xen: add pvUSB backend

Add a backend for para-virtualized USB devices for xen domains.

The backend is using host-libusb to forward USB requests from a
domain via libusb to the real device(s) passed through.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Message-id: 1463062421-613-4-git-send-email-jgross@suse.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

3 files changed, 1087 insertions, 0 deletions

diff --git a/hw/usb/Makefile.objs b/hw/usb/Makefile.objs
index 2717027d34..98b5c9d273 100644
--- a/hw/usb/Makefile.objs
+++ b/hw/usb/Makefile.objs
@@ -38,3 +38,7 @@ common-obj-$(CONFIG_USB_REDIR) += redirect.o quirks.o
 
 # usb pass-through
 common-obj-y += $(patsubst %,host-%.o,$(HOST_USB))
+
+ifeq ($(CONFIG_USB_LIBUSB),y)
+common-obj-$(CONFIG_XEN_BACKEND) += xen-usb.o
+endif
diff --git a/hw/usb/xen-usb.c b/hw/usb/xen-usb.c
new file mode 100644
index 0000000000..664df04181
--- /dev/null
+++ b/hw/usb/xen-usb.c
@@ -0,0 +1,1080 @@
+/*
+ *  xen paravirt usb device backend
+ *
+ *  (c) Juergen Gross <jgross@suse.com>
+ *
+ *  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; under version 2 of the License.
+ *
+ *  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, see <http://www.gnu.org/licenses/>.
+ *
+ *  Contributions after 2012-01-13 are licensed under the terms of the
+ *  GNU GPL, version 2 or (at your option) any later version.
+ */
+
+#include <libusb.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+#include <sys/time.h>
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qemu/config-file.h"
+#include "hw/sysbus.h"
+#include "hw/usb.h"
+#include "hw/xen/xen_backend.h"
+#include "monitor/qdev.h"
+#include "qapi/qmp/qbool.h"
+#include "qapi/qmp/qint.h"
+#include "qapi/qmp/qstring.h"
+#include "sys/user.h"
+
+#include <xen/io/ring.h>
+#include <xen/io/usbif.h>
+
+/*
+ * Check for required support of usbif.h: USBIF_SHORT_NOT_OK was the last
+ * macro added we rely on.
+ */
+#ifdef USBIF_SHORT_NOT_OK
+
+#define TR(xendev, lvl, fmt, args...)                               \
+    {                                                               \
+        struct timeval tv;                                          \
+                                                                    \
+        gettimeofday(&tv, NULL);                                    \
+        xen_be_printf(xendev, lvl, "%8ld.%06ld xen-usb(%s):" fmt,   \
+                      tv.tv_sec, tv.tv_usec, __func__, ##args);     \
+    }
+#define TR_BUS(xendev, fmt, args...) TR(xendev, 2, fmt, ##args)
+#define TR_REQ(xendev, fmt, args...) TR(xendev, 3, fmt, ##args)
+
+#define USBBACK_MAXPORTS        USBIF_PIPE_PORT_MASK
+#define USB_DEV_ADDR_SIZE       (USBIF_PIPE_DEV_MASK + 1)
+
+/* USB wire protocol: structure describing control request parameter. */
+struct usbif_ctrlrequest {
+    uint8_t    bRequestType;
+    uint8_t    bRequest;
+    uint16_t   wValue;
+    uint16_t   wIndex;
+    uint16_t   wLength;
+};
+
+struct usbback_info;
+struct usbback_req;
+
+struct usbback_stub {
+    USBDevice     *dev;
+    USBPort       port;
+    unsigned int  speed;
+    bool          attached;
+    QTAILQ_HEAD(submit_q_head, usbback_req) submit_q;
+};
+
+struct usbback_req {
+    struct usbback_info      *usbif;
+    struct usbback_stub      *stub;
+    struct usbif_urb_request req;
+    USBPacket                packet;
+
+    unsigned int             nr_buffer_segs; /* # of transfer_buffer segments */
+    unsigned int             nr_extra_segs;  /* # of iso_frame_desc segments  */
+
+    QTAILQ_ENTRY(usbback_req) q;
+
+    void                     *buffer;
+    void                     *isoc_buffer;
+    struct libusb_transfer   *xfer;
+};
+
+struct usbback_hotplug {
+    QSIMPLEQ_ENTRY(usbback_hotplug) q;
+    unsigned                 port;
+};
+
+struct usbback_info {
+    struct XenDevice         xendev;  /* must be first */
+    USBBus                   bus;
+    void                     *urb_sring;
+    void                     *conn_sring;
+    struct usbif_urb_back_ring urb_ring;
+    struct usbif_conn_back_ring conn_ring;
+    int                      num_ports;
+    int                      usb_ver;
+    bool                     ring_error;
+    QTAILQ_HEAD(req_free_q_head, usbback_req) req_free_q;
+    QSIMPLEQ_HEAD(hotplug_q_head, usbback_hotplug) hotplug_q;
+    struct usbback_stub      ports[USBBACK_MAXPORTS];
+    struct usbback_stub      *addr_table[USB_DEV_ADDR_SIZE];
+    QEMUBH                   *bh;
+};
+
+static struct usbback_req *usbback_get_req(struct usbback_info *usbif)
+{
+    struct usbback_req *usbback_req;
+
+    if (QTAILQ_EMPTY(&usbif->req_free_q)) {
