flags);
	} else {
		dev->net->stats.tx_errors++;

		switch (urb->status) {
		case -EPIPE:
			usbnet_defer_kevent (dev, EVENT_TX_HALT);
			break;

		/* software-driven interface shutdown */
		case -ECONNRESET:		// async unlink
		case -ESHUTDOWN:		// hardware gone
			break;

		/* like rx, tx gets controller i/o faults during hub_wq
		 * delays and so it uses the same throttling mechanism.
		 */
		case -EPROTO:
		case -ETIME:
		case -EILSEQ:
			usb_mark_last_busy(dev->udev);
			if (!timer_pending (&dev->delay)) {
				mod_timer (&dev->delay,
					jiffies + THROTTLE_JIFFIES);
				netif_dbg(dev, link, dev->net,
					  "tx throttle %d\n", urb->status);
			}
			netif_stop_queue (dev->net);
			break;
		default:
			netif_dbg(dev, tx_err, dev->net,
				  "tx err %d\n", entry->urb->status);
			break;
		}
	}

	usb_autopm_put_interface_async(dev->intf);
	(void) defer_bh(dev, skb, &dev->txq, tx_done);
}

/*-------------------------------------------------------------------------*/

void usbnet_tx_timeout(struct net_device *net, unsigned int txqueue)
{
	struct usbnet		*dev = netdev_priv(net);

	unlink_urbs (dev, &dev->txq);
	queue_work(system_bh_wq, &dev->bh_work);
	/* this needs to be handled individually because the generic layer
	 * doesn't know what is sufficient and could not restore private
	 * information if a remedy of an unconditional reset were used.
	 */
	if (dev->driver_info->recover)
		(dev->driver_info->recover)(dev);
}
EXPORT_SYMBOL_GPL(usbnet_tx_timeout);

/*-------------------------------------------------------------------------*/

static int build_dma_sg(const struct sk_buff *skb, struct urb *urb)
{
	unsigned num_sgs, total_len = 0;
	int i, s = 0;

	num_sgs = skb_shinfo(skb)->nr_frags + 1;
	if (num_sgs == 1)
		return 0;

	/* reserve one for zero packet */
	urb->sg = kmalloc_array(num_sgs + 1, sizeof(struct scatterlist),
				GFP_ATOMIC);
	if (!urb->sg)
		return -ENOMEM;

	urb->num_sgs = num_sgs;
	sg_init_table(urb->sg, urb->num_sgs + 1);

	sg_set_buf(&urb->sg[s++], skb->data, skb_headlen(skb));
	total_len += skb_headlen(skb);

	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
		skb_frag_t *f = &skb_shinfo(skb)->frags[i];

		total_len += skb_frag_size(f);
		sg_set_page(&urb->sg[i + s], skb_frag_page(f), skb_frag_size(f),
			    skb_frag_off(f));
	}
	urb->transfer_buffer_length = total_len;

	return 1;
}

netdev_tx_t usbnet_start_xmit(struct sk_buff *skb, struct net_device *net)
{
	struct usbnet		*dev = netdev_priv(net);
	unsigned int			length;
	struct urb		*urb = NULL;
	struct skb_data		*entry;
	const struct driver_info *info = dev->driver_info;
	unsigned long		flags;
	int retval;

	if (skb)
		skb_tx_timestamp(skb);

	// some devices want funky USB-level framing, for
	// win32 driver (usually) and/or hardware quirks
	if (info->tx_fixup) {
		skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
		if (!skb) {
			/* packet collected; minidriver waiting for more */
			if (info->flags & FLAG_MULTI_PACKET)
				goto not_drop;
			netif_dbg(dev, tx_err, dev->net, "can't tx_fixup skb\n");
			goto drop;
		}
	}

	if (!(urb = usb_alloc_urb (0, GFP_ATOMIC))) {
		netif_dbg(dev, tx_err, dev->net, "no urb\n");
		goto drop;
	}

	entry = (struct skb_data *) skb->cb;
	entry->urb = urb;
	entry->dev = dev;

	usb_fill_bulk_urb (urb, dev->udev, dev->out,
			skb->data, skb->len, tx_complete, skb);
	if (dev->can_dma_sg) {
		if (build_dma_sg(skb, urb) < 0)
			goto drop;
	}
	length = urb->transfer_buffer_length;

