Subject: USB: usbnet (8/9) module for RNDIS devices

From: David Brownell <[email-masked]>
Date: Sat, 13 Aug 2005 14:18:13 -0700

This driver is EXPERIMENTAL, new, and only lightly tested.
But it ought to be useful.  :)
This adds host-side RNDIS support to the "usbnet" driver, so Linux can talk
to various devices (often based on WinCE) that otherwise only Windows could
talk to.

Tested with little-endian Linux talking to a Linux-USB Ethernet/RNDIS based
peripheral.  This also includes updates from Eddie C. Dost <[email-masked]>
for big-endian SPARC Linux talking to a Nokia 9500 Communicator.

Signed-off-by: David Brownell <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>

---
 drivers/usb/net/Kconfig  |   14 +
 drivers/usb/net/Makefile |    1 
 drivers/usb/net/rndis.c  |  614 +++++++++++++++++++++++++++++++++++++++++++++++
 drivers/usb/net/usbnet.c |    9 
 4 files changed, 630 insertions(+), 8 deletions(-)

--- gregkh-2.6.orig/drivers/usb/net/Makefile	2005-08-15 17:51:25.000000000 -0700
+++ gregkh-2.6/drivers/usb/net/Makefile	2005-08-15 17:51:26.000000000 -0700
@@ -10,6 +10,7 @@
 obj-$(CONFIG_USB_NET_CDCETHER)	+= cdc_ether.o
 obj-$(CONFIG_USB_NET_GL620A)	+= gl620a.o
 obj-$(CONFIG_USB_NET_NET1080)	+= net1080.o
+obj-$(CONFIG_USB_NET_RNDIS)	+= rndis.o
 obj-$(CONFIG_USB_NET_SIMPLE)	+= simple.o
 obj-$(CONFIG_USB_NET_ZAURUS)	+= zaurus.o
 obj-$(CONFIG_USB_USBNET)	+= usbnet.o
--- gregkh-2.6.orig/drivers/usb/net/Kconfig	2005-08-15 17:51:25.000000000 -0700
+++ gregkh-2.6/drivers/usb/net/Kconfig	2005-08-15 17:51:26.000000000 -0700
@@ -213,6 +213,20 @@
 	  on this design:  one NetChip 1080 chips and supporting logic,
 	  supporting LEDs that indicate traffic
 
+config USB_NET_RNDIS
+	tristate "RNDIS devices (EXPERIMENTAL)"
+	depends on USB_USBNET && EXPERIMENTAL
+	select USB_NET_CDCETHER
+	default n
+	help
+	  Choose this option to support "Remote NDIS" usb networking links,
+	  as encouraged by Microsoft (instead of CDC Ethernet!) for use in
+	  various devices that may only support this protocol.
+
+	  Avoid using this protocol unless you have no better options.
+	  The protocol specification is incomplete, and is controlled by
+	  (and for) Microsoft; it isn't an "Open" ecosystem or market.
+
 config USB_NET_SIMPLE
 	tristate "Simple USB Network Links"
 	depends on USB_USBNET
--- gregkh-2.6.orig/drivers/usb/net/usbnet.c	2005-08-15 17:51:25.000000000 -0700
+++ gregkh-2.6/drivers/usb/net/usbnet.c	2005-08-15 17:51:26.000000000 -0700
@@ -103,6 +103,7 @@
  * 		disconnect; other cleanups. (db)  Flush net1080 fifos
  * 		after several sequential framing errors. (Johannes Erdfelt)
  * 22-aug-2003	AX8817X support (Dave Hollis).