+        usbback_req = g_new0(struct usbback_req, 1);
+    } else {
+        usbback_req = QTAILQ_FIRST(&usbif->req_free_q);
+        QTAILQ_REMOVE(&usbif->req_free_q, usbback_req, q);
+    }
+    return usbback_req;
+}
+
+static void usbback_put_req(struct usbback_req *usbback_req)
+{
+    struct usbback_info *usbif;
+
+    usbif = usbback_req->usbif;
+    memset(usbback_req, 0, sizeof(*usbback_req));
+    QTAILQ_INSERT_HEAD(&usbif->req_free_q, usbback_req, q);
+}
+
+static int usbback_gnttab_map(struct usbback_req *usbback_req)
+{
+    unsigned int nr_segs, i, prot;
+    uint32_t ref[USBIF_MAX_SEGMENTS_PER_REQUEST];
+    struct usbback_info *usbif = usbback_req->usbif;
+    struct XenDevice *xendev = &usbif->xendev;
+    struct usbif_request_segment *seg;
+    void *addr;
+
+    nr_segs = usbback_req->nr_buffer_segs + usbback_req->nr_extra_segs;
+    if (!nr_segs) {
+        return 0;
+    }
+
+    if (nr_segs > USBIF_MAX_SEGMENTS_PER_REQUEST) {
+        xen_be_printf(xendev, 0, "bad number of segments in request (%d)\n",
+                      nr_segs);
+        return -EINVAL;
+    }
+
+    for (i = 0; i < nr_segs; i++) {
+        if ((unsigned)usbback_req->req.seg[i].offset +
+            (unsigned)usbback_req->req.seg[i].length > PAGE_SIZE) {
+            xen_be_printf(xendev, 0, "segment crosses page boundary\n");
+            return -EINVAL;
+        }
+    }
+
+    if (usbback_req->nr_buffer_segs) {
+        prot = PROT_READ;
+        if (usbif_pipein(usbback_req->req.pipe)) {
+                prot |= PROT_WRITE;
+        }
+        for (i = 0; i < usbback_req->nr_buffer_segs; i++) {
+            ref[i] = usbback_req->req.seg[i].gref;
+        }
+        usbback_req->buffer = xengnttab_map_domain_grant_refs(xendev->gnttabdev,
+            usbback_req->nr_buffer_segs, xendev->dom, ref, prot);
+
+        if (!usbback_req->buffer) {
+            return -ENOMEM;
+        }
+
+        for (i = 0; i < usbback_req->nr_buffer_segs; i++) {
+            seg = usbback_req->req.seg + i;
+            addr = usbback_req->buffer + i * PAGE_SIZE + seg->offset;
+            qemu_iovec_add(&usbback_req->packet.iov, addr, seg->length);
+        }
+    }
+
+    if (!usbif_pipeisoc(usbback_req->req.pipe)) {
+        return 0;
+    }
+
+    /*
+     * Right now isoc requests are not supported.
+     * Prepare supporting those by doing the work needed on the guest
+     * interface side.
+     */
+
+    if (!usbback_req->nr_extra_segs) {
+        xen_be_printf(xendev, 0, "iso request without descriptor segments\n");
+        return -EINVAL;
+    }
+
+    prot = PROT_READ | PROT_WRITE;
+    for (i = 0; i < usbback_req->nr_extra_segs; i++) {
+        ref[i] = usbback_req->req.seg[i + usbback_req->req.nr_buffer_segs].gref;
+    }
+    usbback_req->isoc_buffer = xengnttab_map_domain_grant_refs(
+         xendev->gnttabdev, usbback_req->nr_extra_segs, xendev->dom, ref, prot);
+
+    if (!usbback_req->isoc_buffer) {
+        return -ENOMEM;
+    }
+
+    return 0;
+}
+
+static int usbback_init_packet(struct usbback_req *usbback_req)
+{
+    struct XenDevice *xendev = &usbback_req->usbif->xendev;
+    USBPacket *packet = &usbback_req->packet;
+    USBDevice *dev = usbback_req->stub->dev;
+    USBEndpoint *ep;
+    unsigned int pid, ep_nr;
+    bool sok;
+    int ret = 0;
+
+    qemu_iovec_init(&packet->iov, USBIF_MAX_SEGMENTS_PER_REQUEST);
+    pid = usbif_pipein(usbback_req->req.pipe) ? USB_TOKEN_IN : USB_TOKEN_OUT;
+    ep_nr = usbif_pipeendpoint(usbback_req->req.pipe);
+    sok = !!(usbback_req->req.transfer_flags & USBIF_SHORT_NOT_OK);
+    if (usbif_pipectrl(usbback_req->req.pipe)) {
+        ep_nr = 0;
+        sok = false;
+    }
+    ep = usb_ep_get(dev, pid, ep_nr);
+    usb_packet_setup(packet, pid, ep, 0, 1, sok, true);
+
+    switch (usbif_pipetype(usbback_req->req.pipe)) {
+    case USBIF_PIPE_TYPE_ISOC:
+        TR_REQ(xendev, "iso transfer %s: buflen: %x, %d frames\n",
+               (pid == USB_TOKEN_IN) ? "in" : "out",
+               usbback_req->req.buffer_length,
+               usbback_req->req.u.isoc.nr_frame_desc_segs);
+        ret = -EINVAL;  /* isoc not implemented yet */
+        break;
+
+    case USBIF_PIPE_TYPE_INT:
+        TR_REQ(xendev, "int transfer %s: buflen: %x\n",
+               (pid == USB_TOKEN_IN) ? "in" : "out",
+               usbback_req->req.buffer_length);
+        break;
+
+    case USBIF_PIPE_TYPE_CTRL:
+        packet->parameter = *(uint64_t *)usbback_req->req.u.ctrl;
+        TR_REQ(xendev, "ctrl parameter: %lx, buflen: %x\n", packet->parameter,
+               usbback_req->req.buffer_length);
+        break;
