/*
 * f_fs.c -- user mode file system API for USB composite function controllers
 *
 * Copyright (C) 2010 Samsung Electronics
 * Author: Michal Nazarewicz <mina86@mina86.com>
 *
 * Based on inode.c (GadgetFS) which was:
 * Copyright (C) 2003-2004 David Brownell
 * Copyright (C) 2003 Agilent Technologies
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */


/* #define DEBUG */
/* #define VERBOSE_DEBUG */

#include <linux/blkdev.h>
#include <linux/pagemap.h>
#include <linux/export.h>
#include <linux/hid.h>
#include <asm/unaligned.h>

#include <linux/usb/composite.h>
#include <linux/usb/functionfs.h>


#define FUNCTIONFS_MAGIC        0xa647361 /* Chosen by a honest dice roll ;) */


/* Debugging ****************************************************************/

#ifdef VERBOSE_DEBUG
#  define pr_vdebug pr_debug
#  define ffs_dump_mem(prefix, ptr, len) \
        print_hex_dump_bytes(pr_fmt(prefix ": "), DUMP_PREFIX_NONE, ptr, len)
#else
#  define pr_vdebug(...)                 do { } while (0)
#  define ffs_dump_mem(prefix, ptr, len) do { } while (0)
#endif /* VERBOSE_DEBUG */

#define ENTER()    pr_vdebug("%s()\n", __func__)


/* The data structure and setup file ****************************************/

enum ffs_state {
        /*
         * Waiting for descriptors and strings.
         *
         * In this state no open(2), read(2) or write(2) on epfiles
         * may succeed (which should not be the problem as there
         * should be no such files opened in the first place).
         */
        FFS_READ_DESCRIPTORS,
        FFS_READ_STRINGS,

        /*
         * We've got descriptors and strings.  We are or have called
         * functionfs_ready_callback().  functionfs_bind() may have
         * been called but we don't know.
         *
         * This is the only state in which operations on epfiles may
         * succeed.
         */
        FFS_ACTIVE,

        /*
         * All endpoints have been closed.  This state is also set if
         * we encounter an unrecoverable error.  The only
         * unrecoverable error is situation when after reading strings
         * from user space we fail to initialise epfiles or
         * functionfs_ready_callback() returns with error (<0).
         *
         * In this state no open(2), read(2) or write(2) (both on ep0
         * as well as epfile) may succeed (at this point epfiles are
         * unlinked and all closed so this is not a problem; ep0 is
         * also closed but ep0 file exists and so open(2) on ep0 must
         * fail).
         */
        FFS_CLOSING
};


enum ffs_setup_state {
        /* There is no setup request pending. */
        FFS_NO_SETUP,
        /*
         * User has read events and there was a setup request event
         * there.  The next read/write on ep0 will handle the
         * request.
         */
        FFS_SETUP_PENDING,
        /*
         * There was event pending but before user space handled it
         * some other event was introduced which canceled existing
         * setup.  If this state is set read/write on ep0 return
         * -EIDRM.  This state is only set when adding event.
         */
        FFS_SETUP_CANCELED
};



struct ffs_epfile;
struct ffs_function;

struct ffs_data {
        struct usb_gadget               *gadget;

        /*
         * Protect access read/write operations, only one read/write
         * at a time.  As a consequence protects ep0req and company.
         * While setup request is being processed (queued) this is
         * held.
         */
        struct mutex                    mutex;

        /*
         * Protect access to endpoint related structures (basically
         * usb_ep_queue(), usb_ep_dequeue(), etc. calls) except for
         * endpoint zero.
         */
        spinlock_t                      eps_lock;

        /*
         * XXX REVISIT do we need our own request? Since we are not
         * handling setup requests immediately user space may be so
         * slow that another setup will be sent to the gadget but this
         * time not to us but another function and then there could be
         * a race.  Is that the case? Or maybe we can use cdev->req
         * after all, maybe we just need some spinlock for that?
         */
        struct usb_request              *ep0req;                /* P: mutex */
        struct completion               ep0req_completion;      /* P: mutex */
        int                             ep0req_status;          /* P: mutex */

        /* reference counter */
        atomic_t                        ref;
        /* how many files are opened (EP0 and others) */
        atomic_t                        opened;

        /* EP0 state */
        enum ffs_state                  state;

        /*
         * Possible transitions:
         * + FFS_NO_SETUP       -> FFS_SETUP_PENDING  -- P: ev.waitq.lock
         *               happens only in ep0 read which is P: mutex
         * + FFS_SETUP_PENDING  -> FFS_NO_SETUP       -- P: ev.waitq.lock
         *               happens only in ep0 i/o  which is P: mutex
         * + FFS_SETUP_PENDING  -> FFS_SETUP_CANCELED -- P: ev.waitq.lock
         * + FFS_SETUP_CANCELED -> FFS_NO_SETUP       -- cmpxchg
         */
        enum ffs_setup_state            setup_state;

#define FFS_SETUP_STATE(ffs)                                    \
        ((enum ffs_setup_state)cmpxchg(&(ffs)->setup_state,     \
                                       FFS_SETUP_CANCELED, FFS_NO_SETUP))

        /* Events & such. */
        struct {
                u8                              types[4];
                unsigned short                  count;
                /* XXX REVISIT need to update it in some places, or do we? */
                unsigned short                  can_stall;
                struct usb_ctrlrequest          setup;

                wait_queue_head_t               waitq;
        } ev; /* the whole structure, P: ev.waitq.lock */

        /* Flags */
        unsigned long                   flags;
#define FFS_FL_CALL_CLOSED_CALLBACK 0
#define FFS_FL_BOUND                1

        /* Active function */
        struct ffs_function             *func;

        /*
         * Device name, write once when file system is mounted.
         * Intended for user to read if she wants.
         */
        const char                      *dev_name;
        /* Private data for our user (ie. gadget).  Managed by user. */
        void                            *private_data;

        /* filled by __ffs_data_got_descs() */
        /*
         * Real descriptors are 16 bytes after raw_descs (so you need
         * to skip 16 bytes (ie. ffs->raw_descs + 16) to get to the
         * first full speed descriptor).  raw_descs_length and
         * raw_fs_descs_length do not have those 16 bytes added.
         */
        const void                      *raw_descs;
        unsigned                        raw_descs_length;
        unsigned                        raw_fs_descs_length;
        unsigned                        fs_descs_count;
        unsigned                        hs_descs_count;

        unsigned short                  strings_count;
        unsigned short                  interfaces_count;
        unsigned short                  eps_count;
        unsigned short                  _pad1;

        /* filled by __ffs_data_got_strings() */
        /* ids in stringtabs are set in functionfs_bind() */
        const void                      *raw_strings;
        struct usb_gadget_strings       **stringtabs;

        /*
         * File system's super block, write once when file system is
         * mounted.
         */
        struct super_block              *sb;

        /* File permissions, written once when fs is mounted */
        struct ffs_file_perms {
                umode_t                         mode;
                uid_t                           uid;
                gid_t                           gid;
        }                               file_perms;

        /*
         * The endpoint files, filled by ffs_epfiles_create(),
         * destroyed by ffs_epfiles_destroy().
         */
        struct ffs_epfile               *epfiles;
};

/* Reference counter handling */
static void ffs_data_get(struct ffs_data *ffs);
static void ffs_data_put(struct ffs_data *ffs);
/* Creates new ffs_data object. */
static struct ffs_data *__must_check ffs_data_new(void) __attribute__((malloc));

/* Opened counter handling. */
static void ffs_data_opened(struct ffs_data *ffs);
static void ffs_data_closed(struct ffs_data *ffs);

/* Called with ffs->mutex held; take over ownership of data. */
static int __must_check
__ffs_data_got_descs(struct ffs_data *ffs, char *data, size_t len);
static int __must_check
__ffs_data_got_strings(struct ffs_data *ffs, char *data, size_t len);


/* The function structure ***************************************************/

struct ffs_ep;

struct ffs_function {
        struct usb_configuration        *conf;
        struct usb_gadget               *gadget;
        struct ffs_data                 *ffs;

        struct ffs_ep                   *eps;
        u8                              eps_revmap[16];
        short                           *interfaces_nums;

        struct usb_function             function;
};


static struct ffs_function *ffs_func_from_usb(struct usb_function *f)
{
        return container_of(f, struct ffs_function, function);
}

static void ffs_func_free(struct ffs_function *func);

static void ffs_func_eps_disable(struct ffs_function *func);
static int __must_check ffs_func_eps_enable(struct ffs_function *func);

static int ffs_func_bind(struct usb_configuration *,
                         struct usb_function *);
static void ffs_func_unbind(struct usb_configuration *,
                            struct usb_function *);
static int ffs_func_set_alt(struct usb_function *, unsigned, unsigned);
static void ffs_func_disable(struct usb_function *);
static int ffs_func_setup(struct usb_function *,
                          const struct usb_ctrlrequest *);
static void ffs_func_suspend(struct usb_function *);
static void ffs_func_resume(struct usb_function *);


static int ffs_func_revmap_ep(struct ffs_function *func, u8 num);
static int ffs_func_revmap_intf(struct ffs_function *func, u8 intf);


