/*
   * Network block device - make block devices work over TCP
   *
   * Note that you can not swap over this thing, yet. Seems to work but
   * deadlocks sometimes - you can not swap over TCP in general.
   * 

   * Copyright 1997-2000, 2008 Pavel Machek <pavel@suse.cz>

   * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
   *

   * This file is released under GPLv2 or later.

   *

   * (part of code stolen from loop.c)

   */
  
  #include <linux/major.h>
  
  #include <linux/blkdev.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/sched.h>
  #include <linux/fs.h>
  #include <linux/bio.h>
  #include <linux/stat.h>
  #include <linux/errno.h>
  #include <linux/file.h>
  #include <linux/ioctl.h>

  #include <linux/compiler.h>
  #include <linux/err.h>
  #include <linux/kernel.h>

  #include <net/sock.h>

  #include <linux/net.h>

  #include <linux/kthread.h>

  #include <asm/uaccess.h>

  #include <asm/system.h>

  #include <asm/types.h>
  
  #include <linux/nbd.h>
  
  #define LO_MAGIC 0x68797548
  
  #ifdef NDEBUG
  #define dprintk(flags, fmt...)
  #else /* NDEBUG */
  #define dprintk(flags, fmt...) do { \
  	if (debugflags & (flags)) printk(KERN_DEBUG fmt); \
  } while (0)
  #define DBG_IOCTL       0x0004
  #define DBG_INIT        0x0010
  #define DBG_EXIT        0x0020
  #define DBG_BLKDEV      0x0100
  #define DBG_RX          0x0200
  #define DBG_TX          0x0400
  static unsigned int debugflags;
  #endif /* NDEBUG */

  static unsigned int nbds_max = 16;

  static struct nbd_device *nbd_dev;

  static int max_part;

  
  /*
   * Use just one lock (or at most 1 per NIC). Two arguments for this:
   * 1. Each NIC is essentially a synchronization point for all servers
   *    accessed through that NIC so there's no need to have more locks
   *    than NICs anyway.
   * 2. More locks lead to more "Dirty cache line bouncing" which will slow
   *    down each lock to the point where they're actually slower than just
   *    a single lock.
   * Thanks go to Jens Axboe and Al Viro for their LKML emails explaining this!
   */
  static DEFINE_SPINLOCK(nbd_lock);
  
  #ifndef NDEBUG
  static const char *ioctl_cmd_to_ascii(int cmd)
  {
  	switch (cmd) {
  	case NBD_SET_SOCK: return "set-sock";
  	case NBD_SET_BLKSIZE: return "set-blksize";
  	case NBD_SET_SIZE: return "set-size";
  	case NBD_DO_IT: return "do-it";
  	case NBD_CLEAR_SOCK: return "clear-sock";
  	case NBD_CLEAR_QUE: return "clear-que";
  	case NBD_PRINT_DEBUG: return "print-debug";
  	case NBD_SET_SIZE_BLOCKS: return "set-size-blocks";
  	case NBD_DISCONNECT: return "disconnect";
  	case BLKROSET: return "set-read-only";
  	case BLKFLSBUF: return "flush-buffer-cache";
  	}
  	return "unknown";
  }
  
  static const char *nbdcmd_to_ascii(int cmd)
  {
  	switch (cmd) {
  	case  NBD_CMD_READ: return "read";
  	case NBD_CMD_WRITE: return "write";
  	case  NBD_CMD_DISC: return "disconnect";
  	}
  	return "invalid";
  }
  #endif /* NDEBUG */
  
  static void nbd_end_request(struct request *req)
  {

  	int error = req->errors ? -EIO : 0;

  	struct request_queue *q = req->q;

  	unsigned long flags;
  
  	dprintk(DBG_BLKDEV, "%s: request %p: %s
  ", req->rq_disk->disk_name,

  			req, error ? "failed" : "done");

  
  	spin_lock_irqsave(q->queue_lock, flags);

  	__blk_end_request(req, error, req->nr_sectors << 9);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  static void sock_shutdown(struct nbd_device *lo, int lock)
  {
  	/* Forcibly shutdown the socket causing all listeners
  	 * to error
  	 *
  	 * FIXME: This code is duplicated from sys_shutdown, but
  	 * there should be a more generic interface rather than
  	 * calling socket ops directly here */
  	if (lock)
  		mutex_lock(&lo->tx_lock);
  	if (lo->sock) {
  		printk(KERN_WARNING "%s: shutting down socket
  ",
  			lo->disk->disk_name);

  		kernel_sock_shutdown(lo->sock, SHUT_RDWR);

  		lo->sock = NULL;
  	}
  	if (lock)
  		mutex_unlock(&lo->tx_lock);
  }
  
  static void nbd_xmit_timeout(unsigned long arg)
  {
  	struct task_struct *task = (struct task_struct *)arg;
  
  	printk(KERN_WARNING "nbd: killing hung xmit (%s, pid: %d)
  ",
  		task->comm, task->pid);
  	force_sig(SIGKILL, task);
  }

  /*
   *  Send or receive packet.
   */

  static int sock_xmit(struct nbd_device *lo, int send, void *buf, int size,

  		int msg_flags)
  {

  	struct socket *sock = lo->sock;

  	int result;
  	struct msghdr msg;
  	struct kvec iov;

  	sigset_t blocked, oldset;

  	if (unlikely(!sock)) {
  		printk(KERN_ERR "%s: Attempted %s on closed socket in sock_xmit
  ",
  		       lo->disk->disk_name, (send ? "send" : "recv"));
  		return -EINVAL;
  	}