+
+    case USBIF_PIPE_TYPE_BULK:
+        TR_REQ(xendev, "bulk transfer %s: buflen: %x\n",
+               (pid == USB_TOKEN_IN) ? "in" : "out",
+               usbback_req->req.buffer_length);
+        break;
+    default:
+        ret = -EINVAL;
+        break;
+    }
+
+    return ret;
+}
+
+static void usbback_do_response(struct usbback_req *usbback_req, int32_t status,
+                                int32_t actual_length, int32_t error_count)
+{
+    struct usbback_info *usbif;
+    struct usbif_urb_response *res;
+    struct XenDevice *xendev;
+    unsigned int notify;
+
+    usbif = usbback_req->usbif;
+    xendev = &usbif->xendev;
+
+    TR_REQ(xendev, "id %d, status %d, length %d, errcnt %d\n",
+           usbback_req->req.id, status, actual_length, error_count);
+
+    if (usbback_req->packet.iov.iov) {
+        qemu_iovec_destroy(&usbback_req->packet.iov);
+    }
+
+    if (usbback_req->buffer) {
+        xengnttab_unmap(xendev->gnttabdev, usbback_req->buffer,
+                        usbback_req->nr_buffer_segs);
+        usbback_req->buffer = NULL;
+    }
+
+    if (usbback_req->isoc_buffer) {
+        xengnttab_unmap(xendev->gnttabdev, usbback_req->isoc_buffer,
+                        usbback_req->nr_extra_segs);
+        usbback_req->isoc_buffer = NULL;
+    }
+
+    res = RING_GET_RESPONSE(&usbif->urb_ring, usbif->urb_ring.rsp_prod_pvt);
+    res->id = usbback_req->req.id;
+    res->status = status;
+    res->actual_length = actual_length;
+    res->error_count = error_count;
+    res->start_frame = 0;
+    usbif->urb_ring.rsp_prod_pvt++;
+    RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&usbif->urb_ring, notify);
+
+    if (notify) {
+        xen_be_send_notify(xendev);
+    }
+
+    usbback_put_req(usbback_req);
+}
+
+static void usbback_do_response_ret(struct usbback_req *usbback_req,
+                                    int32_t status)
+{
+    usbback_do_response(usbback_req, status, 0, 0);
+}
+
+static int32_t usbback_xlat_status(int status)
+{
+    switch (status) {
+    case USB_RET_SUCCESS:
+        return 0;
+    case USB_RET_NODEV:
+        return -ENODEV;
+    case USB_RET_STALL:
+        return -EPIPE;
+    case USB_RET_BABBLE:
+        return -EOVERFLOW;
+    case USB_RET_IOERROR:
+        return -EPROTO;
+    }
+
+    return -ESHUTDOWN;
+}
+
+static void usbback_packet_complete(USBPacket *packet)
+{
+    struct usbback_req *usbback_req;
+    int32_t status;
+
+    usbback_req = container_of(packet, struct usbback_req, packet);
+
+    QTAILQ_REMOVE(&usbback_req->stub->submit_q, usbback_req, q);
+
+    status = usbback_xlat_status(packet->status);
+    usbback_do_response(usbback_req, status, packet->actual_length, 0);
+}
+
+static void usbback_set_address(struct usbback_info *usbif,
+                                struct usbback_stub *stub,
+                                unsigned int cur_addr, unsigned int new_addr)
+{
+    if (cur_addr) {
+        usbif->addr_table[cur_addr] = NULL;
+    }
+    if (new_addr) {
+        usbif->addr_table[new_addr] = stub;
+    }
+}
+
+static bool usbback_cancel_req(struct usbback_req *usbback_req)
+{
+    bool ret = false;
+
+    if (usb_packet_is_inflight(&usbback_req->packet)) {
+        usb_cancel_packet(&usbback_req->packet);
+        ret = true;
+    }
+    return ret;
+}
+
+static void usbback_process_unlink_req(struct usbback_req *usbback_req)
+{
+    struct usbback_info *usbif;
+    struct usbback_req *unlink_req;
+    unsigned int id, devnum;
+    int ret;
+
+    usbif = usbback_req->usbif;
+    ret = 0;
+    id = usbback_req->req.u.unlink.unlink_id;
+    TR_REQ(&usbif->xendev, "unlink id %d\n", id);
+    devnum = usbif_pipedevice(usbback_req->req.pipe);
+    if (unlikely(devnum == 0)) {
+        usbback_req->stub = usbif->ports +
+                            usbif_pipeportnum(usbback_req->req.pipe);
+        if (unlikely(!usbback_req->stub)) {
+            ret = -ENODEV;
+            goto fail_response;
+        }
+    } else {
+        if (unlikely(!usbif->addr_table[devnum])) {
+            ret = -ENODEV;
+            goto fail_response;
+        }
+        usbback_req->stub = usbif->addr_table[devnum];
+    }
+
+    QTAILQ_FOREACH(unlink_req, &usbback_req->stub->submit_q, q) {
+        if (unlink_req->req.id == id) {
+            if (usbback_cancel_req(unlink_req)) {
+                usbback_do_response_ret(unlink_req, -EPROTO);
+            }
+            break;
+        }
+    }
+
+fail_response:
+    usbback_do_response_ret(usbback_req, ret);
+}
+
+/*
+ * Checks whether a request can be handled at once or should be forwarded
+ * to the usb framework.
