// SPDX-License-Identifier: GPL-2.0+
/*
 * f_rndis.c -- RNDIS link function driver
 *
 * Copyright (C) 2003-2005,2008 David Brownell
 * Copyright (C) 2003-2004 Robert Schwebel, Benedikt Spranger
 * Copyright (C) 2008 Nokia Corporation
 * Copyright (C) 2009 Samsung Electronics
 *                    Author: Michal Nazarewicz (mina86@mina86.com)
 */

/* #define VERBOSE_DEBUG */

#include <linux/cleanup.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/etherdevice.h>

#include <linux/atomic.h>

#include <linux/usb/gadget.h>

#include "u_ether.h"
#include "u_ether_configfs.h"
#include "u_rndis.h"
#include "rndis.h"
#include "configfs.h"

/*
 * This function is an RNDIS Ethernet port -- a Microsoft protocol that's
 * been promoted instead of the standard CDC Ethernet.  The published RNDIS
 * spec is ambiguous, incomplete, and needlessly complex.  Variants such as
 * ActiveSync have even worse status in terms of specification.
 *
 * In short:  it's a protocol controlled by (and for) Microsoft, not for an
 * Open ecosystem or markets.  Linux supports it *only* because Microsoft
 * doesn't support the CDC Ethernet standard.
 *
 * The RNDIS data transfer model is complex, with multiple Ethernet packets
 * per USB message, and out of band data.  The control model is built around
 * what's essentially an "RNDIS RPC" protocol.  It's all wrapped in a CDC ACM
 * (modem, not Ethernet) veneer, with those ACM descriptors being entirely
 * useless (they're ignored).  RNDIS expects to be the only function in its
 * configuration, so it's no real help if you need composite devices; and
 * it expects to be the first configuration too.
 *
 * There is a single technical advantage of RNDIS over CDC Ethernet, if you
 * discount the fluff that its RPC can be made to deliver: it doesn't need
 * a NOP altsetting for the data interface.  That lets it work on some of the
 * "so smart it's stupid" hardware which takes over configuration changes
 * from the software, and adds restrictions like "no altsettings".
 *
 * Unfortunately MSFT's RNDIS drivers are buggy.  They hang or oops, and
 * have all sorts of contrary-to-specification oddities that can prevent
 * them from working sanely.  Since bugfixes (or accurate specs, letting
 * Linux work around those bugs) are unlikely to ever come from MSFT, you
 * may want to avoid using RNDIS on purely operational grounds.
 *
 * Omissions from the RNDIS 1.0 specification include:
 *
 *   - Power management ... references data that's scattered around lots
 *     of other documentation, which is incorrect/incomplete there too.
 *
 *   - There are various undocumented protocol requirements, like the need
 *     to send garbage in some control-OUT messages.
 *
 *   - MS-Windows drivers sometimes emit undocumented requests.
 */

struct f_rndis {
        struct gether                   port;
        u8                              ctrl_id, data_id;
        u8                              ethaddr[ETH_ALEN];
        u32                             vendorID;
        const char                      *manufacturer;
        struct rndis_params             *params;

        struct usb_ep                   *notify;
        struct usb_request              *notify_req;
        atomic_t                        notify_count;
};

static inline struct f_rndis *func_to_rndis(struct usb_function *f)
{
        return container_of(f, struct f_rndis, port.func);
}

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

/*
 */

#define RNDIS_STATUS_INTERVAL_MS        32
#define STATUS_BYTECOUNT                8       /* 8 bytes data */


/* interface descriptor: */

static struct usb_interface_descriptor rndis_control_intf = {
        .bLength =              sizeof rndis_control_intf,
        .bDescriptorType =      USB_DT_INTERFACE,

        /* .bInterfaceNumber = DYNAMIC */
        /* status endpoint is optional; this could be patched later */
        .bNumEndpoints =        1,
        .bInterfaceClass =      USB_CLASS_COMM,
        .bInterfaceSubClass =   USB_CDC_SUBCLASS_ACM,
        .bInterfaceProtocol =   USB_CDC_ACM_PROTO_VENDOR,
        /* .iInterface = DYNAMIC */
};

static struct usb_cdc_header_desc header_desc = {
        .bLength =              sizeof header_desc,
        .bDescriptorType =      USB_DT_CS_INTERFACE,
        .bDescriptorSubType =   USB_CDC_HEADER_TYPE,