	/* don't assume the hardware handles USB_ZERO_PACKET
	 * NOTE:  strictly conforming cdc-ether devices should expect
	 * the ZLP here, but ignore the one-byte packet.
	 * NOTE2: CDC NCM specification is different from CDC ECM when
	 * handling ZLP/short packets, so cdc_ncm driver will make short
	 * packet itself if needed.
	 */
	if (length % dev->maxpacket == 0) {
		if (!(info->flags & FLAG_SEND_ZLP)) {
			if (!(info->flags & FLAG_MULTI_PACKET)) {
				length++;
				if (skb_tailroom(skb) && !urb->num_sgs) {
					skb->data[skb->len] = 0;
					__skb_put(skb, 1);
				} else if (urb->num_sgs)
					sg_set_buf(&urb->sg[urb->num_sgs++],
							dev->padding_pkt, 1);
			}
		} else
			urb->transfer_flags |= URB_ZERO_PACKET;
	}
	urb->transfer_buffer_length = length;

	if (info->flags & FLAG_MULTI_PACKET) {
		/* Driver has set number of packets and a length delta.
		 * Calculate the complete length and ensure that it's
		 * positive.
		 */
		entry->length += length;
		if (WARN_ON_ONCE(entry->length <= 0))
			entry->length = length;
	} else {
		usbnet_set_skb_tx_stats(skb, 1, length);
	}

	spin_lock_irqsave(&dev->txq.lock, flags);
	retval = usb_autopm_get_interface_async(dev->intf);
	if (retval < 0) {
		spin_unlock_irqrestore(&dev->txq.lock, flags);
		goto drop;
	}
	if (netif_queue_stopped(net)) {
		usb_autopm_put_interface_async(dev->intf);
		spin_unlock_irqrestore(&dev->txq.lock, flags);
		goto drop;
	}

#ifdef CONFIG_PM
	/* if this triggers the device is still a sleep */
	if (test_bit(EVENT_DEV_ASLEEP, &dev->flags)) {
		/* transmission will be done in resume */
		usb_anchor_urb(urb, &dev->deferred);
		/* no use to process more packets */
		netif_stop_queue(net);
		usb_put_urb(urb);
		spin_unlock_irqrestore(&dev->txq.lock, flags);
		netdev_dbg(dev->net, "Delaying transmission for resumption\n");
		goto deferred;
	}
#endif

	switch ((retval = usb_submit_urb (urb, GFP_ATOMIC))) {
	case -EPIPE:
		netif_stop_queue (net);
		usbnet_defer_kevent (dev, EVENT_TX_HALT);
		usb_autopm_put_interface_async(dev->intf);
		break;
	default:
		usb_autopm_put_interface_async(dev->intf);
		netif_dbg(dev, tx_err, dev->net,
			  "tx: submit urb err %d\n", retval);
		break;
	case 0:
		netif_trans_update(net);
		__usbnet_queue_skb(&dev->txq, skb, tx_start);
		netdev_sent_queue(net, skb->len);
		if (dev->txq.qlen >= TX_QLEN (dev))
			netif_stop_queue (net);
	}
	spin_unlock_irqrestore (&dev->txq.lock, flags);

	if (retval) {
		netif_dbg(dev, tx_err, dev->net, "drop, code %d\n", retval);
drop:
		dev->net->stats.tx_dropped++;
not_drop:
		if (skb)
			dev_kfree_skb_any (skb);
		if (urb) {
			kfree(urb->sg);
			usb_free_urb(urb);
		}
	} else
		netif_dbg(dev, tx_queued, dev->net,
			  "> tx, len %u, type 0x%x\n", length, skb->protocol);
#ifdef CONFIG_PM
deferred:
#endif
	return NETDEV_TX_OK;
}
EXPORT_SYMBOL_GPL(usbnet_start_xmit);

static int rx_alloc_submit(struct usbnet *dev, gfp_t flags)
{
	struct urb	*urb;
	int		i;
	int		ret = 0;