+ *
  * 14-jun-2004  Trivial patch for AX8817X based Buffalo LUA-U2-KTX in Japan
  *		(Neil Bortnak)
  * 03-nov-2004	Trivial patch for KC2190 (KC-190) chip. (Jonathan McDowell)
@@ -1357,14 +1358,6 @@
 	.driver_info =	(unsigned long) &prolific_info,
 },
 #endif
-
-#ifdef	CONFIG_USB_RNDIS
-{
-	/* RNDIS is MSFT's un-official variant of CDC ACM */
-	USB_INTERFACE_INFO (USB_CLASS_COMM, 2 /* ACM */, 0x0ff),
-	.driver_info = (unsigned long) &rndis_info,
-},
-#endif
 	{ },		// END
 };
 MODULE_DEVICE_TABLE (usb, products);
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gregkh-2.6/drivers/usb/net/rndis.c	2005-08-15 17:51:26.000000000 -0700
@@ -0,0 +1,614 @@
+/*
+ * RNDIS  Networking Links
+ * Copyright (C) 2005 by David Brownell
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+// #define	DEBUG			// error path messages, extra info
+// #define	VERBOSE			// more; success messages
+
+#include <linux/config.h>
+#ifdef	CONFIG_USB_DEBUG
+#   define DEBUG
+#endif
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/netdevice.h>
+#include <linux/etherdevice.h>
+#include <linux/ethtool.h>
+#include <linux/workqueue.h>
+#include <linux/mii.h>
+#include <linux/usb.h>
+#include <linux/usb_cdc.h>
+
+#include "usbnet.h"
+
+
+/*
+ * RNDIS is NDIS remoted over USB.  It's a MSFT variant of CDC ACM ... of
+ * course ACM was intended for modems, not Ethernet links!  USB's standard
+ * for Ethernet links is "CDC Ethernet", which is significantly simpler.
+ */
+
+/*
+ * CONTROL uses CDC "encapsulated commands" with funky notifications.
+ *  - control-out:  SEND_ENCAPSULATED
+ *  - interrupt-in:  RESPONSE_AVAILABLE
+ *  - control-in:  GET_ENCAPSULATED
+ *
+ * We'll try to ignore the RESPONSE_AVAILABLE notifications.
+ */
+struct rndis_msg_hdr {
+	__le32	msg_type;			/* RNDIS_MSG_* */
+	__le32	msg_len;
+	// followed by data that varies between messages
+	__le32	request_id;
+	__le32	status;
+	// ... and more
+} __attribute__ ((packed));
+
+/* RNDIS defines this (absurdly huge) control timeout */
+#define	RNDIS_CONTROL_TIMEOUT_MS	(10 * 1000)
+
+
+#define ccpu2 __constant_cpu_to_le32
+
+#define RNDIS_MSG_COMPLETION	ccpu2(0x80000000)
+
+/* codes for "msg_type" field of rndis messages;
+ * only the data channel uses packet messages (maybe batched);
+ * everything else goes on the control channel.
+ */
+#define RNDIS_MSG_PACKET	ccpu2(0x00000001)	/* 1-N packets */
+#define RNDIS_MSG_INIT		ccpu2(0x00000002)
+#define RNDIS_MSG_INIT_C 	(RNDIS_MSG_INIT|RNDIS_MSG_COMPLETION)
+#define RNDIS_MSG_HALT		ccpu2(0x00000003)
+#define RNDIS_MSG_QUERY		ccpu2(0x00000004)
+#define RNDIS_MSG_QUERY_C 	(RNDIS_MSG_QUERY|RNDIS_MSG_COMPLETION)
+#define RNDIS_MSG_SET		ccpu2(0x00000005)
+#define RNDIS_MSG_SET_C 	(RNDIS_MSG_SET|RNDIS_MSG_COMPLETION)
+#define RNDIS_MSG_RESET		ccpu2(0x00000006)
+#define RNDIS_MSG_RESET_C 	(RNDIS_MSG_RESET|RNDIS_MSG_COMPLETION)
+#define RNDIS_MSG_INDICATE	ccpu2(0x00000007)
+#define RNDIS_MSG_KEEPALIVE	ccpu2(0x00000008)
+#define RNDIS_MSG_KEEPALIVE_C 	(RNDIS_MSG_KEEPALIVE|RNDIS_MSG_COMPLETION)
+
+/* codes for "status" field of completion messages */
+#define	RNDIS_STATUS_SUCCESS		ccpu2(0x00000000)
+#define	RNDIS_STATUS_FAILURE		ccpu2(0xc0000001)
+#define	RNDIS_STATUS_INVALID_DATA	ccpu2(0xc0010015)
+#define	RNDIS_STATUS_NOT_SUPPORTED	ccpu2(0xc00000bb)
+#define	RNDIS_STATUS_MEDIA_CONNECT	ccpu2(0x4001000b)
+#define	RNDIS_STATUS_MEDIA_DISCONNECT	ccpu2(0x4001000c)
+
+
+struct rndis_data_hdr {
+	__le32	msg_type;		/* RNDIS_MSG_PACKET */
