code review request: simple usb stream interface (susi)

/*
 * Simple USB Stream Interface (SUSI)
 *
 * Copyright (C) 2007 Edwin Olson ([email protected])
 * Copyright (C) 2001-2004 Greg Kroah-Hartman ([email protected])
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License as
 *	published by the Free Software Foundation, version 2.
 *
 * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
 * but has been rewritten to be easier to read and use.
 *
 */

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kref.h>
#include <linux/kfifo.h>
#include <asm/uaccess.h>
#include <linux/usb.h>
#include <linux/mutex.h>
#include <linux/poll.h>

/* Define these values to match your devices */
#define USB_SUSI_VENDOR_ID	0x00ed
#define USB_SUSI_PRODUCT_ID	0x0001

/* table of devices that work with this driver */
static struct usb_device_id susi_table [] = {
	{ USB_DEVICE(USB_SUSI_VENDOR_ID, USB_SUSI_PRODUCT_ID) },
	{ }					/* Terminating entry */
};
MODULE_DEVICE_TABLE(usb, susi_table);


/* Get a minor range for your devices from the usb maintainer */
#define USB_SUSI_MINOR_BASE	192

/* our private defines. if this grows any larger, use your own .h file */
#define MAX_TRANSFER		(PAGE_SIZE - 512)
#define WRITES_IN_FLIGHT	8

/* Structure to hold all of our device specific stuff */
struct usb_susi {
	struct usb_device       *udev;			/* the usb device for this device */
	struct usb_interface    *interface;		/* the interface for this device */
	struct semaphore	write_sem;		/* limiting the number of writes in progress */
	struct semaphore        read_sem;               /* block readers until we have data */
	unsigned char           *bulk_in_buffer;	/* the buffer to receive data */
	size_t			bulk_in_size;		/* the size of the receive buffer */
	__u8			bulk_in_endpointAddr;	/* the address of the bulk in endpoint */
	__u8			bulk_out_endpointAddr;	/* the address of the bulk out endpoint */
	struct kref		kref;
	struct mutex		io_mutex;		/* synchronize I/O with disconnect */

	struct urb              *read_urb;
	int                     read_pending;           /* is a read URB outstanding? */

	struct kfifo            *read_fifo;
	spinlock_t              spinlock;

	wait_queue_head_t       readq, writeq;          /* read and write queues */
};

#define to_susi_dev(d) container_of(d, struct usb_susi, kref)

static struct usb_driver susi_driver;

static void susi_delete(struct kref *kref)
{
	struct usb_susi *dev = to_susi_dev(kref);

	usb_put_dev(dev->udev);
	kfifo_free(dev->read_fifo);
	kfree(dev->bulk_in_buffer);
	kfree(dev);
}

static int susi_open(struct inode *inode, struct file *file)
{
	struct usb_susi *dev;
	struct usb_interface *interface;
	int subminor;
	int retval = 0;

	subminor = iminor(inode);

	interface = usb_find_interface(&susi_driver, subminor);
	if (!interface) {
		err ("%s - error, can't find device for minor %d",
		     __FUNCTION__, subminor);
		retval = -ENODEV;
		goto exit;
	}

	dev = usb_get_intfdata(interface);
	if (!dev) {
		retval = -ENODEV;
		goto exit;
	}

	/* prevent the device from being autosuspended */
	retval = usb_autopm_get_interface(interface);
	if (retval)
		goto exit;

	/* increment our usage count for the device */
	kref_get(&dev->kref);

	/* save our object in the file's private structure */
	file->private_data = dev;

exit:
	return retval;
}

static int susi_release(struct inode *inode, struct file *file)
{
	struct usb_susi *dev;

	dev = (struct usb_susi *)file->private_data;
	if (dev == NULL)
		return -ENODEV;

	/* allow the device to be autosuspended */
	mutex_lock(&dev->io_mutex);
	if (dev->interface)
		usb_autopm_put_interface(dev->interface);
	mutex_unlock(&dev->io_mutex);

	/* decrement the count on our device */
	kref_put(&dev->kref, susi_delete);
	return 0;
}

static int susi_read_more(struct usb_susi *dev);

static void susi_read_bulk_callback (struct urb *urb)
{
	struct usb_susi *dev;

	dev = (struct usb_susi *)urb->context;

	if (urb != dev->read_urb) {
		err("not our read erb");
	}

	dev->read_pending = 0;

