Staging: USB/IP: add host driver

This adds the USB IP client driver

Brian Merrell cleaned up a lot of this code and submitted it for
inclusion.  Greg also did a lot of cleanup.
Signed-off-by: Brian G. Merrell <bgmerrell@novell.com>
Cc: Takahiro Hirofuchi <hirofuchi@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/usbip/Kconfig

@@ -23,3 +23,14 @@ config USB_IP_VHCI_HCD
 
 	 To compile this driver as a module, choose M here: the
 	 module will be called vhci_hcd.
+
+config USB_IP_HOST
+	tristate "USB IP host driver"
+	depends on USB_IP_COMMON
+	default N
+	---help---
+	 This enables the USB IP device driver which will run on the
+	 host machine.
+
+	 To compile this driver as a module, choose M here: the
+	 module will be called usbip.

drivers/staging/usbip/Makefile

@@ -4,6 +4,9 @@ usbip_common_mod-objs := usbip_common.o usbip_event.o
 obj-$(CONFIG_USB_IP_VHCI_HCD) += vhci-hcd.o
 vhci-hcd-objs := vhci_sysfs.o vhci_tx.o vhci_rx.o vhci_hcd.o
 
+obj-$(CONFIG_USB_IP_HOST) += usbip.o
+usbip-objs := stub_dev.o stub_main.o stub_rx.o stub_tx.o
+
 ifeq ($(CONFIG_USB_DEBUG),y)
 	EXTRA_CFLAGS += -DDEBUG
 endif

drivers/staging/usbip/stub.h

+/*
+ * Copyright (C) 2003-2008 Takahiro Hirofuchi
+ *
+ * This 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 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.
+ */
+
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/module.h>
+#include <linux/net.h>
+
+struct stub_device {
+	struct usb_interface *interface;
+	struct list_head list;
+
+	struct usbip_device ud;
+	__u32 devid;
+
+	/*
+	 * stub_priv preserves private data of each urb.
+	 * It is allocated as stub_priv_cache and assigned to urb->context.
+	 *
+	 * stub_priv is always linked to any one of 3 lists;
+	 *	priv_init: linked to this until the comletion of a urb.
+	 *	priv_tx  : linked to this after the completion of a urb.
+	 *	priv_free: linked to this after the sending of the result.
+	 *
+	 * Any of these list operations should be locked by priv_lock.
+	 */
+	spinlock_t priv_lock;
+	struct list_head priv_init;
+	struct list_head priv_tx;
+	struct list_head priv_free;
+
+	/* see comments for unlinking in stub_rx.c */
+	struct list_head unlink_tx;
+	struct list_head unlink_free;
+
+
+	wait_queue_head_t tx_waitq;
+};
+
+/* private data into urb->priv */
+struct stub_priv {
+	unsigned long seqnum;
+	struct list_head list;
+	struct stub_device *sdev;
+	struct urb *urb;
+
+	int unlinking;
+};
+
+struct stub_unlink {
+	unsigned long seqnum;
+	struct list_head list;
+	__u32 status;
+};
+
+
+extern struct kmem_cache *stub_priv_cache;
+
+
+/*-------------------------------------------------------------------------*/
+/* prototype declarations */
+
+/* stub_tx.c */
+void stub_complete(struct urb *);
+void stub_tx_loop(struct usbip_task *);
+
+/* stub_dev.c */
+extern struct usb_driver stub_driver;
+
+/* stub_rx.c */
+void stub_rx_loop(struct usbip_task *);
+void stub_enqueue_ret_unlink(struct stub_device *, __u32, __u32);
+
+/* stub_main.c */
+int match_busid(char *busid);
+void stub_device_cleanup_urbs(struct stub_device *sdev);