+	__le32	msg_len;		// rndis_data_hdr + data_len + pad
+	__le32	data_offset;		// 36 -- right after header
+	__le32	data_len;		// ... real packet size
+
+	__le32	oob_data_offset;	// zero
+	__le32	oob_data_len;		// zero
+	__le32	num_oob;		// zero
+	__le32	packet_data_offset;	// zero
+
+	__le32	packet_data_len;	// zero
+	__le32	vc_handle;		// zero
+	__le32	reserved;		// zero
+} __attribute__ ((packed));
+
+struct rndis_init {		/* OUT */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_INIT */
+	__le32	msg_len;			// 24
+	__le32	request_id;
+	__le32	major_version;			// of rndis (1.0)
+	__le32	minor_version;
+	__le32	max_transfer_size;
+} __attribute__ ((packed));
+
+struct rndis_init_c {		/* IN */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_INIT_C */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	status;
+	__le32	major_version;			// of rndis (1.0)
+	__le32	minor_version;
+	__le32	device_flags;
+	__le32	medium;				// zero == 802.3
+	__le32	max_packets_per_message;
+	__le32	max_transfer_size;
+	__le32	packet_alignment;		// max 7; (1<<n) bytes
+	__le32	af_list_offset;			// zero
+	__le32	af_list_size;			// zero
+} __attribute__ ((packed));
+
+struct rndis_halt {		/* OUT (no reply) */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_HALT */
+	__le32	msg_len;
+	__le32	request_id;
+} __attribute__ ((packed));
+
+struct rndis_query {		/* OUT */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_QUERY */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	oid;
+	__le32	len;
+	__le32	offset;
+/*?*/	__le32	handle;				// zero
+} __attribute__ ((packed));
+
+struct rndis_query_c {		/* IN */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_QUERY_C */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	status;
+	__le32	len;
+	__le32	offset;
+} __attribute__ ((packed));
+
+struct rndis_set {		/* OUT */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_SET */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	oid;
+	__le32	len;
+	__le32	offset;
+/*?*/	__le32	handle;				// zero
+} __attribute__ ((packed));
+
+struct rndis_set_c {		/* IN */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_SET_C */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	status;
+} __attribute__ ((packed));
+
+struct rndis_reset {		/* IN */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_RESET */
+	__le32	msg_len;
+	__le32	reserved;
+} __attribute__ ((packed));
+
+struct rndis_reset_c {		/* OUT */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_RESET_C */
+	__le32	msg_len;
+	__le32	status;
+	__le32	addressing_lost;
+} __attribute__ ((packed));
+
+struct rndis_indicate {		/* IN (unrequested) */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_INDICATE */
+	__le32	msg_len;
+	__le32	status;
+	__le32	length;
+	__le32	offset;
+/**/	__le32	diag_status;
+	__le32	error_offset;
+/**/	__le32	message;
+} __attribute__ ((packed));
+
+struct rndis_keepalive {	/* OUT (optionally IN) */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_KEEPALIVE */
+	__le32	msg_len;
+	__le32	request_id;
+} __attribute__ ((packed));
+
+struct rndis_keepalive_c {	/* IN (optionally OUT) */
+	// header and:
+	__le32	msg_type;			/* RNDIS_MSG_KEEPALIVE_C */
+	__le32	msg_len;
+	__le32	request_id;
+	__le32	status;
+} __attribute__ ((packed));
+
+/* NOTE:  about 30 OIDs are "mandatory" for peripherals to support ... and
+ * there are gobs more that may optionally be supported.  We'll avoid as much
+ * of that mess as possible.
