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32 results

f_fs.c

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  • f_fs.c 90.36 KiB
    // SPDX-License-Identifier: GPL-2.0+
    /*
     * 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
     */
    
    
    /* #define DEBUG */
    /* #define VERBOSE_DEBUG */
    
    #include <linux/blkdev.h>
    #include <linux/pagemap.h>
    #include <linux/export.h>
    #include <linux/fs_parser.h>
    #include <linux/hid.h>
    #include <linux/mm.h>
    #include <linux/module.h>
    #include <linux/scatterlist.h>
    #include <linux/sched/signal.h>
    #include <linux/uio.h>
    #include <linux/vmalloc.h>
    #include <asm/unaligned.h>
    
    #include <linux/usb/ccid.h>
    #include <linux/usb/composite.h>
    #include <linux/usb/functionfs.h>
    
    #include <linux/aio.h>
    #include <linux/mmu_context.h>
    #include <linux/poll.h>
    #include <linux/eventfd.h>
    
    #include "u_fs.h"
    #include "u_f.h"
    #include "u_os_desc.h"
    #include "configfs.h"
    
    #define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest dice roll ;) */
    
    /* 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(const char *dev_name)
    	__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 inline enum ffs_setup_state
    ffs_setup_state_clear_cancelled(struct ffs_data *ffs)
    {
    	return (enum ffs_setup_state)
    		cmpxchg(&ffs->setup_state, FFS_SETUP_CANCELLED, FFS_NO_SETUP);
    }
    
    
    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 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 bool ffs_func_req_match(struct usb_function *,
    			       const struct usb_ctrlrequest *,
    			       bool config0);
    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, [2]: super speed */
    	struct usb_endpoint_descriptor	*descs[3];
    
    	u8				num;
    
    	int				status;	/* P: epfile->mutex */
    };
    
    struct ffs_epfile {
    	/* Protects ep->ep and ep->req. */
    	struct mutex			mutex;
    
    	struct ffs_data			*ffs;
    	struct ffs_ep			*ep;	/* P: ffs->eps_lock */
    
    	struct dentry			*dentry;
    
    	/*
    	 * Buffer for holding data from partial reads which may happen since
    	 * we’re rounding user read requests to a multiple of a max packet size.
    	 *
    	 * The pointer is initialised with NULL value and may be set by
    	 * __ffs_epfile_read_data function to point to a temporary buffer.
    	 *
    	 * In normal operation, calls to __ffs_epfile_read_buffered will consume
    	 * data from said buffer and eventually free it.  Importantly, while the
    	 * function is using the buffer, it sets the pointer to NULL.  This is
    	 * all right since __ffs_epfile_read_data and __ffs_epfile_read_buffered
    	 * can never run concurrently (they are synchronised by epfile->mutex)
    	 * so the latter will not assign a new value to the pointer.
    	 *
    	 * Meanwhile ffs_func_eps_disable frees the buffer (if the pointer is
    	 * valid) and sets the pointer to READ_BUFFER_DROP value.  This special
    	 * value is crux of the synchronisation between ffs_func_eps_disable and
    	 * __ffs_epfile_read_data.
    	 *
    	 * Once __ffs_epfile_read_data is about to finish it will try to set the
    	 * pointer back to its old value (as described above), but seeing as the
    	 * pointer is not-NULL (namely READ_BUFFER_DROP) it will instead free
    	 * the buffer.
    	 *
    	 * == State transitions ==
    	 *
    	 * • ptr == NULL:  (initial state)
    	 *   ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP
    	 *   ◦ __ffs_epfile_read_buffered:    nop
    	 *   ◦ __ffs_epfile_read_data allocates temp buffer: go to ptr == buf
    	 *   ◦ reading finishes:              n/a, not in ‘and reading’ state
    	 * • ptr == DROP:
    	 *   ◦ __ffs_epfile_read_buffer_free: nop
    	 *   ◦ __ffs_epfile_read_buffered:    go to ptr == NULL
    	 *   ◦ __ffs_epfile_read_data allocates temp buffer: free buf, nop
    	 *   ◦ reading finishes:              n/a, not in ‘and reading’ state
    	 * • ptr == buf:
    	 *   ◦ __ffs_epfile_read_buffer_free: free buf, go to ptr == DROP
    	 *   ◦ __ffs_epfile_read_buffered:    go to ptr == NULL and reading
    	 *   ◦ __ffs_epfile_read_data:        n/a, __ffs_epfile_read_buffered
    	 *                                    is always called first
    	 *   ◦ reading finishes:              n/a, not in ‘and reading’ state
    	 * • ptr == NULL and reading:
    	 *   ◦ __ffs_epfile_read_buffer_free: go to ptr == DROP and reading
    	 *   ◦ __ffs_epfile_read_buffered:    n/a, mutex is held
    	 *   ◦ __ffs_epfile_read_data:        n/a, mutex is held
    	 *   ◦ reading finishes and …
    	 *     … all data read:               free buf, go to ptr == NULL
    	 *     … otherwise:                   go to ptr == buf and reading
    	 * • ptr == DROP and reading:
    	 *   ◦ __ffs_epfile_read_buffer_free: nop
    	 *   ◦ __ffs_epfile_read_buffered:    n/a, mutex is held
    	 *   ◦ __ffs_epfile_read_data:        n/a, mutex is held
    	 *   ◦ reading finishes:              free buf, go to ptr == DROP
    	 */
    	struct ffs_buffer		*read_buffer;
    #define READ_BUFFER_DROP ((struct ffs_buffer *)ERR_PTR(-ESHUTDOWN))
    
    	char				name[5];
    
    	unsigned char			in;	/* P: ffs->eps_lock */
    	unsigned char			isoc;	/* P: ffs->eps_lock */
    
    	unsigned char			_pad;
    };
    
    struct ffs_buffer {
    	size_t length;
    	char *data;
    	char storage[];
    };
    
    /*  ffs_io_data structure ***************************************************/
    
    struct ffs_io_data {
    	bool aio;
    	bool read;
    
    	struct kiocb *kiocb;
    	struct iov_iter data;
    	const void *to_free;
    	char *buf;
    
    	struct mm_struct *mm;
    	struct work_struct work;
    
    	struct usb_ep *ep;
    	struct usb_request *req;
    	struct sg_table sgt;
    	bool use_sg;
    
    	struct ffs_data *ffs;
    };
    
    struct ffs_desc_helper {
    	struct ffs_data *ffs;
    	unsigned interfaces_count;
    	unsigned eps_count;
    };
    
    static int  __must_check ffs_epfiles_create(struct ffs_data *ffs);
    static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count);
    
    static struct dentry *
    ffs_sb_create_file(struct super_block *sb, const char *name, void *data,
    		   const struct file_operations *fops);
    
    /* Devices management *******************************************************/
    
    DEFINE_MUTEX(ffs_lock);
    EXPORT_SYMBOL_GPL(ffs_lock);
    
    static struct ffs_dev *_ffs_find_dev(const char *name);
    static struct ffs_dev *_ffs_alloc_dev(void);
    static void _ffs_free_dev(struct ffs_dev *dev);
    static void *ffs_acquire_dev(const char *dev_name);
    static void ffs_release_dev(struct ffs_data *ffs_data);
    static int ffs_ready(struct ffs_data *ffs);
    static void ffs_closed(struct ffs_data *ffs);
    
    /* 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(&ffs->ep0req_completion);
    }
    
    static int __ffs_ep0_queue_wait(struct ffs_data *ffs, char *data, size_t len)
    	__releases(&ffs->ev.waitq.lock)
    {
    	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;
    
    	reinit_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 req->status ? req->status : req->actual;
    }
    
    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_clear_cancelled(ffs) == FFS_SETUP_CANCELLED)
    		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 = ffs_ready(ffs);
    			if (unlikely(ret < 0)) {
    				ffs->state = FFS_CLOSING;
    				return ret;
    			}
    
    			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_clear_cancelled(ffs)) {
    		case FFS_SETUP_CANCELLED:
    			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_CANCELLED 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_clear_cancelled(ffs) ==
    		    FFS_SETUP_CANCELLED) {
    			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;
    }
    
    /* Called with ffs->ev.waitq.lock and ffs->mutex held, both released on exit. */
    static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf,
    				     size_t n)
    	__releases(&ffs->ev.waitq.lock)
    {
    	/*
    	 * n cannot be bigger than ffs->ev.count, which cannot be bigger than
    	 * size of ffs->ev.types array (which is four) so that's how much space
    	 * we reserve.
    	 */
    	struct usb_functionfs_event events[ARRAY_SIZE(ffs->ev.types)];
    	const size_t size = n * sizeof *events;
    	unsigned i = 0;
    
    	memset(events, 0, size);
    
    	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);
    
    	ffs->ev.count -= n;
    	if (ffs->ev.count)
    		memmove(ffs->ev.types, ffs->ev.types + n,
    			ffs->ev.count * sizeof *ffs->ev.types);
    
    	spin_unlock_irq(&ffs->ev.waitq.lock);
    	mutex_unlock(&ffs->mutex);
    
    	return unlikely(copy_to_user(buf, events, size)) ? -EFAULT : size;
    }
    
    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_clear_cancelled(ffs) == FFS_SETUP_CANCELLED)
    		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_clear_cancelled(ffs)) {
    	case FFS_SETUP_CANCELLED:
    		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;
    		}
    
    		/* unlocks spinlock */
    		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_clear_cancelled(ffs) ==
    		    FFS_SETUP_CANCELLED) {
    			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 __poll_t ffs_ep0_poll(struct file *file, poll_table *wait)
    {
    	struct ffs_data *ffs = file->private_data;
    	__poll_t mask = EPOLLWRNORM;
    	int ret;
    
    	poll_wait(file, &ffs->ev.waitq, wait);
    
    	ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
    	if (unlikely(ret < 0))
    		return mask;
    
    	switch (ffs->state) {
    	case FFS_READ_DESCRIPTORS:
    	case FFS_READ_STRINGS:
    		mask |= EPOLLOUT;
    		break;
    
    	case FFS_ACTIVE:
    		switch (ffs->setup_state) {
    		case FFS_NO_SETUP:
    			if (ffs->ev.count)
    				mask |= EPOLLIN;
    			break;
    
    		case FFS_SETUP_PENDING:
    		case FFS_SETUP_CANCELLED:
    			mask |= (EPOLLIN | EPOLLOUT);
    			break;
    		}
    	case FFS_CLOSING:
    		break;
    	case FFS_DEACTIVATED:
    		break;
    	}
    
    	mutex_unlock(&ffs->mutex);
    
    	return mask;
    }
    
    static const struct file_operations ffs_ep0_operations = {
    	.llseek =	no_llseek,
    