drivers/staging/usbip/stub_main.c

+/*
+ * Copyright (C) 2003-2008 Takahiro Hirofuchi
+ *
+ * This 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 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.
+ */
+
+
+#include "usbip_common.h"
+#include "stub.h"
+
+/* Version Information */
+#define DRIVER_VERSION "1.0"
+#define DRIVER_AUTHOR "Takahiro Hirofuchi"
+#define DRIVER_DESC "Stub Driver for USB/IP"
+
+/* stub_priv is allocated from stub_priv_cache */
+struct kmem_cache *stub_priv_cache;
+
+/*-------------------------------------------------------------------------*/
+
+/* Define sysfs entries for the usbip driver */
+
+
+/*
+ * busid_tables defines matching busids that usbip can grab. A user can change
+ * dynamically what device is locally used and what device is exported to a
+ * remote host.
+ */
+#define MAX_BUSID 16
+static char busid_table[MAX_BUSID][BUS_ID_SIZE];
+static spinlock_t busid_table_lock;
+
+
+int match_busid(char *busid)
+{
+	int i;
+
+	spin_lock(&busid_table_lock);
+
+	for (i = 0; i < MAX_BUSID; i++)
+		if (busid_table[i][0])
+			if (!strncmp(busid_table[i], busid, BUS_ID_SIZE)) {
+				/* already registerd */
+				spin_unlock(&busid_table_lock);
+				return 0;
+			}
+
+	spin_unlock(&busid_table_lock);
+
+	return 1;
+}
+
+static ssize_t show_match_busid(struct device_driver *drv, char *buf)
+{
+	int i;
+	char *out = buf;
+
+	spin_lock(&busid_table_lock);
+
+	for (i = 0; i < MAX_BUSID; i++)
+		if (busid_table[i][0])
+			out += sprintf(out, "%s ", busid_table[i]);
+
+	spin_unlock(&busid_table_lock);
+
+	out += sprintf(out, "\n");
+
+	return out - buf;
+}
+
+static int add_match_busid(char *busid)
+{
+	int i;
+
+	if (!match_busid(busid))
+		return 0;
+
+	spin_lock(&busid_table_lock);
+
+	for (i = 0; i < MAX_BUSID; i++)
+		if (!busid_table[i][0]) {
+			strncpy(busid_table[i], busid, BUS_ID_SIZE);
+			spin_unlock(&busid_table_lock);
+			return 0;
+		}
+
+	spin_unlock(&busid_table_lock);
+
+	return -1;
+}
+
+static int del_match_busid(char *busid)
+{
+	int i;
+
+	spin_lock(&busid_table_lock);
+
+	for (i = 0; i < MAX_BUSID; i++)
+		if (!strncmp(busid_table[i], busid, BUS_ID_SIZE)) {
+			/* found */
+			memset(busid_table[i], 0, BUS_ID_SIZE);
+			spin_unlock(&busid_table_lock);
+			return 0;
+		}
+
+	spin_unlock(&busid_table_lock);
+
+	return -1;
+}
+
+static ssize_t store_match_busid(struct device_driver *dev, const char *buf,
+		size_t count)
+{
+	int len;
+	char busid[BUS_ID_SIZE];
+
+	if (count < 5)
+		return -EINVAL;
+
+	/* strnlen() does not include \0 */
+	len = strnlen(buf + 4, BUS_ID_SIZE);
+
+	/* busid needs to include \0 termination */
+	if (!(len < BUS_ID_SIZE))
+		return -EINVAL;
+
+	strncpy(busid, buf + 4, BUS_ID_SIZE);
+
+
+	if (!strncmp(buf, "add ", 4)) {
+		if (add_match_busid(busid) < 0)
+			return -ENOMEM;
+		else {
+			udbg("add busid %s\n", busid);
+			return count;
+		}
+	} else if (!strncmp(buf, "del ", 4)) {
+		if (del_match_busid(busid) < 0)
+			return -ENODEV;
+		else {
+			udbg("del busid %s\n", busid);
+			return count;
+		}
+	} else
+		return -EINVAL;
+}
+
+static DRIVER_ATTR(match_busid, S_IRUSR|S_IWUSR, show_match_busid,