+ */
+#define OID_802_3_PERMANENT_ADDRESS	ccpu2(0x01010101)
+#define OID_GEN_CURRENT_PACKET_FILTER	ccpu2(0x0001010e)
+
+/*
+ * RNDIS notifications from device: command completion; "reverse"
+ * keepalives; etc
+ */
+static void rndis_status(struct usbnet *dev, struct urb *urb)
+{
+	devdbg(dev, "rndis status urb, len %d stat %d",
+		urb->actual_length, urb->status);
+	// FIXME for keepalives, respond immediately (asynchronously)
+	// if not an RNDIS status, do like cdc_status(dev,urb) does
+}
+
+/*
+ * RPC done RNDIS-style.  Caller guarantees:
+ * - message is properly byteswapped
+ * - there's no other request pending
+ * - buf can hold up to 1KB response (required by RNDIS spec)
+ * On return, the first few entries are already byteswapped.
+ *
+ * Call context is likely probe(), before interface name is known,
+ * which is why we won't try to use it in the diagnostics.
+ */
+static int rndis_command(struct usbnet *dev, struct rndis_msg_hdr *buf)
+{
+	struct cdc_state	*info = (void *) &dev->data;
+	int			retval;
+	unsigned		count;
+	__le32			rsp;
+	u32			xid = 0, msg_len, request_id;
+
+	/* REVISIT when this gets called from contexts other than probe() or
+	 * disconnect(): either serialize, or dispatch responses on xid
+	 */
+
+	/* Issue the request; don't bother byteswapping our xid */
+	if (likely(buf->msg_type != RNDIS_MSG_HALT
+			&& buf->msg_type != RNDIS_MSG_RESET)) {
+		xid = dev->xid++;
+		if (!xid)
+			xid = dev->xid++;
+		buf->request_id = (__force __le32) xid;
+	}
+	retval = usb_control_msg(dev->udev,
+		usb_sndctrlpipe(dev->udev, 0),
+		USB_CDC_SEND_ENCAPSULATED_COMMAND,
+		USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+		0, info->u->bMasterInterface0,
+		buf, le32_to_cpu(buf->msg_len),
+		RNDIS_CONTROL_TIMEOUT_MS);
+	if (unlikely(retval < 0 || xid == 0))
+		return retval;
+
+	// REVISIT:  seems like some devices discard responses when
+	// we time out and cancel our "get response" requests...