+ * Return value is:
+ * 0 in case of usb framework is needed
+ * 1 in case of local handling (no error)
+ * The request response has been queued already if return value not 0.
+ */
+static int usbback_check_and_submit(struct usbback_req *usbback_req)
+{
+    struct usbback_info *usbif;
+    unsigned int devnum;
+    struct usbback_stub *stub;
+    struct usbif_ctrlrequest *ctrl;
+    int ret;
+    uint16_t wValue;
+
+    usbif = usbback_req->usbif;
+    stub = NULL;
+    devnum = usbif_pipedevice(usbback_req->req.pipe);
+    ctrl = (struct usbif_ctrlrequest *)usbback_req->req.u.ctrl;
+    wValue = le16_to_cpu(ctrl->wValue);
+
+    /*
+     * When the device is first connected or resetted, USB device has no
+     * address. In this initial state, following requests are sent to device
+     * address (#0),
+     *
+     *  1. GET_DESCRIPTOR (with Descriptor Type is "DEVICE") is sent,
+     *     and OS knows what device is connected to.
+     *
+     *  2. SET_ADDRESS is sent, and then device has its address.
+     *
+     * In the next step, SET_CONFIGURATION is sent to addressed device, and
+     * then the device is finally ready to use.
+     */
+    if (unlikely(devnum == 0)) {
+        stub = usbif->ports + usbif_pipeportnum(usbback_req->req.pipe) - 1;
+        if (!stub->dev || !stub->attached) {
+            ret = -ENODEV;
+            goto do_response;
+        }
+
+        switch (ctrl->bRequest) {
+        case USB_REQ_GET_DESCRIPTOR:
+            /*
+             * GET_DESCRIPTOR request to device #0.
+             * through normal transfer.
+             */
+            TR_REQ(&usbif->xendev, "devnum 0 GET_DESCRIPTOR\n");
+            usbback_req->stub = stub;
+            return 0;
+        case USB_REQ_SET_ADDRESS:
+            /*
+             * SET_ADDRESS request to device #0.
+             * add attached device to addr_table.
+             */
+            TR_REQ(&usbif->xendev, "devnum 0 SET_ADDRESS\n");
+            usbback_set_address(usbif, stub, 0, wValue);
+            ret = 0;
+            break;
+        default:
+            ret = -EINVAL;
+            break;
+        }
+        goto do_response;
+    }
+
+    if (unlikely(!usbif->addr_table[devnum])) {
+            ret = -ENODEV;
+            goto do_response;
+    }
+    usbback_req->stub = usbif->addr_table[devnum];
+
+    /*
+     * Check special request
+     */
+    if (ctrl->bRequest != USB_REQ_SET_ADDRESS) {
+        return 0;
+    }
+
+    /*
+     * SET_ADDRESS request to addressed device.
+     * change addr or remove from addr_table.
+     */
+    usbback_set_address(usbif, usbback_req->stub, devnum, wValue);
+    ret = 0;
+
+do_response:
+    usbback_do_response_ret(usbback_req, ret);
+    return 1;
+}
+
+static void usbback_dispatch(struct usbback_req *usbback_req)
+{
+    int ret;
+    unsigned int devnum;
+    struct usbback_info *usbif;
+
+    usbif = usbback_req->usbif;
+
+    TR_REQ(&usbif->xendev, "start req_id %d pipe %08x\n", usbback_req->req.id,
+           usbback_req->req.pipe);
+
+    /* unlink request */
+    if (unlikely(usbif_pipeunlink(usbback_req->req.pipe))) {
+        usbback_process_unlink_req(usbback_req);
+        return;
+    }
+
+    if (usbif_pipectrl(usbback_req->req.pipe)) {
+        if (usbback_check_and_submit(usbback_req)) {
+            return;
+        }
+    } else {
+        devnum = usbif_pipedevice(usbback_req->req.pipe);
+        usbback_req->stub = usbif->addr_table[devnum];
+
+        if (!usbback_req->stub || !usbback_req->stub->attached) {
+            ret = -ENODEV;
+            goto fail_response;
+        }
+    }
+
+    QTAILQ_INSERT_TAIL(&usbback_req->stub->submit_q, usbback_req, q);
+
+    usbback_req->nr_buffer_segs = usbback_req->req.nr_buffer_segs;
+    usbback_req->nr_extra_segs = usbif_pipeisoc(usbback_req->req.pipe) ?