/* The endpoints structures *************************************************/

struct ffs_ep {
        struct usb_ep                   *ep;    /* P: ffs->eps_lock */
        struct usb_request              *req;   /* P: epfile->mutex */

        /* [0]: full speed, [1]: high speed */
        struct usb_endpoint_descriptor  *descs[2];

        u8                              num;

        int                             status; /* P: epfile->mutex */
};

struct ffs_epfile {
        /* Protects ep->ep and ep->req. */
        struct mutex                    mutex;
        wait_queue_head_t               wait;

        struct ffs_data                 *ffs;
        struct ffs_ep                   *ep;    /* P: ffs->eps_lock */

        struct dentry                   *dentry;

        char                            name[5];

        unsigned char                   in;     /* P: ffs->eps_lock */
        unsigned char                   isoc;   /* P: ffs->eps_lock */

        unsigned char                   _pad;
};

static int  __must_check ffs_epfiles_create(struct ffs_data *ffs);
static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count);

static struct inode *__must_check
ffs_sb_create_file(struct super_block *sb, const char *name, void *data,
                   const struct file_operations *fops,
                   struct dentry **dentry_p);


/* Misc helper functions ****************************************************/

static int ffs_mutex_lock(struct mutex *mutex, unsigned nonblock)
        __attribute__((warn_unused_result, nonnull));
static char *ffs_prepare_buffer(const char * __user buf, size_t len)
        __attribute__((warn_unused_result, nonnull));


/* Control file aka ep0 *****************************************************/

static void ffs_ep0_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct ffs_data *ffs = req->context;

        complete_all(&ffs->ep0req_completion);
}

static int __ffs_ep0_queue_wait(struct ffs_data *ffs, char *data, size_t len)
{
        struct usb_request *req = ffs->ep0req;
        int ret;

        req->zero     = len < le16_to_cpu(ffs->ev.setup.wLength);

        spin_unlock_irq(&ffs->ev.waitq.lock);

        req->buf      = data;
        req->length   = len;

        /*
         * UDC layer requires to provide a buffer even for ZLP, but should
         * not use it at all. Let's provide some poisoned pointer to catch
         * possible bug in the driver.
         */
        if (req->buf == NULL)
                req->buf = (void *)0xDEADBABE;

        INIT_COMPLETION(ffs->ep0req_completion);

        ret = usb_ep_queue(ffs->gadget->ep0, req, GFP_ATOMIC);
        if (unlikely(ret < 0))
                return ret;

        ret = wait_for_completion_interruptible(&ffs->ep0req_completion);
        if (unlikely(ret)) {
                usb_ep_dequeue(ffs->gadget->ep0, req);
                return -EINTR;
        }

        ffs->setup_state = FFS_NO_SETUP;
        return ffs->ep0req_status;
}

static int __ffs_ep0_stall(struct ffs_data *ffs)
{
        if (ffs->ev.can_stall) {
                pr_vdebug("ep0 stall\n");
                usb_ep_set_halt(ffs->gadget->ep0);
                ffs->setup_state = FFS_NO_SETUP;
                return -EL2HLT;
        } else {
                pr_debug("bogus ep0 stall!\n");
                return -ESRCH;
        }
}

static ssize_t ffs_ep0_write(struct file *file, const char __user *buf,
                             size_t len, loff_t *ptr)
{
        struct ffs_data *ffs = file->private_data;
        ssize_t ret;
        char *data;

        ENTER();

        /* Fast check if setup was canceled */
        if (FFS_SETUP_STATE(ffs) == FFS_SETUP_CANCELED)
                return -EIDRM;

        /* Acquire mutex */
        ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret < 0))
                return ret;

        /* Check state */
        switch (ffs->state) {
        case FFS_READ_DESCRIPTORS:
        case FFS_READ_STRINGS:
                /* Copy data */
                if (unlikely(len < 16)) {
                        ret = -EINVAL;
                        break;
                }

                data = ffs_prepare_buffer(buf, len);
                if (IS_ERR(data)) {
                        ret = PTR_ERR(data);
                        break;
                }

                /* Handle data */
                if (ffs->state == FFS_READ_DESCRIPTORS) {
                        pr_info("read descriptors\n");
                        ret = __ffs_data_got_descs(ffs, data, len);
                        if (unlikely(ret < 0))
                                break;

                        ffs->state = FFS_READ_STRINGS;
                        ret = len;
                } else {
                        pr_info("read strings\n");
                        ret = __ffs_data_got_strings(ffs, data, len);
                        if (unlikely(ret < 0))
                                break;

                        ret = ffs_epfiles_create(ffs);
                        if (unlikely(ret)) {
                                ffs->state = FFS_CLOSING;
                                break;
                        }

                        ffs->state = FFS_ACTIVE;
                        mutex_unlock(&ffs->mutex);

                        ret = functionfs_ready_callback(ffs);
                        if (unlikely(ret < 0)) {
                                ffs->state = FFS_CLOSING;
                                return ret;
                        }

                        set_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags);
                        return len;
                }
                break;

        case FFS_ACTIVE:
                data = NULL;
                /*
                 * We're called from user space, we can use _irq
                 * rather then _irqsave
                 */
                spin_lock_irq(&ffs->ev.waitq.lock);
                switch (FFS_SETUP_STATE(ffs)) {
                case FFS_SETUP_CANCELED:
                        ret = -EIDRM;
                        goto done_spin;

                case FFS_NO_SETUP:
                        ret = -ESRCH;
                        goto done_spin;

                case FFS_SETUP_PENDING:
                        break;
                }

                /* FFS_SETUP_PENDING */
                if (!(ffs->ev.setup.bRequestType & USB_DIR_IN)) {
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                        ret = __ffs_ep0_stall(ffs);
                        break;
                }

                /* FFS_SETUP_PENDING and not stall */
                len = min(len, (size_t)le16_to_cpu(ffs->ev.setup.wLength));

                spin_unlock_irq(&ffs->ev.waitq.lock);

                data = ffs_prepare_buffer(buf, len);
                if (IS_ERR(data)) {
                        ret = PTR_ERR(data);
                        break;
                }

                spin_lock_irq(&ffs->ev.waitq.lock);

                /*
                 * We are guaranteed to be still in FFS_ACTIVE state
                 * but the state of setup could have changed from
                 * FFS_SETUP_PENDING to FFS_SETUP_CANCELED so we need
                 * to check for that.  If that happened we copied data
                 * from user space in vain but it's unlikely.
                 *
                 * For sure we are not in FFS_NO_SETUP since this is
                 * the only place FFS_SETUP_PENDING -> FFS_NO_SETUP
                 * transition can be performed and it's protected by
                 * mutex.
                 */
                if (FFS_SETUP_STATE(ffs) == FFS_SETUP_CANCELED) {
                        ret = -EIDRM;
done_spin:
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                } else {
                        /* unlocks spinlock */
                        ret = __ffs_ep0_queue_wait(ffs, data, len);
                }
                kfree(data);
                break;

        default:
                ret = -EBADFD;
                break;
        }

        mutex_unlock(&ffs->mutex);
        return ret;
}

static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf,
                                     size_t n)
{
        /*
         * We are holding ffs->ev.waitq.lock and ffs->mutex and we need
         * to release them.
         */
        struct usb_functionfs_event events[n];
        unsigned i = 0;

        memset(events, 0, sizeof events);

        do {
                events[i].type = ffs->ev.types[i];
                if (events[i].type == FUNCTIONFS_SETUP) {
                        events[i].u.setup = ffs->ev.setup;
                        ffs->setup_state = FFS_SETUP_PENDING;
                }
        } while (++i < n);

        if (n < ffs->ev.count) {
                ffs->ev.count -= n;
                memmove(ffs->ev.types, ffs->ev.types + n,
                        ffs->ev.count * sizeof *ffs->ev.types);
        } else {
                ffs->ev.count = 0;
        }

        spin_unlock_irq(&ffs->ev.waitq.lock);
        mutex_unlock(&ffs->mutex);

        return unlikely(__copy_to_user(buf, events, sizeof events))
                ? -EFAULT : sizeof events;
}

static ssize_t ffs_ep0_read(struct file *file, char __user *buf,
                            size_t len, loff_t *ptr)
{
        struct ffs_data *ffs = file->private_data;
        char *data = NULL;
        size_t n;
        int ret;