+
+	/* ignore status endpoint, just poll the control channel;
+	 * the request probably completed immediately
+	 */
+	rsp = buf->msg_type | RNDIS_MSG_COMPLETION;
+	for (count = 0; count < 10; count++) {
+		memset(buf, 0, 1024);
+		retval = usb_control_msg(dev->udev,
+			usb_rcvctrlpipe(dev->udev, 0),
+			USB_CDC_GET_ENCAPSULATED_RESPONSE,
+			USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+			0, info->u->bMasterInterface0,
+			buf, 1024,
+			RNDIS_CONTROL_TIMEOUT_MS);
+		if (likely(retval >= 8)) {
+			msg_len = le32_to_cpu(buf->msg_len);
+			request_id = (__force u32) buf->request_id;
+			if (likely(buf->msg_type == rsp)) {
+				if (likely(request_id == xid)) {
+					if (unlikely(rsp == RNDIS_MSG_RESET_C))
+						return 0;
+					if (likely(RNDIS_STATUS_SUCCESS
+							== buf->status))
+						return 0;
+					dev_dbg(&info->control->dev,
+						"rndis reply status %08x\n",
+						le32_to_cpu(buf->status));
+					return -EL3RST;
+				}
+				dev_dbg(&info->control->dev,
+					"rndis reply id %d expected %d\n",
+					request_id, xid);
+				/* then likely retry */
+			} else switch (buf->msg_type) {
+			case RNDIS_MSG_INDICATE: {	/* fault */
+				// struct rndis_indicate *msg = (void *)buf;
+				dev_info(&info->control->dev,
+					 "rndis fault indication\n");
+				}
+				break;
+			case RNDIS_MSG_KEEPALIVE: {	/* ping */
+				struct rndis_keepalive_c *msg = (void *)buf;
+
+				msg->msg_type = RNDIS_MSG_KEEPALIVE_C;
+				msg->msg_len = ccpu2(sizeof *msg);
+				msg->status = RNDIS_STATUS_SUCCESS;
+				retval = usb_control_msg(dev->udev,
+					usb_sndctrlpipe(dev->udev, 0),
+					USB_CDC_SEND_ENCAPSULATED_COMMAND,
+					USB_TYPE_CLASS | USB_RECIP_INTERFACE,
+					0, info->u->bMasterInterface0,
+					msg, sizeof *msg,
+					RNDIS_CONTROL_TIMEOUT_MS);
+				if (unlikely(retval < 0))
+					dev_dbg(&info->control->dev,
+						"rndis keepalive err %d\n",
+						retval);
+				}
+				break;
+			default:
+				dev_dbg(&info->control->dev,
+					"unexpected rndis msg %08x len %d\n",
+					le32_to_cpu(buf->msg_type), msg_len);
+			}
+		} else {
+			/* device probably issued a protocol stall; ignore */
+			dev_dbg(&info->control->dev,
+				"rndis response error, code %d\n", retval);
+		}
+		msleep(2);
+	}
+	dev_dbg(&info->control->dev, "rndis response timeout\n");
+	return -ETIMEDOUT;
+}
+
+static int rndis_bind(struct usbnet *dev, struct usb_interface *intf)
+{
+	int			retval;
+	struct net_device	*net = dev->net;
+	union {
+		void			*buf;
+		struct rndis_msg_hdr	*header;
+		struct rndis_init	*init;
+		struct rndis_init_c	*init_c;
+		struct rndis_query	*get;
+		struct rndis_query_c	*get_c;
+		struct rndis_set	*set;
+		struct rndis_set_c	*set_c;
+	} u;
+	u32			tmp;
+
+	/* we can't rely on i/o from stack working, or stack allocation */
+	u.buf = kmalloc(1024, GFP_KERNEL);
+	if (!u.buf)
+		return -ENOMEM;
+	retval = usbnet_generic_cdc_bind(dev, intf);
+	if (retval < 0)
+		goto done;
+
+	net->hard_header_len += sizeof (struct rndis_data_hdr);
+
+	/* initialize; max transfer is 16KB at full speed */
+	u.init->msg_type = RNDIS_MSG_INIT;