+							store_match_busid);
+
+
+
+/*-------------------------------------------------------------------------*/
+
+/* Cleanup functions used to free private data */
+
+static struct stub_priv *stub_priv_pop_from_listhead(struct list_head *listhead)
+{
+	struct stub_priv *priv, *tmp;
+
+	list_for_each_entry_safe(priv, tmp, listhead, list) {
+		list_del(&priv->list);
+		return priv;
+	}
+
+	return NULL;
+}
+
+static struct stub_priv *stub_priv_pop(struct stub_device *sdev)
+{
+	unsigned long flags;
+	struct stub_priv *priv;
+
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	priv = stub_priv_pop_from_listhead(&sdev->priv_init);
+	if (priv) {
+		spin_unlock_irqrestore(&sdev->priv_lock, flags);
+		return priv;
+	}
+
+	priv = stub_priv_pop_from_listhead(&sdev->priv_tx);
+	if (priv) {
+		spin_unlock_irqrestore(&sdev->priv_lock, flags);
+		return priv;
+	}
+
+	priv = stub_priv_pop_from_listhead(&sdev->priv_free);
+	if (priv) {
+		spin_unlock_irqrestore(&sdev->priv_lock, flags);
+		return priv;
+	}
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+	return NULL;
+}
+
+void stub_device_cleanup_urbs(struct stub_device *sdev)
+{
+	struct stub_priv *priv;
+
+	udbg("free sdev %p\n", sdev);
+
+	while ((priv = stub_priv_pop(sdev))) {
+		struct urb *urb = priv->urb;
+
+		udbg("   free urb %p\n", urb);
+		usb_kill_urb(urb);
+
+		kmem_cache_free(stub_priv_cache, priv);
+
+		if (urb->transfer_buffer != NULL)
+			kfree(urb->transfer_buffer);
+
+		if (urb->setup_packet != NULL)
+			kfree(urb->setup_packet);
+
+		usb_free_urb(urb);
+	}
+}
+
+
+/*-------------------------------------------------------------------------*/
+
+static int __init usb_stub_init(void)
+{
+	int ret;
+
+	stub_priv_cache = kmem_cache_create("stub_priv",
+					    sizeof(struct stub_priv), 0,
+					    SLAB_HWCACHE_ALIGN, NULL);
+
+	if (!stub_priv_cache) {
+		printk(KERN_ERR KBUILD_MODNAME
+		       ": create stub_priv_cache error\n");
+		return -ENOMEM;
+	}
+
+	ret = usb_register(&stub_driver);
+	if (ret) {
+		printk(KERN_ERR KBUILD_MODNAME ": usb_register failed %d\n",
+		       ret);
+		goto error_usb_register;
+	}
+
+	printk(KERN_INFO KBUILD_MODNAME ":"
+	       DRIVER_DESC ":" DRIVER_VERSION "\n");
+
+	memset(busid_table, 0, sizeof(busid_table));
+	spin_lock_init(&busid_table_lock);
+
+	ret = driver_create_file(&stub_driver.drvwrap.driver,
+				 &driver_attr_match_busid);
+
+	if (ret) {
+		printk(KERN_ERR KBUILD_MODNAME ": create driver sysfs\n");
+		goto error_create_file;
+	}
+
+	return ret;
+error_create_file:
+	usb_deregister(&stub_driver);
+error_usb_register:
+	kmem_cache_destroy(stub_priv_cache);
+	return ret;
+}
+
+static void __exit usb_stub_exit(void)
+{
+	driver_remove_file(&stub_driver.drvwrap.driver,
+			   &driver_attr_match_busid);
+
+	/*
+	 * deregister() calls stub_disconnect() for all devices. Device
+	 * specific data is cleared in stub_disconnect().
+	 */
+	usb_deregister(&stub_driver);
+
+	kmem_cache_destroy(stub_priv_cache);
+}
+
+module_init(usb_stub_init);
+module_exit(usb_stub_exit);
+
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");