    	.open =		ffs_ep0_open,
    	.write =	ffs_ep0_write,
    	.read =		ffs_ep0_read,
    	.release =	ffs_ep0_release,
    	.unlocked_ioctl =	ffs_ep0_ioctl,
    	.poll =		ffs_ep0_poll,
    };
    
    
    /* "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_copy_to_iter(void *data, int data_len, struct iov_iter *iter)
    {
    	ssize_t ret = copy_to_iter(data, data_len, iter);
    	if (likely(ret == data_len))
    		return ret;
    
    	if (unlikely(iov_iter_count(iter)))
    		return -EFAULT;
    
    	/*
    	 * Dear user space developer!
    	 *
    	 * TL;DR: To stop getting below error message in your kernel log, change
    	 * user space code using functionfs to align read buffers to a max
    	 * packet size.
    	 *
    	 * Some UDCs (e.g. dwc3) require request sizes to be a multiple of a max
    	 * packet size.  When unaligned buffer is passed to functionfs, it
    	 * internally uses a larger, aligned buffer so that such UDCs are happy.
    	 *
    	 * Unfortunately, this means that host may send more data than was
    	 * requested in read(2) system call.  f_fs doesn’t know what to do with
    	 * that excess data so it simply drops it.
    	 *
    	 * Was the buffer aligned in the first place, no such problem would
    	 * happen.
    	 *
    	 * Data may be dropped only in AIO reads.  Synchronous reads are handled
    	 * by splitting a request into multiple parts.  This splitting may still
    	 * be a problem though so it’s likely best to align the buffer
    	 * regardless of it being AIO or not..
    	 *
    	 * This only affects OUT endpoints, i.e. reading data with a read(2),
    	 * aio_read(2) etc. system calls.  Writing data to an IN endpoint is not
    	 * affected.
    	 */
    	pr_err("functionfs read size %d > requested size %zd, dropping excess data. "
    	       "Align read buffer size to max packet size to avoid the problem.\n",
    	       data_len, ret);
    
    	return ret;
    }
    
    /*
     * allocate a virtually contiguous buffer and create a scatterlist describing it
     * @sg_table	- pointer to a place to be filled with sg_table contents
     * @size	- required buffer size
     */
    static void *ffs_build_sg_list(struct sg_table *sgt, size_t sz)
    {
    	struct page **pages;
    	void *vaddr, *ptr;
    	unsigned int n_pages;
    	int i;
    
    	vaddr = vmalloc(sz);
    	if (!vaddr)
    		return NULL;
    
    	n_pages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
    	pages = kvmalloc_array(n_pages, sizeof(struct page *), GFP_KERNEL);
    	if (!pages) {
    		vfree(vaddr);
    
    		return NULL;
    	}
    	for (i = 0, ptr = vaddr; i < n_pages; ++i, ptr += PAGE_SIZE)
    		pages[i] = vmalloc_to_page(ptr);
    
    	if (sg_alloc_table_from_pages(sgt, pages, n_pages, 0, sz, GFP_KERNEL)) {
    		kvfree(pages);
    		vfree(vaddr);
    
    		return NULL;
    	}
    	kvfree(pages);
    
    	return vaddr;
    }
    
    static inline void *ffs_alloc_buffer(struct ffs_io_data *io_data,
    	size_t data_len)
    {
    	if (io_data->use_sg)
    		return ffs_build_sg_list(&io_data->sgt, data_len);
    
    	return kmalloc(data_len, GFP_KERNEL);
    }
    
    static inline void ffs_free_buffer(struct ffs_io_data *io_data)
    {
    	if (!io_data->buf)
    		return;
    
    	if (io_data->use_sg) {
    		sg_free_table(&io_data->sgt);
    		vfree(io_data->buf);
    	} else {
    		kfree(io_data->buf);
    	}
    }
    
    static void ffs_user_copy_worker(struct work_struct *work)
    {
    	struct ffs_io_data *io_data = container_of(work, struct ffs_io_data,
    						   work);
    	int ret = io_data->req->status ? io_data->req->status :
    					 io_data->req->actual;
    	bool kiocb_has_eventfd = io_data->kiocb->ki_flags & IOCB_EVENTFD;
    
    	if (io_data->read && ret > 0) {
    		mm_segment_t oldfs = get_fs();
    
    		set_fs(USER_DS);
    		use_mm(io_data->mm);
    		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
    		unuse_mm(io_data->mm);
    		set_fs(oldfs);
    	}
    
    	io_data->kiocb->ki_complete(io_data->kiocb, ret, ret);
    
    	if (io_data->ffs->ffs_eventfd && !kiocb_has_eventfd)
    		eventfd_signal(io_data->ffs->ffs_eventfd, 1);
    
    	usb_ep_free_request(io_data->ep, io_data->req);
    
    	if (io_data->read)
    		kfree(io_data->to_free);
    	ffs_free_buffer(io_data);
    	kfree(io_data);
    }
    
    static void ffs_epfile_async_io_complete(struct usb_ep *_ep,
    					 struct usb_request *req)
    {
    	struct ffs_io_data *io_data = req->context;
    	struct ffs_data *ffs = io_data->ffs;
    
    	ENTER();
    
    	INIT_WORK(&io_data->work, ffs_user_copy_worker);
    	queue_work(ffs->io_completion_wq, &io_data->work);
    }
    
    static void __ffs_epfile_read_buffer_free(struct ffs_epfile *epfile)
    {
    	/*
    	 * See comment in struct ffs_epfile for full read_buffer pointer
    	 * synchronisation story.
    	 */
    	struct ffs_buffer *buf = xchg(&epfile->read_buffer, READ_BUFFER_DROP);
    	if (buf && buf != READ_BUFFER_DROP)
    		kfree(buf);
    }
    
    /* Assumes epfile->mutex is held. */
    static ssize_t __ffs_epfile_read_buffered(struct ffs_epfile *epfile,
    					  struct iov_iter *iter)
    {
    	/*
    	 * Null out epfile->read_buffer so ffs_func_eps_disable does not free
    	 * the buffer while we are using it.  See comment in struct ffs_epfile
    	 * for full read_buffer pointer synchronisation story.
    	 */
    	struct ffs_buffer *buf = xchg(&epfile->read_buffer, NULL);
    	ssize_t ret;
    	if (!buf || buf == READ_BUFFER_DROP)
    		return 0;
    
    	ret = copy_to_iter(buf->data, buf->length, iter);
    	if (buf->length == ret) {
    		kfree(buf);
    		return ret;
    	}
    
    	if (unlikely(iov_iter_count(iter))) {
    		ret = -EFAULT;
    	} else {
    		buf->length -= ret;
    		buf->data += ret;
    	}
    
    	if (cmpxchg(&epfile->read_buffer, NULL, buf))
    		kfree(buf);
    
    	return ret;
    }
    
    /* Assumes epfile->mutex is held. */
    static ssize_t __ffs_epfile_read_data(struct ffs_epfile *epfile,
    				      void *data, int data_len,
    				      struct iov_iter *iter)
    {
    	struct ffs_buffer *buf;
    
    	ssize_t ret = copy_to_iter(data, data_len, iter);
    	if (likely(data_len == ret))
    		return ret;
    
    	if (unlikely(iov_iter_count(iter)))
    		return -EFAULT;
    
    	/* See ffs_copy_to_iter for more context. */
    	pr_warn("functionfs read size %d > requested size %zd, splitting request into multiple reads.",
    		data_len, ret);
    
    	data_len -= ret;
    	buf = kmalloc(sizeof(*buf) + data_len, GFP_KERNEL);
    	if (!buf)
    		return -ENOMEM;
    	buf->length = data_len;
    	buf->data = buf->storage;
    	memcpy(buf->storage, data + ret, data_len);
    
    	/*
    	 * At this point read_buffer is NULL or READ_BUFFER_DROP (if
    	 * ffs_func_eps_disable has been called in the meanwhile).  See comment
    	 * in struct ffs_epfile for full read_buffer pointer synchronisation
    	 * story.
    	 */
    	if (unlikely(cmpxchg(&epfile->read_buffer, NULL, buf)))
    		kfree(buf);
    
    	return ret;
    }
    
    static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
    {
    	struct ffs_epfile *epfile = file->private_data;
    	struct usb_request *req;
    	struct ffs_ep *ep;
    	char *data = NULL;
    	ssize_t ret, data_len = -EINVAL;
    	int halt;
    
    	/* Are we still active? */
    	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
    		return -ENODEV;
    
    	/* Wait for endpoint to be enabled */
    	ep = epfile->ep;
    	if (!ep) {
    		if (file->f_flags & O_NONBLOCK)
    			return -EAGAIN;
    
    		ret = wait_event_interruptible(
    				epfile->ffs->wait, (ep = epfile->ep));
    		if (ret)
    			return -EINTR;
    	}
    
    	/* Do we halt? */
    	halt = (!io_data->read == !epfile->in);
    	if (halt && epfile->isoc)
    		return -EINVAL;
    
    	/* We will be using request and read_buffer */
    	ret = ffs_mutex_lock(&epfile->mutex, file->f_flags & O_NONBLOCK);
    	if (unlikely(ret))
    		goto error;
    
    	/* Allocate & copy */
    	if (!halt) {
    		struct usb_gadget *gadget;
    
    		/*
    		 * Do we have buffered data from previous partial read?  Check
    		 * that for synchronous case only because we do not have
    		 * facility to ‘wake up’ a pending asynchronous read and push
    		 * buffered data to it which we would need to make things behave
    		 * consistently.
    		 */
    		if (!io_data->aio && io_data->read) {
    			ret = __ffs_epfile_read_buffered(epfile, &io_data->data);
    			if (ret)
    				goto error_mutex;
    		}
    