+	u.init->msg_len = ccpu2(sizeof *u.init);
+	u.init->major_version = ccpu2(1);
+	u.init->minor_version = ccpu2(0);
+	u.init->max_transfer_size = ccpu2(net->mtu + net->hard_header_len);
+
+	retval = rndis_command(dev, u.header);
+	if (unlikely(retval < 0)) {
+		/* it might not even be an RNDIS device!! */
+		dev_err(&intf->dev, "RNDIS init failed, %d\n", retval);
+fail:
+		usb_driver_release_interface(driver_of(intf),
+			((struct cdc_state *)&(dev->data))->data);
+		goto done;
+	}
+	dev->hard_mtu = le32_to_cpu(u.init_c->max_transfer_size);
+	/* REVISIT:  peripheral "alignment" request is ignored ... */
+	dev_dbg(&intf->dev, "hard mtu %u, align %d\n", dev->hard_mtu,
+		1 << le32_to_cpu(u.init_c->packet_alignment));
+
+	/* get designated host ethernet address */
+	memset(u.get, 0, sizeof *u.get);
+	u.get->msg_type = RNDIS_MSG_QUERY;
+	u.get->msg_len = ccpu2(sizeof *u.get);
+	u.get->oid = OID_802_3_PERMANENT_ADDRESS;
+
+	retval = rndis_command(dev, u.header);
+	if (unlikely(retval < 0)) {
+		dev_err(&intf->dev, "rndis get ethaddr, %d\n", retval);
+		goto fail;
+	}
+	tmp = le32_to_cpu(u.get_c->offset);
+	if (unlikely((tmp + 8) > (1024 - ETH_ALEN)
+			|| u.get_c->len != ccpu2(ETH_ALEN))) {
+		dev_err(&intf->dev, "rndis ethaddr off %d len %d ?\n",
+			tmp, le32_to_cpu(u.get_c->len));
+		retval = -EDOM;
+		goto fail;
+	}
+	memcpy(net->dev_addr, tmp + (char *)&u.get_c->request_id, ETH_ALEN);
+
+	/* set a nonzero filter to enable data transfers */
+	memset(u.set, 0, sizeof *u.set);
+	u.set->msg_type = RNDIS_MSG_SET;
+	u.set->msg_len = ccpu2(4 + sizeof *u.set);
+	u.set->oid = OID_GEN_CURRENT_PACKET_FILTER;
+	u.set->len = ccpu2(4);
+	u.set->offset = ccpu2((sizeof *u.set) - 8);
+	*(__le32 *)(u.buf + sizeof *u.set) = ccpu2(DEFAULT_FILTER);
+
+	retval = rndis_command(dev, u.header);
+	if (unlikely(retval < 0)) {
+		dev_err(&intf->dev, "rndis set packet filter, %d\n", retval);
+		goto fail;
+	}
+
+	retval = 0;
+done:
+	kfree(u.buf);
+	return retval;
+}
+
+static void rndis_unbind(struct usbnet *dev, struct usb_interface *intf)
+{
+	struct rndis_halt	*halt;
+
+	/* try to clear any rndis state/activity (no i/o from stack!) */
+	halt = kcalloc(1, sizeof *halt, SLAB_KERNEL);
+	if (halt) {
+		halt->msg_type = RNDIS_MSG_HALT;
+		halt->msg_len = ccpu2(sizeof *halt);
+		(void) rndis_command(dev, (void *)halt);
+		kfree(halt);
+	}
+
+	return usbnet_cdc_unbind(dev, intf);
+}
+
+/*
+ * DATA -- host must not write zlps
+ */
+static int rndis_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
+{
+	/* peripheral may have batched packets to us... */
+	while (likely(skb->len)) {
+		struct rndis_data_hdr	*hdr = (void *)skb->data;
+		struct sk_buff		*skb2;
+		u32			msg_len, data_offset, data_len;
+
+		msg_len = le32_to_cpu(hdr->msg_len);
+		data_offset = le32_to_cpu(hdr->data_offset);
+		data_len = le32_to_cpu(hdr->data_len);
+
+		/* don't choke if we see oob, per-packet data, etc */
+		if (unlikely(hdr->msg_type != RNDIS_MSG_PACKET
+				|| skb->len < msg_len
+				|| (data_offset + data_len + 8) > msg_len)) {
+			dev->stats.rx_frame_errors++;