+                                 usbback_req->req.u.isoc.nr_frame_desc_segs : 0;
+
+    ret = usbback_init_packet(usbback_req);
+    if (ret) {
+        xen_be_printf(&usbif->xendev, 0, "invalid request\n");
+        ret = -ESHUTDOWN;
+        goto fail_free_urb;
+    }
+
+    ret = usbback_gnttab_map(usbback_req);
+    if (ret) {
+        xen_be_printf(&usbif->xendev, 0, "invalid buffer, ret=%d\n", ret);
+        ret = -ESHUTDOWN;
+        goto fail_free_urb;
+    }
+
+    usb_handle_packet(usbback_req->stub->dev, &usbback_req->packet);
+    if (usbback_req->packet.status != USB_RET_ASYNC) {
+        usbback_packet_complete(&usbback_req->packet);
+    }
+    return;
+
+fail_free_urb:
+    QTAILQ_REMOVE(&usbback_req->stub->submit_q, usbback_req, q);
+
+fail_response:
+    usbback_do_response_ret(usbback_req, ret);
+}
+
+static void usbback_hotplug_notify(struct usbback_info *usbif)
+{
+    struct usbif_conn_back_ring *ring = &usbif->conn_ring;
+    struct usbif_conn_request req;
+    struct usbif_conn_response *res;
+    struct usbback_hotplug *usb_hp;
+    unsigned int notify;
+
+    if (!usbif->conn_sring) {
+        return;
+    }
+
+    /* Check for full ring. */
+    if ((RING_SIZE(ring) - ring->rsp_prod_pvt - ring->req_cons) == 0) {
+        xen_be_send_notify(&usbif->xendev);
+        return;
+    }
+
+    usb_hp = QSIMPLEQ_FIRST(&usbif->hotplug_q);
+    QSIMPLEQ_REMOVE_HEAD(&usbif->hotplug_q, q);
+
+    RING_COPY_REQUEST(ring, ring->req_cons, &req);
+    ring->req_cons++;
+    ring->sring->req_event = ring->req_cons + 1;
+
+    res = RING_GET_RESPONSE(ring, ring->rsp_prod_pvt);
+    res->id = req.id;
+    res->portnum = usb_hp->port;
+    res->speed = usbif->ports[usb_hp->port - 1].speed;
+    ring->rsp_prod_pvt++;
+    RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(ring, notify);
+
+    if (notify) {
+        xen_be_send_notify(&usbif->xendev);
+    }
+
+    TR_BUS(&usbif->xendev, "hotplug port %d speed %d\n", usb_hp->port,
+           res->speed);
+
+    g_free(usb_hp);
+
+    if (!QSIMPLEQ_EMPTY(&usbif->hotplug_q)) {
+        qemu_bh_schedule(usbif->bh);
+    }
+}
+
+static void usbback_bh(void *opaque)
+{
+    struct usbback_info *usbif;
+    struct usbif_urb_back_ring *urb_ring;
+    struct usbback_req *usbback_req;
+    RING_IDX rc, rp;
+    unsigned int more_to_do;
+
+    usbif = opaque;
+    if (usbif->ring_error) {
+        return;
+    }
+
+    if (!QSIMPLEQ_EMPTY(&usbif->hotplug_q)) {
+        usbback_hotplug_notify(usbif);
+    }
+
+    urb_ring = &usbif->urb_ring;
+    rc = urb_ring->req_cons;
+    rp = urb_ring->sring->req_prod;
+    xen_rmb(); /* Ensure we see queued requests up to 'rp'. */
+
+    if (RING_REQUEST_PROD_OVERFLOW(urb_ring, rp)) {
+        rc = urb_ring->rsp_prod_pvt;
+        xen_be_printf(&usbif->xendev, 0, "domU provided bogus ring requests "
+                      "(%#x - %#x = %u). Halting ring processing.\n",
+                      rp, rc, rp - rc);
+        usbif->ring_error = true;
+        return;
+    }
+
+    while (rc != rp) {
+        if (RING_REQUEST_CONS_OVERFLOW(urb_ring, rc)) {
+            break;
+        }
+        usbback_req = usbback_get_req(usbif);
+
+        RING_COPY_REQUEST(urb_ring, rc, &usbback_req->req);
+        usbback_req->usbif = usbif;
+
+        usbback_dispatch(usbback_req);
+
+        urb_ring->req_cons = ++rc;
+    }
+
+    RING_FINAL_CHECK_FOR_REQUESTS(urb_ring, more_to_do);
+    if (more_to_do) {
+        qemu_bh_schedule(usbif->bh);
+    }
+}
+
+static void usbback_hotplug_enq(struct usbback_info *usbif, unsigned port)
+{
+    struct usbback_hotplug *usb_hp;
+
+    usb_hp = g_new0(struct usbback_hotplug, 1);
+    usb_hp->port = port;
+    QSIMPLEQ_INSERT_TAIL(&usbif->hotplug_q, usb_hp, q);
+    usbback_hotplug_notify(usbif);
+}
+
+static void usbback_portid_remove(struct usbback_info *usbif, unsigned port)
+{
+    USBPort *p;
+
+    if (!usbif->ports[port - 1].dev) {
+        return;
+    }
+