	/* don't refill the queue all at once */
	for (i = 0; i < 10 && dev->rxq.qlen < RX_QLEN(dev); i++) {
		urb = usb_alloc_urb(0, flags);
		if (urb != NULL) {
			ret = rx_submit(dev, urb, flags);
			if (ret)
				goto err;
		} else {
			ret = -ENOMEM;
			goto err;
		}
	}
err:
	return ret;
}

static inline void usb_free_skb(struct sk_buff *skb)
{
	struct skb_data *entry = (struct skb_data *)skb->cb;

	usb_free_urb(entry->urb);
	dev_kfree_skb(skb);
}

/*-------------------------------------------------------------------------*/

// work (work deferred from completions, in_irq) or timer

static void usbnet_bh(struct timer_list *t)
{
	struct usbnet		*dev = timer_container_of(dev, t, delay);
	unsigned int bytes_compl = 0, pkts_compl = 0;
	struct sk_buff		*skb;
	struct skb_data		*entry;

	while ((skb = skb_dequeue (&dev->done))) {
		entry = (struct skb_data *) skb->cb;
		switch (entry->state) {
		case rx_done:
			if (rx_process(dev, skb))
				usb_free_skb(skb);
			continue;
		case tx_done:
			bytes_compl += skb->len;
			pkts_compl++;
			kfree(entry->urb->sg);
			fallthrough;
		case rx_cleanup:
			usb_free_skb(skb);
			continue;
		default:
			netdev_dbg(dev->net, "bogus skb state %d\n", entry->state);
		}
	}

	spin_lock_bh(&dev->bql_spinlock);
	netdev_completed_queue(dev->net, pkts_compl, bytes_compl);
	spin_unlock_bh(&dev->bql_spinlock);

	/* restart RX again after disabling due to high error rate */
	clear_bit(EVENT_RX_KILL, &dev->flags);

	/* waiting for all pending urbs to complete?
	 * only then can we forgo submitting anew
	 */
	if (waitqueue_active(&dev->wait)) {
		if (dev->txq.qlen + dev->rxq.qlen + dev->done.qlen == 0)
			wake_up_all(&dev->wait);

	// or are we maybe short a few urbs?
	} else if (netif_running (dev->net) &&
		   netif_device_present (dev->net) &&
		   netif_carrier_ok(dev->net) &&
		   !usbnet_going_away(dev) &&
		   !timer_pending(&dev->delay) &&
		   !test_bit(EVENT_RX_PAUSED, &dev->flags) &&
		   !test_bit(EVENT_RX_HALT, &dev->flags)) {
		int	temp = dev->rxq.qlen;

		if (temp < RX_QLEN(dev)) {
			if (rx_alloc_submit(dev, GFP_ATOMIC) == -ENOLINK)
				return;
			if (temp != dev->rxq.qlen)
				netif_dbg(dev, link, dev->net,
					  "rxqlen %d --> %d\n",
					  temp, dev->rxq.qlen);
			if (dev->rxq.qlen < RX_QLEN(dev))
				queue_work(system_bh_wq, &dev->bh_work);
		}
		if (dev->txq.qlen < TX_QLEN (dev))
			netif_wake_queue (dev->net);
	}
}

static void usbnet_bh_work(struct work_struct *work)
{
	struct usbnet *dev = from_work(dev, work, bh_work);

	usbnet_bh(&dev->delay);
}


/*-------------------------------------------------------------------------
 *
 * USB Device Driver support
 *
 *-------------------------------------------------------------------------*/