        ENTER();

        /* Fast check if setup was canceled */
        if (FFS_SETUP_STATE(ffs) == FFS_SETUP_CANCELED)
                return -EIDRM;

        /* Acquire mutex */
        ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
        if (unlikely(ret < 0))
                return ret;

        /* Check state */
        if (ffs->state != FFS_ACTIVE) {
                ret = -EBADFD;
                goto done_mutex;
        }

        /*
         * We're called from user space, we can use _irq rather then
         * _irqsave
         */
        spin_lock_irq(&ffs->ev.waitq.lock);

        switch (FFS_SETUP_STATE(ffs)) {
        case FFS_SETUP_CANCELED:
                ret = -EIDRM;
                break;

        case FFS_NO_SETUP:
                n = len / sizeof(struct usb_functionfs_event);
                if (unlikely(!n)) {
                        ret = -EINVAL;
                        break;
                }

                if ((file->f_flags & O_NONBLOCK) && !ffs->ev.count) {
                        ret = -EAGAIN;
                        break;
                }

                if (wait_event_interruptible_exclusive_locked_irq(ffs->ev.waitq,
                                                        ffs->ev.count)) {
                        ret = -EINTR;
                        break;
                }

                return __ffs_ep0_read_events(ffs, buf,
                                             min(n, (size_t)ffs->ev.count));

        case FFS_SETUP_PENDING:
                if (ffs->ev.setup.bRequestType & USB_DIR_IN) {
                        spin_unlock_irq(&ffs->ev.waitq.lock);
                        ret = __ffs_ep0_stall(ffs);
                        goto done_mutex;
                }

                len = min(len, (size_t)le16_to_cpu(ffs->ev.setup.wLength));

                spin_unlock_irq(&ffs->ev.waitq.lock);

                if (likely(len)) {
                        data = kmalloc(len, GFP_KERNEL);
                        if (unlikely(!data)) {
                                ret = -ENOMEM;
                                goto done_mutex;
                        }
                }

                spin_lock_irq(&ffs->ev.waitq.lock);

                /* See ffs_ep0_write() */
                if (FFS_SETUP_STATE(ffs) == FFS_SETUP_CANCELED) {
                        ret = -EIDRM;
                        break;
                }

                /* unlocks spinlock */
                ret = __ffs_ep0_queue_wait(ffs, data, len);
                if (likely(ret > 0) && unlikely(__copy_to_user(buf, data, len)))
                        ret = -EFAULT;
                goto done_mutex;

        default:
                ret = -EBADFD;
                break;
        }

        spin_unlock_irq(&ffs->ev.waitq.lock);
done_mutex:
        mutex_unlock(&ffs->mutex);
        kfree(data);
        return ret;
}

static int ffs_ep0_open(struct inode *inode, struct file *file)
{
        struct ffs_data *ffs = inode->i_private;

        ENTER();

        if (unlikely(ffs->state == FFS_CLOSING))
                return -EBUSY;

        file->private_data = ffs;
        ffs_data_opened(ffs);

        return 0;
}

static int ffs_ep0_release(struct inode *inode, struct file *file)
{
        struct ffs_data *ffs = file->private_data;

        ENTER();

        ffs_data_closed(ffs);

        return 0;
}

static long ffs_ep0_ioctl(struct file *file, unsigned code, unsigned long value)
{
        struct ffs_data *ffs = file->private_data;
        struct usb_gadget *gadget = ffs->gadget;
        long ret;

        ENTER();

        if (code == FUNCTIONFS_INTERFACE_REVMAP) {
                struct ffs_function *func = ffs->func;
                ret = func ? ffs_func_revmap_intf(func, value) : -ENODEV;
        } else if (gadget && gadget->ops->ioctl) {
                ret = gadget->ops->ioctl(gadget, code, value);
        } else {
                ret = -ENOTTY;
        }

        return ret;
}

static const struct file_operations ffs_ep0_operations = {
        .owner =        THIS_MODULE,
        .llseek =       no_llseek,

        .open =         ffs_ep0_open,
        .write =        ffs_ep0_write,
        .read =         ffs_ep0_read,
        .release =      ffs_ep0_release,
        .unlocked_ioctl =       ffs_ep0_ioctl,
};


/* "Normal" endpoints operations ********************************************/

static void ffs_epfile_io_complete(struct usb_ep *_ep, struct usb_request *req)
{
        ENTER();
        if (likely(req->context)) {
                struct ffs_ep *ep = _ep->driver_data;
                ep->status = req->status ? req->status : req->actual;
                complete(req->context);
        }
}

static ssize_t ffs_epfile_io(struct file *file,
                             char __user *buf, size_t len, int read)
{
        struct ffs_epfile *epfile = file->private_data;
        struct ffs_ep *ep;
        char *data = NULL;
        ssize_t ret;
        int halt;

        goto first_try;
        do {
                spin_unlock_irq(&epfile->ffs->eps_lock);
                mutex_unlock(&epfile->mutex);

first_try:
                /* Are we still active? */
                if (WARN_ON(epfile->ffs->state != FFS_ACTIVE)) {
                        ret = -ENODEV;
                        goto error;
                }

                /* Wait for endpoint to be enabled */
                ep = epfile->ep;
                if (!ep) {
                        if (file->f_flags & O_NONBLOCK) {
                                ret = -EAGAIN;
                                goto error;
                        }

                        if (wait_event_interruptible(epfile->wait,
                                                     (ep = epfile->ep))) {
                                ret = -EINTR;
                                goto error;
                        }
                }

                /* Do we halt? */
                halt = !read == !epfile->in;
                if (halt && epfile->isoc) {
                        ret = -EINVAL;
                        goto error;
                }

                /* Allocate & copy */
                if (!halt && !data) {
                        data = kzalloc(len, GFP_KERNEL);
                        if (unlikely(!data))
                                return -ENOMEM;

                        if (!read &&
                            unlikely(__copy_from_user(data, buf, len))) {
                                ret = -EFAULT;
                                goto error;
                        }
                }

                /* We will be using request */
                ret = ffs_mutex_lock(&epfile->mutex,
                                     file->f_flags & O_NONBLOCK);
                if (unlikely(ret))
                        goto error;

                /*
                 * We're called from user space, we can use _irq rather then
                 * _irqsave
                 */
                spin_lock_irq(&epfile->ffs->eps_lock);

                /*
                 * While we were acquiring mutex endpoint got disabled
                 * or changed?
                 */
        } while (unlikely(epfile->ep != ep));

        /* Halt */
        if (unlikely(halt)) {
                if (likely(epfile->ep == ep) && !WARN_ON(!ep->ep))
                        usb_ep_set_halt(ep->ep);
                spin_unlock_irq(&epfile->ffs->eps_lock);
                ret = -EBADMSG;
        } else {
                /* Fire the request */
                DECLARE_COMPLETION_ONSTACK(done);

                struct usb_request *req = ep->req;
                req->context  = &done;
                req->complete = ffs_epfile_io_complete;
                req->buf      = data;
                req->length   = len;

                ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);

                spin_unlock_irq(&epfile->ffs->eps_lock);

                if (unlikely(ret < 0)) {
                        /* nop */
                } else if (unlikely(wait_for_completion_interruptible(&done))) {
                        ret = -EINTR;
                        usb_ep_dequeue(ep->ep, req);
                } else {
                        ret = ep->status;
                        if (read && ret > 0 &&
                            unlikely(copy_to_user(buf, data, ret)))
                                ret = -EFAULT;
                }
        }

        mutex_unlock(&epfile->mutex);
error:
        kfree(data);
        return ret;
}

static ssize_t
ffs_epfile_write(struct file *file, const char __user *buf, size_t len,
                 loff_t *ptr)
{
        ENTER();

        return ffs_epfile_io(file, (char __user *)buf, len, 0);
}

static ssize_t
ffs_epfile_read(struct file *file, char __user *buf, size_t len, loff_t *ptr)
{
        ENTER();

        return ffs_epfile_io(file, buf, len, 1);
}

static int
ffs_epfile_open(struct inode *inode, struct file *file)
{
        struct ffs_epfile *epfile = inode->i_private;

        ENTER();

        if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
                return -ENODEV;

        file->private_data = epfile;
        ffs_data_opened(epfile->ffs);

        return 0;
}

static int
ffs_epfile_release(struct inode *inode, struct file *file)
{
        struct ffs_epfile *epfile = inode->i_private;

        ENTER();

        ffs_data_closed(epfile->ffs);

        return 0;
}

static long ffs_epfile_ioctl(struct file *file, unsigned code,
                             unsigned long value)
{
        struct ffs_epfile *epfile = file->private_data;
        int ret;

