// SPDX-License-Identifier: GPL-2.0+
/*
 * inode.c -- user mode filesystem api for usb gadget controllers
 *
 * Copyright (C) 2003-2004 David Brownell
 * Copyright (C) 2003 Agilent Technologies
 */


/* #define VERBOSE_DEBUG */

#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/fs_context.h>
#include <linux/pagemap.h>
#include <linux/uts.h>
#include <linux/wait.h>
#include <linux/compiler.h>
#include <linux/uaccess.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/poll.h>
#include <linux/kthread.h>
#include <linux/aio.h>
#include <linux/uio.h>
#include <linux/refcount.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/moduleparam.h>

#include <linux/usb/gadgetfs.h>
#include <linux/usb/gadget.h>


/*
 * The gadgetfs API maps each endpoint to a file descriptor so that you
 * can use standard synchronous read/write calls for I/O.  There's some
 * O_NONBLOCK and O_ASYNC/FASYNC style i/o support.  Example usermode
 * drivers show how this works in practice.  You can also use AIO to
 * eliminate I/O gaps between requests, to help when streaming data.
 *
 * Key parts that must be USB-specific are protocols defining how the
 * read/write operations relate to the hardware state machines.  There
 * are two types of files.  One type is for the device, implementing ep0.
 * The other type is for each IN or OUT endpoint.  In both cases, the
 * user mode driver must configure the hardware before using it.
 *
 * - First, dev_config() is called when /dev/gadget/$CHIP is configured
 *   (by writing configuration and device descriptors).  Afterwards it
 *   may serve as a source of device events, used to handle all control
 *   requests other than basic enumeration.
 *
 * - Then, after a SET_CONFIGURATION control request, ep_config() is
 *   called when each /dev/gadget/ep* file is configured (by writing
 *   endpoint descriptors).  Afterwards these files are used to write()
 *   IN data or to read() OUT data.  To halt the endpoint, a "wrong
 *   direction" request is issued (like reading an IN endpoint).
 *
 * Unlike "usbfs" the only ioctl()s are for things that are rare, and maybe
 * not possible on all hardware.  For example, precise fault handling with
 * respect to data left in endpoint fifos after aborted operations; or
 * selective clearing of endpoint halts, to implement SET_INTERFACE.
 */

#define DRIVER_DESC     "USB Gadget filesystem"
#define DRIVER_VERSION  "24 Aug 2004"

static const char driver_desc [] = DRIVER_DESC;
static const char shortname [] = "gadgetfs";

MODULE_DESCRIPTION (DRIVER_DESC);
MODULE_AUTHOR ("David Brownell");
MODULE_LICENSE ("GPL");

static int ep_open(struct inode *, struct file *);


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

#define GADGETFS_MAGIC          0xaee71ee7

/* /dev/gadget/$CHIP represents ep0 and the whole device */
enum ep0_state {
        /* DISABLED is the initial state. */
        STATE_DEV_DISABLED = 0,

        /* Only one open() of /dev/gadget/$CHIP; only one file tracks
         * ep0/device i/o modes and binding to the controller.  Driver
         * must always write descriptors to initialize the device, then
         * the device becomes UNCONNECTED until enumeration.
         */
        STATE_DEV_OPENED,

        /* From then on, ep0 fd is in either of two basic modes:
         * - (UN)CONNECTED: read usb_gadgetfs_event(s) from it
         * - SETUP: read/write will transfer control data and succeed;
         *   or if "wrong direction", performs protocol stall
         */
        STATE_DEV_UNCONNECTED,
        STATE_DEV_CONNECTED,
        STATE_DEV_SETUP,

        /* UNBOUND means the driver closed ep0, so the device won't be
         * accessible again (DEV_DISABLED) until all fds are closed.
         */
        STATE_DEV_UNBOUND,
};

/* enough for the whole queue: most events invalidate others */
#define N_EVENT                 5

struct dev_data {
        spinlock_t                      lock;
        refcount_t                      count;
        int                             udc_usage;
        enum ep0_state                  state;          /* P: lock */
        struct usb_gadgetfs_event       event [N_EVENT];
        unsigned                        ev_next;
        struct fasync_struct            *fasync;
        u8                              current_config;

        /* drivers reading ep0 MUST handle control requests (SETUP)
         * reported that way; else the host will time out.
         */
        unsigned                        usermode_setup : 1,
                                        setup_in : 1,
                                        setup_can_stall : 1,
                                        setup_out_ready : 1,
                                        setup_out_error : 1,
                                        setup_abort : 1,
                                        gadget_registered : 1;
        unsigned                        setup_wLength;

        /* the rest is basically write-once */
        struct usb_config_descriptor    *config, *hs_config;
        struct usb_device_descriptor    *dev;
        struct usb_request              *req;
        struct usb_gadget               *gadget;
        struct list_head                epfiles;
        void                            *buf;
        wait_queue_head_t               wait;
        struct super_block              *sb;
        struct dentry                   *dentry;

        /* except this scratch i/o buffer for ep0 */
        u8                              rbuf [256];
};

static inline void get_dev (struct dev_data *data)
{
        refcount_inc (&data->count);
}

static void put_dev (struct dev_data *data)
{
        if (likely (!refcount_dec_and_test (&data->count)))
                return;
        /* needs no more cleanup */
        BUG_ON (waitqueue_active (&data->wait));
        kfree (data);
}

static struct dev_data *dev_new (void)
{
        struct dev_data         *dev;

        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
        if (!dev)
                return NULL;
        dev->state = STATE_DEV_DISABLED;
        refcount_set (&dev->count, 1);
        spin_lock_init (&dev->lock);
        INIT_LIST_HEAD (&dev->epfiles);
        init_waitqueue_head (&dev->wait);
        return dev;
}

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

/* other /dev/gadget/$ENDPOINT files represent endpoints */
enum ep_state {
        STATE_EP_DISABLED = 0,
        STATE_EP_READY,
        STATE_EP_ENABLED,
        STATE_EP_UNBOUND,
};

struct ep_data {
        struct mutex                    lock;
        enum ep_state                   state;
        refcount_t                      count;
        struct dev_data                 *dev;
        /* must hold dev->lock before accessing ep or req */
        struct usb_ep                   *ep;
        struct usb_request              *req;
        ssize_t                         status;
        char                            name [16];
        struct usb_endpoint_descriptor  desc, hs_desc;
        struct list_head                epfiles;
        wait_queue_head_t               wait;
        struct dentry                   *dentry;
};

static inline void get_ep (struct ep_data *data)
{
        refcount_inc (&data->count);
}

static void put_ep (struct ep_data *data)
{
        if (likely (!refcount_dec_and_test (&data->count)))
                return;
        put_dev (data->dev);
        /* needs no more cleanup */
        BUG_ON (!list_empty (&data->epfiles));
        BUG_ON (waitqueue_active (&data->wait));
        kfree (data);
}

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

/* most "how to use the hardware" policy choices are in userspace:
 * mapping endpoint roles (which the driver needs) to the capabilities
 * which the usb controller has.  most of those capabilities are exposed
 * implicitly, starting with the driver name and then endpoint names.
 */

static const char *CHIP;

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

/* NOTE:  don't use dev_printk calls before binding to the gadget
 * at the end of ep0 configuration, or after unbind.
 */

/* too wordy: dev_printk(level , &(d)->gadget->dev , fmt , ## args) */
#define xprintk(d,level,fmt,args...) \
        printk(level "%s: " fmt , shortname , ## args)

#ifdef DEBUG
#define DBG(dev,fmt,args...) \
        xprintk(dev , KERN_DEBUG , fmt , ## args)
#else
#define DBG(dev,fmt,args...) \
        do { } while (0)
#endif /* DEBUG */

#ifdef VERBOSE_DEBUG
#define VDEBUG  DBG
#else
#define VDEBUG(dev,fmt,args...) \
        do { } while (0)
#endif /* DEBUG */

#define ERROR(dev,fmt,args...) \
        xprintk(dev , KERN_ERR , fmt , ## args)
#define INFO(dev,fmt,args...) \
        xprintk(dev , KERN_INFO , fmt , ## args)