// precondition: never called in_interrupt

void usbnet_disconnect(struct usb_interface *intf)
{
	struct usbnet		*dev;
	struct usb_device	*xdev;
	struct net_device	*net;
	struct urb		*urb;

	dev = usb_get_intfdata(intf);
	usb_set_intfdata(intf, NULL);
	if (!dev)
		return;
	usbnet_mark_going_away(dev);

	xdev = interface_to_usbdev (intf);

	netif_info(dev, probe, dev->net, "unregister '%s' usb-%s-%s, %s\n",
		   intf->dev.driver->name,
		   xdev->bus->bus_name, xdev->devpath,
		   dev->driver_info->description);

	net = dev->net;
	unregister_netdev (net);

	cancel_work_sync(&dev->kevent);

	while ((urb = usb_get_from_anchor(&dev->deferred))) {
		dev_kfree_skb(urb->context);
		kfree(urb->sg);
		usb_free_urb(urb);
	}

	if (dev->driver_info->unbind)
		dev->driver_info->unbind(dev, intf);

	usb_kill_urb(dev->interrupt);
	usb_free_urb(dev->interrupt);
	kfree(dev->padding_pkt);

	free_netdev(net);
}
EXPORT_SYMBOL_GPL(usbnet_disconnect);

static const struct net_device_ops usbnet_netdev_ops = {
	.ndo_open		= usbnet_open,
	.ndo_stop		= usbnet_stop,
	.ndo_start_xmit		= usbnet_start_xmit,
	.ndo_tx_timeout		= usbnet_tx_timeout,
	.ndo_set_rx_mode	= usbnet_set_rx_mode,
	.ndo_change_mtu		= usbnet_change_mtu,
	.ndo_set_mac_address 	= eth_mac_addr,
	.ndo_validate_addr	= eth_validate_addr,
};

/*-------------------------------------------------------------------------*/

// precondition: never called in_interrupt

static const struct device_type wlan_type = {
	.name	= "wlan",
};

static const struct device_type wwan_type = {
	.name	= "wwan",
};

int
usbnet_probe(struct usb_interface *udev, const struct usb_device_id *prod)
{
	struct usbnet			*dev;
	struct net_device		*net;
	struct usb_host_interface	*interface;
	const struct driver_info	*info;
	struct usb_device		*xdev;
	int				status;
	const char			*name;
	struct usb_driver 	*driver = to_usb_driver(udev->dev.driver);

	/* usbnet already took usb runtime pm, so have to enable the feature
	 * for usb interface, otherwise usb_autopm_get_interface may return
	 * failure if RUNTIME_PM is enabled.
	 */
	if (!driver->supports_autosuspend) {
		driver->supports_autosuspend = 1;
		pm_runtime_enable(&udev->dev);
	}

	name = udev->dev.driver->name;
	info = (const struct driver_info *) prod->driver_info;
	if (!info) {
		dev_dbg (&udev->dev, "blacklisted by %s\n", name);
		return -ENODEV;
	}
	xdev = interface_to_usbdev (udev);
	interface = udev->cur_altsetting;

	status = -ENOMEM;

	// set up our own records
	net = alloc_etherdev(sizeof(*dev));
	if (!net)
		goto out;

	/* netdev_printk() needs this so do it as early as possible */
	SET_NETDEV_DEV(net, &udev->dev);

	dev = netdev_priv(net);
	dev->udev = xdev;
	dev->intf = udev;
	dev->driver_info = info;
	dev->driver_name = name;
	dev->rx_speed = SPEED_UNSET;
	dev->tx_speed = SPEED_UNSET;

	dev->msg_enable = netif_msg_init (msg_level, NETIF_MSG_DRV
				| NETIF_MSG_PROBE | NETIF_MSG_LINK);
	init_waitqueue_head(&dev->wait);
	skb_queue_head_init (&dev->rxq);
	skb_queue_head_init (&dev->txq);
	skb_queue_head_init (&dev->done);
	skb_queue_head_init(&dev->rxq_pause);
	spin_lock_init(&dev->bql_spinlock);
	INIT_WORK(&dev->bh_work, usbnet_bh_work);
	INIT_WORK (&dev->kevent, usbnet_deferred_kevent);
	init_usb_anchor(&dev->deferred);
	timer_setup(&dev->delay, usbnet_bh, 0);
	mutex_init (&dev->phy_mutex);
	mutex_init(&dev->interrupt_mutex);
	dev->interrupt_count = 0;

	dev->net = net;
	strscpy(net->name, "usb%d", sizeof(net->name));

