f_fs.c

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/*
 * f_fs.c -- user mode file system API for USB composite function controllers
 *
 * Copyright (C) 2010 Samsung Electronics
 * Author: Michal Nazarewicz <[email protected]>
 *
 * 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;
}