drivers/staging/usbip/stub_tx.c

+/*
+ * Copyright (C) 2003-2008 Takahiro Hirofuchi
+ *
+ * This 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 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.
+ */
+
+#include "usbip_common.h"
+#include "stub.h"
+
+
+static void stub_free_priv_and_urb(struct stub_priv *priv)
+{
+	struct urb *urb = priv->urb;
+
+	kfree(urb->setup_packet);
+	kfree(urb->transfer_buffer);
+	list_del(&priv->list);
+	kmem_cache_free(stub_priv_cache, priv);
+	usb_free_urb(urb);
+}
+
+/* be in spin_lock_irqsave(&sdev->priv_lock, flags) */
+void stub_enqueue_ret_unlink(struct stub_device *sdev, __u32 seqnum,
+			     __u32 status)
+{
+	struct stub_unlink *unlink;
+
+	unlink = kzalloc(sizeof(struct stub_unlink), GFP_ATOMIC);
+	if (!unlink) {
+		dev_err(&sdev->interface->dev, "alloc stub_unlink\n");
+		usbip_event_add(&sdev->ud, VDEV_EVENT_ERROR_MALLOC);
+		return;
+	}
+
+	unlink->seqnum = seqnum;
+	unlink->status = status;
+
+	list_add_tail(&unlink->list, &sdev->unlink_tx);
+}
+
+/**
+ * stub_complete - completion handler of a usbip urb
+ * @urb: pointer to the urb completed
+ * @regs:
+ *
+ * When a urb has completed, the USB core driver calls this function mostly in
+ * the interrupt context. To return the result of a urb, the completed urb is
+ * linked to the pending list of returning.
+ *
+ */
+void stub_complete(struct urb *urb)
+{
+	struct stub_priv *priv = (struct stub_priv *) urb->context;
+	struct stub_device *sdev = priv->sdev;
+	unsigned long flags;
+
+	dbg_stub_tx("complete! status %d\n", urb->status);
+
+
+	switch (urb->status) {
+	case 0:
+		/* OK */
+		break;
+	case -ENOENT:
+		uinfo("stopped by a call of usb_kill_urb() because of"
+					"cleaning up a virtual connection\n");
+		return;
+	case -ECONNRESET:
+		uinfo("unlinked by a call of usb_unlink_urb()\n");
+		break;
+	case -EPIPE:
+		uinfo("endpoint %d is stalled\n", usb_pipeendpoint(urb->pipe));
+		break;
+	case -ESHUTDOWN:
+		uinfo("device removed?\n");
+		break;
+	default:
+		uinfo("urb completion with non-zero status %d\n", urb->status);
+	}
+
+	/* link a urb to the queue of tx. */
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	if (priv->unlinking) {
+		stub_enqueue_ret_unlink(sdev, priv->seqnum, urb->status);
+		stub_free_priv_and_urb(priv);
+	} else
+		list_move_tail(&priv->list, &sdev->priv_tx);
+
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+
+	/* wake up tx_thread */
+	wake_up(&sdev->tx_waitq);
+}
+
+
+/*-------------------------------------------------------------------------*/
+/* fill PDU */
+
+static inline void setup_base_pdu(struct usbip_header_basic *base,
+		__u32 command, __u32 seqnum)
+{
+	base->command = command;
+	base->seqnum  = seqnum;
+	base->devid   = 0;
+	base->ep      = 0;
+	base->direction   = 0;
+}
+
+static void setup_ret_submit_pdu(struct usbip_header *rpdu, struct urb *urb)
+{
+	struct stub_priv *priv = (struct stub_priv *) urb->context;
+
+	setup_base_pdu(&rpdu->base, USBIP_RET_SUBMIT, priv->seqnum);
+
+	usbip_pack_pdu(rpdu, urb, USBIP_RET_SUBMIT, 1);
+}
+