	/* sync/async unlink faults aren't errors */
	if (urb->status &&
	    !(urb->status == -ENOENT ||
	      urb->status == -ECONNRESET ||
	      urb->status == -ESHUTDOWN)) {
		err("%s - nonzero read bulk status received: %d",
		    __FUNCTION__, urb->status);
	}

	kfifo_put(dev->read_fifo, urb->transfer_buffer, urb->actual_length);
	wake_up_interruptible(&dev->readq);

	susi_read_more(dev);
}

static int susi_read_more(struct usb_susi *dev)
{
	int retval;
	int fifo_space = dev->read_fifo->size - kfifo_len(dev->read_fifo);

	if (dev->read_pending)
		return 0;

	if (fifo_space < dev->bulk_in_size)
		return 0;

	dev->read_pending = 1;
	// XXX what is correct requested read length?
	usb_fill_bulk_urb(dev->read_urb, dev->udev,
			  usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
			  dev->bulk_in_buffer, dev->bulk_in_size,
			  susi_read_bulk_callback, dev);

	retval = usb_submit_urb(dev->read_urb, GFP_ATOMIC);
	if (retval)
		err("%s - failed submitting read urb, error %d", __FUNCTION__, retval);

	return retval;
}

#define TBUF_LEN 256

static ssize_t susi_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
{
	struct usb_susi *dev;
	char tbuf[TBUF_LEN];
	int retval;
	int xfersize;

	dev = (struct usb_susi *)file->private_data;

	mutex_lock(&dev->io_mutex);

	if (!dev->interface) {		/* disconnect() was called */
		retval = -ENODEV;
		goto exit;
	}

	while (kfifo_len(dev->read_fifo) == 0) {
		mutex_unlock(&dev->io_mutex);
		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;
		if (wait_event_interruptible(dev->readq, kfifo_len(dev->read_fifo)!=0))
			return -ERESTARTSYS;
		mutex_lock(&dev->io_mutex);
	}

	xfersize = count < TBUF_LEN ? count : TBUF_LEN; // min(count, TBUF_LEN);

	xfersize = kfifo_get(dev->read_fifo, tbuf, TBUF_LEN);

	if (copy_to_user(buffer, tbuf, xfersize))
		retval = -EFAULT;
	else
		retval = xfersize;

	susi_read_more(dev);
	
exit:
	mutex_unlock(&dev->io_mutex);
	return retval;
}

static void susi_write_bulk_callback(struct urb *urb)
{
	struct usb_susi *dev;

	dev = (struct usb_susi *)urb->context;

	/* sync/async unlink faults aren't errors */
	if (urb->status &&
	    !(urb->status == -ENOENT ||
	      urb->status == -ECONNRESET ||
	      urb->status == -ESHUTDOWN)) {
		err("%s - nonzero write bulk status received: %d",
		    __FUNCTION__, urb->status);
	}

	/* free up our allocated buffer */
	usb_buffer_free(urb->dev, urb->transfer_buffer_length,
			urb->transfer_buffer, urb->transfer_dma);

	/* we can write more, so wake up the queue. */
	wake_up_interruptible(&dev->writeq);

	up(&dev->write_sem);
}

static ssize_t susi_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)
{
	struct usb_susi *dev;
	int retval = 0;
	struct urb *urb = NULL;
	char *buf = NULL;
	size_t writesize = min(count, (size_t)MAX_TRANSFER);

	dev = (struct usb_susi *)file->private_data;

	/* verify that we actually have some data to write */
	if (count == 0)
		goto exit;

	/* limit the number of URBs in flight to stop a user from using up all RAM */
	if (down_interruptible(&dev->write_sem)) {
		retval = -ERESTARTSYS;
		goto exit;
	}

	mutex_lock(&dev->io_mutex);
	if (!dev->interface) {		/* disconnect() was called */
		retval = -ENODEV;
		goto error;
	}

	/* create a urb, and a buffer for it, and copy the data to the urb */
	urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!urb) {
		retval = -ENOMEM;
		goto error;
	}

	buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL, &urb->transfer_dma);
	if (!buf) {
		retval = -ENOMEM;
		goto error;
	}

	if (copy_from_user(buf, user_buffer, writesize)) {
		retval = -EFAULT;
		goto error;
	}

	/* initialize the urb properly */
	usb_fill_bulk_urb(urb, dev->udev,
			  usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
			  buf, writesize, susi_write_bulk_callback, dev);
	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

	/* send the data out the bulk port */
	retval = usb_submit_urb(urb, GFP_KERNEL);
	if (retval) {
		err("%s - failed submitting write urb, error %d", __FUNCTION__, retval);
		goto error;
	}

	/* release our reference to this urb, the USB core will eventually free it entirely */
	usb_free_urb(urb);

	mutex_unlock(&dev->io_mutex);
	return writesize;

error:
	if (urb) {
		usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
		usb_free_urb(urb);
	}
	mutex_unlock(&dev->io_mutex);
	up(&dev->write_sem);

exit:
	return retval;
}

static unsigned int susi_poll(struct file *file, poll_table *wait)
{
  	struct usb_susi *dev;
	unsigned int mask = 0;

	dev = (struct usb_susi *)file->private_data;
	mutex_lock(&dev->io_mutex);

	poll_wait(file, &dev->readq, wait);
	poll_wait(file, &dev->writeq, wait);

	if (kfifo_len(dev->read_fifo))
		mask |= POLLIN | POLLRDNORM;
	if (down_trylock(&dev->write_sem) == 0) {
		// this would be prettier if there was a semaphore_value() call
		mask |= POLLOUT | POLLWRNORM;
		up(&dev->write_sem); 
	}
	mutex_unlock(&dev->io_mutex);

	return mask;
}

static const struct file_operations susi_fops = {
	.owner =	THIS_MODULE,
	.read =		susi_read,
	.write =	susi_write,
	.open =		susi_open,
	.poll =         susi_poll,
	.release =	susi_release,
};