        ENTER();

        if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
                return -ENODEV;

        spin_lock_irq(&epfile->ffs->eps_lock);
        if (likely(epfile->ep)) {
                switch (code) {
                case FUNCTIONFS_FIFO_STATUS:
                        ret = usb_ep_fifo_status(epfile->ep->ep);
                        break;
                case FUNCTIONFS_FIFO_FLUSH:
                        usb_ep_fifo_flush(epfile->ep->ep);
                        ret = 0;
                        break;
                case FUNCTIONFS_CLEAR_HALT:
                        ret = usb_ep_clear_halt(epfile->ep->ep);
                        break;
                case FUNCTIONFS_ENDPOINT_REVMAP:
                        ret = epfile->ep->num;
                        break;
                default:
                        ret = -ENOTTY;
                }
        } else {
                ret = -ENODEV;
        }
        spin_unlock_irq(&epfile->ffs->eps_lock);

        return ret;
}

static const struct file_operations ffs_epfile_operations = {
        .owner =        THIS_MODULE,
        .llseek =       no_llseek,

        .open =         ffs_epfile_open,
        .write =        ffs_epfile_write,
        .read =         ffs_epfile_read,
        .release =      ffs_epfile_release,
        .unlocked_ioctl =       ffs_epfile_ioctl,
};


/* File system and super block operations ***********************************/

/*
 * Mounting the file system creates a controller file, used first for
 * function configuration then later for event monitoring.
 */

static struct inode *__must_check
ffs_sb_make_inode(struct super_block *sb, void *data,
                  const struct file_operations *fops,
                  const struct inode_operations *iops,
                  struct ffs_file_perms *perms)
{
        struct inode *inode;

        ENTER();

        inode = new_inode(sb);

        if (likely(inode)) {
                struct timespec current_time = CURRENT_TIME;

                inode->i_ino     = get_next_ino();
                inode->i_mode    = perms->mode;
                inode->i_uid     = perms->uid;
                inode->i_gid     = perms->gid;
                inode->i_atime   = current_time;
                inode->i_mtime   = current_time;
                inode->i_ctime   = current_time;
                inode->i_private = data;
                if (fops)
                        inode->i_fop = fops;
                if (iops)
                        inode->i_op  = iops;
        }

        return inode;
}

/* Create "regular" file */
static struct inode *ffs_sb_create_file(struct super_block *sb,
                                        const char *name, void *data,
                                        const struct file_operations *fops,
                                        struct dentry **dentry_p)

{
        struct ffs_data *ffs = sb->s_fs_info;
        struct dentry   *dentry;
        struct inode    *inode;

        ENTER();

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

        inode = ffs_sb_make_inode(sb, data, fops, NULL, &ffs->file_perms);
        if (unlikely(!inode)) {
                dput(dentry);
                return NULL;
        }

        d_add(dentry, inode);
        if (dentry_p)
                *dentry_p = dentry;

        return inode;
}

/* Super block */
static const struct super_operations ffs_sb_operations = {
        .statfs =       simple_statfs,
        .drop_inode =   generic_delete_inode,
};

struct ffs_sb_fill_data {
        struct ffs_file_perms perms;
        umode_t root_mode;
        const char *dev_name;
        union {
                /* set by ffs_fs_mount(), read by ffs_sb_fill() */
                void *private_data;
                /* set by ffs_sb_fill(), read by ffs_fs_mount */
                struct ffs_data *ffs_data;
        };
};

static int ffs_sb_fill(struct super_block *sb, void *_data, int silent)
{
        struct ffs_sb_fill_data *data = _data;
        struct inode    *inode;
        struct ffs_data *ffs;

        ENTER();

        /* Initialise data */
        ffs = ffs_data_new();
        if (unlikely(!ffs))
                goto Enomem;

        ffs->sb              = sb;
        ffs->dev_name        = kstrdup(data->dev_name, GFP_KERNEL);
        if (unlikely(!ffs->dev_name))
                goto Enomem;
        ffs->file_perms      = data->perms;
        ffs->private_data    = data->private_data;

        /* used by the caller of this function */
        data->ffs_data       = ffs;

        sb->s_fs_info        = ffs;
        sb->s_blocksize      = PAGE_CACHE_SIZE;
        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
        sb->s_magic          = FUNCTIONFS_MAGIC;
        sb->s_op             = &ffs_sb_operations;
        sb->s_time_gran      = 1;

        /* Root inode */
        data->perms.mode = data->root_mode;
        inode = ffs_sb_make_inode(sb, NULL,
                                  &simple_dir_operations,
                                  &simple_dir_inode_operations,
                                  &data->perms);
        sb->s_root = d_make_root(inode);
        if (unlikely(!sb->s_root))
                goto Enomem;

        /* EP0 file */
        if (unlikely(!ffs_sb_create_file(sb, "ep0", ffs,
                                         &ffs_ep0_operations, NULL)))
                goto Enomem;

        return 0;

Enomem:
        return -ENOMEM;
}

static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts)
{
        ENTER();

        if (!opts || !*opts)
                return 0;

        for (;;) {
                char *end, *eq, *comma;
                unsigned long value;

                /* Option limit */
                comma = strchr(opts, ',');
                if (comma)
                        *comma = 0;

                /* Value limit */
                eq = strchr(opts, '=');
                if (unlikely(!eq)) {
                        pr_err("'=' missing in %s\n", opts);
                        return -EINVAL;
                }
                *eq = 0;

                /* Parse value */
                value = simple_strtoul(eq + 1, &end, 0);
                if (unlikely(*end != ',' && *end != 0)) {
                        pr_err("%s: invalid value: %s\n", opts, eq + 1);
                        return -EINVAL;
                }

                /* Interpret option */
                switch (eq - opts) {
                case 5:
                        if (!memcmp(opts, "rmode", 5))
                                data->root_mode  = (value & 0555) | S_IFDIR;
                        else if (!memcmp(opts, "fmode", 5))
                                data->perms.mode = (value & 0666) | S_IFREG;
                        else
                                goto invalid;
                        break;

                case 4:
                        if (!memcmp(opts, "mode", 4)) {
                                data->root_mode  = (value & 0555) | S_IFDIR;
                                data->perms.mode = (value & 0666) | S_IFREG;
                        } else {
                                goto invalid;
                        }
                        break;

                case 3:
                        if (!memcmp(opts, "uid", 3))
                                data->perms.uid = value;
                        else if (!memcmp(opts, "gid", 3))
                                data->perms.gid = value;
                        else
                                goto invalid;
                        break;

                default:
invalid:
                        pr_err("%s: invalid option\n", opts);
                        return -EINVAL;
                }

                /* Next iteration */
                if (!comma)
                        break;
                opts = comma + 1;
        }

        return 0;
}

/* "mount -t functionfs dev_name /dev/function" ends up here */

static struct dentry *
ffs_fs_mount(struct file_system_type *t, int flags,
              const char *dev_name, void *opts)
{
        struct ffs_sb_fill_data data = {
                .perms = {
                        .mode = S_IFREG | 0600,
                        .uid = 0,
                        .gid = 0
                },
                .root_mode = S_IFDIR | 0500,
        };
        struct dentry *rv;
        int ret;
        void *ffs_dev;

        ENTER();

        ret = ffs_fs_parse_opts(&data, opts);
        if (unlikely(ret < 0))
                return ERR_PTR(ret);

        ffs_dev = functionfs_acquire_dev_callback(dev_name);
        if (IS_ERR(ffs_dev))
                return ffs_dev;

        data.dev_name = dev_name;
        data.private_data = ffs_dev;
        rv = mount_nodev(t, flags, &data, ffs_sb_fill);

        /* data.ffs_data is set by ffs_sb_fill */
        if (IS_ERR(rv))
                functionfs_release_dev_callback(data.ffs_data);

        return rv;
}

static void
ffs_fs_kill_sb(struct super_block *sb)
{
        ENTER();

        kill_litter_super(sb);
        if (sb->s_fs_info) {
                functionfs_release_dev_callback(sb->s_fs_info);
                ffs_data_put(sb->s_fs_info);
        }
}

static struct file_system_type ffs_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "functionfs",
        .mount          = ffs_fs_mount,
        .kill_sb        = ffs_fs_kill_sb,
};


/* Driver's main init/cleanup functions *************************************/

static int functionfs_init(void)
{
        int ret;