        .bcdCDC =               cpu_to_le16(0x0110),
};

static struct usb_cdc_call_mgmt_descriptor call_mgmt_descriptor = {
        .bLength =              sizeof call_mgmt_descriptor,
        .bDescriptorType =      USB_DT_CS_INTERFACE,
        .bDescriptorSubType =   USB_CDC_CALL_MANAGEMENT_TYPE,

        .bmCapabilities =       0x00,
        .bDataInterface =       0x01,
};

static struct usb_cdc_acm_descriptor rndis_acm_descriptor = {
        .bLength =              sizeof rndis_acm_descriptor,
        .bDescriptorType =      USB_DT_CS_INTERFACE,
        .bDescriptorSubType =   USB_CDC_ACM_TYPE,

        .bmCapabilities =       0x00,
};

static struct usb_cdc_union_desc rndis_union_desc = {
        .bLength =              sizeof(rndis_union_desc),
        .bDescriptorType =      USB_DT_CS_INTERFACE,
        .bDescriptorSubType =   USB_CDC_UNION_TYPE,
        /* .bMasterInterface0 = DYNAMIC */
        /* .bSlaveInterface0 =  DYNAMIC */
};

/* the data interface has two bulk endpoints */

static struct usb_interface_descriptor rndis_data_intf = {
        .bLength =              sizeof rndis_data_intf,
        .bDescriptorType =      USB_DT_INTERFACE,

        /* .bInterfaceNumber = DYNAMIC */
        .bNumEndpoints =        2,
        .bInterfaceClass =      USB_CLASS_CDC_DATA,
        .bInterfaceSubClass =   0,
        .bInterfaceProtocol =   0,
        /* .iInterface = DYNAMIC */
};


static struct usb_interface_assoc_descriptor
rndis_iad_descriptor = {
        .bLength =              sizeof rndis_iad_descriptor,
        .bDescriptorType =      USB_DT_INTERFACE_ASSOCIATION,

        .bFirstInterface =      0, /* XXX, hardcoded */
        .bInterfaceCount =      2,      // control + data
        .bFunctionClass =       USB_CLASS_COMM,
        .bFunctionSubClass =    USB_CDC_SUBCLASS_ETHERNET,
        .bFunctionProtocol =    USB_CDC_PROTO_NONE,
        /* .iFunction = DYNAMIC */
};

/* full speed support: */

static struct usb_endpoint_descriptor fs_notify_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_INT,
        .wMaxPacketSize =       cpu_to_le16(STATUS_BYTECOUNT),
        .bInterval =            RNDIS_STATUS_INTERVAL_MS,
};

static struct usb_endpoint_descriptor fs_in_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
};

static struct usb_endpoint_descriptor fs_out_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_OUT,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
};

static struct usb_descriptor_header *eth_fs_function[] = {
        (struct usb_descriptor_header *) &rndis_iad_descriptor,

        /* control interface matches ACM, not Ethernet */
        (struct usb_descriptor_header *) &rndis_control_intf,
        (struct usb_descriptor_header *) &header_desc,
        (struct usb_descriptor_header *) &call_mgmt_descriptor,
        (struct usb_descriptor_header *) &rndis_acm_descriptor,
        (struct usb_descriptor_header *) &rndis_union_desc,
        (struct usb_descriptor_header *) &fs_notify_desc,

        /* data interface has no altsetting */
        (struct usb_descriptor_header *) &rndis_data_intf,
        (struct usb_descriptor_header *) &fs_in_desc,
        (struct usb_descriptor_header *) &fs_out_desc,
        NULL,
};

/* high speed support: */

static struct usb_endpoint_descriptor hs_notify_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_INT,
        .wMaxPacketSize =       cpu_to_le16(STATUS_BYTECOUNT),
        .bInterval =            USB_MS_TO_HS_INTERVAL(RNDIS_STATUS_INTERVAL_MS)
};

static struct usb_endpoint_descriptor hs_in_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
        .wMaxPacketSize =       cpu_to_le16(512),
};

static struct usb_endpoint_descriptor hs_out_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_OUT,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
        .wMaxPacketSize =       cpu_to_le16(512),
};

static struct usb_descriptor_header *eth_hs_function[] = {
        (struct usb_descriptor_header *) &rndis_iad_descriptor,

        /* control interface matches ACM, not Ethernet */
        (struct usb_descriptor_header *) &rndis_control_intf,
        (struct usb_descriptor_header *) &header_desc,
        (struct usb_descriptor_header *) &call_mgmt_descriptor,
        (struct usb_descriptor_header *) &rndis_acm_descriptor,
        (struct usb_descriptor_header *) &rndis_union_desc,
        (struct usb_descriptor_header *) &hs_notify_desc,