+    p = &(usbif->ports[port - 1].port);
+    snprintf(p->path, sizeof(p->path), "%d", 99);
+
+    object_unparent(OBJECT(usbif->ports[port - 1].dev));
+    usbif->ports[port - 1].dev = NULL;
+    usbif->ports[port - 1].speed = USBIF_SPEED_NONE;
+    usbif->ports[port - 1].attached = false;
+    usbback_hotplug_enq(usbif, port);
+
+    TR_BUS(&usbif->xendev, "port %d removed\n", port);
+}
+
+static void usbback_portid_add(struct usbback_info *usbif, unsigned port,
+                               char *busid)
+{
+    unsigned speed;
+    char *portname;
+    USBPort *p;
+    Error *local_err = NULL;
+    QDict *qdict;
+    QemuOpts *opts;
+
+    if (usbif->ports[port - 1].dev) {
+        return;
+    }
+
+    portname = strchr(busid, '-');
+    if (!portname) {
+        xen_be_printf(&usbif->xendev, 0, "device %s illegal specification\n",
+                      busid);
+        return;
+    }
+    portname++;
+    p = &(usbif->ports[port - 1].port);
+    snprintf(p->path, sizeof(p->path), "%s", portname);
+
+    qdict = qdict_new();
+    qdict_put(qdict, "driver", qstring_from_str("usb-host"));
+    qdict_put(qdict, "hostbus", qint_from_int(atoi(busid)));
+    qdict_put(qdict, "hostport", qstring_from_str(portname));
+    opts = qemu_opts_from_qdict(qemu_find_opts("device"), qdict, &local_err);
+    if (local_err) {
+        goto err;
+    }
+    usbif->ports[port - 1].dev = USB_DEVICE(qdev_device_add(opts, &local_err));
+    if (!usbif->ports[port - 1].dev) {
+        goto err;
+    }
+    QDECREF(qdict);
+    snprintf(p->path, sizeof(p->path), "%d", port);
+    speed = usbif->ports[port - 1].dev->speed;
+    switch (speed) {
+    case USB_SPEED_LOW:
+        speed = USBIF_SPEED_LOW;
+        break;
+    case USB_SPEED_FULL:
+        speed = USBIF_SPEED_FULL;
+        break;
+    case USB_SPEED_HIGH:
+        speed = (usbif->usb_ver < USB_VER_USB20) ?
+                USBIF_SPEED_NONE : USBIF_SPEED_HIGH;
+        break;
+    default:
+        speed = USBIF_SPEED_NONE;
+        break;
+    }
+    if (speed == USBIF_SPEED_NONE) {
+        xen_be_printf(&usbif->xendev, 0, "device %s wrong speed\n", busid);
+        object_unparent(OBJECT(usbif->ports[port - 1].dev));
+        usbif->ports[port - 1].dev = NULL;
+        return;
+    }
+    usb_device_reset(usbif->ports[port - 1].dev);
+    usbif->ports[port - 1].speed = speed;
+    usbif->ports[port - 1].attached = true;
+    QTAILQ_INIT(&usbif->ports[port - 1].submit_q);
+    usbback_hotplug_enq(usbif, port);
+
+    TR_BUS(&usbif->xendev, "port %d attached\n", port);
+    return;
+
+err:
+    QDECREF(qdict);
+    snprintf(p->path, sizeof(p->path), "%d", 99);
+    xen_be_printf(&usbif->xendev, 0, "device %s could not be opened\n", busid);
+}
+
+static void usbback_process_port(struct usbback_info *usbif, unsigned port)
+{
+    char node[8];
+    char *busid;
+
+    snprintf(node, sizeof(node), "port/%d", port);
+    busid = xenstore_read_be_str(&usbif->xendev, node);
+    if (busid == NULL) {
+        xen_be_printf(&usbif->xendev, 0, "xenstore_read %s failed\n", node);
+        return;
+    }
+
+    /* Remove portid, if the port is not connected.  */
+    if (strlen(busid) == 0) {
+        usbback_portid_remove(usbif, port);
+    } else {
+        usbback_portid_add(usbif, port, busid);
+    }
+
+    g_free(busid);
+}
+
+static void usbback_disconnect(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+    struct usbback_req *req, *tmp;
+    unsigned int i;
+
+    TR_BUS(xendev, "start\n");
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+
+    xen_be_unbind_evtchn(xendev);
+
+    if (usbif->urb_sring) {
+        xengnttab_unmap(xendev->gnttabdev, usbif->urb_sring, 1);
+        usbif->urb_sring = NULL;
+    }
+    if (usbif->conn_sring) {
+        xengnttab_unmap(xendev->gnttabdev, usbif->conn_sring, 1);
+        usbif->conn_sring = NULL;
+    }
+
+    for (i = 0; i < usbif->num_ports; i++) {
+        if (!usbif->ports[i].dev) {
+            continue;