	/* rx and tx sides can use different message sizes;
	 * bind() should set rx_urb_size in that case.
	 */
	dev->hard_mtu = net->mtu + net->hard_header_len;
	net->min_mtu = 0;
	net->max_mtu = ETH_MAX_MTU;

	net->netdev_ops = &usbnet_netdev_ops;
	net->watchdog_timeo = TX_TIMEOUT_JIFFIES;
	net->ethtool_ops = &usbnet_ethtool_ops;
	net->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS;

	// allow device-specific bind/init procedures
	// NOTE net->name still not usable ...
	if (info->bind) {
		status = info->bind (dev, udev);
		if (status < 0)
			goto out1;

		/* heuristic: rename to "eth%d" if we are not sure this link
		 * is two-host (these links keep "usb%d")
		 */
		if ((dev->driver_info->flags & FLAG_ETHER) != 0 &&
		    !usbnet_needs_usb_name_format(dev, net))
			strscpy(net->name, "eth%d", sizeof(net->name));
		/* WLAN devices should always be named "wlan%d" */
		if ((dev->driver_info->flags & FLAG_WLAN) != 0)
			strscpy(net->name, "wlan%d", sizeof(net->name));
		/* WWAN devices should always be named "wwan%d" */
		if ((dev->driver_info->flags & FLAG_WWAN) != 0)
			strscpy(net->name, "wwan%d", sizeof(net->name));

		/* devices that cannot do ARP */
		if ((dev->driver_info->flags & FLAG_NOARP) != 0)
			net->flags |= IFF_NOARP;

		/* maybe the remote can't receive an Ethernet MTU */
		if (net->mtu > (dev->hard_mtu - net->hard_header_len))
			net->mtu = dev->hard_mtu - net->hard_header_len;
	} else if (!info->in || !info->out)
		status = usbnet_get_endpoints (dev, udev);
	else {
		u8 ep_addrs[3] = {
			info->in + USB_DIR_IN, info->out + USB_DIR_OUT, 0
		};

		dev->in = usb_rcvbulkpipe (xdev, info->in);
		dev->out = usb_sndbulkpipe (xdev, info->out);
		if (!(info->flags & FLAG_NO_SETINT))
			status = usb_set_interface (xdev,
				interface->desc.bInterfaceNumber,
				interface->desc.bAlternateSetting);
		else
			status = 0;

		if (status == 0 && !usb_check_bulk_endpoints(udev, ep_addrs))
			status = -EINVAL;
	}
	if (status >= 0 && dev->status)
		status = init_status (dev, udev);
	if (status < 0)
		goto out3;

	if (!dev->rx_urb_size)
		dev->rx_urb_size = dev->hard_mtu;
	dev->maxpacket = usb_maxpacket(dev->udev, dev->out);
	if (dev->maxpacket == 0) {
		/* that is a broken device */
		status = -ENODEV;
		goto out4;
	}

	/* this flags the device for user space */
	if (!is_valid_ether_addr(net->dev_addr))
		eth_hw_addr_random(net);

	if ((dev->driver_info->flags & FLAG_WLAN) != 0)
		SET_NETDEV_DEVTYPE(net, &wlan_type);
	if ((dev->driver_info->flags & FLAG_WWAN) != 0)
		SET_NETDEV_DEVTYPE(net, &wwan_type);

	/* initialize max rx_qlen and tx_qlen */
	usbnet_update_max_qlen(dev);

	if (dev->can_dma_sg && !(info->flags & FLAG_SEND_ZLP) &&
		!(info->flags & FLAG_MULTI_PACKET)) {
		dev->padding_pkt = kzalloc(1, GFP_KERNEL);
		if (!dev->padding_pkt) {
			status = -ENOMEM;
			goto out4;
		}
	}

	status = register_netdev (net);
	if (status)
		goto out5;
	netif_info(dev, probe, dev->net,
		   "register '%s' at usb-%s-%s, %s, %pM\n",
		   udev->dev.driver->name,
		   xdev->bus->bus_name, xdev->devpath,
		   dev->driver_info->description,
		   net->dev_addr);