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

/* SYNCHRONOUS ENDPOINT OPERATIONS (bulk/intr/iso)
 *
 * After opening, configure non-control endpoints.  Then use normal
 * stream read() and write() requests; and maybe ioctl() to get more
 * precise FIFO status when recovering from cancellation.
 */

static void epio_complete (struct usb_ep *ep, struct usb_request *req)
{
        struct ep_data  *epdata = ep->driver_data;

        if (!req->context)
                return;
        if (req->status)
                epdata->status = req->status;
        else
                epdata->status = req->actual;
        complete ((struct completion *)req->context);
}

/* tasklock endpoint, returning when it's connected.
 * still need dev->lock to use epdata->ep.
 */
static int
get_ready_ep (unsigned f_flags, struct ep_data *epdata, bool is_write)
{
        int     val;

        if (f_flags & O_NONBLOCK) {
                if (!mutex_trylock(&epdata->lock))
                        goto nonblock;
                if (epdata->state != STATE_EP_ENABLED &&
                    (!is_write || epdata->state != STATE_EP_READY)) {
                        mutex_unlock(&epdata->lock);
nonblock:
                        val = -EAGAIN;
                } else
                        val = 0;
                return val;
        }

        val = mutex_lock_interruptible(&epdata->lock);
        if (val < 0)
                return val;

        switch (epdata->state) {
        case STATE_EP_ENABLED:
                return 0;
        case STATE_EP_READY:                    /* not configured yet */
                if (is_write)
                        return 0;
                fallthrough;
        case STATE_EP_UNBOUND:                  /* clean disconnect */
                break;
        // case STATE_EP_DISABLED:              /* "can't happen" */
        default:                                /* error! */
                pr_debug ("%s: ep %p not available, state %d\n",
                                shortname, epdata, epdata->state);
        }
        mutex_unlock(&epdata->lock);
        return -ENODEV;
}

static ssize_t
ep_io (struct ep_data *epdata, void *buf, unsigned len)
{
        DECLARE_COMPLETION_ONSTACK (done);
        int value;

        spin_lock_irq (&epdata->dev->lock);
        if (likely (epdata->ep != NULL)) {
                struct usb_request      *req = epdata->req;

                req->context = &done;
                req->complete = epio_complete;
                req->buf = buf;
                req->length = len;
                value = usb_ep_queue (epdata->ep, req, GFP_ATOMIC);
        } else
                value = -ENODEV;
        spin_unlock_irq (&epdata->dev->lock);

        if (likely (value == 0)) {
                value = wait_for_completion_interruptible(&done);
                if (value != 0) {
                        spin_lock_irq (&epdata->dev->lock);
                        if (likely (epdata->ep != NULL)) {
                                DBG (epdata->dev, "%s i/o interrupted\n",
                                                epdata->name);
                                usb_ep_dequeue (epdata->ep, epdata->req);
                                spin_unlock_irq (&epdata->dev->lock);

                                wait_for_completion(&done);
                                if (epdata->status == -ECONNRESET)
                                        epdata->status = -EINTR;
                        } else {
                                spin_unlock_irq (&epdata->dev->lock);

                                DBG (epdata->dev, "endpoint gone\n");
                                epdata->status = -ENODEV;
                        }
                }
                return epdata->status;
        }
        return value;
}

static int
ep_release (struct inode *inode, struct file *fd)
{
        struct ep_data          *data = fd->private_data;
        int value;

        value = mutex_lock_interruptible(&data->lock);
        if (value < 0)
                return value;

        /* clean up if this can be reopened */
        if (data->state != STATE_EP_UNBOUND) {
                data->state = STATE_EP_DISABLED;
                data->desc.bDescriptorType = 0;
                data->hs_desc.bDescriptorType = 0;
                usb_ep_disable(data->ep);
        }
        mutex_unlock(&data->lock);
        put_ep (data);
        return 0;
}

static long ep_ioctl(struct file *fd, unsigned code, unsigned long value)
{
        struct ep_data          *data = fd->private_data;
        int                     status;

        if ((status = get_ready_ep (fd->f_flags, data, false)) < 0)
                return status;

        spin_lock_irq (&data->dev->lock);
        if (likely (data->ep != NULL)) {
                switch (code) {
                case GADGETFS_FIFO_STATUS:
                        status = usb_ep_fifo_status (data->ep);
                        break;
                case GADGETFS_FIFO_FLUSH:
                        usb_ep_fifo_flush (data->ep);
                        break;
                case GADGETFS_CLEAR_HALT:
                        status = usb_ep_clear_halt (data->ep);
                        break;
                default:
                        status = -ENOTTY;
                }
        } else
                status = -ENODEV;
        spin_unlock_irq (&data->dev->lock);
        mutex_unlock(&data->lock);
        return status;
}

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

/* ASYNCHRONOUS ENDPOINT I/O OPERATIONS (bulk/intr/iso) */

struct kiocb_priv {
        struct usb_request      *req;
        struct ep_data          *epdata;
        struct kiocb            *iocb;
        struct mm_struct        *mm;
        struct work_struct      work;
        void                    *buf;
        struct iov_iter         to;
        const void              *to_free;
        unsigned                actual;
};

static int ep_aio_cancel(struct kiocb *iocb)
{
        struct kiocb_priv       *priv = iocb->private;
        struct ep_data          *epdata;
        int                     value;

        local_irq_disable();
        epdata = priv->epdata;
        // spin_lock(&epdata->dev->lock);
        if (likely(epdata && epdata->ep && priv->req))
                value = usb_ep_dequeue (epdata->ep, priv->req);
        else
                value = -EINVAL;
        // spin_unlock(&epdata->dev->lock);
        local_irq_enable();

        return value;
}

static void ep_user_copy_worker(struct work_struct *work)
{
        struct kiocb_priv *priv = container_of(work, struct kiocb_priv, work);
        struct mm_struct *mm = priv->mm;
        struct kiocb *iocb = priv->iocb;
        size_t ret;

        kthread_use_mm(mm);
        ret = copy_to_iter(priv->buf, priv->actual, &priv->to);
        kthread_unuse_mm(mm);
        if (!ret)
                ret = -EFAULT;

        /* completing the iocb can drop the ctx and mm, don't touch mm after */
        iocb->ki_complete(iocb, ret, ret);

        kfree(priv->buf);
        kfree(priv->to_free);
        kfree(priv);
}

static void ep_aio_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct kiocb            *iocb = req->context;
        struct kiocb_priv       *priv = iocb->private;
        struct ep_data          *epdata = priv->epdata;

        /* lock against disconnect (and ideally, cancel) */
        spin_lock(&epdata->dev->lock);
        priv->req = NULL;
        priv->epdata = NULL;

        /* if this was a write or a read returning no data then we
         * don't need to copy anything to userspace, so we can
         * complete the aio request immediately.
         */
        if (priv->to_free == NULL || unlikely(req->actual == 0)) {
                kfree(req->buf);
                kfree(priv->to_free);
                kfree(priv);
                iocb->private = NULL;
                /* aio_complete() reports bytes-transferred _and_ faults */

                iocb->ki_complete(iocb,
                                req->actual ? req->actual : (long)req->status,
                                req->status);
        } else {
                /* ep_copy_to_user() won't report both; we hide some faults */
                if (unlikely(0 != req->status))
                        DBG(epdata->dev, "%s fault %d len %d\n",
                                ep->name, req->status, req->actual);

                priv->buf = req->buf;
                priv->actual = req->actual;
                INIT_WORK(&priv->work, ep_user_copy_worker);
                schedule_work(&priv->work);
        }

        usb_ep_free_request(ep, req);
        spin_unlock(&epdata->dev->lock);
        put_ep(epdata);
}

static ssize_t ep_aio(struct kiocb *iocb,
                      struct kiocb_priv *priv,
                      struct ep_data *epdata,
                      char *buf,
                      size_t len)
{
        struct usb_request *req;
        ssize_t value;

        iocb->private = priv;
        priv->iocb = iocb;

        kiocb_set_cancel_fn(iocb, ep_aio_cancel);
        get_ep(epdata);
        priv->epdata = epdata;
        priv->actual = 0;
        priv->mm = current->mm; /* mm teardown waits for iocbs in exit_aio() */