+			devdbg(dev, "bad rndis message %d/%d/%d/%d, len %d",
+				le32_to_cpu(hdr->msg_type),
+				msg_len, data_offset, data_len, skb->len);
+			return 0;
+		}
+		skb_pull(skb, 8 + data_offset);
+
+		/* at most one packet left? */
+		if (likely((data_len - skb->len) <= sizeof *hdr)) {
+			skb_trim(skb, data_len);
+			break;
+		}
+
+		/* try to return all the packets in the batch */
+		skb2 = skb_clone(skb, GFP_ATOMIC);
+		if (unlikely(!skb2))
+			break;
+		skb_pull(skb, msg_len - sizeof *hdr);
+		skb_trim(skb2, data_len);
+		usbnet_skb_return(dev, skb2);
+	}
+
+	/* caller will usbnet_skb_return the remaining packet */
+	return 1;
+}
+
+static struct sk_buff *
+rndis_tx_fixup(struct usbnet *dev, struct sk_buff *skb, unsigned flags)
+{
+	struct rndis_data_hdr	*hdr;
+	struct sk_buff		*skb2;
+	unsigned		len = skb->len;
+
+	if (likely(!skb_cloned(skb))) {
+		int	room = skb_headroom(skb);
+
+		/* enough head room as-is? */
+		if (unlikely((sizeof *hdr) <= room))
+			goto fill;
+
+		/* enough room, but needs to be readjusted? */
+		room += skb_tailroom(skb);
+		if (likely((sizeof *hdr) <= room)) {
+			skb->data = memmove(skb->head + sizeof *hdr,
+					    skb->data, len);
+			skb->tail = skb->data + len;
+			goto fill;
+		}
+	}
+
+	/* create a new skb, with the correct size (and tailpad) */
+	skb2 = skb_copy_expand(skb, sizeof *hdr, 1, flags);
+	dev_kfree_skb_any(skb);
+	if (unlikely(!skb2))
+		return skb2;
+	skb = skb2;
+
+	/* fill out the RNDIS header.  we won't bother trying to batch
+	 * packets; Linux minimizes wasted bandwidth through tx queues.
+	 */
+fill:
+	hdr = (void *) __skb_push(skb, sizeof *hdr);
+	memset(hdr, 0, sizeof *hdr);
+	hdr->msg_type = RNDIS_MSG_PACKET;
+	hdr->msg_len = cpu_to_le32(skb->len);
+	hdr->data_offset = ccpu2(sizeof(*hdr) - 8);
+	hdr->data_len = cpu_to_le32(len);
+
+	/* FIXME make the last packet always be short ... */
+	return skb;
+}
+
+
+static const struct driver_info	rndis_info = {
+	.description =	"RNDIS device",
+	.flags =	FLAG_ETHER | FLAG_FRAMING_RN,
+	.bind =		rndis_bind,
+	.unbind =	rndis_unbind,
+	.status =	rndis_status,
+	.rx_fixup =	rndis_rx_fixup,
+	.tx_fixup =	rndis_tx_fixup,
+};
+
+#undef ccpu2
+
+
+/*-------------------------------------------------------------------------*/
+
+static const struct usb_device_id	products [] = {
+{
+	/* RNDIS is MSFT's un-official variant of CDC ACM */
+	USB_INTERFACE_INFO(USB_CLASS_COMM, 2 /* ACM */, 0x0ff),
+	.driver_info = (unsigned long) &rndis_info,
+},
+	{ },		// END
+};
+MODULE_DEVICE_TABLE(usb, products);
+
+static struct usb_driver rndis_driver = {
+	.owner =	THIS_MODULE,
+	.name =		"rndis",
+	.id_table =	products,
+	.probe =	usbnet_probe,
+	.disconnect =	usbnet_disconnect,
+	.suspend =	usbnet_suspend,
+	.resume =	usbnet_resume,
+};
+
+static int __init rndis_init(void)
+{
+ 	return usb_register(&rndis_driver);
+}
+module_init(rndis_init);
+
+static void __exit rndis_exit(void)
+{
+ 	usb_deregister(&rndis_driver);
+}
+module_exit(rndis_exit);
+
+MODULE_AUTHOR("David Brownell");
+MODULE_DESCRIPTION("USB Host side RNDIS driver");
+MODULE_LICENSE("GPL");