	// ok, it's ready to go.
	usb_set_intfdata (udev, dev);

	netif_device_attach (net);

	if (dev->driver_info->flags & FLAG_LINK_INTR)
		usbnet_link_change(dev, 0, 0);

	return 0;

out5:
	kfree(dev->padding_pkt);
out4:
	usb_free_urb(dev->interrupt);
out3:
	if (info->unbind)
		info->unbind (dev, udev);
out1:
	/* subdrivers must undo all they did in bind() if they
	 * fail it, but we may fail later and a deferred kevent
	 * may trigger an error resubmitting itself and, worse,
	 * schedule a timer. So we kill it all just in case.
	 */
	usbnet_mark_going_away(dev);
	cancel_work_sync(&dev->kevent);
	timer_delete_sync(&dev->delay);
	free_netdev(net);
out:
	return status;
}
EXPORT_SYMBOL_GPL(usbnet_probe);

/*-------------------------------------------------------------------------*/

/*
 * suspend the whole driver as soon as the first interface is suspended
 * resume only when the last interface is resumed
 */

int usbnet_suspend(struct usb_interface *intf, pm_message_t message)
{
	struct usbnet		*dev = usb_get_intfdata(intf);

	if (!dev->suspend_count++) {
		spin_lock_irq(&dev->txq.lock);
		/* don't autosuspend while transmitting */
		if (dev->txq.qlen && PMSG_IS_AUTO(message)) {
			dev->suspend_count--;
			spin_unlock_irq(&dev->txq.lock);
			return -EBUSY;
		} else {
			set_bit(EVENT_DEV_ASLEEP, &dev->flags);
			spin_unlock_irq(&dev->txq.lock);
		}
		/*
		 * accelerate emptying of the rx and queues, to avoid
		 * having everything error out.
		 */
		netif_device_detach (dev->net);
		usbnet_terminate_urbs(dev);
		__usbnet_status_stop_force(dev);

		/*
		 * reattach so runtime management can use and
		 * wake the device
		 */
		netif_device_attach (dev->net);
	}
	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_suspend);

int usbnet_resume(struct usb_interface *intf)
{
	struct usbnet		*dev = usb_get_intfdata(intf);
	struct sk_buff          *skb;
	struct urb              *res;
	int                     retval;

	if (!--dev->suspend_count) {
		/* resume interrupt URB if it was previously submitted */
		__usbnet_status_start_force(dev, GFP_NOIO);

		spin_lock_irq(&dev->txq.lock);
		while ((res = usb_get_from_anchor(&dev->deferred))) {

			skb = (struct sk_buff *)res->context;
			retval = usb_submit_urb(res, GFP_ATOMIC);
			if (retval < 0) {
				dev_kfree_skb_any(skb);
				kfree(res->sg);
				usb_free_urb(res);
				usb_autopm_put_interface_async(dev->intf);
			} else {
				netif_trans_update(dev->net);
				__skb_queue_tail(&dev->txq, skb);
			}
		}

		smp_mb();
		clear_bit(EVENT_DEV_ASLEEP, &dev->flags);
		spin_unlock_irq(&dev->txq.lock);

		if (test_bit(EVENT_DEV_OPEN, &dev->flags)) {
			/* handle remote wakeup ASAP
			 * we cannot race against stop
			 */
			if (netif_device_present(dev->net) &&
				!timer_pending(&dev->delay) &&
				!test_bit(EVENT_RX_HALT, &dev->flags))
					rx_alloc_submit(dev, GFP_NOIO);

			if (!(dev->txq.qlen >= TX_QLEN(dev)))
				netif_tx_wake_all_queues(dev->net);
			queue_work(system_bh_wq, &dev->bh_work);
		}
	}

	if (test_and_clear_bit(EVENT_DEVICE_REPORT_IDLE, &dev->flags))
		usb_autopm_get_interface_no_resume(intf);

	return 0;
}
EXPORT_SYMBOL_GPL(usbnet_resume);