        ENTER();

        ret = register_filesystem(&ffs_fs_type);
        if (likely(!ret))
                pr_info("file system registered\n");
        else
                pr_err("failed registering file system (%d)\n", ret);

        return ret;
}

static void functionfs_cleanup(void)
{
        ENTER();

        pr_info("unloading\n");
        unregister_filesystem(&ffs_fs_type);
}


/* ffs_data and ffs_function construction and destruction code **************/

static void ffs_data_clear(struct ffs_data *ffs);
static void ffs_data_reset(struct ffs_data *ffs);

static void ffs_data_get(struct ffs_data *ffs)
{
        ENTER();

        atomic_inc(&ffs->ref);
}

static void ffs_data_opened(struct ffs_data *ffs)
{
        ENTER();

        atomic_inc(&ffs->ref);
        atomic_inc(&ffs->opened);
}

static void ffs_data_put(struct ffs_data *ffs)
{
        ENTER();

        if (unlikely(atomic_dec_and_test(&ffs->ref))) {
                pr_info("%s(): freeing\n", __func__);
                ffs_data_clear(ffs);
                BUG_ON(waitqueue_active(&ffs->ev.waitq) ||
                       waitqueue_active(&ffs->ep0req_completion.wait));
                kfree(ffs->dev_name);
                kfree(ffs);
        }
}

static void ffs_data_closed(struct ffs_data *ffs)
{
        ENTER();

        if (atomic_dec_and_test(&ffs->opened)) {
                ffs->state = FFS_CLOSING;
                ffs_data_reset(ffs);
        }

        ffs_data_put(ffs);
}

static struct ffs_data *ffs_data_new(void)
{
        struct ffs_data *ffs = kzalloc(sizeof *ffs, GFP_KERNEL);
        if (unlikely(!ffs))
                return 0;

        ENTER();

        atomic_set(&ffs->ref, 1);
        atomic_set(&ffs->opened, 0);
        ffs->state = FFS_READ_DESCRIPTORS;
        mutex_init(&ffs->mutex);
        spin_lock_init(&ffs->eps_lock);
        init_waitqueue_head(&ffs->ev.waitq);
        init_completion(&ffs->ep0req_completion);

        /* XXX REVISIT need to update it in some places, or do we? */
        ffs->ev.can_stall = 1;

        return ffs;
}

static void ffs_data_clear(struct ffs_data *ffs)
{
        ENTER();

        if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags))
                functionfs_closed_callback(ffs);

        BUG_ON(ffs->gadget);

        if (ffs->epfiles)
                ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count);

        kfree(ffs->raw_descs);
        kfree(ffs->raw_strings);
        kfree(ffs->stringtabs);
}

static void ffs_data_reset(struct ffs_data *ffs)
{
        ENTER();

        ffs_data_clear(ffs);

        ffs->epfiles = NULL;
        ffs->raw_descs = NULL;
        ffs->raw_strings = NULL;
        ffs->stringtabs = NULL;

        ffs->raw_descs_length = 0;
        ffs->raw_fs_descs_length = 0;
        ffs->fs_descs_count = 0;
        ffs->hs_descs_count = 0;

        ffs->strings_count = 0;
        ffs->interfaces_count = 0;
        ffs->eps_count = 0;

        ffs->ev.count = 0;

        ffs->state = FFS_READ_DESCRIPTORS;
        ffs->setup_state = FFS_NO_SETUP;
        ffs->flags = 0;
}


static int functionfs_bind(struct ffs_data *ffs, struct usb_composite_dev *cdev)
{
        struct usb_gadget_strings **lang;
        int first_id;

        ENTER();

        if (WARN_ON(ffs->state != FFS_ACTIVE
                 || test_and_set_bit(FFS_FL_BOUND, &ffs->flags)))
                return -EBADFD;

        first_id = usb_string_ids_n(cdev, ffs->strings_count);
        if (unlikely(first_id < 0))
                return first_id;

        ffs->ep0req = usb_ep_alloc_request(cdev->gadget->ep0, GFP_KERNEL);
        if (unlikely(!ffs->ep0req))
                return -ENOMEM;
        ffs->ep0req->complete = ffs_ep0_complete;
        ffs->ep0req->context = ffs;

        lang = ffs->stringtabs;
        for (lang = ffs->stringtabs; *lang; ++lang) {
                struct usb_string *str = (*lang)->strings;
                int id = first_id;
                for (; str->s; ++id, ++str)
                        str->id = id;
        }

        ffs->gadget = cdev->gadget;
        ffs_data_get(ffs);
        return 0;
}

static void functionfs_unbind(struct ffs_data *ffs)
{
        ENTER();

        if (!WARN_ON(!ffs->gadget)) {
                usb_ep_free_request(ffs->gadget->ep0, ffs->ep0req);
                ffs->ep0req = NULL;
                ffs->gadget = NULL;
                ffs_data_put(ffs);
                clear_bit(FFS_FL_BOUND, &ffs->flags);
        }
}

static int ffs_epfiles_create(struct ffs_data *ffs)
{
        struct ffs_epfile *epfile, *epfiles;
        unsigned i, count;

        ENTER();

        count = ffs->eps_count;
        epfiles = kcalloc(count, sizeof(*epfiles), GFP_KERNEL);
        if (!epfiles)
                return -ENOMEM;

        epfile = epfiles;
        for (i = 1; i <= count; ++i, ++epfile) {
                epfile->ffs = ffs;
                mutex_init(&epfile->mutex);
                init_waitqueue_head(&epfile->wait);
                sprintf(epfiles->name, "ep%u",  i);
                if (!unlikely(ffs_sb_create_file(ffs->sb, epfiles->name, epfile,
                                                 &ffs_epfile_operations,
                                                 &epfile->dentry))) {
                        ffs_epfiles_destroy(epfiles, i - 1);
                        return -ENOMEM;
                }
        }

        ffs->epfiles = epfiles;
        return 0;
}

static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
{
        struct ffs_epfile *epfile = epfiles;

        ENTER();

        for (; count; --count, ++epfile) {
                BUG_ON(mutex_is_locked(&epfile->mutex) ||
                       waitqueue_active(&epfile->wait));
                if (epfile->dentry) {
                        d_delete(epfile->dentry);
                        dput(epfile->dentry);
                        epfile->dentry = NULL;
                }
        }

        kfree(epfiles);
}

static int functionfs_bind_config(struct usb_composite_dev *cdev,
                                  struct usb_configuration *c,
                                  struct ffs_data *ffs)
{
        struct ffs_function *func;
        int ret;

        ENTER();

        func = kzalloc(sizeof *func, GFP_KERNEL);
        if (unlikely(!func))
                return -ENOMEM;

        func->function.name    = "Function FS Gadget";
        func->function.strings = ffs->stringtabs;

        func->function.bind    = ffs_func_bind;
        func->function.unbind  = ffs_func_unbind;
        func->function.set_alt = ffs_func_set_alt;
        func->function.disable = ffs_func_disable;
        func->function.setup   = ffs_func_setup;
        func->function.suspend = ffs_func_suspend;
        func->function.resume  = ffs_func_resume;

        func->conf   = c;
        func->gadget = cdev->gadget;
        func->ffs = ffs;
        ffs_data_get(ffs);

        ret = usb_add_function(c, &func->function);
        if (unlikely(ret))
                ffs_func_free(func);

        return ret;
}

static void ffs_func_free(struct ffs_function *func)
{
        struct ffs_ep *ep         = func->eps;
        unsigned count            = func->ffs->eps_count;
        unsigned long flags;

        ENTER();

        /* cleanup after autoconfig */
        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        do {
                if (ep->ep && ep->req)
                        usb_ep_free_request(ep->ep, ep->req);
                ep->req = NULL;
                ++ep;
        } while (--count);
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);

        ffs_data_put(func->ffs);

        kfree(func->eps);
        /*
         * eps and interfaces_nums are allocated in the same chunk so
         * only one free is required.  Descriptors are also allocated
         * in the same chunk.
         */

        kfree(func);
}

static void ffs_func_eps_disable(struct ffs_function *func)
{
        struct ffs_ep *ep         = func->eps;
        struct ffs_epfile *epfile = func->ffs->epfiles;
        unsigned count            = func->ffs->eps_count;
        unsigned long flags;

        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        do {
                /* pending requests get nuked */
                if (likely(ep->ep))
                        usb_ep_disable(ep->ep);
                epfile->ep = NULL;

                ++ep;
                ++epfile;
        } while (--count);
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
}

static int ffs_func_eps_enable(struct ffs_function *func)
{
        struct ffs_data *ffs      = func->ffs;
        struct ffs_ep *ep         = func->eps;
        struct ffs_epfile *epfile = ffs->epfiles;
        unsigned count            = ffs->eps_count;
        unsigned long flags;
        int ret = 0;

        spin_lock_irqsave(&func->ffs->eps_lock, flags);
        do {
                struct usb_endpoint_descriptor *ds;
                ds = ep->descs[ep->descs[1] ? 1 : 0];

                ep->ep->driver_data = ep;
                ep->ep->desc = ds;
                ret = usb_ep_enable(ep->ep);
                if (likely(!ret)) {
                        epfile->ep = ep;
                        epfile->in = usb_endpoint_dir_in(ds);
                        epfile->isoc = usb_endpoint_xfer_isoc(ds);
                } else {
                        break;
                }

                wake_up(&epfile->wait);