        /* data interface has no altsetting */
        (struct usb_descriptor_header *) &rndis_data_intf,
        (struct usb_descriptor_header *) &hs_in_desc,
        (struct usb_descriptor_header *) &hs_out_desc,
        NULL,
};

/* super speed support: */

static struct usb_endpoint_descriptor ss_notify_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_INT,
        .wMaxPacketSize =       cpu_to_le16(STATUS_BYTECOUNT),
        .bInterval =            USB_MS_TO_HS_INTERVAL(RNDIS_STATUS_INTERVAL_MS)
};

static struct usb_ss_ep_comp_descriptor ss_intr_comp_desc = {
        .bLength =              sizeof ss_intr_comp_desc,
        .bDescriptorType =      USB_DT_SS_ENDPOINT_COMP,

        /* the following 3 values can be tweaked if necessary */
        /* .bMaxBurst =         0, */
        /* .bmAttributes =      0, */
        .wBytesPerInterval =    cpu_to_le16(STATUS_BYTECOUNT),
};

static struct usb_endpoint_descriptor ss_in_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_IN,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
        .wMaxPacketSize =       cpu_to_le16(1024),
};

static struct usb_endpoint_descriptor ss_out_desc = {
        .bLength =              USB_DT_ENDPOINT_SIZE,
        .bDescriptorType =      USB_DT_ENDPOINT,

        .bEndpointAddress =     USB_DIR_OUT,
        .bmAttributes =         USB_ENDPOINT_XFER_BULK,
        .wMaxPacketSize =       cpu_to_le16(1024),
};

static struct usb_ss_ep_comp_descriptor ss_bulk_comp_desc = {
        .bLength =              sizeof ss_bulk_comp_desc,
        .bDescriptorType =      USB_DT_SS_ENDPOINT_COMP,

        /* the following 2 values can be tweaked if necessary */
        /* .bMaxBurst =         0, */
        /* .bmAttributes =      0, */
};

static struct usb_descriptor_header *eth_ss_function[] = {
        (struct usb_descriptor_header *) &rndis_iad_descriptor,

        /* control interface matches ACM, not Ethernet */
        (struct usb_descriptor_header *) &rndis_control_intf,
        (struct usb_descriptor_header *) &header_desc,
        (struct usb_descriptor_header *) &call_mgmt_descriptor,
        (struct usb_descriptor_header *) &rndis_acm_descriptor,
        (struct usb_descriptor_header *) &rndis_union_desc,
        (struct usb_descriptor_header *) &ss_notify_desc,
        (struct usb_descriptor_header *) &ss_intr_comp_desc,

        /* data interface has no altsetting */
        (struct usb_descriptor_header *) &rndis_data_intf,
        (struct usb_descriptor_header *) &ss_in_desc,
        (struct usb_descriptor_header *) &ss_bulk_comp_desc,
        (struct usb_descriptor_header *) &ss_out_desc,
        (struct usb_descriptor_header *) &ss_bulk_comp_desc,
        NULL,
};

/* string descriptors: */

static struct usb_string rndis_string_defs[] = {
        [0].s = "RNDIS Communications Control",
        [1].s = "RNDIS Ethernet Data",
        [2].s = "RNDIS",
        {  } /* end of list */
};

static struct usb_gadget_strings rndis_string_table = {
        .language =             0x0409, /* en-us */
        .strings =              rndis_string_defs,
};

static struct usb_gadget_strings *rndis_strings[] = {
        &rndis_string_table,
        NULL,
};

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

static struct sk_buff *rndis_add_header(struct gether *port,
                                        struct sk_buff *skb)
{
        struct sk_buff *skb2;

        if (!skb)
                return NULL;

        skb2 = skb_realloc_headroom(skb, sizeof(struct rndis_packet_msg_type));
        rndis_add_hdr(skb2);

        dev_kfree_skb(skb);
        return skb2;
}

static void rndis_response_available(void *_rndis)
{
        struct f_rndis                  *rndis = _rndis;
        struct usb_request              *req = rndis->notify_req;
        struct usb_composite_dev        *cdev = rndis->port.func.config->cdev;
        __le32                          *data = req->buf;
        int                             status;

        if (atomic_inc_return(&rndis->notify_count) != 1)
                return;