    		/*
    		 * if we _do_ wait above, the epfile->ffs->gadget might be NULL
    		 * before the waiting completes, so do not assign to 'gadget'
    		 * earlier
    		 */
    		gadget = epfile->ffs->gadget;
    
    		spin_lock_irq(&epfile->ffs->eps_lock);
    		/* In the meantime, endpoint got disabled or changed. */
    		if (epfile->ep != ep) {
    			ret = -ESHUTDOWN;
    			goto error_lock;
    		}
    		data_len = iov_iter_count(&io_data->data);
    		/*
    		 * Controller may require buffer size to be aligned to
    		 * maxpacketsize of an out endpoint.
    		 */
    		if (io_data->read)
    			data_len = usb_ep_align_maybe(gadget, ep->ep, data_len);
    
    		io_data->use_sg = gadget->sg_supported && data_len > PAGE_SIZE;
    		spin_unlock_irq(&epfile->ffs->eps_lock);
    
    		data = ffs_alloc_buffer(io_data, data_len);
    		if (unlikely(!data)) {
    			ret = -ENOMEM;
    			goto error_mutex;
    		}
    		if (!io_data->read &&
    		    !copy_from_iter_full(data, data_len, &io_data->data)) {
    			ret = -EFAULT;
    			goto error_mutex;
    		}
    	}
    
    	spin_lock_irq(&epfile->ffs->eps_lock);
    
    	if (epfile->ep != ep) {
    		/* In the meantime, endpoint got disabled or changed. */
    		ret = -ESHUTDOWN;
    	} else if (halt) {
    		ret = usb_ep_set_halt(ep->ep);
    		if (!ret)
    			ret = -EBADMSG;
    	} else if (unlikely(data_len == -EINVAL)) {
    		/*
    		 * Sanity Check: even though data_len can't be used
    		 * uninitialized at the time I write this comment, some
    		 * compilers complain about this situation.
    		 * In order to keep the code clean from warnings, data_len is
    		 * being initialized to -EINVAL during its declaration, which
    		 * means we can't rely on compiler anymore to warn no future
    		 * changes won't result in data_len being used uninitialized.
    		 * For such reason, we're adding this redundant sanity check
    		 * here.
    		 */
    		WARN(1, "%s: data_len == -EINVAL\n", __func__);
    		ret = -EINVAL;
    	} else if (!io_data->aio) {
    		DECLARE_COMPLETION_ONSTACK(done);
    		bool interrupted = false;
    
    		req = ep->req;
    		if (io_data->use_sg) {
    			req->buf = NULL;
    			req->sg	= io_data->sgt.sgl;
    			req->num_sgs = io_data->sgt.nents;
    		} else {
    			req->buf = data;
    		}
    		req->length = data_len;
    
    		io_data->buf = data;
    
    		req->context  = &done;
    		req->complete = ffs_epfile_io_complete;
    
    		ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
    		if (unlikely(ret < 0))
    			goto error_lock;
    
    		spin_unlock_irq(&epfile->ffs->eps_lock);
    
    		if (unlikely(wait_for_completion_interruptible(&done))) {
    			/*
    			 * To avoid race condition with ffs_epfile_io_complete,
    			 * dequeue the request first then check
    			 * status. usb_ep_dequeue API should guarantee no race
    			 * condition with req->complete callback.
    			 */
    			usb_ep_dequeue(ep->ep, req);
    			wait_for_completion(&done);
    			interrupted = ep->status < 0;
    		}
    
    		if (interrupted)
    			ret = -EINTR;
    		else if (io_data->read && ep->status > 0)
    			ret = __ffs_epfile_read_data(epfile, data, ep->status,
    						     &io_data->data);
    		else
    			ret = ep->status;
    		goto error_mutex;
    	} else if (!(req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC))) {
    		ret = -ENOMEM;
    	} else {
    		if (io_data->use_sg) {
    			req->buf = NULL;
    			req->sg	= io_data->sgt.sgl;
    			req->num_sgs = io_data->sgt.nents;
    		} else {
    			req->buf = data;
    		}
    		req->length = data_len;
    
    		io_data->buf = data;
    		io_data->ep = ep->ep;
    		io_data->req = req;
    		io_data->ffs = epfile->ffs;
    
    		req->context  = io_data;
    		req->complete = ffs_epfile_async_io_complete;
    
    		ret = usb_ep_queue(ep->ep, req, GFP_ATOMIC);
    		if (unlikely(ret)) {
    			usb_ep_free_request(ep->ep, req);
    			goto error_lock;
    		}
    
    		ret = -EIOCBQUEUED;
    		/*
    		 * Do not kfree the buffer in this function.  It will be freed
    		 * by ffs_user_copy_worker.
    		 */
    		data = NULL;
    	}
    
    error_lock:
    	spin_unlock_irq(&epfile->ffs->eps_lock);
    error_mutex:
    	mutex_unlock(&epfile->mutex);
    error:
    	if (ret != -EIOCBQUEUED) /* don't free if there is iocb queued */
    		ffs_free_buffer(io_data);
    	return ret;
    }
    
    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_aio_cancel(struct kiocb *kiocb)
    {
    	struct ffs_io_data *io_data = kiocb->private;
    	struct ffs_epfile *epfile = kiocb->ki_filp->private_data;
    	int value;
    
    	ENTER();
    
    	spin_lock_irq(&epfile->ffs->eps_lock);
    
    	if (likely(io_data && io_data->ep && io_data->req))
    		value = usb_ep_dequeue(io_data->ep, io_data->req);
    	else
    		value = -EINVAL;
    
    	spin_unlock_irq(&epfile->ffs->eps_lock);
    
    	return value;
    }
    
    static ssize_t ffs_epfile_write_iter(struct kiocb *kiocb, struct iov_iter *from)
    {
    	struct ffs_io_data io_data, *p = &io_data;
    	ssize_t res;
    
    	ENTER();
    
    	if (!is_sync_kiocb(kiocb)) {
    		p = kzalloc(sizeof(io_data), GFP_KERNEL);
    		if (unlikely(!p))
    			return -ENOMEM;
    		p->aio = true;
    	} else {
    		memset(p, 0, sizeof(*p));
    		p->aio = false;
    	}
    
    	p->read = false;
    	p->kiocb = kiocb;
    	p->data = *from;
    	p->mm = current->mm;
    
    	kiocb->private = p;
    
    	if (p->aio)
    		kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);
    
    	res = ffs_epfile_io(kiocb->ki_filp, p);
    	if (res == -EIOCBQUEUED)
    		return res;
    	if (p->aio)
    		kfree(p);
    	else
    		*from = p->data;
    	return res;
    }
    
    static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
    {
    	struct ffs_io_data io_data, *p = &io_data;
    	ssize_t res;
    
    	ENTER();
    
    	if (!is_sync_kiocb(kiocb)) {
    		p = kzalloc(sizeof(io_data), GFP_KERNEL);
    		if (unlikely(!p))
    			return -ENOMEM;
    		p->aio = true;
    	} else {
    		memset(p, 0, sizeof(*p));
    		p->aio = false;
    	}
    
    	p->read = true;
    	p->kiocb = kiocb;
    	if (p->aio) {
    		p->to_free = dup_iter(&p->data, to, GFP_KERNEL);
    		if (!p->to_free) {
    			kfree(p);
    			return -ENOMEM;
    		}
    	} else {
    		p->data = *to;
    		p->to_free = NULL;
    	}
    	p->mm = current->mm;
    
    	kiocb->private = p;
    
    	if (p->aio)
    		kiocb_set_cancel_fn(kiocb, ffs_aio_cancel);
    
    	res = ffs_epfile_io(kiocb->ki_filp, p);
    	if (res == -EIOCBQUEUED)
    		return res;
    
    	if (p->aio) {
    		kfree(p->to_free);
    		kfree(p);
    	} else {
    		*to = p->data;
    	}
    	return res;
    }
    
    static int
    ffs_epfile_release(struct inode *inode, struct file *file)
    {
    	struct ffs_epfile *epfile = inode->i_private;
    
    	ENTER();
    
    	__ffs_epfile_read_buffer_free(epfile);
    	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;
    	struct ffs_ep *ep;
    	int ret;
    
    	ENTER();
    
    	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
    		return -ENODEV;
    
    	/* Wait for endpoint to be enabled */
    	ep = epfile->ep;
    	if (!ep) {
    		if (file->f_flags & O_NONBLOCK)
    			return -EAGAIN;
    
    		ret = wait_event_interruptible(
    				epfile->ffs->wait, (ep = epfile->ep));
    		if (ret)
    			return -EINTR;
    	}
    
    	spin_lock_irq(&epfile->ffs->eps_lock);
    
    	/* In the meantime, endpoint got disabled or changed. */
    	if (epfile->ep != ep) {
    		spin_unlock_irq(&epfile->ffs->eps_lock);
    		return -ESHUTDOWN;
    	}
    
    	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;
    	case FUNCTIONFS_ENDPOINT_DESC:
    	{
    		int desc_idx;
    		struct usb_endpoint_descriptor *desc;
    
    		switch (epfile->ffs->gadget->speed) {
    		case USB_SPEED_SUPER:
    			desc_idx = 2;
    			break;
    		case USB_SPEED_HIGH:
    			desc_idx = 1;
    			break;
    		default:
    			desc_idx = 0;
    		}
    		desc = epfile->ep->descs[desc_idx];
    
    		spin_unlock_irq(&epfile->ffs->eps_lock);
    		ret = copy_to_user((void __user *)value, desc, desc->bLength);
    		if (ret)
    			ret = -EFAULT;
    		return ret;
    	}
    	default:
    		ret = -ENOTTY;
    	}
    	spin_unlock_irq(&epfile->ffs->eps_lock);
    
    	return ret;
    }
    
    #ifdef CONFIG_COMPAT
    static long ffs_epfile_compat_ioctl(struct file *file, unsigned code,
    		unsigned long value)
    {
    	return ffs_epfile_ioctl(file, code, value);
    }
    #endif
    
    static const struct file_operations ffs_epfile_operations = {
    	.llseek =	no_llseek,
    
    	.open =		ffs_epfile_open,
    	.write_iter =	ffs_epfile_write_iter,
    	.read_iter =	ffs_epfile_read_iter,
    	.release =	ffs_epfile_release,
    	.unlocked_ioctl =	ffs_epfile_ioctl,
    #ifdef CONFIG_COMPAT
    	.compat_ioctl = ffs_epfile_compat_ioctl,
    #endif
    };
    
    
    /* 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 timespec64 ts = current_time(inode);
    
    		inode->i_ino	 = get_next_ino();
    		inode->i_mode    = perms->mode;
    		inode->i_uid     = perms->uid;
    		inode->i_gid     = perms->gid;
    		inode->i_atime   = ts;
    		inode->i_mtime   = ts;
    		inode->i_ctime   = ts;
    		inode->i_private = data;
    		if (fops)
    			inode->i_fop = fops;
    		if (iops)
    			inode->i_op  = iops;
    	}
    
    	return inode;
    }
    
    /* Create "regular" file */
    static struct dentry *ffs_sb_create_file(struct super_block *sb,
    					const char *name, void *data,
    					const struct file_operations *fops)
    {
    	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);
    	return dentry;
    }
    
    /* 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;
    	bool no_disconnect;
    	struct ffs_data *ffs_data;
    };
    
    static int ffs_sb_fill(struct super_block *sb, struct fs_context *fc)
    {
    	struct ffs_sb_fill_data *data = fc->fs_private;
    	struct inode	*inode;
    	struct ffs_data	*ffs = data->ffs_data;
    
    	ENTER();
    
    	ffs->sb              = sb;
    	data->ffs_data       = NULL;
    	sb->s_fs_info        = ffs;
    	sb->s_blocksize      = PAGE_SIZE;
    	sb->s_blocksize_bits = PAGE_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))
    		return -ENOMEM;
    