+static void setup_ret_unlink_pdu(struct usbip_header *rpdu,
+		struct stub_unlink *unlink)
+{
+	setup_base_pdu(&rpdu->base, USBIP_RET_UNLINK, unlink->seqnum);
+
+	rpdu->u.ret_unlink.status = unlink->status;
+}
+
+
+/*-------------------------------------------------------------------------*/
+/* send RET_SUBMIT */
+
+static struct stub_priv *dequeue_from_priv_tx(struct stub_device *sdev)
+{
+	unsigned long flags;
+	struct stub_priv *priv, *tmp;
+
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	list_for_each_entry_safe(priv, tmp, &sdev->priv_tx, list) {
+		list_move_tail(&priv->list, &sdev->priv_free);
+		spin_unlock_irqrestore(&sdev->priv_lock, flags);
+		return priv;
+	}
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+
+	return NULL;
+}
+
+static int stub_send_ret_submit(struct stub_device *sdev)
+{
+	unsigned long flags;
+	struct stub_priv *priv, *tmp;
+
+	struct msghdr msg;
+	struct kvec iov[3];
+	size_t txsize;
+
+	size_t total_size = 0;
+
+	while ((priv = dequeue_from_priv_tx(sdev)) != NULL) {
+		int ret;
+		struct urb *urb = priv->urb;
+		struct usbip_header pdu_header;
+		void *iso_buffer = NULL;
+
+		txsize = 0;
+		memset(&pdu_header, 0, sizeof(pdu_header));
+		memset(&msg, 0, sizeof(msg));
+		memset(&iov, 0, sizeof(iov));
+
+		dbg_stub_tx("setup txdata urb %p\n", urb);
+
+
+		/* 1. setup usbip_header */
+		setup_ret_submit_pdu(&pdu_header, urb);
+		usbip_header_correct_endian(&pdu_header, 1);
+
+		iov[0].iov_base = &pdu_header;
+		iov[0].iov_len  = sizeof(pdu_header);
+		txsize += sizeof(pdu_header);
+
+		/* 2. setup transfer buffer */
+		if (usb_pipein(urb->pipe) && urb->actual_length > 0) {
+			iov[1].iov_base = urb->transfer_buffer;
+			iov[1].iov_len  = urb->actual_length;
+			txsize += urb->actual_length;
+		}
+
+		/* 3. setup iso_packet_descriptor */
+		if (usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS) {
+			ssize_t len = 0;
+
+			iso_buffer = usbip_alloc_iso_desc_pdu(urb, &len);
+			if (!iso_buffer) {
+				usbip_event_add(&sdev->ud,
+						SDEV_EVENT_ERROR_MALLOC);
+				return -1;
+			}
+
+			iov[2].iov_base = iso_buffer;
+			iov[2].iov_len  = len;
+			txsize += len;
+		}
+
+		ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg, iov,
+				     3, txsize);
+		if (ret != txsize) {
+			dev_err(&sdev->interface->dev,
+				"sendmsg failed!, retval %d for %zd\n",
+				ret, txsize);
+			kfree(iso_buffer);
+			usbip_event_add(&sdev->ud, SDEV_EVENT_ERROR_TCP);
+			return -1;
+		}
+
+		kfree(iso_buffer);
+		dbg_stub_tx("send txdata\n");
+
+		total_size += txsize;
+	}
+
+
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	list_for_each_entry_safe(priv, tmp, &sdev->priv_free, list) {
+		stub_free_priv_and_urb(priv);
+	}
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+
+	return total_size;
+}
+
+
+/*-------------------------------------------------------------------------*/
+/* send RET_UNLINK */
+
+static struct stub_unlink *dequeue_from_unlink_tx(struct stub_device *sdev)
+{
+	unsigned long flags;
+	struct stub_unlink *unlink, *tmp;
+