        /* Send RNDIS RESPONSE_AVAILABLE notification; a
         * USB_CDC_NOTIFY_RESPONSE_AVAILABLE "should" work too
         *
         * This is the only notification defined by RNDIS.
         */
        data[0] = cpu_to_le32(1);
        data[1] = cpu_to_le32(0);

        status = usb_ep_queue(rndis->notify, req, GFP_ATOMIC);
        if (status) {
                atomic_dec(&rndis->notify_count);
                DBG(cdev, "notify/0 --> %d\n", status);
        }
}

static void rndis_response_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct f_rndis                  *rndis = req->context;
        struct usb_composite_dev        *cdev = rndis->port.func.config->cdev;
        int                             status = req->status;

        /* after TX:
         *  - USB_CDC_GET_ENCAPSULATED_RESPONSE (ep0/control)
         *  - RNDIS_RESPONSE_AVAILABLE (status/irq)
         */
        switch (status) {
        case -ECONNRESET:
        case -ESHUTDOWN:
                /* connection gone */
                atomic_set(&rndis->notify_count, 0);
                break;
        default:
                DBG(cdev, "RNDIS %s response error %d, %d/%d\n",
                        ep->name, status,
                        req->actual, req->length);
                fallthrough;
        case 0:
                if (ep != rndis->notify)
                        break;

                /* handle multiple pending RNDIS_RESPONSE_AVAILABLE
                 * notifications by resending until we're done
                 */
                if (atomic_dec_and_test(&rndis->notify_count))
                        break;
                status = usb_ep_queue(rndis->notify, req, GFP_ATOMIC);
                if (status) {
                        atomic_dec(&rndis->notify_count);
                        DBG(cdev, "notify/1 --> %d\n", status);
                }
                break;
        }
}

static void rndis_command_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct f_rndis                  *rndis = req->context;
        int                             status;

        /* received RNDIS command from USB_CDC_SEND_ENCAPSULATED_COMMAND */
//      spin_lock(&dev->lock);
        status = rndis_msg_parser(rndis->params, (u8 *) req->buf);
        if (status < 0)
                pr_err("RNDIS command error %d, %d/%d\n",
                        status, req->actual, req->length);
//      spin_unlock(&dev->lock);
}

static int
rndis_setup(struct usb_function *f, const struct usb_ctrlrequest *ctrl)
{
        struct f_rndis          *rndis = func_to_rndis(f);
        struct usb_composite_dev *cdev = f->config->cdev;
        struct usb_request      *req = cdev->req;
        int                     value = -EOPNOTSUPP;
        u16                     w_index = le16_to_cpu(ctrl->wIndex);
        u16                     w_value = le16_to_cpu(ctrl->wValue);
        u16                     w_length = le16_to_cpu(ctrl->wLength);

        /* composite driver infrastructure handles everything except
         * CDC class messages; interface activation uses set_alt().
         */
        switch ((ctrl->bRequestType << 8) | ctrl->bRequest) {

        /* RNDIS uses the CDC command encapsulation mechanism to implement
         * an RPC scheme, with much getting/setting of attributes by OID.
         */
        case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8)
                        | USB_CDC_SEND_ENCAPSULATED_COMMAND:
                if (w_value || w_index != rndis->ctrl_id)
                        goto invalid;
                /* read the request; process it later */
                value = w_length;
                req->complete = rndis_command_complete;
                req->context = rndis;
                /* later, rndis_response_available() sends a notification */
                break;

        case ((USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8)
                        | USB_CDC_GET_ENCAPSULATED_RESPONSE:
                if (w_value || w_index != rndis->ctrl_id)
                        goto invalid;
                else {
                        u8 *buf;
                        u32 n;

                        /* return the result */
                        buf = rndis_get_next_response(rndis->params, &n);
                        if (buf) {
                                memcpy(req->buf, buf, n);
                                req->complete = rndis_response_complete;
                                req->context = rndis;
                                rndis_free_response(rndis->params, buf);
                                value = n;
                        }
                        /* else stalls ... spec says to avoid that */
                }
                break;

        default:
invalid:
                VDBG(cdev, "invalid control req%02x.%02x v%04x i%04x l%d\n",
                        ctrl->bRequestType, ctrl->bRequest,
                        w_value, w_index, w_length);
        }