    	/* EP0 file */
    	if (unlikely(!ffs_sb_create_file(sb, "ep0", ffs,
    					 &ffs_ep0_operations)))
    		return -ENOMEM;
    
    	return 0;
    }
    
    enum {
    	Opt_no_disconnect,
    	Opt_rmode,
    	Opt_fmode,
    	Opt_mode,
    	Opt_uid,
    	Opt_gid,
    };
    
    static const struct fs_parameter_spec ffs_fs_param_specs[] = {
    	fsparam_bool	("no_disconnect",	Opt_no_disconnect),
    	fsparam_u32	("rmode",		Opt_rmode),
    	fsparam_u32	("fmode",		Opt_fmode),
    	fsparam_u32	("mode",		Opt_mode),
    	fsparam_u32	("uid",			Opt_uid),
    	fsparam_u32	("gid",			Opt_gid),
    	{}
    };
    
    static const struct fs_parameter_description ffs_fs_fs_parameters = {
    	.name		= "kAFS",
    	.specs		= ffs_fs_param_specs,
    };
    
    static int ffs_fs_parse_param(struct fs_context *fc, struct fs_parameter *param)
    {
    	struct ffs_sb_fill_data *data = fc->fs_private;
    	struct fs_parse_result result;
    	int opt;
    
    	ENTER();
    
    	opt = fs_parse(fc, &ffs_fs_fs_parameters, param, &result);
    	if (opt < 0)
    		return opt;
    
    	switch (opt) {
    	case Opt_no_disconnect:
    		data->no_disconnect = result.boolean;
    		break;
    	case Opt_rmode:
    		data->root_mode  = (result.uint_32 & 0555) | S_IFDIR;
    		break;
    	case Opt_fmode:
    		data->perms.mode = (result.uint_32 & 0666) | S_IFREG;
    		break;
    	case Opt_mode:
    		data->root_mode  = (result.uint_32 & 0555) | S_IFDIR;
    		data->perms.mode = (result.uint_32 & 0666) | S_IFREG;
    		break;
    
    	case Opt_uid:
    		data->perms.uid = make_kuid(current_user_ns(), result.uint_32);
    		if (!uid_valid(data->perms.uid))
    			goto unmapped_value;
    		break;
    	case Opt_gid:
    		data->perms.gid = make_kgid(current_user_ns(), result.uint_32);
    		if (!gid_valid(data->perms.gid))
    			goto unmapped_value;
    		break;
    
    	default:
    		return -ENOPARAM;
    	}
    
    	return 0;
    
    unmapped_value:
    	return invalf(fc, "%s: unmapped value: %u", param->key, result.uint_32);
    }
    
    /*
     * Set up the superblock for a mount.
     */
    static int ffs_fs_get_tree(struct fs_context *fc)
    {
    	struct ffs_sb_fill_data *ctx = fc->fs_private;
    	void *ffs_dev;
    	struct ffs_data	*ffs;
    
    	ENTER();
    
    	if (!fc->source)
    		return invalf(fc, "No source specified");
    
    	ffs = ffs_data_new(fc->source);
    	if (unlikely(!ffs))
    		return -ENOMEM;
    	ffs->file_perms = ctx->perms;
    	ffs->no_disconnect = ctx->no_disconnect;
    
    	ffs->dev_name = kstrdup(fc->source, GFP_KERNEL);
    	if (unlikely(!ffs->dev_name)) {
    		ffs_data_put(ffs);
    		return -ENOMEM;
    	}
    
    	ffs_dev = ffs_acquire_dev(ffs->dev_name);
    	if (IS_ERR(ffs_dev)) {
    		ffs_data_put(ffs);
    		return PTR_ERR(ffs_dev);
    	}
    
    	ffs->private_data = ffs_dev;
    	ctx->ffs_data = ffs;
    	return get_tree_nodev(fc, ffs_sb_fill);
    }
    
    static void ffs_fs_free_fc(struct fs_context *fc)
    {
    	struct ffs_sb_fill_data *ctx = fc->fs_private;
    
    	if (ctx) {
    		if (ctx->ffs_data) {
    			ffs_release_dev(ctx->ffs_data);
    			ffs_data_put(ctx->ffs_data);
    		}
    
    		kfree(ctx);
    	}
    }
    
    static const struct fs_context_operations ffs_fs_context_ops = {
    	.free		= ffs_fs_free_fc,
    	.parse_param	= ffs_fs_parse_param,
    	.get_tree	= ffs_fs_get_tree,
    };
    
    static int ffs_fs_init_fs_context(struct fs_context *fc)
    {
    	struct ffs_sb_fill_data *ctx;
    
    	ctx = kzalloc(sizeof(struct ffs_sb_fill_data), GFP_KERNEL);
    	if (!ctx)
    		return -ENOMEM;
    
    	ctx->perms.mode = S_IFREG | 0600;
    	ctx->perms.uid = GLOBAL_ROOT_UID;
    	ctx->perms.gid = GLOBAL_ROOT_GID;
    	ctx->root_mode = S_IFDIR | 0500;
    	ctx->no_disconnect = false;
    
    	fc->fs_private = ctx;
    	fc->ops = &ffs_fs_context_ops;
    	return 0;
    }
    
    static void
    ffs_fs_kill_sb(struct super_block *sb)
    {
    	ENTER();
    
    	kill_litter_super(sb);
    	if (sb->s_fs_info) {
    		ffs_release_dev(sb->s_fs_info);
    		ffs_data_closed(sb->s_fs_info);
    	}
    }
    
    static struct file_system_type ffs_fs_type = {
    	.owner		= THIS_MODULE,
    	.name		= "functionfs",
    	.init_fs_context = ffs_fs_init_fs_context,
    	.parameters	= &ffs_fs_fs_parameters,
    	.kill_sb	= ffs_fs_kill_sb,
    };
    MODULE_ALIAS_FS("functionfs");
    
    
    /* 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();
    
    	refcount_inc(&ffs->ref);
    }
    
    static void ffs_data_opened(struct ffs_data *ffs)
    {
    	ENTER();
    
    	refcount_inc(&ffs->ref);
    	if (atomic_add_return(1, &ffs->opened) == 1 &&
    			ffs->state == FFS_DEACTIVATED) {
    		ffs->state = FFS_CLOSING;
    		ffs_data_reset(ffs);
    	}
    }
    
    static void ffs_data_put(struct ffs_data *ffs)
    {
    	ENTER();
    
    	if (unlikely(refcount_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) ||
    		       waitqueue_active(&ffs->wait));
    		destroy_workqueue(ffs->io_completion_wq);
    		kfree(ffs->dev_name);
    		kfree(ffs);
    	}
    }
    
    static void ffs_data_closed(struct ffs_data *ffs)
    {
    	ENTER();
    
    	if (atomic_dec_and_test(&ffs->opened)) {
    		if (ffs->no_disconnect) {
    			ffs->state = FFS_DEACTIVATED;
    			if (ffs->epfiles) {
    				ffs_epfiles_destroy(ffs->epfiles,
    						   ffs->eps_count);
    				ffs->epfiles = NULL;
    			}
    			if (ffs->setup_state == FFS_SETUP_PENDING)
    				__ffs_ep0_stall(ffs);
    		} else {
    			ffs->state = FFS_CLOSING;
    			ffs_data_reset(ffs);
    		}
    	}
    	if (atomic_read(&ffs->opened) < 0) {
    		ffs->state = FFS_CLOSING;
    		ffs_data_reset(ffs);
    	}
    
    	ffs_data_put(ffs);
    }
    
    static struct ffs_data *ffs_data_new(const char *dev_name)
    {
    	struct ffs_data *ffs = kzalloc(sizeof *ffs, GFP_KERNEL);
    	if (unlikely(!ffs))
    		return NULL;
    
    	ENTER();
    
    	ffs->io_completion_wq = alloc_ordered_workqueue("%s", 0, dev_name);
    	if (!ffs->io_completion_wq) {
    		kfree(ffs);
    		return NULL;
    	}
    
    	refcount_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_waitqueue_head(&ffs->wait);
    	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();
    
    	ffs_closed(ffs);
    
    	BUG_ON(ffs->gadget);
    
    	if (ffs->epfiles)
    		ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count);
    
    	if (ffs->ffs_eventfd)
    		eventfd_ctx_put(ffs->ffs_eventfd);
    
    	kfree(ffs->raw_descs_data);
    	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_data = NULL;
    	ffs->raw_descs = NULL;
    	ffs->raw_strings = NULL;
    	ffs->stringtabs = NULL;
    
    	ffs->raw_descs_length = 0;
    	ffs->fs_descs_count = 0;
    	ffs->hs_descs_count = 0;
    	ffs->ss_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;
    	if (lang) {
    		for (; *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;
    		clear_bit(FFS_FL_BOUND, &ffs->flags);
    		ffs_data_put(ffs);
    	}
    }
    
    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);
    		if (ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
    			sprintf(epfile->name, "ep%02x", ffs->eps_addrmap[i]);
    		else
    			sprintf(epfile->name, "ep%u", i);
    		epfile->dentry = ffs_sb_create_file(ffs->sb, epfile->name,
    						 epfile,
    						 &ffs_epfile_operations);
    		if (unlikely(!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));
    		if (epfile->dentry) {
    			d_delete(epfile->dentry);
    			dput(epfile->dentry);
    			epfile->dentry = NULL;
    		}
    	}
    
    	kfree(epfiles);
    }
    
    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);
    	while (count--) {
    		/* pending requests get nuked */
    		if (likely(ep->ep))
    			usb_ep_disable(ep->ep);
    		++ep;
    
    		if (epfile) {
    			epfile->ep = NULL;
    			__ffs_epfile_read_buffer_free(epfile);
    			++epfile;
    		}
    	}
    	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);
    	while(count--) {
    		ep->ep->driver_data = ep;
    
    		ret = config_ep_by_speed(func->gadget, &func->function, ep->ep);
    		if (ret) {
    			pr_err("%s: config_ep_by_speed(%s) returned %d\n",
    					__func__, ep->ep->name, ret);
    			break;
    		}
    
    		ret = usb_ep_enable(ep->ep);
    		if (likely(!ret)) {
    			epfile->ep = ep;
    			epfile->in = usb_endpoint_dir_in(ep->ep->desc);
    			epfile->isoc = usb_endpoint_xfer_isoc(ep->ep->desc);
    		} else {
    			break;
    		}
    