                ++ep;
                ++epfile;
        } while (--count);
        spin_unlock_irqrestore(&func->ffs->eps_lock, flags);

        return ret;
}


/* Parsing and building descriptors and strings *****************************/

/*
 * This validates if data pointed by data is a valid USB descriptor as
 * well as record how many interfaces, endpoints and strings are
 * required by given configuration.  Returns address after the
 * descriptor or NULL if data is invalid.
 */

enum ffs_entity_type {
        FFS_DESCRIPTOR, FFS_INTERFACE, FFS_STRING, FFS_ENDPOINT
};

typedef int (*ffs_entity_callback)(enum ffs_entity_type entity,
                                   u8 *valuep,
                                   struct usb_descriptor_header *desc,
                                   void *priv);

static int __must_check ffs_do_desc(char *data, unsigned len,
                                    ffs_entity_callback entity, void *priv)
{
        struct usb_descriptor_header *_ds = (void *)data;
        u8 length;
        int ret;

        ENTER();

        /* At least two bytes are required: length and type */
        if (len < 2) {
                pr_vdebug("descriptor too short\n");
                return -EINVAL;
        }

        /* If we have at least as many bytes as the descriptor takes? */
        length = _ds->bLength;
        if (len < length) {
                pr_vdebug("descriptor longer then available data\n");
                return -EINVAL;
        }

#define __entity_check_INTERFACE(val)  1
#define __entity_check_STRING(val)     (val)
#define __entity_check_ENDPOINT(val)   ((val) & USB_ENDPOINT_NUMBER_MASK)
#define __entity(type, val) do {                                        \
                pr_vdebug("entity " #type "(%02x)\n", (val));           \
                if (unlikely(!__entity_check_ ##type(val))) {           \
                        pr_vdebug("invalid entity's value\n");          \
                        return -EINVAL;                                 \
                }                                                       \
                ret = entity(FFS_ ##type, &val, _ds, priv);             \
                if (unlikely(ret < 0)) {                                \
                        pr_debug("entity " #type "(%02x); ret = %d\n",  \
                                 (val), ret);                           \
                        return ret;                                     \
                }                                                       \
        } while (0)

        /* Parse descriptor depending on type. */
        switch (_ds->bDescriptorType) {
        case USB_DT_DEVICE:
        case USB_DT_CONFIG:
        case USB_DT_STRING:
        case USB_DT_DEVICE_QUALIFIER:
                /* function can't have any of those */
                pr_vdebug("descriptor reserved for gadget: %d\n",
                      _ds->bDescriptorType);
                return -EINVAL;

        case USB_DT_INTERFACE: {
                struct usb_interface_descriptor *ds = (void *)_ds;
                pr_vdebug("interface descriptor\n");
                if (length != sizeof *ds)
                        goto inv_length;

                __entity(INTERFACE, ds->bInterfaceNumber);
                if (ds->iInterface)
                        __entity(STRING, ds->iInterface);
        }
                break;

        case USB_DT_ENDPOINT: {
                struct usb_endpoint_descriptor *ds = (void *)_ds;
                pr_vdebug("endpoint descriptor\n");
                if (length != USB_DT_ENDPOINT_SIZE &&
                    length != USB_DT_ENDPOINT_AUDIO_SIZE)
                        goto inv_length;
                __entity(ENDPOINT, ds->bEndpointAddress);
        }
                break;

        case HID_DT_HID:
                pr_vdebug("hid descriptor\n");
                if (length != sizeof(struct hid_descriptor))
                        goto inv_length;
                break;

        case USB_DT_OTG:
                if (length != sizeof(struct usb_otg_descriptor))
                        goto inv_length;
                break;

        case USB_DT_INTERFACE_ASSOCIATION: {
                struct usb_interface_assoc_descriptor *ds = (void *)_ds;
                pr_vdebug("interface association descriptor\n");
                if (length != sizeof *ds)
                        goto inv_length;
                if (ds->iFunction)
                        __entity(STRING, ds->iFunction);
        }
                break;

        case USB_DT_OTHER_SPEED_CONFIG:
        case USB_DT_INTERFACE_POWER:
        case USB_DT_DEBUG:
        case USB_DT_SECURITY:
        case USB_DT_CS_RADIO_CONTROL:
                /* TODO */
                pr_vdebug("unimplemented descriptor: %d\n", _ds->bDescriptorType);
                return -EINVAL;

        default:
                /* We should never be here */
                pr_vdebug("unknown descriptor: %d\n", _ds->bDescriptorType);
                return -EINVAL;

inv_length:
                pr_vdebug("invalid length: %d (descriptor %d)\n",
                          _ds->bLength, _ds->bDescriptorType);
                return -EINVAL;
        }

#undef __entity
#undef __entity_check_DESCRIPTOR
#undef __entity_check_INTERFACE
#undef __entity_check_STRING
#undef __entity_check_ENDPOINT

        return length;
}

static int __must_check ffs_do_descs(unsigned count, char *data, unsigned len,
                                     ffs_entity_callback entity, void *priv)
{
        const unsigned _len = len;
        unsigned long num = 0;

        ENTER();

        for (;;) {
                int ret;

                if (num == count)
                        data = NULL;

                /* Record "descriptor" entity */
                ret = entity(FFS_DESCRIPTOR, (u8 *)num, (void *)data, priv);
                if (unlikely(ret < 0)) {
                        pr_debug("entity DESCRIPTOR(%02lx); ret = %d\n",
                                 num, ret);
                        return ret;
                }

                if (!data)
                        return _len - len;

                ret = ffs_do_desc(data, len, entity, priv);
                if (unlikely(ret < 0)) {
                        pr_debug("%s returns %d\n", __func__, ret);
                        return ret;
                }

                len -= ret;
                data += ret;
                ++num;
        }
}

static int __ffs_data_do_entity(enum ffs_entity_type type,
                                u8 *valuep, struct usb_descriptor_header *desc,
                                void *priv)
{
        struct ffs_data *ffs = priv;

        ENTER();

        switch (type) {
        case FFS_DESCRIPTOR:
                break;

        case FFS_INTERFACE:
                /*
                 * Interfaces are indexed from zero so if we
                 * encountered interface "n" then there are at least
                 * "n+1" interfaces.
                 */
                if (*valuep >= ffs->interfaces_count)
                        ffs->interfaces_count = *valuep + 1;
                break;

        case FFS_STRING:
                /*
                 * Strings are indexed from 1 (0 is magic ;) reserved
                 * for languages list or some such)
                 */
                if (*valuep > ffs->strings_count)
                        ffs->strings_count = *valuep;
                break;

        case FFS_ENDPOINT:
                /* Endpoints are indexed from 1 as well. */
                if ((*valuep & USB_ENDPOINT_NUMBER_MASK) > ffs->eps_count)
                        ffs->eps_count = (*valuep & USB_ENDPOINT_NUMBER_MASK);
                break;
        }

        return 0;
}

static int __ffs_data_got_descs(struct ffs_data *ffs,
                                char *const _data, size_t len)
{
        unsigned fs_count, hs_count;
        int fs_len, ret = -EINVAL;
        char *data = _data;

        ENTER();

        if (unlikely(get_unaligned_le32(data) != FUNCTIONFS_DESCRIPTORS_MAGIC ||
                     get_unaligned_le32(data + 4) != len))
                goto error;
        fs_count = get_unaligned_le32(data +  8);
        hs_count = get_unaligned_le32(data + 12);

        if (!fs_count && !hs_count)
                goto einval;

        data += 16;
        len  -= 16;

        if (likely(fs_count)) {
                fs_len = ffs_do_descs(fs_count, data, len,
                                      __ffs_data_do_entity, ffs);
                if (unlikely(fs_len < 0)) {
                        ret = fs_len;
                        goto error;
                }

                data += fs_len;
                len  -= fs_len;
        } else {
                fs_len = 0;
        }

        if (likely(hs_count)) {
                ret = ffs_do_descs(hs_count, data, len,
                                   __ffs_data_do_entity, ffs);
                if (unlikely(ret < 0))
                        goto error;
        } else {
                ret = 0;
        }

        if (unlikely(len != ret))
                goto einval;

        ffs->raw_fs_descs_length = fs_len;
        ffs->raw_descs_length    = fs_len + ret;
        ffs->raw_descs           = _data;
        ffs->fs_descs_count      = fs_count;
        ffs->hs_descs_count      = hs_count;

        return 0;

einval:
        ret = -EINVAL;
error:
        kfree(_data);
        return ret;
}

static int __ffs_data_got_strings(struct ffs_data *ffs,
                                  char *const _data, size_t len)
{
        u32 str_count, needed_count, lang_count;
        struct usb_gadget_strings **stringtabs, *t;
        struct usb_string *strings, *s;
        const char *data = _data;