        /* each kiocb is coupled to one usb_request, but we can't
         * allocate or submit those if the host disconnected.
         */
        spin_lock_irq(&epdata->dev->lock);
        value = -ENODEV;
        if (unlikely(epdata->ep == NULL))
                goto fail;

        req = usb_ep_alloc_request(epdata->ep, GFP_ATOMIC);
        value = -ENOMEM;
        if (unlikely(!req))
                goto fail;

        priv->req = req;
        req->buf = buf;
        req->length = len;
        req->complete = ep_aio_complete;
        req->context = iocb;
        value = usb_ep_queue(epdata->ep, req, GFP_ATOMIC);
        if (unlikely(0 != value)) {
                usb_ep_free_request(epdata->ep, req);
                goto fail;
        }
        spin_unlock_irq(&epdata->dev->lock);
        return -EIOCBQUEUED;

fail:
        spin_unlock_irq(&epdata->dev->lock);
        kfree(priv->to_free);
        kfree(priv);
        put_ep(epdata);
        return value;
}

static ssize_t
ep_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct ep_data *epdata = file->private_data;
        size_t len = iov_iter_count(to);
        ssize_t value;
        char *buf;

        if ((value = get_ready_ep(file->f_flags, epdata, false)) < 0)
                return value;

        /* halt any endpoint by doing a "wrong direction" i/o call */
        if (usb_endpoint_dir_in(&epdata->desc)) {
                if (usb_endpoint_xfer_isoc(&epdata->desc) ||
                    !is_sync_kiocb(iocb)) {
                        mutex_unlock(&epdata->lock);
                        return -EINVAL;
                }
                DBG (epdata->dev, "%s halt\n", epdata->name);
                spin_lock_irq(&epdata->dev->lock);
                if (likely(epdata->ep != NULL))
                        usb_ep_set_halt(epdata->ep);
                spin_unlock_irq(&epdata->dev->lock);
                mutex_unlock(&epdata->lock);
                return -EBADMSG;
        }

        buf = kmalloc(len, GFP_KERNEL);
        if (unlikely(!buf)) {
                mutex_unlock(&epdata->lock);
                return -ENOMEM;
        }
        if (is_sync_kiocb(iocb)) {
                value = ep_io(epdata, buf, len);
                if (value >= 0 && (copy_to_iter(buf, value, to) != value))
                        value = -EFAULT;
        } else {
                struct kiocb_priv *priv = kzalloc(sizeof *priv, GFP_KERNEL);
                value = -ENOMEM;
                if (!priv)
                        goto fail;
                priv->to_free = dup_iter(&priv->to, to, GFP_KERNEL);
                if (!priv->to_free) {
                        kfree(priv);
                        goto fail;
                }
                value = ep_aio(iocb, priv, epdata, buf, len);
                if (value == -EIOCBQUEUED)
                        buf = NULL;
        }
fail:
        kfree(buf);
        mutex_unlock(&epdata->lock);
        return value;
}

static ssize_t ep_config(struct ep_data *, const char *, size_t);

static ssize_t
ep_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
        struct file *file = iocb->ki_filp;
        struct ep_data *epdata = file->private_data;
        size_t len = iov_iter_count(from);
        bool configured;
        ssize_t value;
        char *buf;

        if ((value = get_ready_ep(file->f_flags, epdata, true)) < 0)
                return value;

        configured = epdata->state == STATE_EP_ENABLED;

        /* halt any endpoint by doing a "wrong direction" i/o call */
        if (configured && !usb_endpoint_dir_in(&epdata->desc)) {
                if (usb_endpoint_xfer_isoc(&epdata->desc) ||
                    !is_sync_kiocb(iocb)) {
                        mutex_unlock(&epdata->lock);
                        return -EINVAL;
                }
                DBG (epdata->dev, "%s halt\n", epdata->name);
                spin_lock_irq(&epdata->dev->lock);
                if (likely(epdata->ep != NULL))
                        usb_ep_set_halt(epdata->ep);
                spin_unlock_irq(&epdata->dev->lock);
                mutex_unlock(&epdata->lock);
                return -EBADMSG;
        }

        buf = kmalloc(len, GFP_KERNEL);
        if (unlikely(!buf)) {
                mutex_unlock(&epdata->lock);
                return -ENOMEM;
        }

        if (unlikely(!copy_from_iter_full(buf, len, from))) {
                value = -EFAULT;
                goto out;
        }

        if (unlikely(!configured)) {
                value = ep_config(epdata, buf, len);
        } else if (is_sync_kiocb(iocb)) {
                value = ep_io(epdata, buf, len);
        } else {
                struct kiocb_priv *priv = kzalloc(sizeof *priv, GFP_KERNEL);
                value = -ENOMEM;
                if (priv) {
                        value = ep_aio(iocb, priv, epdata, buf, len);
                        if (value == -EIOCBQUEUED)
                                buf = NULL;
                }
        }
out:
        kfree(buf);
        mutex_unlock(&epdata->lock);
        return value;
}

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

/* used after endpoint configuration */
static const struct file_operations ep_io_operations = {
        .owner =        THIS_MODULE,

        .open =         ep_open,
        .release =      ep_release,
        .llseek =       no_llseek,
        .unlocked_ioctl = ep_ioctl,
        .read_iter =    ep_read_iter,
        .write_iter =   ep_write_iter,
};

/* ENDPOINT INITIALIZATION
 *
 *     fd = open ("/dev/gadget/$ENDPOINT", O_RDWR)
 *     status = write (fd, descriptors, sizeof descriptors)
 *
 * That write establishes the endpoint configuration, configuring
 * the controller to process bulk, interrupt, or isochronous transfers
 * at the right maxpacket size, and so on.
 *
 * The descriptors are message type 1, identified by a host order u32
 * at the beginning of what's written.  Descriptor order is: full/low
 * speed descriptor, then optional high speed descriptor.
 */
static ssize_t
ep_config (struct ep_data *data, const char *buf, size_t len)
{
        struct usb_ep           *ep;
        u32                     tag;
        int                     value, length = len;

        if (data->state != STATE_EP_READY) {
                value = -EL2HLT;
                goto fail;
        }

        value = len;
        if (len < USB_DT_ENDPOINT_SIZE + 4)
                goto fail0;

        /* we might need to change message format someday */
        memcpy(&tag, buf, 4);
        if (tag != 1) {
                DBG(data->dev, "config %s, bad tag %d\n", data->name, tag);
                goto fail0;
        }
        buf += 4;
        len -= 4;

        /* NOTE:  audio endpoint extensions not accepted here;
         * just don't include the extra bytes.
         */

        /* full/low speed descriptor, then high speed */
        memcpy(&data->desc, buf, USB_DT_ENDPOINT_SIZE);
        if (data->desc.bLength != USB_DT_ENDPOINT_SIZE
                        || data->desc.bDescriptorType != USB_DT_ENDPOINT)
                goto fail0;
        if (len != USB_DT_ENDPOINT_SIZE) {
                if (len != 2 * USB_DT_ENDPOINT_SIZE)
                        goto fail0;
                memcpy(&data->hs_desc, buf + USB_DT_ENDPOINT_SIZE,
                        USB_DT_ENDPOINT_SIZE);
                if (data->hs_desc.bLength != USB_DT_ENDPOINT_SIZE
                                || data->hs_desc.bDescriptorType
                                        != USB_DT_ENDPOINT) {
                        DBG(data->dev, "config %s, bad hs length or type\n",
                                        data->name);
                        goto fail0;
                }
        }