    		++ep;
    		++epfile;
    	}
    
    	wake_up_interruptible(&ffs->wait);
    	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
    };
    
    enum ffs_os_desc_type {
    	FFS_OS_DESC, FFS_OS_DESC_EXT_COMPAT, FFS_OS_DESC_EXT_PROP
    };
    
    typedef int (*ffs_entity_callback)(enum ffs_entity_type entity,
    				   u8 *valuep,
    				   struct usb_descriptor_header *desc,
    				   void *priv);
    
    typedef int (*ffs_os_desc_callback)(enum ffs_os_desc_type entity,
    				    struct usb_os_desc_header *h, void *data,
    				    unsigned len, void *priv);
    
    static int __must_check ffs_do_single_desc(char *data, unsigned len,
    					   ffs_entity_callback entity,
    					   void *priv, int *current_class)
    {
    	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);
    		*current_class = ds->bInterfaceClass;
    	}
    		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 USB_TYPE_CLASS | 0x01:
                    if (*current_class == USB_INTERFACE_CLASS_HID) {
    			pr_vdebug("hid descriptor\n");
    			if (length != sizeof(struct hid_descriptor))
    				goto inv_length;
    			break;
    		} else if (*current_class == USB_INTERFACE_CLASS_CCID) {
    			pr_vdebug("ccid descriptor\n");
    			if (length != sizeof(struct ccid_descriptor))
    				goto inv_length;
    			break;
    		} else {
    			pr_vdebug("unknown descriptor: %d for class %d\n",
    			      _ds->bDescriptorType, *current_class);
    			return -EINVAL;
    		}
    
    	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_SS_ENDPOINT_COMP:
    		pr_vdebug("EP SS companion descriptor\n");
    		if (length != sizeof(struct usb_ss_ep_comp_descriptor))
    			goto inv_length;
    		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;
    	int current_class = -1;
    
    	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_single_desc(data, len, entity, priv,
    			&current_class);
    		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_desc_helper *helper = priv;
    	struct usb_endpoint_descriptor *d;
    
    	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 >= helper->interfaces_count)
    			helper->interfaces_count = *valuep + 1;
    		break;
    
    	case FFS_STRING:
    		/*
    		 * Strings are indexed from 1 (0 is reserved
    		 * for languages list)
    		 */
    		if (*valuep > helper->ffs->strings_count)
    			helper->ffs->strings_count = *valuep;
    		break;
    
    	case FFS_ENDPOINT:
    		d = (void *)desc;
    		helper->eps_count++;
    		if (helper->eps_count >= FFS_MAX_EPS_COUNT)
    			return -EINVAL;
    		/* Check if descriptors for any speed were already parsed */
    		if (!helper->ffs->eps_count && !helper->ffs->interfaces_count)
    			helper->ffs->eps_addrmap[helper->eps_count] =
    				d->bEndpointAddress;
    		else if (helper->ffs->eps_addrmap[helper->eps_count] !=
    				d->bEndpointAddress)
    			return -EINVAL;
    		break;
    	}
    
    	return 0;
    }
    
    static int __ffs_do_os_desc_header(enum ffs_os_desc_type *next_type,
    				   struct usb_os_desc_header *desc)
    {
    	u16 bcd_version = le16_to_cpu(desc->bcdVersion);
    	u16 w_index = le16_to_cpu(desc->wIndex);
    
    	if (bcd_version != 1) {
    		pr_vdebug("unsupported os descriptors version: %d",
    			  bcd_version);
    		return -EINVAL;
    	}
    	switch (w_index) {
    	case 0x4:
    		*next_type = FFS_OS_DESC_EXT_COMPAT;
    		break;
    	case 0x5:
    		*next_type = FFS_OS_DESC_EXT_PROP;
    		break;
    	default:
    		pr_vdebug("unsupported os descriptor type: %d", w_index);
    		return -EINVAL;
    	}
    
    	return sizeof(*desc);
    }
    
    /*
     * Process all extended compatibility/extended property descriptors
     * of a feature descriptor
     */
    static int __must_check ffs_do_single_os_desc(char *data, unsigned len,
    					      enum ffs_os_desc_type type,
    					      u16 feature_count,
    					      ffs_os_desc_callback entity,
    					      void *priv,
    					      struct usb_os_desc_header *h)
    {
    	int ret;
    	const unsigned _len = len;
    
    	ENTER();
    
    	/* loop over all ext compat/ext prop descriptors */
    	while (feature_count--) {
    		ret = entity(type, h, data, len, priv);
    		if (unlikely(ret < 0)) {
    			pr_debug("bad OS descriptor, type: %d\n", type);
    			return ret;
    		}
    		data += ret;
    		len -= ret;
    	}
    	return _len - len;
    }
    
    /* Process a number of complete Feature Descriptors (Ext Compat or Ext Prop) */
    static int __must_check ffs_do_os_descs(unsigned count,
    					char *data, unsigned len,
    					ffs_os_desc_callback entity, void *priv)
    {
    	const unsigned _len = len;
    	unsigned long num = 0;
    
    	ENTER();
    
    	for (num = 0; num < count; ++num) {
    		int ret;
    		enum ffs_os_desc_type type;
    		u16 feature_count;
    		struct usb_os_desc_header *desc = (void *)data;
    
    		if (len < sizeof(*desc))
    			return -EINVAL;
    
    		/*
    		 * Record "descriptor" entity.
    		 * Process dwLength, bcdVersion, wIndex, get b/wCount.
    		 * Move the data pointer to the beginning of extended
    		 * compatibilities proper or extended properties proper
    		 * portions of the data
    		 */
    		if (le32_to_cpu(desc->dwLength) > len)
    			return -EINVAL;
    
    		ret = __ffs_do_os_desc_header(&type, desc);
    		if (unlikely(ret < 0)) {
    			pr_debug("entity OS_DESCRIPTOR(%02lx); ret = %d\n",
    				 num, ret);
    			return ret;
    		}
    		/*
    		 * 16-bit hex "?? 00" Little Endian looks like 8-bit hex "??"
    		 */
    		feature_count = le16_to_cpu(desc->wCount);
    		if (type == FFS_OS_DESC_EXT_COMPAT &&
    		    (feature_count > 255 || desc->Reserved))
    				return -EINVAL;
    		len -= ret;
    		data += ret;
    
    		/*
    		 * Process all function/property descriptors
    		 * of this Feature Descriptor
    		 */
    		ret = ffs_do_single_os_desc(data, len, type,
    					    feature_count, entity, priv, desc);
    		if (unlikely(ret < 0)) {
    			pr_debug("%s returns %d\n", __func__, ret);
    			return ret;
    		}
    
    		len -= ret;
    		data += ret;
    	}
    	return _len - len;
    }
    
    /**
     * Validate contents of the buffer from userspace related to OS descriptors.
     */
    static int __ffs_data_do_os_desc(enum ffs_os_desc_type type,
    				 struct usb_os_desc_header *h, void *data,
    				 unsigned len, void *priv)
    {
    	struct ffs_data *ffs = priv;
    	u8 length;
    
    	ENTER();
    
    	switch (type) {
    	case FFS_OS_DESC_EXT_COMPAT: {
    		struct usb_ext_compat_desc *d = data;
    		int i;
    
    		if (len < sizeof(*d) ||
    		    d->bFirstInterfaceNumber >= ffs->interfaces_count)
    			return -EINVAL;
    		if (d->Reserved1 != 1) {
    			/*
    			 * According to the spec, Reserved1 must be set to 1
    			 * but older kernels incorrectly rejected non-zero
    			 * values.  We fix it here to avoid returning EINVAL
    			 * in response to values we used to accept.
    			 */
    			pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n");
    			d->Reserved1 = 1;
    		}
    		for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i)
    			if (d->Reserved2[i])
    				return -EINVAL;
    
    		length = sizeof(struct usb_ext_compat_desc);
    	}
    		break;
    	case FFS_OS_DESC_EXT_PROP: {
    		struct usb_ext_prop_desc *d = data;
    		u32 type, pdl;
    		u16 pnl;
    
    		if (len < sizeof(*d) || h->interface >= ffs->interfaces_count)
    			return -EINVAL;
    		length = le32_to_cpu(d->dwSize);
    		if (len < length)
    			return -EINVAL;
    		type = le32_to_cpu(d->dwPropertyDataType);
    		if (type < USB_EXT_PROP_UNICODE ||
    		    type > USB_EXT_PROP_UNICODE_MULTI) {
    			pr_vdebug("unsupported os descriptor property type: %d",
    				  type);
    			return -EINVAL;
    		}
    		pnl = le16_to_cpu(d->wPropertyNameLength);
    		if (length < 14 + pnl) {
    			pr_vdebug("invalid os descriptor length: %d pnl:%d (descriptor %d)\n",
    				  length, pnl, type);
    			return -EINVAL;
    		}
    		pdl = le32_to_cpu(*(__le32 *)((u8 *)data + 10 + pnl));
    		if (length != 14 + pnl + pdl) {
    			pr_vdebug("invalid os descriptor length: %d pnl:%d pdl:%d (descriptor %d)\n",
    				  length, pnl, pdl, type);
    			return -EINVAL;
    		}
    		++ffs->ms_os_descs_ext_prop_count;
    		/* property name reported to the host as "WCHAR"s */
    		ffs->ms_os_descs_ext_prop_name_len += pnl * 2;
    		ffs->ms_os_descs_ext_prop_data_len += pdl;
    	}
    		break;
    	default:
    		pr_vdebug("unknown descriptor: %d\n", type);
    		return -EINVAL;
    	}
    	return length;
    }
    
    static int __ffs_data_got_descs(struct ffs_data *ffs,
    				char *const _data, size_t len)
    {
    	char *data = _data, *raw_descs;
    	unsigned os_descs_count = 0, counts[3], flags;
    	int ret = -EINVAL, i;
    	struct ffs_desc_helper helper;
    
    	ENTER();
    
    	if (get_unaligned_le32(data + 4) != len)
    		goto error;
    
    	switch (get_unaligned_le32(data)) {
    	case FUNCTIONFS_DESCRIPTORS_MAGIC:
    		flags = FUNCTIONFS_HAS_FS_DESC | FUNCTIONFS_HAS_HS_DESC;
    		data += 8;
    		len  -= 8;
    		break;
    	case FUNCTIONFS_DESCRIPTORS_MAGIC_V2:
    		flags = get_unaligned_le32(data + 8);
    		ffs->user_flags = flags;
    		if (flags & ~(FUNCTIONFS_HAS_FS_DESC |
    			      FUNCTIONFS_HAS_HS_DESC |
    			      FUNCTIONFS_HAS_SS_DESC |
    			      FUNCTIONFS_HAS_MS_OS_DESC |
    			      FUNCTIONFS_VIRTUAL_ADDR |
    			      FUNCTIONFS_EVENTFD |
    			      FUNCTIONFS_ALL_CTRL_RECIP |
    			      FUNCTIONFS_CONFIG0_SETUP)) {
    			ret = -ENOSYS;
    			goto error;
    		}
    		data += 12;
    		len  -= 12;
    		break;
    	default:
    		goto error;
    	}
    
    	if (flags & FUNCTIONFS_EVENTFD) {
    		if (len < 4)
    			goto error;
    		ffs->ffs_eventfd =
    			eventfd_ctx_fdget((int)get_unaligned_le32(data));
    		if (IS_ERR(ffs->ffs_eventfd)) {
    			ret = PTR_ERR(ffs->ffs_eventfd);
    			ffs->ffs_eventfd = NULL;
    			goto error;
    		}
    		data += 4;
    		len  -= 4;
    	}
    