/*
 * usb class driver info in order to get a minor number from the usb core,
 * and to have the device registered with the driver core
 */
static struct usb_class_driver susi_class = {
	.name =		"susi%d",
	.fops =		&susi_fops,
	.minor_base =	USB_SUSI_MINOR_BASE,
};

static int susi_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
	struct usb_susi *dev;
	struct usb_host_interface *iface_desc;
	struct usb_endpoint_descriptor *endpoint;
	size_t buffer_size;
	int i;
	int retval = -ENOMEM;

	/* allocate memory for our device state and initialize it */
	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (!dev) {
		err("Out of memory");
		goto error;
	}
	kref_init(&dev->kref);
	sema_init(&dev->write_sem, WRITES_IN_FLIGHT);
	sema_init(&dev->read_sem, 0);
	mutex_init(&dev->io_mutex);

	dev->udev = usb_get_dev(interface_to_usbdev(interface));
	dev->interface = interface;

	/* set up the endpoint information */
	/* use only the first bulk-in and bulk-out endpoints */
	iface_desc = interface->cur_altsetting;
	for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
		endpoint = &iface_desc->endpoint[i].desc;

		if (!dev->bulk_in_endpointAddr &&
		    usb_endpoint_is_bulk_in(endpoint)) {
			/* we found a bulk in endpoint */
			buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);
			dev->bulk_in_size = buffer_size;
			dev->bulk_in_size = 512; // XXXX
			dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
			dev->bulk_in_buffer = kmalloc(dev->bulk_in_size, GFP_KERNEL);
			if (!dev->bulk_in_buffer) {
				err("Could not allocate bulk_in_buffer");
				goto error;
			}
		}

		if (!dev->bulk_out_endpointAddr &&
		    usb_endpoint_is_bulk_out(endpoint)) {
			/* we found a bulk out endpoint */
			dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
		}
	}
	if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
		err("Could not find both bulk-in and bulk-out endpoints");
		goto error;
	}

	/* save our data pointer in this interface device */
	usb_set_intfdata(interface, dev);

	/* we can register the device now, as it is ready */
	retval = usb_register_dev(interface, &susi_class);
	if (retval) {
		/* something prevented us from registering this driver */
		err("Not able to get a minor for this device.");
		usb_set_intfdata(interface, NULL);
		goto error;
	}

	/* allocate the read urb */
	dev->read_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->read_urb) {
		retval = -ENOMEM;
		goto error;
	}

	dev->spinlock = SPIN_LOCK_UNLOCKED;
	dev->read_fifo = kfifo_alloc(4096, GFP_KERNEL, &dev->spinlock);
	if (!dev->read_fifo) {
		retval = -ENOMEM;
		goto error;
	}

	init_waitqueue_head(&dev->readq);
	init_waitqueue_head(&dev->writeq);

	/* start reading... */
	susi_read_more(dev);

	/* let the user know what node this device is now attached to */
	info("susi device now attached to susi-%d", interface->minor);
	return 0;

error:
	if (dev)
		kref_put(&dev->kref, susi_delete);
	return retval;
}

static void susi_disconnect(struct usb_interface *interface)
{
	struct usb_susi *dev;
	int minor = interface->minor;

	/* prevent susi_open() from racing susi_disconnect() */
	lock_kernel();

	dev = usb_get_intfdata(interface);
	usb_set_intfdata(interface, NULL);

	/* give back our minor */
	usb_deregister_dev(interface, &susi_class);

	/* prevent more I/O from starting */
	mutex_lock(&dev->io_mutex);
	dev->interface = NULL;
	mutex_unlock(&dev->io_mutex);

	unlock_kernel();

	/* decrement our usage count */
	kref_put(&dev->kref, susi_delete);

	info("USB Susieton #%d now disconnected", minor);
}

static struct usb_driver susi_driver = {
	.name =		"susieton",
	.probe =	susi_probe,
	.disconnect =	susi_disconnect,
	.id_table =	susi_table,
};

static int __init usb_susi_init(void)
{
	int result;

	/* register this driver with the USB subsystem */
	result = usb_register(&susi_driver);
	if (result)
		err("usb_register failed. Error number %d", result);

	return result;
}

static void __exit usb_susi_exit(void)
{
	/* deregister this driver with the USB subsystem */
	usb_deregister(&susi_driver);
}

module_init(usb_susi_init);
module_exit(usb_susi_exit);

MODULE_LICENSE("GPL");