/*
 * Either a subdriver implements manage_power, then it is assumed to always
 * be ready to be suspended or it reports the readiness to be suspended
 * explicitly
 */
void usbnet_device_suggests_idle(struct usbnet *dev)
{
	if (!test_and_set_bit(EVENT_DEVICE_REPORT_IDLE, &dev->flags)) {
		dev->intf->needs_remote_wakeup = 1;
		usb_autopm_put_interface_async(dev->intf);
	}
}
EXPORT_SYMBOL(usbnet_device_suggests_idle);

/*
 * For devices that can do without special commands
 */
int usbnet_manage_power(struct usbnet *dev, int on)
{
	dev->intf->needs_remote_wakeup = on;
	return 0;
}
EXPORT_SYMBOL(usbnet_manage_power);

void usbnet_link_change(struct usbnet *dev, bool link, bool need_reset)
{
	/* update link after link is reseted */
	if (link && !need_reset) {
		set_bit(EVENT_LINK_CARRIER_ON, &dev->flags);
	} else {
		clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags);
		netif_carrier_off(dev->net);
	}

	if (need_reset && link)
		usbnet_defer_kevent(dev, EVENT_LINK_RESET);
	else
		usbnet_defer_kevent(dev, EVENT_LINK_CHANGE);
}
EXPORT_SYMBOL(usbnet_link_change);

/*-------------------------------------------------------------------------*/
static int __usbnet_read_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
			     u16 value, u16 index, void *data, u16 size)
{
	void *buf = NULL;
	int err = -ENOMEM;

	netdev_dbg(dev->net, "usbnet_read_cmd cmd=0x%02x reqtype=%02x"
		   " value=0x%04x index=0x%04x size=%d\n",
		   cmd, reqtype, value, index, size);

	if (size) {
		buf = kmalloc(size, GFP_NOIO);
		if (!buf)
			goto out;
	}

	err = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
			      cmd, reqtype, value, index, buf, size,
			      USB_CTRL_GET_TIMEOUT);
	if (err > 0 && err <= size) {
		if (data)
			memcpy(data, buf, err);
		else
			netdev_dbg(dev->net,
				   "Huh? Data requested but thrown away.\n");
	}
	kfree(buf);
out:
	return err;
}

static int __usbnet_write_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
			      u16 value, u16 index, const void *data,
			      u16 size)
{
	void *buf = NULL;
	int err = -ENOMEM;

	netdev_dbg(dev->net, "usbnet_write_cmd cmd=0x%02x reqtype=%02x"
		   " value=0x%04x index=0x%04x size=%d\n",
		   cmd, reqtype, value, index, size);

	if (data) {
		buf = kmemdup(data, size, GFP_NOIO);
		if (!buf)
			goto out;
	} else {
        if (size) {
            WARN_ON_ONCE(1);
            err = -EINVAL;
            goto out;
        }
    }

	err = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0),
			      cmd, reqtype, value, index, buf, size,
			      USB_CTRL_SET_TIMEOUT);
	kfree(buf);

out:
	return err;
}

/*
 * The function can't be called inside suspend/resume callback,
 * otherwise deadlock will be caused.
 */
int usbnet_read_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
		    u16 value, u16 index, void *data, u16 size)
{
	int ret;

	if (usb_autopm_get_interface(dev->intf) < 0)
		return -ENODEV;
	ret = __usbnet_read_cmd(dev, cmd, reqtype, value, index,
				data, size);
	usb_autopm_put_interface(dev->intf);
	return ret;
}
EXPORT_SYMBOL_GPL(usbnet_read_cmd);

/*
 * The function can't be called inside suspend/resume callback,
 * otherwise deadlock will be caused.
 */
int usbnet_write_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
		     u16 value, u16 index, const void *data, u16 size)
{
	int ret;

	if (usb_autopm_get_interface(dev->intf) < 0)
		return -ENODEV;
	ret = __usbnet_write_cmd(dev, cmd, reqtype, value, index,
				 data, size);
	usb_autopm_put_interface(dev->intf);
	return ret;
}
EXPORT_SYMBOL_GPL(usbnet_write_cmd);