        ENTER();

        if (unlikely(get_unaligned_le32(data) != FUNCTIONFS_STRINGS_MAGIC ||
                     get_unaligned_le32(data + 4) != len))
                goto error;
        str_count  = get_unaligned_le32(data + 8);
        lang_count = get_unaligned_le32(data + 12);

        /* if one is zero the other must be zero */
        if (unlikely(!str_count != !lang_count))
                goto error;

        /* Do we have at least as many strings as descriptors need? */
        needed_count = ffs->strings_count;
        if (unlikely(str_count < needed_count))
                goto error;

        /*
         * If we don't need any strings just return and free all
         * memory.
         */
        if (!needed_count) {
                kfree(_data);
                return 0;
        }

        /* Allocate everything in one chunk so there's less maintenance. */
        {
                struct {
                        struct usb_gadget_strings *stringtabs[lang_count + 1];
                        struct usb_gadget_strings stringtab[lang_count];
                        struct usb_string strings[lang_count*(needed_count+1)];
                } *d;
                unsigned i = 0;

                d = kmalloc(sizeof *d, GFP_KERNEL);
                if (unlikely(!d)) {
                        kfree(_data);
                        return -ENOMEM;
                }

                stringtabs = d->stringtabs;
                t = d->stringtab;
                i = lang_count;
                do {
                        *stringtabs++ = t++;
                } while (--i);
                *stringtabs = NULL;

                stringtabs = d->stringtabs;
                t = d->stringtab;
                s = d->strings;
                strings = s;
        }

        /* For each language */
        data += 16;
        len -= 16;

        do { /* lang_count > 0 so we can use do-while */
                unsigned needed = needed_count;

                if (unlikely(len < 3))
                        goto error_free;
                t->language = get_unaligned_le16(data);
                t->strings  = s;
                ++t;

                data += 2;
                len -= 2;

                /* For each string */
                do { /* str_count > 0 so we can use do-while */
                        size_t length = strnlen(data, len);

                        if (unlikely(length == len))
                                goto error_free;

                        /*
                         * User may provide more strings then we need,
                         * if that's the case we simply ignore the
                         * rest
                         */
                        if (likely(needed)) {
                                /*
                                 * s->id will be set while adding
                                 * function to configuration so for
                                 * now just leave garbage here.
                                 */
                                s->s = data;
                                --needed;
                                ++s;
                        }

                        data += length + 1;
                        len -= length + 1;
                } while (--str_count);

                s->id = 0;   /* terminator */
                s->s = NULL;
                ++s;

        } while (--lang_count);

        /* Some garbage left? */
        if (unlikely(len))
                goto error_free;

        /* Done! */
        ffs->stringtabs = stringtabs;
        ffs->raw_strings = _data;

        return 0;

error_free:
        kfree(stringtabs);
error:
        kfree(_data);
        return -EINVAL;
}


/* Events handling and management *******************************************/

static void __ffs_event_add(struct ffs_data *ffs,
                            enum usb_functionfs_event_type type)
{
        enum usb_functionfs_event_type rem_type1, rem_type2 = type;

        int neg = 0;

        /*
         * Abort any unhandled setup
         *
         * We do not need to worry about some cmpxchg() changing value
         * of ffs->setup_state without holding the lock because when
         * state is FFS_SETUP_PENDING cmpxchg() in several places in
         * the source does nothing.
         */
        if (ffs->setup_state == FFS_SETUP_PENDING)
                ffs->setup_state = FFS_SETUP_CANCELED;

        switch (type) {
        case FUNCTIONFS_RESUME:
                rem_type2 = FUNCTIONFS_SUSPEND;
                /* FALL THROUGH */
        case FUNCTIONFS_SUSPEND:
        case FUNCTIONFS_SETUP:
                rem_type1 = type;
                /* Discard all similar events */
                break;

        case FUNCTIONFS_BIND:
        case FUNCTIONFS_UNBIND:
        case FUNCTIONFS_DISABLE:
        case FUNCTIONFS_ENABLE:
                /* Discard everything other then power management. */
                rem_type1 = FUNCTIONFS_SUSPEND;
                rem_type2 = FUNCTIONFS_RESUME;
                neg = 1;
                break;

        default:
                BUG();
        }

        {
                u8 *ev  = ffs->ev.types, *out = ev;
                unsigned n = ffs->ev.count;
                for (; n; --n, ++ev)
                        if ((*ev == rem_type1 || *ev == rem_type2) == neg)
                                *out++ = *ev;
                        else
                                pr_vdebug("purging event %d\n", *ev);
                ffs->ev.count = out - ffs->ev.types;
        }

        pr_vdebug("adding event %d\n", type);
        ffs->ev.types[ffs->ev.count++] = type;
        wake_up_locked(&ffs->ev.waitq);
}

static void ffs_event_add(struct ffs_data *ffs,
                          enum usb_functionfs_event_type type)
{
        unsigned long flags;
        spin_lock_irqsave(&ffs->ev.waitq.lock, flags);
        __ffs_event_add(ffs, type);
        spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);
}


/* Bind/unbind USB function hooks *******************************************/

static int __ffs_func_bind_do_descs(enum ffs_entity_type type, u8 *valuep,
                                    struct usb_descriptor_header *desc,
                                    void *priv)
{
        struct usb_endpoint_descriptor *ds = (void *)desc;
        struct ffs_function *func = priv;
        struct ffs_ep *ffs_ep;

        /*
         * If hs_descriptors is not NULL then we are reading hs
         * descriptors now
         */
        const int isHS = func->function.hs_descriptors != NULL;
        unsigned idx;

        if (type != FFS_DESCRIPTOR)
                return 0;

        if (isHS)
                func->function.hs_descriptors[(long)valuep] = desc;
        else
                func->function.descriptors[(long)valuep]    = desc;

        if (!desc || desc->bDescriptorType != USB_DT_ENDPOINT)
                return 0;

        idx = (ds->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK) - 1;
        ffs_ep = func->eps + idx;

        if (unlikely(ffs_ep->descs[isHS])) {
                pr_vdebug("two %sspeed descriptors for EP %d\n",
                          isHS ? "high" : "full",
                          ds->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
                return -EINVAL;
        }
        ffs_ep->descs[isHS] = ds;

        ffs_dump_mem(": Original  ep desc", ds, ds->bLength);
        if (ffs_ep->ep) {
                ds->bEndpointAddress = ffs_ep->descs[0]->bEndpointAddress;
                if (!ds->wMaxPacketSize)
                        ds->wMaxPacketSize = ffs_ep->descs[0]->wMaxPacketSize;
        } else {
                struct usb_request *req;
                struct usb_ep *ep;

                pr_vdebug("autoconfig\n");
                ep = usb_ep_autoconfig(func->gadget, ds);
                if (unlikely(!ep))
                        return -ENOTSUPP;
                ep->driver_data = func->eps + idx;

                req = usb_ep_alloc_request(ep, GFP_KERNEL);
                if (unlikely(!req))
                        return -ENOMEM;

                ffs_ep->ep  = ep;
                ffs_ep->req = req;
                func->eps_revmap[ds->bEndpointAddress &
                                 USB_ENDPOINT_NUMBER_MASK] = idx + 1;
        }
        ffs_dump_mem(": Rewritten ep desc", ds, ds->bLength);

        return 0;
}

static int __ffs_func_bind_do_nums(enum ffs_entity_type type, u8 *valuep,
                                   struct usb_descriptor_header *desc,
                                   void *priv)
{
        struct ffs_function *func = priv;
        unsigned idx;
        u8 newValue;

        switch (type) {
        default:
        case FFS_DESCRIPTOR:
                /* Handled in previous pass by __ffs_func_bind_do_descs() */
                return 0;

        case FFS_INTERFACE:
                idx = *valuep;
                if (func->interfaces_nums[idx] < 0) {
                        int id = usb_interface_id(func->conf, &func->function);
                        if (unlikely(id < 0))
                                return id;
                        func->interfaces_nums[idx] = id;
                }
                newValue = func->interfaces_nums[idx];
                break;

        case FFS_STRING:
                /* String' IDs are allocated when fsf_data is bound to cdev */
                newValue = func->ffs->stringtabs[0]->strings[*valuep - 1].id;
                break;

        case FFS_ENDPOINT:
                /*
                 * USB_DT_ENDPOINT are handled in
                 * __ffs_func_bind_do_descs().
                 */
                if (desc->bDescriptorType == USB_DT_ENDPOINT)
                        return 0;

                idx = (*valuep & USB_ENDPOINT_NUMBER_MASK) - 1;
                if (unlikely(!func->eps[idx].ep))
                        return -EINVAL;