        spin_lock_irq (&data->dev->lock);
        if (data->dev->state == STATE_DEV_UNBOUND) {
                value = -ENOENT;
                goto gone;
        } else {
                ep = data->ep;
                if (ep == NULL) {
                        value = -ENODEV;
                        goto gone;
                }
        }
        switch (data->dev->gadget->speed) {
        case USB_SPEED_LOW:
        case USB_SPEED_FULL:
                ep->desc = &data->desc;
                break;
        case USB_SPEED_HIGH:
                /* fails if caller didn't provide that descriptor... */
                ep->desc = &data->hs_desc;
                break;
        default:
                DBG(data->dev, "unconnected, %s init abandoned\n",
                                data->name);
                value = -EINVAL;
                goto gone;
        }
        value = usb_ep_enable(ep);
        if (value == 0) {
                data->state = STATE_EP_ENABLED;
                value = length;
        }
gone:
        spin_unlock_irq (&data->dev->lock);
        if (value < 0) {
fail:
                data->desc.bDescriptorType = 0;
                data->hs_desc.bDescriptorType = 0;
        }
        return value;
fail0:
        value = -EINVAL;
        goto fail;
}

static int
ep_open (struct inode *inode, struct file *fd)
{
        struct ep_data          *data = inode->i_private;
        int                     value = -EBUSY;

        if (mutex_lock_interruptible(&data->lock) != 0)
                return -EINTR;
        spin_lock_irq (&data->dev->lock);
        if (data->dev->state == STATE_DEV_UNBOUND)
                value = -ENOENT;
        else if (data->state == STATE_EP_DISABLED) {
                value = 0;
                data->state = STATE_EP_READY;
                get_ep (data);
                fd->private_data = data;
                VDEBUG (data->dev, "%s ready\n", data->name);
        } else
                DBG (data->dev, "%s state %d\n",
                        data->name, data->state);
        spin_unlock_irq (&data->dev->lock);
        mutex_unlock(&data->lock);
        return value;
}

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

/* EP0 IMPLEMENTATION can be partly in userspace.
 *
 * Drivers that use this facility receive various events, including
 * control requests the kernel doesn't handle.  Drivers that don't
 * use this facility may be too simple-minded for real applications.
 */

static inline void ep0_readable (struct dev_data *dev)
{
        wake_up (&dev->wait);
        kill_fasync (&dev->fasync, SIGIO, POLL_IN);
}

static void clean_req (struct usb_ep *ep, struct usb_request *req)
{
        struct dev_data         *dev = ep->driver_data;

        if (req->buf != dev->rbuf) {
                kfree(req->buf);
                req->buf = dev->rbuf;
        }
        req->complete = epio_complete;
        dev->setup_out_ready = 0;
}

static void ep0_complete (struct usb_ep *ep, struct usb_request *req)
{
        struct dev_data         *dev = ep->driver_data;
        unsigned long           flags;
        int                     free = 1;

        /* for control OUT, data must still get to userspace */
        spin_lock_irqsave(&dev->lock, flags);
        if (!dev->setup_in) {
                dev->setup_out_error = (req->status != 0);
                if (!dev->setup_out_error)
                        free = 0;
                dev->setup_out_ready = 1;
                ep0_readable (dev);
        }

        /* clean up as appropriate */
        if (free && req->buf != &dev->rbuf)
                clean_req (ep, req);
        req->complete = epio_complete;
        spin_unlock_irqrestore(&dev->lock, flags);
}

static int setup_req (struct usb_ep *ep, struct usb_request *req, u16 len)
{
        struct dev_data *dev = ep->driver_data;

        if (dev->setup_out_ready) {
                DBG (dev, "ep0 request busy!\n");
                return -EBUSY;
        }
        if (len > sizeof (dev->rbuf))
                req->buf = kmalloc(len, GFP_ATOMIC);
        if (req->buf == NULL) {
                req->buf = dev->rbuf;
                return -ENOMEM;
        }
        req->complete = ep0_complete;
        req->length = len;
        req->zero = 0;
        return 0;
}

static ssize_t
ep0_read (struct file *fd, char __user *buf, size_t len, loff_t *ptr)
{
        struct dev_data                 *dev = fd->private_data;
        ssize_t                         retval;
        enum ep0_state                  state;

        spin_lock_irq (&dev->lock);
        if (dev->state <= STATE_DEV_OPENED) {
                retval = -EINVAL;
                goto done;
        }

        /* report fd mode change before acting on it */
        if (dev->setup_abort) {
                dev->setup_abort = 0;
                retval = -EIDRM;
                goto done;
        }

        /* control DATA stage */
        if ((state = dev->state) == STATE_DEV_SETUP) {

                if (dev->setup_in) {            /* stall IN */
                        VDEBUG(dev, "ep0in stall\n");
                        (void) usb_ep_set_halt (dev->gadget->ep0);
                        retval = -EL2HLT;
                        dev->state = STATE_DEV_CONNECTED;

                } else if (len == 0) {          /* ack SET_CONFIGURATION etc */
                        struct usb_ep           *ep = dev->gadget->ep0;
                        struct usb_request      *req = dev->req;

                        if ((retval = setup_req (ep, req, 0)) == 0) {
                                ++dev->udc_usage;
                                spin_unlock_irq (&dev->lock);
                                retval = usb_ep_queue (ep, req, GFP_KERNEL);
                                spin_lock_irq (&dev->lock);
                                --dev->udc_usage;
                        }
                        dev->state = STATE_DEV_CONNECTED;

                        /* assume that was SET_CONFIGURATION */
                        if (dev->current_config) {
                                unsigned power;

                                if (gadget_is_dualspeed(dev->gadget)
                                                && (dev->gadget->speed
                                                        == USB_SPEED_HIGH))
                                        power = dev->hs_config->bMaxPower;
                                else
                                        power = dev->config->bMaxPower;
                                usb_gadget_vbus_draw(dev->gadget, 2 * power);
                        }

                } else {                        /* collect OUT data */
                        if ((fd->f_flags & O_NONBLOCK) != 0
                                        && !dev->setup_out_ready) {
                                retval = -EAGAIN;
                                goto done;
                        }
                        spin_unlock_irq (&dev->lock);
                        retval = wait_event_interruptible (dev->wait,
                                        dev->setup_out_ready != 0);

                        /* FIXME state could change from under us */
                        spin_lock_irq (&dev->lock);
                        if (retval)
                                goto done;

                        if (dev->state != STATE_DEV_SETUP) {
                                retval = -ECANCELED;
                                goto done;
                        }
                        dev->state = STATE_DEV_CONNECTED;

                        if (dev->setup_out_error)
                                retval = -EIO;
                        else {
                                len = min (len, (size_t)dev->req->actual);
                                ++dev->udc_usage;
                                spin_unlock_irq(&dev->lock);
                                if (copy_to_user (buf, dev->req->buf, len))
                                        retval = -EFAULT;
                                else
                                        retval = len;
                                spin_lock_irq(&dev->lock);
                                --dev->udc_usage;
                                clean_req (dev->gadget->ep0, dev->req);
                                /* NOTE userspace can't yet choose to stall */
                        }
                }
                goto done;
        }

        /* else normal: return event data */
        if (len < sizeof dev->event [0]) {
                retval = -EINVAL;
                goto done;
        }
        len -= len % sizeof (struct usb_gadgetfs_event);
        dev->usermode_setup = 1;

scan:
        /* return queued events right away */
        if (dev->ev_next != 0) {
                unsigned                i, n;

                n = len / sizeof (struct usb_gadgetfs_event);
                if (dev->ev_next < n)
                        n = dev->ev_next;

                /* ep0 i/o has special semantics during STATE_DEV_SETUP */
                for (i = 0; i < n; i++) {
                        if (dev->event [i].type == GADGETFS_SETUP) {
                                dev->state = STATE_DEV_SETUP;
                                n = i + 1;
                                break;
                        }
                }
                spin_unlock_irq (&dev->lock);
                len = n * sizeof (struct usb_gadgetfs_event);
                if (copy_to_user (buf, &dev->event, len))
                        retval = -EFAULT;
                else
                        retval = len;
                if (len > 0) {
                        /* NOTE this doesn't guard against broken drivers;
                         * concurrent ep0 readers may lose events.
                         */
                        spin_lock_irq (&dev->lock);
                        if (dev->ev_next > n) {
                                memmove(&dev->event[0], &dev->event[n],
                                        sizeof (struct usb_gadgetfs_event)
                                                * (dev->ev_next - n));
                        }
                        dev->ev_next -= n;
                        spin_unlock_irq (&dev->lock);
                }
                return retval;
        }
        if (fd->f_flags & O_NONBLOCK) {
                retval = -EAGAIN;
                goto done;
        }

        switch (state) {
        default:
                DBG (dev, "fail %s, state %d\n", __func__, state);
                retval = -ESRCH;
                break;
        case STATE_DEV_UNCONNECTED:
        case STATE_DEV_CONNECTED:
                spin_unlock_irq (&dev->lock);
                DBG (dev, "%s wait\n", __func__);