        /* respond with data transfer or status phase? */
        if (value >= 0) {
                DBG(cdev, "rndis req%02x.%02x v%04x i%04x l%d\n",
                        ctrl->bRequestType, ctrl->bRequest,
                        w_value, w_index, w_length);
                req->zero = (value < w_length);
                req->length = value;
                value = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
                if (value < 0)
                        ERROR(cdev, "rndis response on err %d\n", value);
        }

        /* device either stalls (value < 0) or reports success */
        return value;
}


static int rndis_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
{
        struct f_rndis          *rndis = func_to_rndis(f);
        struct usb_composite_dev *cdev = f->config->cdev;

        /* we know alt == 0 */

        if (intf == rndis->ctrl_id) {
                VDBG(cdev, "reset rndis control %d\n", intf);
                usb_ep_disable(rndis->notify);

                if (!rndis->notify->desc) {
                        VDBG(cdev, "init rndis ctrl %d\n", intf);
                        if (config_ep_by_speed(cdev->gadget, f, rndis->notify))
                                goto fail;
                }
                usb_ep_enable(rndis->notify);

        } else if (intf == rndis->data_id) {
                struct net_device       *net;

                if (rndis->port.in_ep->enabled) {
                        DBG(cdev, "reset rndis\n");
                        gether_disconnect(&rndis->port);
                }

                if (!rndis->port.in_ep->desc || !rndis->port.out_ep->desc) {
                        DBG(cdev, "init rndis\n");
                        if (config_ep_by_speed(cdev->gadget, f,
                                               rndis->port.in_ep) ||
                            config_ep_by_speed(cdev->gadget, f,
                                               rndis->port.out_ep)) {
                                rndis->port.in_ep->desc = NULL;
                                rndis->port.out_ep->desc = NULL;
                                goto fail;
                        }
                }

                /* Avoid ZLPs; they can be troublesome. */
                rndis->port.is_zlp_ok = false;

                /* RNDIS should be in the "RNDIS uninitialized" state,
                 * either never activated or after rndis_uninit().
                 *
                 * We don't want data to flow here until a nonzero packet
                 * filter is set, at which point it enters "RNDIS data
                 * initialized" state ... but we do want the endpoints
                 * to be activated.  It's a strange little state.
                 *
                 * REVISIT the RNDIS gadget code has done this wrong for a
                 * very long time.  We need another call to the link layer
                 * code -- gether_updown(...bool) maybe -- to do it right.
                 */
                rndis->port.cdc_filter = 0;

                DBG(cdev, "RNDIS RX/TX early activation ... \n");
                net = gether_connect(&rndis->port);
                if (IS_ERR(net))
                        return PTR_ERR(net);

                rndis_set_param_dev(rndis->params, net,
                                &rndis->port.cdc_filter);
        } else
                goto fail;

        return 0;
fail:
        return -EINVAL;
}

static void rndis_disable(struct usb_function *f)
{
        struct f_rndis          *rndis = func_to_rndis(f);
        struct usb_composite_dev *cdev = f->config->cdev;

        if (!rndis->notify->enabled)
                return;

        DBG(cdev, "rndis deactivated\n");

        rndis_uninit(rndis->params);
        gether_disconnect(&rndis->port);

        usb_ep_disable(rndis->notify);
        rndis->notify->desc = NULL;
}

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

/*
 * This isn't quite the same mechanism as CDC Ethernet, since the
 * notification scheme passes less data, but the same set of link
 * states must be tested.  A key difference is that altsettings are
 * not used to tell whether the link should send packets or not.
 */

static void rndis_open(struct gether *geth)
{
        struct f_rndis          *rndis = func_to_rndis(&geth->func);
        struct usb_composite_dev *cdev = geth->func.config->cdev;

        DBG(cdev, "%s\n", __func__);

        rndis_set_param_medium(rndis->params, RNDIS_MEDIUM_802_3,
                                gether_bitrate(cdev->gadget) / 100);
        rndis_signal_connect(rndis->params);
}

static void rndis_close(struct gether *geth)
{
        struct f_rndis          *rndis = func_to_rndis(&geth->func);

        DBG(geth->func.config->cdev, "%s\n", __func__);

        rndis_set_param_medium(rndis->params, RNDIS_MEDIUM_802_3, 0);
        rndis_signal_disconnect(rndis->params);
}

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

/* Some controllers can't support RNDIS ... */
static inline bool can_support_rndis(struct usb_configuration *c)
{
        /* everything else is *presumably* fine */
        return true;
}