                {
                        struct usb_endpoint_descriptor **descs;
                        descs = func->eps[idx].descs;
                        newValue = descs[descs[0] ? 0 : 1]->bEndpointAddress;
                }
                break;
        }

        pr_vdebug("%02x -> %02x\n", *valuep, newValue);
        *valuep = newValue;
        return 0;
}

static int ffs_func_bind(struct usb_configuration *c,
                         struct usb_function *f)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;

        const int full = !!func->ffs->fs_descs_count;
        const int high = gadget_is_dualspeed(func->gadget) &&
                func->ffs->hs_descs_count;

        int ret;

        /* Make it a single chunk, less management later on */
        struct {
                struct ffs_ep eps[ffs->eps_count];
                struct usb_descriptor_header
                        *fs_descs[full ? ffs->fs_descs_count + 1 : 0];
                struct usb_descriptor_header
                        *hs_descs[high ? ffs->hs_descs_count + 1 : 0];
                short inums[ffs->interfaces_count];
                char raw_descs[high ? ffs->raw_descs_length
                                    : ffs->raw_fs_descs_length];
        } *data;

        ENTER();

        /* Only high speed but not supported by gadget? */
        if (unlikely(!(full | high)))
                return -ENOTSUPP;

        /* Allocate */
        data = kmalloc(sizeof *data, GFP_KERNEL);
        if (unlikely(!data))
                return -ENOMEM;

        /* Zero */
        memset(data->eps, 0, sizeof data->eps);
        memcpy(data->raw_descs, ffs->raw_descs + 16, sizeof data->raw_descs);
        memset(data->inums, 0xff, sizeof data->inums);
        for (ret = ffs->eps_count; ret; --ret)
                data->eps[ret].num = -1;

        /* Save pointers */
        func->eps             = data->eps;
        func->interfaces_nums = data->inums;

        /*
         * Go through all the endpoint descriptors and allocate
         * endpoints first, so that later we can rewrite the endpoint
         * numbers without worrying that it may be described later on.
         */
        if (likely(full)) {
                func->function.descriptors = data->fs_descs;
                ret = ffs_do_descs(ffs->fs_descs_count,
                                   data->raw_descs,
                                   sizeof data->raw_descs,
                                   __ffs_func_bind_do_descs, func);
                if (unlikely(ret < 0))
                        goto error;
        } else {
                ret = 0;
        }

        if (likely(high)) {
                func->function.hs_descriptors = data->hs_descs;
                ret = ffs_do_descs(ffs->hs_descs_count,
                                   data->raw_descs + ret,
                                   (sizeof data->raw_descs) - ret,
                                   __ffs_func_bind_do_descs, func);
        }

        /*
         * Now handle interface numbers allocation and interface and
         * endpoint numbers rewriting.  We can do that in one go
         * now.
         */
        ret = ffs_do_descs(ffs->fs_descs_count +
                           (high ? ffs->hs_descs_count : 0),
                           data->raw_descs, sizeof data->raw_descs,
                           __ffs_func_bind_do_nums, func);
        if (unlikely(ret < 0))
                goto error;

        /* And we're done */
        ffs_event_add(ffs, FUNCTIONFS_BIND);
        return 0;

error:
        /* XXX Do we need to release all claimed endpoints here? */
        return ret;
}


/* Other USB function hooks *************************************************/

static void ffs_func_unbind(struct usb_configuration *c,
                            struct usb_function *f)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;

        ENTER();

        if (ffs->func == func) {
                ffs_func_eps_disable(func);
                ffs->func = NULL;
        }

        ffs_event_add(ffs, FUNCTIONFS_UNBIND);

        ffs_func_free(func);
}

static int ffs_func_set_alt(struct usb_function *f,
                            unsigned interface, unsigned alt)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;
        int ret = 0, intf;

        if (alt != (unsigned)-1) {
                intf = ffs_func_revmap_intf(func, interface);
                if (unlikely(intf < 0))
                        return intf;
        }

        if (ffs->func)
                ffs_func_eps_disable(ffs->func);

        if (ffs->state != FFS_ACTIVE)
                return -ENODEV;

        if (alt == (unsigned)-1) {
                ffs->func = NULL;
                ffs_event_add(ffs, FUNCTIONFS_DISABLE);
                return 0;
        }

        ffs->func = func;
        ret = ffs_func_eps_enable(func);
        if (likely(ret >= 0))
                ffs_event_add(ffs, FUNCTIONFS_ENABLE);
        return ret;
}

static void ffs_func_disable(struct usb_function *f)
{
        ffs_func_set_alt(f, 0, (unsigned)-1);
}

static int ffs_func_setup(struct usb_function *f,
                          const struct usb_ctrlrequest *creq)
{
        struct ffs_function *func = ffs_func_from_usb(f);
        struct ffs_data *ffs = func->ffs;
        unsigned long flags;
        int ret;

        ENTER();

        pr_vdebug("creq->bRequestType = %02x\n", creq->bRequestType);
        pr_vdebug("creq->bRequest     = %02x\n", creq->bRequest);
        pr_vdebug("creq->wValue       = %04x\n", le16_to_cpu(creq->wValue));
        pr_vdebug("creq->wIndex       = %04x\n", le16_to_cpu(creq->wIndex));
        pr_vdebug("creq->wLength      = %04x\n", le16_to_cpu(creq->wLength));

        /*
         * Most requests directed to interface go through here
         * (notable exceptions are set/get interface) so we need to
         * handle them.  All other either handled by composite or
         * passed to usb_configuration->setup() (if one is set).  No
         * matter, we will handle requests directed to endpoint here
         * as well (as it's straightforward) but what to do with any
         * other request?
         */
        if (ffs->state != FFS_ACTIVE)
                return -ENODEV;

        switch (creq->bRequestType & USB_RECIP_MASK) {
        case USB_RECIP_INTERFACE:
                ret = ffs_func_revmap_intf(func, le16_to_cpu(creq->wIndex));
                if (unlikely(ret < 0))
                        return ret;
                break;

        case USB_RECIP_ENDPOINT:
                ret = ffs_func_revmap_ep(func, le16_to_cpu(creq->wIndex));
                if (unlikely(ret < 0))
                        return ret;
                break;

        default:
                return -EOPNOTSUPP;
        }

        spin_lock_irqsave(&ffs->ev.waitq.lock, flags);
        ffs->ev.setup = *creq;
        ffs->ev.setup.wIndex = cpu_to_le16(ret);
        __ffs_event_add(ffs, FUNCTIONFS_SETUP);
        spin_unlock_irqrestore(&ffs->ev.waitq.lock, flags);

        return 0;
}

static void ffs_func_suspend(struct usb_function *f)
{
        ENTER();
        ffs_event_add(ffs_func_from_usb(f)->ffs, FUNCTIONFS_SUSPEND);
}

static void ffs_func_resume(struct usb_function *f)
{
        ENTER();
        ffs_event_add(ffs_func_from_usb(f)->ffs, FUNCTIONFS_RESUME);
}


/* Endpoint and interface numbers reverse mapping ***************************/

static int ffs_func_revmap_ep(struct ffs_function *func, u8 num)
{
        num = func->eps_revmap[num & USB_ENDPOINT_NUMBER_MASK];
        return num ? num : -EDOM;
}

static int ffs_func_revmap_intf(struct ffs_function *func, u8 intf)
{
        short *nums = func->interfaces_nums;
        unsigned count = func->ffs->interfaces_count;

        for (; count; --count, ++nums) {
                if (*nums >= 0 && *nums == intf)
                        return nums - func->interfaces_nums;
        }

        return -EDOM;
}


/* Misc helper functions ****************************************************/

static int ffs_mutex_lock(struct mutex *mutex, unsigned nonblock)
{
        return nonblock
                ? likely(mutex_trylock(mutex)) ? 0 : -EAGAIN
                : mutex_lock_interruptible(mutex);
}

static char *ffs_prepare_buffer(const char * __user buf, size_t len)
{
        char *data;

        if (unlikely(!len))
                return NULL;

        data = kmalloc(len, GFP_KERNEL);
        if (unlikely(!data))
                return ERR_PTR(-ENOMEM);

        if (unlikely(__copy_from_user(data, buf, len))) {
                kfree(data);
                return ERR_PTR(-EFAULT);
        }

        pr_vdebug("Buffer from user space:\n");
        ffs_dump_mem("", data, len);

        return data;
}