+        }
+        QTAILQ_FOREACH_SAFE(req, &usbif->ports[i].submit_q, q, tmp) {
+            usbback_cancel_req(req);
+        }
+    }
+
+    TR_BUS(xendev, "finished\n");
+}
+
+static int usbback_connect(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+    struct usbif_urb_sring *urb_sring;
+    struct usbif_conn_sring *conn_sring;
+    int urb_ring_ref;
+    int conn_ring_ref;
+    unsigned int i;
+
+    TR_BUS(xendev, "start\n");
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+
+    if (xenstore_read_fe_int(xendev, "urb-ring-ref", &urb_ring_ref)) {
+        xen_be_printf(xendev, 0, "error reading urb-ring-ref\n");
+        return -1;
+    }
+    if (xenstore_read_fe_int(xendev, "conn-ring-ref", &conn_ring_ref)) {
+        xen_be_printf(xendev, 0, "error reading conn-ring-ref\n");
+        return -1;
+    }
+    if (xenstore_read_fe_int(xendev, "event-channel", &xendev->remote_port)) {
+        xen_be_printf(xendev, 0, "error reading event-channel\n");
+        return -1;
+    }
+
+    usbif->urb_sring = xengnttab_map_grant_ref(xendev->gnttabdev, xendev->dom,
+                                               urb_ring_ref,
+                                               PROT_READ | PROT_WRITE);
+    usbif->conn_sring = xengnttab_map_grant_ref(xendev->gnttabdev, xendev->dom,
+                                                conn_ring_ref,
+                                                PROT_READ | PROT_WRITE);
+    if (!usbif->urb_sring || !usbif->conn_sring) {
+        xen_be_printf(xendev, 0, "error mapping rings\n");
+        usbback_disconnect(xendev);
+        return -1;
+    }
+
+    urb_sring = usbif->urb_sring;
+    conn_sring = usbif->conn_sring;
+    BACK_RING_INIT(&usbif->urb_ring, urb_sring, XC_PAGE_SIZE);
+    BACK_RING_INIT(&usbif->conn_ring, conn_sring, XC_PAGE_SIZE);
+
+    xen_be_bind_evtchn(xendev);
+
+    xen_be_printf(xendev, 1, "urb-ring-ref %d, conn-ring-ref %d, "
+                  "remote port %d, local port %d\n", urb_ring_ref,
+                  conn_ring_ref, xendev->remote_port, xendev->local_port);
+
+    for (i = 1; i <= usbif->num_ports; i++) {
+        if (usbif->ports[i - 1].dev) {
+            usbback_hotplug_enq(usbif, i);
+        }
+    }
+
+    return 0;
+}
+
+static void usbback_backend_changed(struct XenDevice *xendev, const char *node)
+{
+    struct usbback_info *usbif;
+    unsigned int i;
+
+    TR_BUS(xendev, "path %s\n", node);
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+    for (i = 1; i <= usbif->num_ports; i++) {
+        usbback_process_port(usbif, i);
+    }
+}
+
+static int usbback_init(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+
+    TR_BUS(xendev, "start\n");
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+
+    if (xenstore_read_be_int(xendev, "num-ports", &usbif->num_ports) ||
+        usbif->num_ports < 1 || usbif->num_ports > USBBACK_MAXPORTS) {
+        xen_be_printf(xendev, 0, "num-ports not readable or out of bounds\n");
+        return -1;
+    }
+    if (xenstore_read_be_int(xendev, "usb-ver", &usbif->usb_ver) ||
+        (usbif->usb_ver != USB_VER_USB11 && usbif->usb_ver != USB_VER_USB20)) {
+        xen_be_printf(xendev, 0, "usb-ver not readable or out of bounds\n");
+        return -1;
+    }
+
+    usbback_backend_changed(xendev, "port");
+
+    TR_BUS(xendev, "finished\n");
+
+    return 0;
+}
+
+static void xen_bus_attach(USBPort *port)
+{
+    struct usbback_info *usbif;
+
+    usbif = port->opaque;
+    TR_BUS(&usbif->xendev, "\n");
+    usbif->ports[port->index].attached = true;
+    usbback_hotplug_enq(usbif, port->index + 1);
+}
+
+static void xen_bus_detach(USBPort *port)
+{
+    struct usbback_info *usbif;
+
+    usbif = port->opaque;
+    TR_BUS(&usbif->xendev, "\n");
+    usbif->ports[port->index].attached = false;
+    usbback_hotplug_enq(usbif, port->index + 1);
+}
+
+static void xen_bus_child_detach(USBPort *port, USBDevice *child)
+{
+    struct usbback_info *usbif;
+