/* ethernet function driver setup/binding */

static int
rndis_bind(struct usb_configuration *c, struct usb_function *f)
{
        struct usb_composite_dev *cdev = c->cdev;
        struct f_rndis          *rndis = func_to_rndis(f);
        struct usb_string       *us;
        int                     status;
        struct usb_ep           *ep;

        struct f_rndis_opts *rndis_opts;
        struct usb_os_desc_table        *os_desc_table __free(kfree) = NULL;
        struct net_device               *net __free(detach_gadget) = NULL;
        struct usb_request              *request __free(free_usb_request) = NULL;

        if (!can_support_rndis(c))
                return -EINVAL;

        rndis_opts = container_of(f->fi, struct f_rndis_opts, func_inst);

        if (cdev->use_os_string) {
                os_desc_table = kzalloc_obj(*os_desc_table);
                if (!os_desc_table)
                        return -ENOMEM;
        }

        scoped_guard(mutex, &rndis_opts->lock) {
                rndis_iad_descriptor.bFunctionClass = rndis_opts->class;
                rndis_iad_descriptor.bFunctionSubClass = rndis_opts->subclass;
                rndis_iad_descriptor.bFunctionProtocol = rndis_opts->protocol;

                if (rndis_opts->bind_count == 0 && !rndis_opts->borrowed_net) {
                        if (!device_is_registered(&rndis_opts->net->dev)) {
                                gether_set_gadget(rndis_opts->net, cdev->gadget);
                                status = gether_register_netdev(rndis_opts->net);
                        } else
                                status = gether_attach_gadget(rndis_opts->net, cdev->gadget);

                        if (status)
                                return status;
                        net = rndis_opts->net;
                }
        }

        us = usb_gstrings_attach(cdev, rndis_strings,
                                 ARRAY_SIZE(rndis_string_defs));
        if (IS_ERR(us))
                return PTR_ERR(us);
        rndis_control_intf.iInterface = us[0].id;
        rndis_data_intf.iInterface = us[1].id;
        rndis_iad_descriptor.iFunction = us[2].id;

        /* allocate instance-specific interface IDs */
        status = usb_interface_id(c, f);
        if (status < 0)
                return status;
        rndis->ctrl_id = status;
        rndis_iad_descriptor.bFirstInterface = status;

        rndis_control_intf.bInterfaceNumber = status;
        rndis_union_desc.bMasterInterface0 = status;

        status = usb_interface_id(c, f);
        if (status < 0)
                return status;
        rndis->data_id = status;

        rndis_data_intf.bInterfaceNumber = status;
        rndis_union_desc.bSlaveInterface0 = status;

        /* allocate instance-specific endpoints */
        ep = usb_ep_autoconfig(cdev->gadget, &fs_in_desc);
        if (!ep)
                return -ENODEV;
        rndis->port.in_ep = ep;

        ep = usb_ep_autoconfig(cdev->gadget, &fs_out_desc);
        if (!ep)
                return -ENODEV;
        rndis->port.out_ep = ep;

        /* NOTE:  a status/notification endpoint is, strictly speaking,
         * optional.  We don't treat it that way though!  It's simpler,
         * and some newer profiles don't treat it as optional.
         */
        ep = usb_ep_autoconfig(cdev->gadget, &fs_notify_desc);
        if (!ep)
                return -ENODEV;
        rndis->notify = ep;

        /* allocate notification request and buffer */
        request = usb_ep_alloc_request(ep, GFP_KERNEL);
        if (!request)
                return -ENOMEM;
        request->buf = kmalloc(STATUS_BYTECOUNT, GFP_KERNEL);
        if (!request->buf)
                return -ENOMEM;
        request->length = STATUS_BYTECOUNT;
        request->context = rndis;
        request->complete = rndis_response_complete;

        /* support all relevant hardware speeds... we expect that when
         * hardware is dual speed, all bulk-capable endpoints work at
         * both speeds
         */
        hs_in_desc.bEndpointAddress = fs_in_desc.bEndpointAddress;
        hs_out_desc.bEndpointAddress = fs_out_desc.bEndpointAddress;
        hs_notify_desc.bEndpointAddress = fs_notify_desc.bEndpointAddress;

        ss_in_desc.bEndpointAddress = fs_in_desc.bEndpointAddress;
        ss_out_desc.bEndpointAddress = fs_out_desc.bEndpointAddress;
        ss_notify_desc.bEndpointAddress = fs_notify_desc.bEndpointAddress;