                /* wait for events */
                retval = wait_event_interruptible (dev->wait,
                                dev->ev_next != 0);
                if (retval < 0)
                        return retval;
                spin_lock_irq (&dev->lock);
                goto scan;
        }

done:
        spin_unlock_irq (&dev->lock);
        return retval;
}

static struct usb_gadgetfs_event *
next_event (struct dev_data *dev, enum usb_gadgetfs_event_type type)
{
        struct usb_gadgetfs_event       *event;
        unsigned                        i;

        switch (type) {
        /* these events purge the queue */
        case GADGETFS_DISCONNECT:
                if (dev->state == STATE_DEV_SETUP)
                        dev->setup_abort = 1;
                fallthrough;
        case GADGETFS_CONNECT:
                dev->ev_next = 0;
                break;
        case GADGETFS_SETUP:            /* previous request timed out */
        case GADGETFS_SUSPEND:          /* same effect */
                /* these events can't be repeated */
                for (i = 0; i != dev->ev_next; i++) {
                        if (dev->event [i].type != type)
                                continue;
                        DBG(dev, "discard old event[%d] %d\n", i, type);
                        dev->ev_next--;
                        if (i == dev->ev_next)
                                break;
                        /* indices start at zero, for simplicity */
                        memmove (&dev->event [i], &dev->event [i + 1],
                                sizeof (struct usb_gadgetfs_event)
                                        * (dev->ev_next - i));
                }
                break;
        default:
                BUG ();
        }
        VDEBUG(dev, "event[%d] = %d\n", dev->ev_next, type);
        event = &dev->event [dev->ev_next++];
        BUG_ON (dev->ev_next > N_EVENT);
        memset (event, 0, sizeof *event);
        event->type = type;
        return event;
}

static ssize_t
ep0_write (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
{
        struct dev_data         *dev = fd->private_data;
        ssize_t                 retval = -ESRCH;

        /* report fd mode change before acting on it */
        if (dev->setup_abort) {
                dev->setup_abort = 0;
                retval = -EIDRM;

        /* data and/or status stage for control request */
        } else if (dev->state == STATE_DEV_SETUP) {

                len = min_t(size_t, len, dev->setup_wLength);
                if (dev->setup_in) {
                        retval = setup_req (dev->gadget->ep0, dev->req, len);
                        if (retval == 0) {
                                dev->state = STATE_DEV_CONNECTED;
                                ++dev->udc_usage;
                                spin_unlock_irq (&dev->lock);
                                if (copy_from_user (dev->req->buf, buf, len))
                                        retval = -EFAULT;
                                else {
                                        if (len < dev->setup_wLength)
                                                dev->req->zero = 1;
                                        retval = usb_ep_queue (
                                                dev->gadget->ep0, dev->req,
                                                GFP_KERNEL);
                                }
                                spin_lock_irq(&dev->lock);
                                --dev->udc_usage;
                                if (retval < 0) {
                                        clean_req (dev->gadget->ep0, dev->req);
                                } else
                                        retval = len;

                                return retval;
                        }

                /* can stall some OUT transfers */
                } else if (dev->setup_can_stall) {
                        VDEBUG(dev, "ep0out stall\n");
                        (void) usb_ep_set_halt (dev->gadget->ep0);
                        retval = -EL2HLT;
                        dev->state = STATE_DEV_CONNECTED;
                } else {
                        DBG(dev, "bogus ep0out stall!\n");
                }
        } else
                DBG (dev, "fail %s, state %d\n", __func__, dev->state);

        return retval;
}

static int
ep0_fasync (int f, struct file *fd, int on)
{
        struct dev_data         *dev = fd->private_data;
        // caller must F_SETOWN before signal delivery happens
        VDEBUG (dev, "%s %s\n", __func__, on ? "on" : "off");
        return fasync_helper (f, fd, on, &dev->fasync);
}

static struct usb_gadget_driver gadgetfs_driver;

static int
dev_release (struct inode *inode, struct file *fd)
{
        struct dev_data         *dev = fd->private_data;

        /* closing ep0 === shutdown all */

        if (dev->gadget_registered) {
                usb_gadget_unregister_driver (&gadgetfs_driver);
                dev->gadget_registered = false;
        }

        /* at this point "good" hardware has disconnected the
         * device from USB; the host won't see it any more.
         * alternatively, all host requests will time out.
         */

        kfree (dev->buf);
        dev->buf = NULL;

        /* other endpoints were all decoupled from this device */
        spin_lock_irq(&dev->lock);
        dev->state = STATE_DEV_DISABLED;
        spin_unlock_irq(&dev->lock);

        put_dev (dev);
        return 0;
}

static __poll_t
ep0_poll (struct file *fd, poll_table *wait)
{
        struct dev_data         *dev = fd->private_data;
        __poll_t                mask = 0;

        if (dev->state <= STATE_DEV_OPENED)
                return DEFAULT_POLLMASK;

        poll_wait(fd, &dev->wait, wait);

        spin_lock_irq(&dev->lock);

        /* report fd mode change before acting on it */
        if (dev->setup_abort) {
                dev->setup_abort = 0;
                mask = EPOLLHUP;
                goto out;
        }

        if (dev->state == STATE_DEV_SETUP) {
                if (dev->setup_in || dev->setup_can_stall)
                        mask = EPOLLOUT;
        } else {
                if (dev->ev_next != 0)
                        mask = EPOLLIN;
        }
out:
        spin_unlock_irq(&dev->lock);
        return mask;
}

static long dev_ioctl (struct file *fd, unsigned code, unsigned long value)
{
        struct dev_data         *dev = fd->private_data;
        struct usb_gadget       *gadget = dev->gadget;
        long ret = -ENOTTY;

        spin_lock_irq(&dev->lock);
        if (dev->state == STATE_DEV_OPENED ||
                        dev->state == STATE_DEV_UNBOUND) {
                /* Not bound to a UDC */
        } else if (gadget->ops->ioctl) {
                ++dev->udc_usage;
                spin_unlock_irq(&dev->lock);

                ret = gadget->ops->ioctl (gadget, code, value);

                spin_lock_irq(&dev->lock);
                --dev->udc_usage;
        }
        spin_unlock_irq(&dev->lock);

        return ret;
}

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

/* The in-kernel gadget driver handles most ep0 issues, in particular
 * enumerating the single configuration (as provided from user space).
 *
 * Unrecognized ep0 requests may be handled in user space.
 */

static void make_qualifier (struct dev_data *dev)
{
        struct usb_qualifier_descriptor         qual;
        struct usb_device_descriptor            *desc;

        qual.bLength = sizeof qual;
        qual.bDescriptorType = USB_DT_DEVICE_QUALIFIER;
        qual.bcdUSB = cpu_to_le16 (0x0200);

        desc = dev->dev;
        qual.bDeviceClass = desc->bDeviceClass;
        qual.bDeviceSubClass = desc->bDeviceSubClass;
        qual.bDeviceProtocol = desc->bDeviceProtocol;

        /* assumes ep0 uses the same value for both speeds ... */
        qual.bMaxPacketSize0 = dev->gadget->ep0->maxpacket;

        qual.bNumConfigurations = 1;
        qual.bRESERVED = 0;

        memcpy (dev->rbuf, &qual, sizeof qual);
}

static int
config_buf (struct dev_data *dev, u8 type, unsigned index)
{
        int             len;
        int             hs = 0;