+    usbif = port->opaque;
+    TR_BUS(&usbif->xendev, "\n");
+}
+
+static void xen_bus_complete(USBPort *port, USBPacket *packet)
+{
+    struct usbback_info *usbif;
+
+    usbif = port->opaque;
+    TR_REQ(&usbif->xendev, "\n");
+    usbback_packet_complete(packet);
+}
+
+static USBPortOps xen_usb_port_ops = {
+    .attach = xen_bus_attach,
+    .detach = xen_bus_detach,
+    .child_detach = xen_bus_child_detach,
+    .complete = xen_bus_complete,
+};
+
+static USBBusOps xen_usb_bus_ops = {
+};
+
+static void usbback_alloc(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+    USBPort *p;
+    unsigned int i, max_grants;
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+
+    usb_bus_new(&usbif->bus, sizeof(usbif->bus), &xen_usb_bus_ops, xen_sysdev);
+    for (i = 0; i < USBBACK_MAXPORTS; i++) {
+        p = &(usbif->ports[i].port);
+        usb_register_port(&usbif->bus, p, usbif, i, &xen_usb_port_ops,
+                          USB_SPEED_MASK_LOW | USB_SPEED_MASK_FULL |
+                          USB_SPEED_MASK_HIGH);
+        snprintf(p->path, sizeof(p->path), "%d", 99);
+    }
+
+    QTAILQ_INIT(&usbif->req_free_q);
+    QSIMPLEQ_INIT(&usbif->hotplug_q);
+    usbif->bh = qemu_bh_new(usbback_bh, usbif);
+
+    /* max_grants: for each request and for the rings (request and connect). */
+    max_grants = USBIF_MAX_SEGMENTS_PER_REQUEST * USB_URB_RING_SIZE + 2;
+    if (xengnttab_set_max_grants(xendev->gnttabdev, max_grants) < 0) {
+        xen_be_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
+                      strerror(errno));
+    }
+}
+
+static int usbback_free(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+    struct usbback_req *usbback_req;
+    struct usbback_hotplug *usb_hp;
+    unsigned int i;
+
+    TR_BUS(xendev, "start\n");
+
+    usbback_disconnect(xendev);
+    usbif = container_of(xendev, struct usbback_info, xendev);
+    for (i = 1; i <= usbif->num_ports; i++) {
+        usbback_portid_remove(usbif, i);
+    }
+
+    while (!QTAILQ_EMPTY(&usbif->req_free_q)) {
+        usbback_req = QTAILQ_FIRST(&usbif->req_free_q);
+        QTAILQ_REMOVE(&usbif->req_free_q, usbback_req, q);
+        g_free(usbback_req);
+    }
+    while (!QSIMPLEQ_EMPTY(&usbif->hotplug_q)) {
+        usb_hp = QSIMPLEQ_FIRST(&usbif->hotplug_q);
+        QSIMPLEQ_REMOVE_HEAD(&usbif->hotplug_q, q);
+        g_free(usb_hp);
+    }
+
+    qemu_bh_delete(usbif->bh);
+
+    for (i = 0; i < USBBACK_MAXPORTS; i++) {
+        usb_unregister_port(&usbif->bus, &(usbif->ports[i].port));
+    }
+
+    usb_bus_release(&usbif->bus);
+
+    TR_BUS(xendev, "finished\n");
+
+    return 0;
+}
+
+static void usbback_event(struct XenDevice *xendev)
+{
+    struct usbback_info *usbif;
+
+    usbif = container_of(xendev, struct usbback_info, xendev);
+    qemu_bh_schedule(usbif->bh);
+}
+
+struct XenDevOps xen_usb_ops = {
+    .size            = sizeof(struct usbback_info),
+    .flags           = DEVOPS_FLAG_NEED_GNTDEV,
+    .init            = usbback_init,
+    .alloc           = usbback_alloc,
+    .free            = usbback_free,
+    .backend_changed = usbback_backend_changed,
+    .initialise      = usbback_connect,
+    .disconnect      = usbback_disconnect,
+    .event           = usbback_event,
+};
+
+#else /* USBIF_SHORT_NOT_OK */
+
+static int usbback_not_supported(void)
+{
+    return -EINVAL;
+}
+
+struct XenDevOps xen_usb_ops = {
+    .backend_register = usbback_not_supported,
+};
+
+#endif
diff --git a/hw/xenpv/xen_machine_pv.c b/hw/xenpv/xen_machine_pv.c
index 48d5bc6047..f68cf48a29 100644
--- a/hw/xenpv/xen_machine_pv.c
+++ b/hw/xenpv/xen_machine_pv.c
@@ -80,6 +80,9 @@ static void xen_init_pv(MachineState *machine)
     xen_be_register("vfb", &xen_framebuffer_ops);
     xen_be_register("qdisk", &xen_blkdev_ops);
     xen_be_register("qnic", &xen_netdev_ops);
+#ifdef CONFIG_USB_LIBUSB
+    xen_be_register("qusb", &xen_usb_ops);
+#endif
 
     /* configure framebuffer */
     if (xenfb_enabled) {