        status = usb_assign_descriptors(f, eth_fs_function, eth_hs_function,
                        eth_ss_function, eth_ss_function);
        if (status)
                return status;

        rndis->port.open = rndis_open;
        rndis->port.close = rndis_close;

        rndis_set_param_medium(rndis->params, RNDIS_MEDIUM_802_3, 0);
        rndis_set_host_mac(rndis->params, rndis->ethaddr);

        if (rndis->manufacturer && rndis->vendorID &&
                        rndis_set_param_vendor(rndis->params, rndis->vendorID,
                                               rndis->manufacturer)) {
                usb_free_all_descriptors(f);
                return -EINVAL;
        }

        if (cdev->use_os_string) {
                os_desc_table[0].os_desc = &rndis_opts->rndis_os_desc;
                os_desc_table[0].if_id = rndis_iad_descriptor.bFirstInterface;
                f->os_desc_table = no_free_ptr(os_desc_table);
                f->os_desc_n = 1;

        }
        rndis->notify_req = no_free_ptr(request);

        rndis_opts->bind_count++;
        retain_and_null_ptr(net);

        /* NOTE:  all that is done without knowing or caring about
         * the network link ... which is unavailable to this code
         * until we're activated via set_alt().
         */

        DBG(cdev, "RNDIS: IN/%s OUT/%s NOTIFY/%s\n",
                        rndis->port.in_ep->name, rndis->port.out_ep->name,
                        rndis->notify->name);
        return 0;
}

void rndis_borrow_net(struct usb_function_instance *f, struct net_device *net)
{
        struct f_rndis_opts *opts;

        opts = container_of(f, struct f_rndis_opts, func_inst);
        if (device_is_registered(&opts->net->dev))
                gether_cleanup(netdev_priv(opts->net));
        else
                free_netdev(opts->net);
        opts->borrowed_net = true;
        opts->net = net;
}
EXPORT_SYMBOL_GPL(rndis_borrow_net);

static inline struct f_rndis_opts *to_f_rndis_opts(struct config_item *item)
{
        return container_of(to_config_group(item), struct f_rndis_opts,
                            func_inst.group);
}

/* f_rndis_item_ops */
USB_ETHERNET_CONFIGFS_ITEM(rndis);

/* f_rndis_opts_dev_addr */
USB_ETHERNET_CONFIGFS_ITEM_ATTR_DEV_ADDR(rndis);

/* f_rndis_opts_host_addr */
USB_ETHERNET_CONFIGFS_ITEM_ATTR_HOST_ADDR(rndis);

/* f_rndis_opts_qmult */
USB_ETHERNET_CONFIGFS_ITEM_ATTR_QMULT(rndis);

/* f_rndis_opts_ifname */
USB_ETHERNET_CONFIGFS_ITEM_ATTR_IFNAME(rndis);

/* f_rndis_opts_class */
USB_ETHER_CONFIGFS_ITEM_ATTR_U8_RW(rndis, class);

/* f_rndis_opts_subclass */
USB_ETHER_CONFIGFS_ITEM_ATTR_U8_RW(rndis, subclass);

/* f_rndis_opts_protocol */
USB_ETHER_CONFIGFS_ITEM_ATTR_U8_RW(rndis, protocol);

static struct configfs_attribute *rndis_attrs[] = {
        &rndis_opts_attr_dev_addr,
        &rndis_opts_attr_host_addr,
        &rndis_opts_attr_qmult,
        &rndis_opts_attr_ifname,
        &rndis_opts_attr_class,
        &rndis_opts_attr_subclass,
        &rndis_opts_attr_protocol,
        NULL,
};

static const struct config_item_type rndis_func_type = {
        .ct_item_ops    = &rndis_item_ops,
        .ct_attrs       = rndis_attrs,
        .ct_owner       = THIS_MODULE,
};

static void rndis_free_inst(struct usb_function_instance *f)
{
        struct f_rndis_opts *opts;

        opts = container_of(f, struct f_rndis_opts, func_inst);
        if (!opts->borrowed_net) {
                if (device_is_registered(&opts->net->dev))
                        gether_cleanup(netdev_priv(opts->net));
                else
                        free_netdev(opts->net);
        }

        kfree(opts->rndis_interf_group);        /* single VLA chunk */
        kfree(opts);
}

static struct usb_function_instance *rndis_alloc_inst(void)
{
        struct f_rndis_opts *opts;
        struct usb_os_desc *descs[1];
        char *names[1];
        struct config_group *rndis_interf_group;