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	list_for_each_entry_safe(unlink, tmp, &sdev->unlink_tx, list) {
+		list_move_tail(&unlink->list, &sdev->unlink_free);
+		spin_unlock_irqrestore(&sdev->priv_lock, flags);
+		return unlink;
+	}
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+
+	return NULL;
+}
+
+
+static int stub_send_ret_unlink(struct stub_device *sdev)
+{
+	unsigned long flags;
+	struct stub_unlink *unlink, *tmp;
+
+	struct msghdr msg;
+	struct kvec iov[1];
+	size_t txsize;
+
+	size_t total_size = 0;
+
+	while ((unlink = dequeue_from_unlink_tx(sdev)) != NULL) {
+		int ret;
+		struct usbip_header pdu_header;
+
+		txsize = 0;
+		memset(&pdu_header, 0, sizeof(pdu_header));
+		memset(&msg, 0, sizeof(msg));
+		memset(&iov, 0, sizeof(iov));
+
+		dbg_stub_tx("setup ret unlink %lu\n", unlink->seqnum);
+
+		/* 1. setup usbip_header */
+		setup_ret_unlink_pdu(&pdu_header, unlink);
+		usbip_header_correct_endian(&pdu_header, 1);
+
+		iov[0].iov_base = &pdu_header;
+		iov[0].iov_len  = sizeof(pdu_header);
+		txsize += sizeof(pdu_header);
+
+		ret = kernel_sendmsg(sdev->ud.tcp_socket, &msg, iov,
+				     1, txsize);
+		if (ret != txsize) {
+			dev_err(&sdev->interface->dev,
+				"sendmsg failed!, retval %d for %zd\n",
+				ret, txsize);
+			usbip_event_add(&sdev->ud, SDEV_EVENT_ERROR_TCP);
+			return -1;
+		}
+
+
+		dbg_stub_tx("send txdata\n");
+
+		total_size += txsize;
+	}
+
+
+	spin_lock_irqsave(&sdev->priv_lock, flags);
+
+	list_for_each_entry_safe(unlink, tmp, &sdev->unlink_free, list) {
+		list_del(&unlink->list);
+		kfree(unlink);
+	}
+
+	spin_unlock_irqrestore(&sdev->priv_lock, flags);
+
+	return total_size;
+}
+
+
+/*-------------------------------------------------------------------------*/
+
+void stub_tx_loop(struct usbip_task *ut)
+{
+	struct usbip_device *ud = container_of(ut, struct usbip_device, tcp_tx);
+	struct stub_device *sdev = container_of(ud, struct stub_device, ud);
+
+	while (1) {
+		if (signal_pending(current)) {
+			dbg_stub_tx("signal catched\n");
+			break;
+		}
+
+		if (usbip_event_happend(ud))
+			break;
+
+		/*
+		 * send_ret_submit comes earlier than send_ret_unlink.  stub_rx
+		 * looks at only priv_init queue. If the completion of a URB is
+		 * earlier than the receive of CMD_UNLINK, priv is moved to
+		 * priv_tx queue and stub_rx does not find the target priv. In
+		 * this case, vhci_rx receives the result of the submit request
+		 * and then receives the result of the unlink request. The
+		 * result of the submit is given back to the usbcore as the
+		 * completion of the unlink request. The request of the
+		 * unlink is ignored. This is ok because a driver who calls
+		 * usb_unlink_urb() understands the unlink was too late by
+		 * getting the status of the given-backed URB which has the
+		 * status of usb_submit_urb().
+		 */
+		if (stub_send_ret_submit(sdev) < 0)
+			break;
+
+		if (stub_send_ret_unlink(sdev) < 0)
+			break;
+
+		wait_event_interruptible(sdev->tx_waitq,
+				(!list_empty(&sdev->priv_tx) ||
+				 !list_empty(&sdev->unlink_tx)));
+	}
+}