        /* only one configuration */
        if (index > 0)
                return -EINVAL;

        if (gadget_is_dualspeed(dev->gadget)) {
                hs = (dev->gadget->speed == USB_SPEED_HIGH);
                if (type == USB_DT_OTHER_SPEED_CONFIG)
                        hs = !hs;
        }
        if (hs) {
                dev->req->buf = dev->hs_config;
                len = le16_to_cpu(dev->hs_config->wTotalLength);
        } else {
                dev->req->buf = dev->config;
                len = le16_to_cpu(dev->config->wTotalLength);
        }
        ((u8 *)dev->req->buf) [1] = type;
        return len;
}

static int
gadgetfs_setup (struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
{
        struct dev_data                 *dev = get_gadget_data (gadget);
        struct usb_request              *req = dev->req;
        int                             value = -EOPNOTSUPP;
        struct usb_gadgetfs_event       *event;
        u16                             w_value = le16_to_cpu(ctrl->wValue);
        u16                             w_length = le16_to_cpu(ctrl->wLength);

        spin_lock (&dev->lock);
        dev->setup_abort = 0;
        if (dev->state == STATE_DEV_UNCONNECTED) {
                if (gadget_is_dualspeed(gadget)
                                && gadget->speed == USB_SPEED_HIGH
                                && dev->hs_config == NULL) {
                        spin_unlock(&dev->lock);
                        ERROR (dev, "no high speed config??\n");
                        return -EINVAL;
                }

                dev->state = STATE_DEV_CONNECTED;

                INFO (dev, "connected\n");
                event = next_event (dev, GADGETFS_CONNECT);
                event->u.speed = gadget->speed;
                ep0_readable (dev);

        /* host may have given up waiting for response.  we can miss control
         * requests handled lower down (device/endpoint status and features);
         * then ep0_{read,write} will report the wrong status. controller
         * driver will have aborted pending i/o.
         */
        } else if (dev->state == STATE_DEV_SETUP)
                dev->setup_abort = 1;

        req->buf = dev->rbuf;
        req->context = NULL;
        switch (ctrl->bRequest) {

        case USB_REQ_GET_DESCRIPTOR:
                if (ctrl->bRequestType != USB_DIR_IN)
                        goto unrecognized;
                switch (w_value >> 8) {

                case USB_DT_DEVICE:
                        value = min (w_length, (u16) sizeof *dev->dev);
                        dev->dev->bMaxPacketSize0 = dev->gadget->ep0->maxpacket;
                        req->buf = dev->dev;
                        break;
                case USB_DT_DEVICE_QUALIFIER:
                        if (!dev->hs_config)
                                break;
                        value = min (w_length, (u16)
                                sizeof (struct usb_qualifier_descriptor));
                        make_qualifier (dev);
                        break;
                case USB_DT_OTHER_SPEED_CONFIG:
                case USB_DT_CONFIG:
                        value = config_buf (dev,
                                        w_value >> 8,
                                        w_value & 0xff);
                        if (value >= 0)
                                value = min (w_length, (u16) value);
                        break;
                case USB_DT_STRING:
                        goto unrecognized;

                default:                // all others are errors
                        break;
                }
                break;

        /* currently one config, two speeds */
        case USB_REQ_SET_CONFIGURATION:
                if (ctrl->bRequestType != 0)
                        goto unrecognized;
                if (0 == (u8) w_value) {
                        value = 0;
                        dev->current_config = 0;
                        usb_gadget_vbus_draw(gadget, 8 /* mA */ );
                        // user mode expected to disable endpoints
                } else {
                        u8      config, power;

                        if (gadget_is_dualspeed(gadget)
                                        && gadget->speed == USB_SPEED_HIGH) {
                                config = dev->hs_config->bConfigurationValue;
                                power = dev->hs_config->bMaxPower;
                        } else {
                                config = dev->config->bConfigurationValue;
                                power = dev->config->bMaxPower;
                        }

                        if (config == (u8) w_value) {
                                value = 0;
                                dev->current_config = config;
                                usb_gadget_vbus_draw(gadget, 2 * power);
                        }
                }

                /* report SET_CONFIGURATION like any other control request,
                 * except that usermode may not stall this.  the next
                 * request mustn't be allowed start until this finishes:
                 * endpoints and threads set up, etc.
                 *
                 * NOTE:  older PXA hardware (before PXA 255: without UDCCFR)
                 * has bad/racey automagic that prevents synchronizing here.
                 * even kernel mode drivers often miss them.
                 */
                if (value == 0) {
                        INFO (dev, "configuration #%d\n", dev->current_config);
                        usb_gadget_set_state(gadget, USB_STATE_CONFIGURED);
                        if (dev->usermode_setup) {
                                dev->setup_can_stall = 0;
                                goto delegate;
                        }
                }
                break;

#ifndef CONFIG_USB_PXA25X
        /* PXA automagically handles this request too */
        case USB_REQ_GET_CONFIGURATION:
                if (ctrl->bRequestType != 0x80)
                        goto unrecognized;
                *(u8 *)req->buf = dev->current_config;
                value = min (w_length, (u16) 1);
                break;
#endif

        default:
unrecognized:
                VDEBUG (dev, "%s req%02x.%02x v%04x i%04x l%d\n",
                        dev->usermode_setup ? "delegate" : "fail",
                        ctrl->bRequestType, ctrl->bRequest,
                        w_value, le16_to_cpu(ctrl->wIndex), w_length);

                /* if there's an ep0 reader, don't stall */
                if (dev->usermode_setup) {
                        dev->setup_can_stall = 1;
delegate:
                        dev->setup_in = (ctrl->bRequestType & USB_DIR_IN)
                                                ? 1 : 0;
                        dev->setup_wLength = w_length;
                        dev->setup_out_ready = 0;
                        dev->setup_out_error = 0;

                        /* read DATA stage for OUT right away */
                        if (unlikely (!dev->setup_in && w_length)) {
                                value = setup_req (gadget->ep0, dev->req,
                                                        w_length);
                                if (value < 0)
                                        break;

                                ++dev->udc_usage;
                                spin_unlock (&dev->lock);
                                value = usb_ep_queue (gadget->ep0, dev->req,
                                                        GFP_KERNEL);
                                spin_lock (&dev->lock);
                                --dev->udc_usage;
                                if (value < 0) {
                                        clean_req (gadget->ep0, dev->req);
                                        break;
                                }

                                /* we can't currently stall these */
                                dev->setup_can_stall = 0;
                        }

                        /* state changes when reader collects event */
                        event = next_event (dev, GADGETFS_SETUP);
                        event->u.setup = *ctrl;
                        ep0_readable (dev);
                        spin_unlock (&dev->lock);
                        return 0;
                }
        }

        /* proceed with data transfer and status phases? */
        if (value >= 0 && dev->state != STATE_DEV_SETUP) {
                req->length = value;
                req->zero = value < w_length;

                ++dev->udc_usage;
                spin_unlock (&dev->lock);
                value = usb_ep_queue (gadget->ep0, req, GFP_KERNEL);
                spin_lock(&dev->lock);
                --dev->udc_usage;
                spin_unlock(&dev->lock);
                if (value < 0) {
                        DBG (dev, "ep_queue --> %d\n", value);
                        req->status = 0;
                }
                return value;
        }

        /* device stalls when value < 0 */
        spin_unlock (&dev->lock);
        return value;
}

static void destroy_ep_files (struct dev_data *dev)
{
        DBG (dev, "%s %d\n", __func__, dev->state);

        /* dev->state must prevent interference */
        spin_lock_irq (&dev->lock);
        while (!list_empty(&dev->epfiles)) {
                struct ep_data  *ep;
                struct inode    *parent;
                struct dentry   *dentry;

                /* break link to FS */
                ep = list_first_entry (&dev->epfiles, struct ep_data, epfiles);
                list_del_init (&ep->epfiles);
                spin_unlock_irq (&dev->lock);

                dentry = ep->dentry;
                ep->dentry = NULL;
                parent = d_inode(dentry->d_parent);

                /* break link to controller */
                mutex_lock(&ep->lock);
                if (ep->state == STATE_EP_ENABLED)
                        (void) usb_ep_disable (ep->ep);
                ep->state = STATE_EP_UNBOUND;
                usb_ep_free_request (ep->ep, ep->req);
                ep->ep = NULL;
                mutex_unlock(&ep->lock);

                wake_up (&ep->wait);
                put_ep (ep);