        opts = kzalloc_obj(*opts);
        if (!opts)
                return ERR_PTR(-ENOMEM);
        opts->rndis_os_desc.ext_compat_id = opts->rndis_ext_compat_id;

        mutex_init(&opts->lock);
        opts->func_inst.free_func_inst = rndis_free_inst;
        opts->net = gether_setup_default();
        if (IS_ERR(opts->net)) {
                struct net_device *net = opts->net;
                kfree(opts);
                return ERR_CAST(net);
        }
        INIT_LIST_HEAD(&opts->rndis_os_desc.ext_prop);

        opts->class = rndis_iad_descriptor.bFunctionClass;
        opts->subclass = rndis_iad_descriptor.bFunctionSubClass;
        opts->protocol = rndis_iad_descriptor.bFunctionProtocol;

        descs[0] = &opts->rndis_os_desc;
        names[0] = "rndis";
        config_group_init_type_name(&opts->func_inst.group, "",
                                    &rndis_func_type);
        rndis_interf_group =
                usb_os_desc_prepare_interf_dir(&opts->func_inst.group, 1, descs,
                                               names, THIS_MODULE);
        if (IS_ERR(rndis_interf_group)) {
                rndis_free_inst(&opts->func_inst);
                return ERR_CAST(rndis_interf_group);
        }
        opts->rndis_interf_group = rndis_interf_group;

        return &opts->func_inst;
}

static void rndis_free(struct usb_function *f)
{
        struct f_rndis *rndis;
        struct f_rndis_opts *opts;

        rndis = func_to_rndis(f);
        rndis_deregister(rndis->params);
        opts = container_of(f->fi, struct f_rndis_opts, func_inst);
        kfree(rndis);
        mutex_lock(&opts->lock);
        opts->refcnt--;
        mutex_unlock(&opts->lock);
}

static void rndis_unbind(struct usb_configuration *c, struct usb_function *f)
{
        struct f_rndis          *rndis = func_to_rndis(f);
        struct f_rndis_opts     *rndis_opts;

        rndis_opts = container_of(f->fi, struct f_rndis_opts, func_inst);

        kfree(f->os_desc_table);
        f->os_desc_n = 0;
        usb_free_all_descriptors(f);

        kfree(rndis->notify_req->buf);
        usb_ep_free_request(rndis->notify, rndis->notify_req);

        rndis_opts->bind_count--;
        if (rndis_opts->bind_count == 0 && !rndis_opts->borrowed_net)
                gether_detach_gadget(rndis_opts->net);
}

static struct usb_function *rndis_alloc(struct usb_function_instance *fi)
{
        struct f_rndis  *rndis;
        struct f_rndis_opts *opts;
        struct rndis_params *params;

        /* allocate and initialize one new instance */
        rndis = kzalloc_obj(*rndis);
        if (!rndis)
                return ERR_PTR(-ENOMEM);

        opts = container_of(fi, struct f_rndis_opts, func_inst);
        mutex_lock(&opts->lock);
        opts->refcnt++;

        gether_get_host_addr_u8(opts->net, rndis->ethaddr);
        rndis->vendorID = opts->vendor_id;
        rndis->manufacturer = opts->manufacturer;

        rndis->port.ioport = netdev_priv(opts->net);
        mutex_unlock(&opts->lock);
        /* RNDIS activates when the host changes this filter */
        rndis->port.cdc_filter = 0;

        /* RNDIS has special (and complex) framing */
        rndis->port.header_len = sizeof(struct rndis_packet_msg_type);
        rndis->port.wrap = rndis_add_header;
        rndis->port.unwrap = rndis_rm_hdr;

        rndis->port.func.name = "rndis";
        /* descriptors are per-instance copies */
        rndis->port.func.bind = rndis_bind;
        rndis->port.func.unbind = rndis_unbind;
        rndis->port.func.set_alt = rndis_set_alt;
        rndis->port.func.setup = rndis_setup;
        rndis->port.func.disable = rndis_disable;
        rndis->port.func.free_func = rndis_free;

        params = rndis_register(rndis_response_available, rndis);
        if (IS_ERR(params)) {
                kfree(rndis);
                return ERR_CAST(params);
        }
        rndis->params = params;

        return &rndis->port.func;
}

DECLARE_USB_FUNCTION_INIT(rndis, rndis_alloc_inst, rndis_alloc);
MODULE_DESCRIPTION("RNDIS link function driver");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("David Brownell");