/*
 * The function can be called inside suspend/resume callback safely
 * and should only be called by suspend/resume callback generally.
 */
int usbnet_read_cmd_nopm(struct usbnet *dev, u8 cmd, u8 reqtype,
			  u16 value, u16 index, void *data, u16 size)
{
	return __usbnet_read_cmd(dev, cmd, reqtype, value, index,
				 data, size);
}
EXPORT_SYMBOL_GPL(usbnet_read_cmd_nopm);

/*
 * The function can be called inside suspend/resume callback safely
 * and should only be called by suspend/resume callback generally.
 */
int usbnet_write_cmd_nopm(struct usbnet *dev, u8 cmd, u8 reqtype,
			  u16 value, u16 index, const void *data,
			  u16 size)
{
	return __usbnet_write_cmd(dev, cmd, reqtype, value, index,
				  data, size);
}
EXPORT_SYMBOL_GPL(usbnet_write_cmd_nopm);

static void usbnet_async_cmd_cb(struct urb *urb)
{
	struct usb_ctrlrequest *req = (struct usb_ctrlrequest *)urb->context;
	int status = urb->status;

	if (status < 0)
		dev_dbg(&urb->dev->dev, "%s failed with %d",
			__func__, status);

	kfree(req);
	usb_free_urb(urb);
}

/*
 * The caller must make sure that device can't be put into suspend
 * state until the control URB completes.
 */
int usbnet_write_cmd_async(struct usbnet *dev, u8 cmd, u8 reqtype,
			   u16 value, u16 index, const void *data, u16 size)
{
	struct usb_ctrlrequest *req;
	struct urb *urb;
	int err = -ENOMEM;
	void *buf = NULL;

	netdev_dbg(dev->net, "usbnet_write_cmd cmd=0x%02x reqtype=%02x"
		   " value=0x%04x index=0x%04x size=%d\n",
		   cmd, reqtype, value, index, size);

	urb = usb_alloc_urb(0, GFP_ATOMIC);
	if (!urb)
		goto fail;

	if (data) {
		buf = kmemdup(data, size, GFP_ATOMIC);
		if (!buf) {
			netdev_err(dev->net, "Error allocating buffer"
				   " in %s!\n", __func__);
			goto fail_free_urb;
		}
	}

	req = kmalloc(sizeof(struct usb_ctrlrequest), GFP_ATOMIC);
	if (!req)
		goto fail_free_buf;

	req->bRequestType = reqtype;
	req->bRequest = cmd;
	req->wValue = cpu_to_le16(value);
	req->wIndex = cpu_to_le16(index);
	req->wLength = cpu_to_le16(size);

	usb_fill_control_urb(urb, dev->udev,
			     usb_sndctrlpipe(dev->udev, 0),
			     (void *)req, buf, size,
			     usbnet_async_cmd_cb, req);
	urb->transfer_flags |= URB_FREE_BUFFER;

	err = usb_submit_urb(urb, GFP_ATOMIC);
	if (err < 0) {
		netdev_err(dev->net, "Error submitting the control"
			   " message: status=%d\n", err);
		goto fail_free_all;
	}
	return 0;

fail_free_all:
	kfree(req);
fail_free_buf:
	kfree(buf);
	/*
	 * avoid a double free
	 * needed because the flag can be set only
	 * after filling the URB
	 */
	urb->transfer_flags = 0;
fail_free_urb:
	usb_free_urb(urb);
fail:
	return err;

}
EXPORT_SYMBOL_GPL(usbnet_write_cmd_async);
/*-------------------------------------------------------------------------*/

static int __init usbnet_init(void)
{
	/* Compiler should optimize this out. */
	BUILD_BUG_ON(
		sizeof_field(struct sk_buff, cb) < sizeof(struct skb_data));

	return 0;
}
module_init(usbnet_init);

static void __exit usbnet_exit(void)
{
}
module_exit(usbnet_exit);

MODULE_AUTHOR("David Brownell");
MODULE_DESCRIPTION("USB network driver framework");
MODULE_LICENSE("GPL");