                /* break link to dcache */
                inode_lock(parent);
                d_delete (dentry);
                dput (dentry);
                inode_unlock(parent);

                spin_lock_irq (&dev->lock);
        }
        spin_unlock_irq (&dev->lock);
}


static struct dentry *
gadgetfs_create_file (struct super_block *sb, char const *name,
                void *data, const struct file_operations *fops);

static int activate_ep_files (struct dev_data *dev)
{
        struct usb_ep   *ep;
        struct ep_data  *data;

        gadget_for_each_ep (ep, dev->gadget) {

                data = kzalloc(sizeof(*data), GFP_KERNEL);
                if (!data)
                        goto enomem0;
                data->state = STATE_EP_DISABLED;
                mutex_init(&data->lock);
                init_waitqueue_head (&data->wait);

                strncpy (data->name, ep->name, sizeof (data->name) - 1);
                refcount_set (&data->count, 1);
                data->dev = dev;
                get_dev (dev);

                data->ep = ep;
                ep->driver_data = data;

                data->req = usb_ep_alloc_request (ep, GFP_KERNEL);
                if (!data->req)
                        goto enomem1;

                data->dentry = gadgetfs_create_file (dev->sb, data->name,
                                data, &ep_io_operations);
                if (!data->dentry)
                        goto enomem2;
                list_add_tail (&data->epfiles, &dev->epfiles);
        }
        return 0;

enomem2:
        usb_ep_free_request (ep, data->req);
enomem1:
        put_dev (dev);
        kfree (data);
enomem0:
        DBG (dev, "%s enomem\n", __func__);
        destroy_ep_files (dev);
        return -ENOMEM;
}

static void
gadgetfs_unbind (struct usb_gadget *gadget)
{
        struct dev_data         *dev = get_gadget_data (gadget);

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

        spin_lock_irq (&dev->lock);
        dev->state = STATE_DEV_UNBOUND;
        while (dev->udc_usage > 0) {
                spin_unlock_irq(&dev->lock);
                usleep_range(1000, 2000);
                spin_lock_irq(&dev->lock);
        }
        spin_unlock_irq (&dev->lock);

        destroy_ep_files (dev);
        gadget->ep0->driver_data = NULL;
        set_gadget_data (gadget, NULL);

        /* we've already been disconnected ... no i/o is active */
        if (dev->req)
                usb_ep_free_request (gadget->ep0, dev->req);
        DBG (dev, "%s done\n", __func__);
        put_dev (dev);
}

static struct dev_data          *the_device;

static int gadgetfs_bind(struct usb_gadget *gadget,
                struct usb_gadget_driver *driver)
{
        struct dev_data         *dev = the_device;

        if (!dev)
                return -ESRCH;
        if (0 != strcmp (CHIP, gadget->name)) {
                pr_err("%s expected %s controller not %s\n",
                        shortname, CHIP, gadget->name);
                return -ENODEV;
        }

        set_gadget_data (gadget, dev);
        dev->gadget = gadget;
        gadget->ep0->driver_data = dev;

        /* preallocate control response and buffer */
        dev->req = usb_ep_alloc_request (gadget->ep0, GFP_KERNEL);
        if (!dev->req)
                goto enomem;
        dev->req->context = NULL;
        dev->req->complete = epio_complete;

        if (activate_ep_files (dev) < 0)
                goto enomem;

        INFO (dev, "bound to %s driver\n", gadget->name);
        spin_lock_irq(&dev->lock);
        dev->state = STATE_DEV_UNCONNECTED;
        spin_unlock_irq(&dev->lock);
        get_dev (dev);
        return 0;

enomem:
        gadgetfs_unbind (gadget);
        return -ENOMEM;
}

static void
gadgetfs_disconnect (struct usb_gadget *gadget)
{
        struct dev_data         *dev = get_gadget_data (gadget);
        unsigned long           flags;

        spin_lock_irqsave (&dev->lock, flags);
        if (dev->state == STATE_DEV_UNCONNECTED)
                goto exit;
        dev->state = STATE_DEV_UNCONNECTED;

        INFO (dev, "disconnected\n");
        next_event (dev, GADGETFS_DISCONNECT);
        ep0_readable (dev);
exit:
        spin_unlock_irqrestore (&dev->lock, flags);
}

static void
gadgetfs_suspend (struct usb_gadget *gadget)
{
        struct dev_data         *dev = get_gadget_data (gadget);
        unsigned long           flags;

        INFO (dev, "suspended from state %d\n", dev->state);
        spin_lock_irqsave(&dev->lock, flags);
        switch (dev->state) {
        case STATE_DEV_SETUP:           // VERY odd... host died??
        case STATE_DEV_CONNECTED:
        case STATE_DEV_UNCONNECTED:
                next_event (dev, GADGETFS_SUSPEND);
                ep0_readable (dev);
                fallthrough;
        default:
                break;
        }
        spin_unlock_irqrestore(&dev->lock, flags);
}

static struct usb_gadget_driver gadgetfs_driver = {
        .function       = (char *) driver_desc,
        .bind           = gadgetfs_bind,
        .unbind         = gadgetfs_unbind,
        .setup          = gadgetfs_setup,
        .reset          = gadgetfs_disconnect,
        .disconnect     = gadgetfs_disconnect,
        .suspend        = gadgetfs_suspend,

        .driver = {
                .name           = shortname,
        },
};

/*----------------------------------------------------------------------*/
/* DEVICE INITIALIZATION
 *
 *     fd = open ("/dev/gadget/$CHIP", O_RDWR)
 *     status = write (fd, descriptors, sizeof descriptors)
 *
 * That write establishes the device configuration, so the kernel can
 * bind to the controller ... guaranteeing it can handle enumeration
 * at all necessary speeds.  Descriptor order is:
 *
 * . message tag (u32, host order) ... for now, must be zero; it
 *      would change to support features like multi-config devices
 * . full/low speed config ... all wTotalLength bytes (with interface,
 *      class, altsetting, endpoint, and other descriptors)
 * . high speed config ... all descriptors, for high speed operation;
 *      this one's optional except for high-speed hardware
 * . device descriptor
 *
 * Endpoints are not yet enabled. Drivers must wait until device
 * configuration and interface altsetting changes create
 * the need to configure (or unconfigure) them.
 *
 * After initialization, the device stays active for as long as that
 * $CHIP file is open.  Events must then be read from that descriptor,
 * such as configuration notifications.
 */

static int is_valid_config(struct usb_config_descriptor *config,
                unsigned int total)
{
        return config->bDescriptorType == USB_DT_CONFIG
                && config->bLength == USB_DT_CONFIG_SIZE
                && total >= USB_DT_CONFIG_SIZE
                && config->bConfigurationValue != 0
                && (config->bmAttributes & USB_CONFIG_ATT_ONE) != 0
                && (config->bmAttributes & USB_CONFIG_ATT_WAKEUP) == 0;
        /* FIXME if gadget->is_otg, _must_ include an otg descriptor */
        /* FIXME check lengths: walk to end */
}

static ssize_t
dev_config (struct file *fd, const char __user *buf, size_t len, loff_t *ptr)
{
        struct dev_data         *dev = fd->private_data;
        ssize_t                 value, length = len;
        unsigned                total;
        u32                     tag;
        char                    *kbuf;

        spin_lock_irq(&dev->lock);
        if (dev->state > STATE_DEV_OPENED) {
                value = ep0_write(fd, buf, len, ptr);
                spin_unlock_irq(&dev->lock);
                return value;
        }
        spin_unlock_irq(&dev->lock);

        if ((len < (USB_DT_CONFIG_SIZE + USB_DT_DEVICE_SIZE + 4)) ||
            (len > PAGE_SIZE * 4))
                return -EINVAL;

        /* we might need to change message format someday */
        if (copy_from_user (&tag, buf, 4))
                return -EFAULT;
        if (tag != 0)
                return -EINVAL;
        buf += 4;
        length -= 4;

        kbuf = memdup_user(buf, length);
        if (IS_ERR(kbuf))
                return PTR_ERR(kbuf);

        spin_lock_irq (&dev->lock);
        value = -EINVAL;
        if (dev->buf) {
                kfree(kbuf);
                goto fail;
        }
        dev->buf = kbuf;