    	/* Read fs_count, hs_count and ss_count (if present) */
    	for (i = 0; i < 3; ++i) {
    		if (!(flags & (1 << i))) {
    			counts[i] = 0;
    		} else if (len < 4) {
    			goto error;
    		} else {
    			counts[i] = get_unaligned_le32(data);
    			data += 4;
    			len  -= 4;
    		}
    	}
    	if (flags & (1 << i)) {
    		if (len < 4) {
    			goto error;
    		}
    		os_descs_count = get_unaligned_le32(data);
    		data += 4;
    		len -= 4;
    	};
    
    	/* Read descriptors */
    	raw_descs = data;
    	helper.ffs = ffs;
    	for (i = 0; i < 3; ++i) {
    		if (!counts[i])
    			continue;
    		helper.interfaces_count = 0;
    		helper.eps_count = 0;
    		ret = ffs_do_descs(counts[i], data, len,
    				   __ffs_data_do_entity, &helper);
    		if (ret < 0)
    			goto error;
    		if (!ffs->eps_count && !ffs->interfaces_count) {
    			ffs->eps_count = helper.eps_count;
    			ffs->interfaces_count = helper.interfaces_count;
    		} else {
    			if (ffs->eps_count != helper.eps_count) {
    				ret = -EINVAL;
    				goto error;
    			}
    			if (ffs->interfaces_count != helper.interfaces_count) {
    				ret = -EINVAL;
    				goto error;
    			}
    		}
    		data += ret;
    		len  -= ret;
    	}
    	if (os_descs_count) {
    		ret = ffs_do_os_descs(os_descs_count, data, len,
    				      __ffs_data_do_os_desc, ffs);
    		if (ret < 0)
    			goto error;
    		data += ret;
    		len -= ret;
    	}
    
    	if (raw_descs == data || len) {
    		ret = -EINVAL;
    		goto error;
    	}
    
    	ffs->raw_descs_data	= _data;
    	ffs->raw_descs		= raw_descs;
    	ffs->raw_descs_length	= data - raw_descs;
    	ffs->fs_descs_count	= counts[0];
    	ffs->hs_descs_count	= counts[1];
    	ffs->ss_descs_count	= counts[2];
    	ffs->ms_os_descs_count	= os_descs_count;
    
    	return 0;
    
    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;
    	const char *data = _data;
    	struct usb_string *s;
    
    	ENTER();
    
    	if (unlikely(len < 16 ||
    		     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. */
    	{
    		unsigned i = 0;
    		vla_group(d);
    		vla_item(d, struct usb_gadget_strings *, stringtabs,
    			lang_count + 1);
    		vla_item(d, struct usb_gadget_strings, stringtab, lang_count);
    		vla_item(d, struct usb_string, strings,
    			lang_count*(needed_count+1));
    
    		char *vlabuf = kmalloc(vla_group_size(d), GFP_KERNEL);
    
    		if (unlikely(!vlabuf)) {
    			kfree(_data);
    			return -ENOMEM;
    		}
    
    		/* Initialize the VLA pointers */
    		stringtabs = vla_ptr(vlabuf, d, stringtabs);
    		t = vla_ptr(vlabuf, d, stringtab);
    		i = lang_count;
    		do {
    			*stringtabs++ = t++;
    		} while (--i);
    		*stringtabs = NULL;
    
    		/* stringtabs = vlabuf = d_stringtabs for later kfree */
    		stringtabs = vla_ptr(vlabuf, d, stringtabs);
    		t = vla_ptr(vlabuf, d, stringtab);
    		s = vla_ptr(vlabuf, d, strings);
    	}
    
    	/* 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_CANCELLED;
    
    	/*
    	 * Logic of this function guarantees that there are at most four pending
    	 * evens on ffs->ev.types queue.  This is important because the queue
    	 * has space for four elements only and __ffs_ep0_read_events function
    	 * depends on that limit as well.  If more event types are added, those
    	 * limits have to be revisited or guaranteed to still hold.
    	 */
    	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:
    		WARN(1, "%d: unknown event, this should not happen\n", type);
    		return;
    	}
    
    	{
    		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);
    	if (ffs->ffs_eventfd)
    		eventfd_signal(ffs->ffs_eventfd, 1);
    }
    
    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_ep_addr2idx(struct ffs_data *ffs, u8 endpoint_address)
    {
    	int i;
    
    	for (i = 1; i < ARRAY_SIZE(ffs->eps_addrmap); ++i)
    		if (ffs->eps_addrmap[i] == endpoint_address)
    			return i;
    	return -ENOENT;
    }
    
    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;
    	unsigned ep_desc_id;
    	int idx;
    	static const char *speed_names[] = { "full", "high", "super" };
    
    	if (type != FFS_DESCRIPTOR)
    		return 0;
    
    	/*
    	 * If ss_descriptors is not NULL, we are reading super speed
    	 * descriptors; if hs_descriptors is not NULL, we are reading high
    	 * speed descriptors; otherwise, we are reading full speed
    	 * descriptors.
    	 */
    	if (func->function.ss_descriptors) {
    		ep_desc_id = 2;
    		func->function.ss_descriptors[(long)valuep] = desc;
    	} else if (func->function.hs_descriptors) {
    		ep_desc_id = 1;
    		func->function.hs_descriptors[(long)valuep] = desc;
    	} else {
    		ep_desc_id = 0;
    		func->function.fs_descriptors[(long)valuep]    = desc;
    	}
    
    	if (!desc || desc->bDescriptorType != USB_DT_ENDPOINT)
    		return 0;
    
    	idx = ffs_ep_addr2idx(func->ffs, ds->bEndpointAddress) - 1;
    	if (idx < 0)
    		return idx;
    
    	ffs_ep = func->eps + idx;
    
    	if (unlikely(ffs_ep->descs[ep_desc_id])) {
    		pr_err("two %sspeed descriptors for EP %d\n",
    			  speed_names[ep_desc_id],
    			  ds->bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
    		return -EINVAL;
    	}
    	ffs_ep->descs[ep_desc_id] = 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;
    		u8 bEndpointAddress;
    		u16 wMaxPacketSize;
    
    		/*
    		 * We back up bEndpointAddress because autoconfig overwrites
    		 * it with physical endpoint address.
    		 */
    		bEndpointAddress = ds->bEndpointAddress;
    		/*
    		 * We back up wMaxPacketSize because autoconfig treats
    		 * endpoint descriptors as if they were full speed.
    		 */
    		wMaxPacketSize = ds->wMaxPacketSize;
    		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;
    		/*
    		 * If we use virtual address mapping, we restore
    		 * original bEndpointAddress value.
    		 */
    		if (func->ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
    			ds->bEndpointAddress = bEndpointAddress;
    		/*
    		 * Restore wMaxPacketSize which was potentially
    		 * overwritten by autoconfig.
    		 */
    		ds->wMaxPacketSize = wMaxPacketSize;
    	}
    	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_do_os_desc(enum ffs_os_desc_type type,
    				      struct usb_os_desc_header *h, void *data,
    				      unsigned len, void *priv)
    {
    	struct ffs_function *func = priv;
    	u8 length = 0;
    
    	switch (type) {
    	case FFS_OS_DESC_EXT_COMPAT: {
    		struct usb_ext_compat_desc *desc = data;
    		struct usb_os_desc_table *t;
    
    		t = &func->function.os_desc_table[desc->bFirstInterfaceNumber];
    		t->if_id = func->interfaces_nums[desc->bFirstInterfaceNumber];
    		memcpy(t->os_desc->ext_compat_id, &desc->CompatibleID,
    		       ARRAY_SIZE(desc->CompatibleID) +
    		       ARRAY_SIZE(desc->SubCompatibleID));
    		length = sizeof(*desc);
    	}
    		break;
    	case FFS_OS_DESC_EXT_PROP: {
    		struct usb_ext_prop_desc *desc = data;
    		struct usb_os_desc_table *t;
    		struct usb_os_desc_ext_prop *ext_prop;
    		char *ext_prop_name;
    		char *ext_prop_data;
    
    		t = &func->function.os_desc_table[h->interface];
    		t->if_id = func->interfaces_nums[h->interface];
    
    		ext_prop = func->ffs->ms_os_descs_ext_prop_avail;
    		func->ffs->ms_os_descs_ext_prop_avail += sizeof(*ext_prop);
    
    		ext_prop->type = le32_to_cpu(desc->dwPropertyDataType);
    		ext_prop->name_len = le16_to_cpu(desc->wPropertyNameLength);
    		ext_prop->data_len = le32_to_cpu(*(__le32 *)
    			usb_ext_prop_data_len_ptr(data, ext_prop->name_len));
    		length = ext_prop->name_len + ext_prop->data_len + 14;
    
    		ext_prop_name = func->ffs->ms_os_descs_ext_prop_name_avail;
    		func->ffs->ms_os_descs_ext_prop_name_avail +=
    			ext_prop->name_len;
    
    		ext_prop_data = func->ffs->ms_os_descs_ext_prop_data_avail;
    		func->ffs->ms_os_descs_ext_prop_data_avail +=
    			ext_prop->data_len;
    		memcpy(ext_prop_data,
    		       usb_ext_prop_data_ptr(data, ext_prop->name_len),
    		       ext_prop->data_len);
    		/* unicode data reported to the host as "WCHAR"s */
    		switch (ext_prop->type) {
    		case USB_EXT_PROP_UNICODE:
    		case USB_EXT_PROP_UNICODE_ENV:
    		case USB_EXT_PROP_UNICODE_LINK:
    		case USB_EXT_PROP_UNICODE_MULTI:
    			ext_prop->data_len *= 2;
    			break;
    		}
    		ext_prop->data = ext_prop_data;
    
    		memcpy(ext_prop_name, usb_ext_prop_name_ptr(data),
    		       ext_prop->name_len);
    		/* property name reported to the host as "WCHAR"s */
    		ext_prop->name_len *= 2;
    		ext_prop->name = ext_prop_name;
    
    		t->os_desc->ext_prop_len +=
    			ext_prop->name_len + ext_prop->data_len + 14;
    		++t->os_desc->ext_prop_count;
    		list_add_tail(&ext_prop->entry, &t->os_desc->ext_prop);
    	}
    		break;
    	default:
    		pr_vdebug("unknown descriptor: %d\n", type);
    	}
    
    	return length;
    }
    
    static inline struct f_fs_opts *ffs_do_functionfs_bind(struct usb_function *f,
    						struct usb_configuration *c)
    {
    	struct ffs_function *func = ffs_func_from_usb(f);
    	struct f_fs_opts *ffs_opts =
    		container_of(f->fi, struct f_fs_opts, func_inst);
    	int ret;
    