        /* full or low speed config */
        dev->config = (void *) kbuf;
        total = le16_to_cpu(dev->config->wTotalLength);
        if (!is_valid_config(dev->config, total) ||
                        total > length - USB_DT_DEVICE_SIZE)
                goto fail;
        kbuf += total;
        length -= total;

        /* optional high speed config */
        if (kbuf [1] == USB_DT_CONFIG) {
                dev->hs_config = (void *) kbuf;
                total = le16_to_cpu(dev->hs_config->wTotalLength);
                if (!is_valid_config(dev->hs_config, total) ||
                                total > length - USB_DT_DEVICE_SIZE)
                        goto fail;
                kbuf += total;
                length -= total;
        } else {
                dev->hs_config = NULL;
        }

        /* could support multiple configs, using another encoding! */

        /* device descriptor (tweaked for paranoia) */
        if (length != USB_DT_DEVICE_SIZE)
                goto fail;
        dev->dev = (void *)kbuf;
        if (dev->dev->bLength != USB_DT_DEVICE_SIZE
                        || dev->dev->bDescriptorType != USB_DT_DEVICE
                        || dev->dev->bNumConfigurations != 1)
                goto fail;
        dev->dev->bcdUSB = cpu_to_le16 (0x0200);

        /* triggers gadgetfs_bind(); then we can enumerate. */
        spin_unlock_irq (&dev->lock);
        if (dev->hs_config)
                gadgetfs_driver.max_speed = USB_SPEED_HIGH;
        else
                gadgetfs_driver.max_speed = USB_SPEED_FULL;

        value = usb_gadget_probe_driver(&gadgetfs_driver);
        if (value != 0) {
                kfree (dev->buf);
                dev->buf = NULL;
        } else {
                /* at this point "good" hardware has for the first time
                 * let the USB the host see us.  alternatively, if users
                 * unplug/replug that will clear all the error state.
                 *
                 * note:  everything running before here was guaranteed
                 * to choke driver model style diagnostics.  from here
                 * on, they can work ... except in cleanup paths that
                 * kick in after the ep0 descriptor is closed.
                 */
                value = len;
                dev->gadget_registered = true;
        }
        return value;

fail:
        spin_unlock_irq (&dev->lock);
        pr_debug ("%s: %s fail %zd, %p\n", shortname, __func__, value, dev);
        kfree (dev->buf);
        dev->buf = NULL;
        return value;
}

static int
dev_open (struct inode *inode, struct file *fd)
{
        struct dev_data         *dev = inode->i_private;
        int                     value = -EBUSY;

        spin_lock_irq(&dev->lock);
        if (dev->state == STATE_DEV_DISABLED) {
                dev->ev_next = 0;
                dev->state = STATE_DEV_OPENED;
                fd->private_data = dev;
                get_dev (dev);
                value = 0;
        }
        spin_unlock_irq(&dev->lock);
        return value;
}

static const struct file_operations ep0_operations = {
        .llseek =       no_llseek,

        .open =         dev_open,
        .read =         ep0_read,
        .write =        dev_config,
        .fasync =       ep0_fasync,
        .poll =         ep0_poll,
        .unlocked_ioctl = dev_ioctl,
        .release =      dev_release,
};

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

/* FILESYSTEM AND SUPERBLOCK OPERATIONS
 *
 * Mounting the filesystem creates a controller file, used first for
 * device configuration then later for event monitoring.
 */


/* FIXME PAM etc could set this security policy without mount options
 * if epfiles inherited ownership and permissons from ep0 ...
 */

static unsigned default_uid;
static unsigned default_gid;
static unsigned default_perm = S_IRUSR | S_IWUSR;

module_param (default_uid, uint, 0644);
module_param (default_gid, uint, 0644);
module_param (default_perm, uint, 0644);


static struct inode *
gadgetfs_make_inode (struct super_block *sb,
                void *data, const struct file_operations *fops,
                int mode)
{
        struct inode *inode = new_inode (sb);

        if (inode) {
                inode->i_ino = get_next_ino();
                inode->i_mode = mode;
                inode->i_uid = make_kuid(&init_user_ns, default_uid);
                inode->i_gid = make_kgid(&init_user_ns, default_gid);
                inode->i_atime = inode->i_mtime = inode->i_ctime
                                = current_time(inode);
                inode->i_private = data;
                inode->i_fop = fops;
        }
        return inode;
}

/* creates in fs root directory, so non-renamable and non-linkable.
 * so inode and dentry are paired, until device reconfig.
 */
static struct dentry *
gadgetfs_create_file (struct super_block *sb, char const *name,
                void *data, const struct file_operations *fops)
{
        struct dentry   *dentry;
        struct inode    *inode;

        dentry = d_alloc_name(sb->s_root, name);
        if (!dentry)
                return NULL;

        inode = gadgetfs_make_inode (sb, data, fops,
                        S_IFREG | (default_perm & S_IRWXUGO));
        if (!inode) {
                dput(dentry);
                return NULL;
        }
        d_add (dentry, inode);
        return dentry;
}

static const struct super_operations gadget_fs_operations = {
        .statfs =       simple_statfs,
        .drop_inode =   generic_delete_inode,
};

static int
gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc)
{
        struct inode    *inode;
        struct dev_data *dev;

        if (the_device)
                return -ESRCH;

        CHIP = usb_get_gadget_udc_name();
        if (!CHIP)
                return -ENODEV;

        /* superblock */
        sb->s_blocksize = PAGE_SIZE;
        sb->s_blocksize_bits = PAGE_SHIFT;
        sb->s_magic = GADGETFS_MAGIC;
        sb->s_op = &gadget_fs_operations;
        sb->s_time_gran = 1;

        /* root inode */
        inode = gadgetfs_make_inode (sb,
                        NULL, &simple_dir_operations,
                        S_IFDIR | S_IRUGO | S_IXUGO);
        if (!inode)
                goto Enomem;
        inode->i_op = &simple_dir_inode_operations;
        if (!(sb->s_root = d_make_root (inode)))
                goto Enomem;

        /* the ep0 file is named after the controller we expect;
         * user mode code can use it for sanity checks, like we do.
         */
        dev = dev_new ();
        if (!dev)
                goto Enomem;

        dev->sb = sb;
        dev->dentry = gadgetfs_create_file(sb, CHIP, dev, &ep0_operations);
        if (!dev->dentry) {
                put_dev(dev);
                goto Enomem;
        }

        /* other endpoint files are available after hardware setup,
         * from binding to a controller.
         */
        the_device = dev;
        return 0;

Enomem:
        kfree(CHIP);
        CHIP = NULL;

        return -ENOMEM;
}

/* "mount -t gadgetfs path /dev/gadget" ends up here */
static int gadgetfs_get_tree(struct fs_context *fc)
{
        return get_tree_single(fc, gadgetfs_fill_super);
}

static const struct fs_context_operations gadgetfs_context_ops = {
        .get_tree       = gadgetfs_get_tree,
};

static int gadgetfs_init_fs_context(struct fs_context *fc)
{
        fc->ops = &gadgetfs_context_ops;
        return 0;
}

static void
gadgetfs_kill_sb (struct super_block *sb)
{
        kill_litter_super (sb);
        if (the_device) {
                put_dev (the_device);
                the_device = NULL;
        }
        kfree(CHIP);
        CHIP = NULL;
}

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

static struct file_system_type gadgetfs_type = {
        .owner          = THIS_MODULE,
        .name           = shortname,
        .init_fs_context = gadgetfs_init_fs_context,
        .kill_sb        = gadgetfs_kill_sb,
};
MODULE_ALIAS_FS("gadgetfs");

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

static int __init init (void)
{
        int status;

        status = register_filesystem (&gadgetfs_type);
        if (status == 0)
                pr_info ("%s: %s, version " DRIVER_VERSION "\n",
                        shortname, driver_desc);
        return status;
}
module_init (init);

static void __exit cleanup (void)
{
        pr_debug ("unregister %s\n", shortname);
        unregister_filesystem (&gadgetfs_type);
}
module_exit (cleanup);