    	ENTER();
    
    	/*
    	 * Legacy gadget triggers binding in functionfs_ready_callback,
    	 * which already uses locking; taking the same lock here would
    	 * cause a deadlock.
    	 *
    	 * Configfs-enabled gadgets however do need ffs_dev_lock.
    	 */
    	if (!ffs_opts->no_configfs)
    		ffs_dev_lock();
    	ret = ffs_opts->dev->desc_ready ? 0 : -ENODEV;
    	func->ffs = ffs_opts->dev->ffs_data;
    	if (!ffs_opts->no_configfs)
    		ffs_dev_unlock();
    	if (ret)
    		return ERR_PTR(ret);
    
    	func->conf = c;
    	func->gadget = c->cdev->gadget;
    
    	/*
    	 * in drivers/usb/gadget/configfs.c:configfs_composite_bind()
    	 * configurations are bound in sequence with list_for_each_entry,
    	 * in each configuration its functions are bound in sequence
    	 * with list_for_each_entry, so we assume no race condition
    	 * with regard to ffs_opts->bound access
    	 */
    	if (!ffs_opts->refcnt) {
    		ret = functionfs_bind(func->ffs, c->cdev);
    		if (ret)
    			return ERR_PTR(ret);
    	}
    	ffs_opts->refcnt++;
    	func->function.strings = func->ffs->stringtabs;
    
    	return ffs_opts;
    }
    
    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 = !!func->ffs->hs_descs_count;
    	const int super = !!func->ffs->ss_descs_count;
    
    	int fs_len, hs_len, ss_len, ret, i;
    	struct ffs_ep *eps_ptr;
    
    	/* Make it a single chunk, less management later on */
    	vla_group(d);
    	vla_item_with_sz(d, struct ffs_ep, eps, ffs->eps_count);
    	vla_item_with_sz(d, struct usb_descriptor_header *, fs_descs,
    		full ? ffs->fs_descs_count + 1 : 0);
    	vla_item_with_sz(d, struct usb_descriptor_header *, hs_descs,
    		high ? ffs->hs_descs_count + 1 : 0);
    	vla_item_with_sz(d, struct usb_descriptor_header *, ss_descs,
    		super ? ffs->ss_descs_count + 1 : 0);
    	vla_item_with_sz(d, short, inums, ffs->interfaces_count);
    	vla_item_with_sz(d, struct usb_os_desc_table, os_desc_table,
    			 c->cdev->use_os_string ? ffs->interfaces_count : 0);
    	vla_item_with_sz(d, char[16], ext_compat,
    			 c->cdev->use_os_string ? ffs->interfaces_count : 0);
    	vla_item_with_sz(d, struct usb_os_desc, os_desc,
    			 c->cdev->use_os_string ? ffs->interfaces_count : 0);
    	vla_item_with_sz(d, struct usb_os_desc_ext_prop, ext_prop,
    			 ffs->ms_os_descs_ext_prop_count);
    	vla_item_with_sz(d, char, ext_prop_name,
    			 ffs->ms_os_descs_ext_prop_name_len);
    	vla_item_with_sz(d, char, ext_prop_data,
    			 ffs->ms_os_descs_ext_prop_data_len);
    	vla_item_with_sz(d, char, raw_descs, ffs->raw_descs_length);
    	char *vlabuf;
    
    	ENTER();
    
    	/* Has descriptors only for speeds gadget does not support */
    	if (unlikely(!(full | high | super)))
    		return -ENOTSUPP;
    
    	/* Allocate a single chunk, less management later on */
    	vlabuf = kzalloc(vla_group_size(d), GFP_KERNEL);
    	if (unlikely(!vlabuf))
    		return -ENOMEM;
    
    	ffs->ms_os_descs_ext_prop_avail = vla_ptr(vlabuf, d, ext_prop);
    	ffs->ms_os_descs_ext_prop_name_avail =
    		vla_ptr(vlabuf, d, ext_prop_name);
    	ffs->ms_os_descs_ext_prop_data_avail =
    		vla_ptr(vlabuf, d, ext_prop_data);
    
    	/* Copy descriptors  */
    	memcpy(vla_ptr(vlabuf, d, raw_descs), ffs->raw_descs,
    	       ffs->raw_descs_length);
    
    	memset(vla_ptr(vlabuf, d, inums), 0xff, d_inums__sz);
    	eps_ptr = vla_ptr(vlabuf, d, eps);
    	for (i = 0; i < ffs->eps_count; i++)
    		eps_ptr[i].num = -1;
    
    	/* Save pointers
    	 * d_eps == vlabuf, func->eps used to kfree vlabuf later
    	*/
    	func->eps             = vla_ptr(vlabuf, d, eps);
    	func->interfaces_nums = vla_ptr(vlabuf, d, 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.fs_descriptors = vla_ptr(vlabuf, d, fs_descs);
    		fs_len = ffs_do_descs(ffs->fs_descs_count,
    				      vla_ptr(vlabuf, d, raw_descs),
    				      d_raw_descs__sz,
    				      __ffs_func_bind_do_descs, func);
    		if (unlikely(fs_len < 0)) {
    			ret = fs_len;
    			goto error;
    		}
    	} else {
    		fs_len = 0;
    	}
    
    	if (likely(high)) {
    		func->function.hs_descriptors = vla_ptr(vlabuf, d, hs_descs);
    		hs_len = ffs_do_descs(ffs->hs_descs_count,
    				      vla_ptr(vlabuf, d, raw_descs) + fs_len,
    				      d_raw_descs__sz - fs_len,
    				      __ffs_func_bind_do_descs, func);
    		if (unlikely(hs_len < 0)) {
    			ret = hs_len;
    			goto error;
    		}
    	} else {
    		hs_len = 0;
    	}
    
    	if (likely(super)) {
    		func->function.ss_descriptors = vla_ptr(vlabuf, d, ss_descs);
    		ss_len = ffs_do_descs(ffs->ss_descs_count,
    				vla_ptr(vlabuf, d, raw_descs) + fs_len + hs_len,
    				d_raw_descs__sz - fs_len - hs_len,
    				__ffs_func_bind_do_descs, func);
    		if (unlikely(ss_len < 0)) {
    			ret = ss_len;
    			goto error;
    		}
    	} else {
    		ss_len = 0;
    	}
    
    	/*
    	 * 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) +
    			   (super ? ffs->ss_descs_count : 0),
    			   vla_ptr(vlabuf, d, raw_descs), d_raw_descs__sz,
    			   __ffs_func_bind_do_nums, func);
    	if (unlikely(ret < 0))
    		goto error;
    
    	func->function.os_desc_table = vla_ptr(vlabuf, d, os_desc_table);
    	if (c->cdev->use_os_string) {
    		for (i = 0; i < ffs->interfaces_count; ++i) {
    			struct usb_os_desc *desc;
    
    			desc = func->function.os_desc_table[i].os_desc =
    				vla_ptr(vlabuf, d, os_desc) +
    				i * sizeof(struct usb_os_desc);
    			desc->ext_compat_id =
    				vla_ptr(vlabuf, d, ext_compat) + i * 16;
    			INIT_LIST_HEAD(&desc->ext_prop);
    		}
    		ret = ffs_do_os_descs(ffs->ms_os_descs_count,
    				      vla_ptr(vlabuf, d, raw_descs) +
    				      fs_len + hs_len + ss_len,
    				      d_raw_descs__sz - fs_len - hs_len -
    				      ss_len,
    				      __ffs_func_bind_do_os_desc, func);
    		if (unlikely(ret < 0))
    			goto error;
    	}
    	func->function.os_desc_n =
    		c->cdev->use_os_string ? ffs->interfaces_count : 0;
    
    	/* 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;
    }
    
    static int ffs_func_bind(struct usb_configuration *c,
    			 struct usb_function *f)
    {
    	struct f_fs_opts *ffs_opts = ffs_do_functionfs_bind(f, c);
    	struct ffs_function *func = ffs_func_from_usb(f);
    	int ret;
    
    	if (IS_ERR(ffs_opts))
    		return PTR_ERR(ffs_opts);
    
    	ret = _ffs_func_bind(c, f);
    	if (ret && !--ffs_opts->refcnt)
    		functionfs_unbind(func->ffs);
    
    	return ret;
    }
    
    
    /* Other USB function hooks *************************************************/
    
    static void ffs_reset_work(struct work_struct *work)
    {
    	struct ffs_data *ffs = container_of(work,
    		struct ffs_data, reset_work);
    	ffs_data_reset(ffs);
    }
    
    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_DEACTIVATED) {
    		ffs->state = FFS_CLOSING;
    		INIT_WORK(&ffs->reset_work, ffs_reset_work);
    		schedule_work(&ffs->reset_work);
    		return -ENODEV;
    	}
    
    	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).  Other request recipient
    	 * types are only handled when the user flag FUNCTIONFS_ALL_CTRL_RECIP
    	 * is being used.
    	 */
    	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;
    		if (func->ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
    			ret = func->ffs->eps_addrmap[ret];
    		break;
    
    	default:
    		if (func->ffs->user_flags & FUNCTIONFS_ALL_CTRL_RECIP)
    			ret = le16_to_cpu(creq->wIndex);
    		else
    			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 creq->wLength == 0 ? USB_GADGET_DELAYED_STATUS : 0;
    }
    
    static bool ffs_func_req_match(struct usb_function *f,
    			       const struct usb_ctrlrequest *creq,
    			       bool config0)
    {
    	struct ffs_function *func = ffs_func_from_usb(f);
    
    	if (config0 && !(func->ffs->user_flags & FUNCTIONFS_CONFIG0_SETUP))
    		return false;
    
    	switch (creq->bRequestType & USB_RECIP_MASK) {
    	case USB_RECIP_INTERFACE:
    		return (ffs_func_revmap_intf(func,
    					     le16_to_cpu(creq->wIndex)) >= 0);
    	case USB_RECIP_ENDPOINT:
    		return (ffs_func_revmap_ep(func,
    					   le16_to_cpu(creq->wIndex)) >= 0);
    	default:
    		return (bool) (func->ffs->user_flags &
    			       FUNCTIONFS_ALL_CTRL_RECIP);
    	}
    }
    
    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;
    }
    
    
    /* Devices management *******************************************************/
    
    static LIST_HEAD(ffs_devices);
    
    static struct ffs_dev *_ffs_do_find_dev(const char *name)
    {
    	struct ffs_dev *dev;
    
    	if (!name)
    		return NULL;
    
    	list_for_each_entry(dev, &ffs_devices, entry) {
    		if (strcmp(dev->name, name) == 0)
    			return dev;
    	}
    
    	return NULL;
    }
    
    /*
     * ffs_lock must be taken by the caller of this function
     */
    static struct ffs_dev *_ffs_get_single_dev(void)
    {
    	struct ffs_dev *dev;
    
    	if (list_is_singular(&ffs_devices)) {
    		dev = list_first_entry(&ffs_devices, struct ffs_dev, entry);
    		if (dev->single)
    			return dev;
    	}
    
    	return NULL;
    }
    
    /*
     * ffs_lock must be taken by the caller of this function
     */
    static struct ffs_dev *_ffs_find_dev(const char *name)
    {
    	struct ffs_dev *dev;
    
    	dev = _ffs_get_single_dev();
    	if (dev)
    		return dev;
    
    	return _ffs_do_find_dev(name);
    }
    
    /* Configfs support *********************************************************/
    
    static inline struct f_fs_opts *to_ffs_opts(struct config_item *item)
    {
    	return container_of(to_config_group(item), struct f_fs_opts,
    			    func_inst.group);
    }
    
    static void ffs_attr_release(struct config_item *item)
    {
    	struct f_fs_opts *opts = to_ffs_opts(item);
    
    	usb_put_function_instance(&opts->func_inst);
    }
    
    static struct configfs_item_operations ffs_item_ops = {
    	.release	= ffs_attr_release,
    };
    
    static const struct config_item_type ffs_func_type = {
    	.ct_item_ops	= &ffs_item_ops,
    	.ct_owner	= THIS_MODULE,
    };
    
    
    /* Function registration interface ******************************************/
    
    static void ffs_free_inst(struct usb_function_instance *f)
    {
    	struct f_fs_opts *opts;
    
    	opts = to_f_fs_opts(f);
    	ffs_dev_lock();
    	_ffs_free_dev(opts->dev);
    	ffs_dev_unlock();
    	kfree(opts);
    }
    
    static int ffs_set_inst_name(struct usb_function_instance *fi, const char *name)
    {
    	if (strlen(name) >= FIELD_SIZEOF(struct ffs_dev, name))
    		return -ENAMETOOLONG;
    	return ffs_name_dev(to_f_fs_opts(fi)->dev, name);
    }
    
    static struct usb_function_instance *ffs_alloc_inst(void)
    {
    	struct f_fs_opts *opts;
    	struct ffs_dev *dev;
    
    	opts = kzalloc(sizeof(*opts), GFP_KERNEL);
    	if (!opts)
    		return ERR_PTR(-ENOMEM);
    
    	opts->func_inst.set_inst_name = ffs_set_inst_name;
    	opts->func_inst.free_func_inst = ffs_free_inst;
    	ffs_dev_lock();
    	dev = _ffs_alloc_dev();
    	ffs_dev_unlock();
    	if (IS_ERR(dev)) {
    		kfree(opts);
    		return ERR_CAST(dev);
    	}
    	opts->dev = dev;
    	dev->opts = opts;
    
    	config_group_init_type_name(&opts->func_inst.group, "",
    				    &ffs_func_type);
    	return &opts->func_inst;
    }
    
    static void ffs_free(struct usb_function *f)
    {
    	kfree(ffs_func_from_usb(f));
    }
    
    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;
    	struct f_fs_opts *opts =
    		container_of(f->fi, struct f_fs_opts, func_inst);
    	struct ffs_ep *ep = func->eps;
    	unsigned count = ffs->eps_count;
    	unsigned long flags;
    
    	ENTER();
    	if (ffs->func == func) {
    		ffs_func_eps_disable(func);
    		ffs->func = NULL;
    	}
    
    	if (!--opts->refcnt)
    		functionfs_unbind(ffs);
    
    	/* cleanup after autoconfig */
    	spin_lock_irqsave(&func->ffs->eps_lock, flags);
    	while (count--) {
    		if (ep->ep && ep->req)
    			usb_ep_free_request(ep->ep, ep->req);
    		ep->req = NULL;
    		++ep;
    	}
    	spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
    	kfree(func->eps);
    	func->eps = NULL;
    	/*
    	 * eps, descriptors and interfaces_nums are allocated in the
    	 * same chunk so only one free is required.
    	 */
    	func->function.fs_descriptors = NULL;
    	func->function.hs_descriptors = NULL;
    	func->function.ss_descriptors = NULL;
    	func->interfaces_nums = NULL;
    
    	ffs_event_add(ffs, FUNCTIONFS_UNBIND);
    }
    
    static struct usb_function *ffs_alloc(struct usb_function_instance *fi)
    {
    	struct ffs_function *func;
    
    	ENTER();
    
    	func = kzalloc(sizeof(*func), GFP_KERNEL);
    	if (unlikely(!func))
    		return ERR_PTR(-ENOMEM);
    
    	func->function.name    = "Function FS Gadget";
    
    	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.req_match = ffs_func_req_match;
    	func->function.suspend = ffs_func_suspend;
    	func->function.resume  = ffs_func_resume;
    	func->function.free_func = ffs_free;
    
    	return &func->function;
    }
    
    /*
     * ffs_lock must be taken by the caller of this function
     */
    static struct ffs_dev *_ffs_alloc_dev(void)
    {
    	struct ffs_dev *dev;
    	int ret;
    
    	if (_ffs_get_single_dev())
    			return ERR_PTR(-EBUSY);
    
    	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    	if (!dev)
    		return ERR_PTR(-ENOMEM);
    
    	if (list_empty(&ffs_devices)) {
    		ret = functionfs_init();
    		if (ret) {
    			kfree(dev);
    			return ERR_PTR(ret);
    		}
    	}
    
    	list_add(&dev->entry, &ffs_devices);
    
    	return dev;
    }
    
    int ffs_name_dev(struct ffs_dev *dev, const char *name)
    {
    	struct ffs_dev *existing;
    	int ret = 0;
    
    	ffs_dev_lock();
    
    	existing = _ffs_do_find_dev(name);
    	if (!existing)
    		strlcpy(dev->name, name, ARRAY_SIZE(dev->name));
    	else if (existing != dev)
    		ret = -EBUSY;
    
    	ffs_dev_unlock();
    
    	return ret;
    }
    EXPORT_SYMBOL_GPL(ffs_name_dev);
    
    int ffs_single_dev(struct ffs_dev *dev)
    {
    	int ret;
    
    	ret = 0;
    	ffs_dev_lock();
    
    	if (!list_is_singular(&ffs_devices))
    		ret = -EBUSY;
    	else
    		dev->single = true;
    
    	ffs_dev_unlock();
    	return ret;
    }
    EXPORT_SYMBOL_GPL(ffs_single_dev);
    
    /*
     * ffs_lock must be taken by the caller of this function
     */
    static void _ffs_free_dev(struct ffs_dev *dev)
    {
    	list_del(&dev->entry);
    
    	/* Clear the private_data pointer to stop incorrect dev access */
    	if (dev->ffs_data)
    		dev->ffs_data->private_data = NULL;
    
    	kfree(dev);
    	if (list_empty(&ffs_devices))
    		functionfs_cleanup();
    }
    
    static void *ffs_acquire_dev(const char *dev_name)
    {
    	struct ffs_dev *ffs_dev;
    
    	ENTER();
    	ffs_dev_lock();
    
    	ffs_dev = _ffs_find_dev(dev_name);
    	if (!ffs_dev)
    		ffs_dev = ERR_PTR(-ENOENT);
    	else if (ffs_dev->mounted)
    		ffs_dev = ERR_PTR(-EBUSY);
    	else if (ffs_dev->ffs_acquire_dev_callback &&
    	    ffs_dev->ffs_acquire_dev_callback(ffs_dev))
    		ffs_dev = ERR_PTR(-ENOENT);
    	else
    		ffs_dev->mounted = true;
    
    	ffs_dev_unlock();
    	return ffs_dev;
    }
    
    static void ffs_release_dev(struct ffs_data *ffs_data)
    {
    	struct ffs_dev *ffs_dev;
    
    	ENTER();
    	ffs_dev_lock();
    
    	ffs_dev = ffs_data->private_data;
    	if (ffs_dev) {
    		ffs_dev->mounted = false;
    
    		if (ffs_dev->ffs_release_dev_callback)
    			ffs_dev->ffs_release_dev_callback(ffs_dev);
    	}
    
    	ffs_dev_unlock();
    }
    
    static int ffs_ready(struct ffs_data *ffs)
    {
    	struct ffs_dev *ffs_obj;
    	int ret = 0;
    
    	ENTER();
    	ffs_dev_lock();
    
    	ffs_obj = ffs->private_data;
    	if (!ffs_obj) {
    		ret = -EINVAL;
    		goto done;
    	}
    	if (WARN_ON(ffs_obj->desc_ready)) {
    		ret = -EBUSY;
    		goto done;
    	}
    
    	ffs_obj->desc_ready = true;
    	ffs_obj->ffs_data = ffs;
    
    	if (ffs_obj->ffs_ready_callback) {
    		ret = ffs_obj->ffs_ready_callback(ffs);
    		if (ret)
    			goto done;
    	}
    
    	set_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags);
    done:
    	ffs_dev_unlock();
    	return ret;
    }
    
    static void ffs_closed(struct ffs_data *ffs)
    {
    	struct ffs_dev *ffs_obj;
    	struct f_fs_opts *opts;
    	struct config_item *ci;
    
    	ENTER();
    	ffs_dev_lock();
    
    	ffs_obj = ffs->private_data;
    	if (!ffs_obj)
    		goto done;
    
    	ffs_obj->desc_ready = false;
    	ffs_obj->ffs_data = NULL;
    
    	if (test_and_clear_bit(FFS_FL_CALL_CLOSED_CALLBACK, &ffs->flags) &&
    	    ffs_obj->ffs_closed_callback)
    		ffs_obj->ffs_closed_callback(ffs);
    
    	if (ffs_obj->opts)
    		opts = ffs_obj->opts;
    	else
    		goto done;
    
    	if (opts->no_configfs || !opts->func_inst.group.cg_item.ci_parent
    	    || !kref_read(&opts->func_inst.group.cg_item.ci_kref))
    		goto done;
    
    	ci = opts->func_inst.group.cg_item.ci_parent->ci_parent;
    	ffs_dev_unlock();
    
    	if (test_bit(FFS_FL_BOUND, &ffs->flags))
    		unregister_gadget_item(ci);
    	return;
    done:
    	ffs_dev_unlock();
    }
    
    /* 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;
    }
    
    DECLARE_USB_FUNCTION_INIT(ffs, ffs_alloc_inst, ffs_alloc);
    MODULE_LICENSE("GPL");
    MODULE_AUTHOR("Michal Nazarewicz");