  	/* Allow interception of SIGKILL only
  	 * Don't allow other signals to interrupt the transmission */

  	siginitsetinv(&blocked, sigmask(SIGKILL));
  	sigprocmask(SIG_SETMASK, &blocked, &oldset);

  
  	do {
  		sock->sk->sk_allocation = GFP_NOIO;
  		iov.iov_base = buf;
  		iov.iov_len = size;
  		msg.msg_name = NULL;
  		msg.msg_namelen = 0;
  		msg.msg_control = NULL;
  		msg.msg_controllen = 0;

  		msg.msg_flags = msg_flags | MSG_NOSIGNAL;

  		if (send) {
  			struct timer_list ti;
  
  			if (lo->xmit_timeout) {
  				init_timer(&ti);
  				ti.function = nbd_xmit_timeout;
  				ti.data = (unsigned long)current;
  				ti.expires = jiffies + lo->xmit_timeout;
  				add_timer(&ti);
  			}

  			result = kernel_sendmsg(sock, &msg, &iov, 1, size);

  			if (lo->xmit_timeout)
  				del_timer_sync(&ti);
  		} else

  			result = kernel_recvmsg(sock, &msg, &iov, 1, size, 0);
  
  		if (signal_pending(current)) {
  			siginfo_t info;

  			printk(KERN_WARNING "nbd (pid %d: %s) got signal %d
  ",

  				task_pid_nr(current), current->comm,

  				dequeue_signal_lock(current, &current->blocked, &info));

  			result = -EINTR;

  			sock_shutdown(lo, !send);

  			break;
  		}
  
  		if (result <= 0) {
  			if (result == 0)
  				result = -EPIPE; /* short read */
  			break;
  		}
  		size -= result;
  		buf += result;
  	} while (size > 0);

  	sigprocmask(SIG_SETMASK, &oldset, NULL);

  
  	return result;
  }

  static inline int sock_send_bvec(struct nbd_device *lo, struct bio_vec *bvec,

  		int flags)
  {
  	int result;
  	void *kaddr = kmap(bvec->bv_page);

  	result = sock_xmit(lo, 1, kaddr + bvec->bv_offset, bvec->bv_len, flags);

  	kunmap(bvec->bv_page);
  	return result;
  }

  /* always call with the tx_lock held */

  static int nbd_send_req(struct nbd_device *lo, struct request *req)
  {

  	int result, flags;

  	struct nbd_request request;
  	unsigned long size = req->nr_sectors << 9;

  
  	request.magic = htonl(NBD_REQUEST_MAGIC);
  	request.type = htonl(nbd_cmd(req));
  	request.from = cpu_to_be64((u64) req->sector << 9);
  	request.len = htonl(size);
  	memcpy(request.handle, &req, sizeof(req));

  	dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%luB)
  ",
  			lo->disk->disk_name, req,
  			nbdcmd_to_ascii(nbd_cmd(req)),
  			(unsigned long long)req->sector << 9,
  			req->nr_sectors << 9);

  	result = sock_xmit(lo, 1, &request, sizeof(request),
  			(nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);

  	if (result <= 0) {
  		printk(KERN_ERR "%s: Send control failed (result %d)
  ",
  				lo->disk->disk_name, result);
  		goto error_out;
  	}
  
  	if (nbd_cmd(req) == NBD_CMD_WRITE) {

  		struct req_iterator iter;
  		struct bio_vec *bvec;

  		/*
  		 * we are really probing at internals to determine
  		 * whether to set MSG_MORE or not...
  		 */

  		rq_for_each_segment(bvec, req, iter) {

  			flags = 0;
  			if (!rq_iter_last(req, iter))
  				flags = MSG_MORE;
  			dprintk(DBG_TX, "%s: request %p: sending %d bytes data
  ",
  					lo->disk->disk_name, req, bvec->bv_len);

  			result = sock_send_bvec(lo, bvec, flags);

  			if (result <= 0) {
  				printk(KERN_ERR "%s: Send data failed (result %d)
  ",
  						lo->disk->disk_name, result);
  				goto error_out;
  			}

  		}
  	}

  	return 0;
  
  error_out:

  	return -EIO;

  }

  static struct request *nbd_find_request(struct nbd_device *lo,
  					struct request *xreq)

  {

  	struct request *req, *tmp;

  	int err;

  	err = wait_event_interruptible(lo->active_wq, lo->active_req != xreq);
  	if (unlikely(err))
  		goto out;

  	spin_lock(&lo->queue_lock);

  	list_for_each_entry_safe(req, tmp, &lo->queue_head, queuelist) {

  		if (req != xreq)
  			continue;
  		list_del_init(&req->queuelist);
  		spin_unlock(&lo->queue_lock);
  		return req;
  	}
  	spin_unlock(&lo->queue_lock);

  
  	err = -ENOENT;
  
  out:
  	return ERR_PTR(err);

  }

  static inline int sock_recv_bvec(struct nbd_device *lo, struct bio_vec *bvec)

  {
  	int result;
  	void *kaddr = kmap(bvec->bv_page);

  	result = sock_xmit(lo, 0, kaddr + bvec->bv_offset, bvec->bv_len,

  			MSG_WAITALL);
  	kunmap(bvec->bv_page);
  	return result;
  }
  
  /* NULL returned = something went wrong, inform userspace */
  static struct request *nbd_read_stat(struct nbd_device *lo)
  {
  	int result;
  	struct nbd_reply reply;
  	struct request *req;

  
  	reply.magic = 0;

  	result = sock_xmit(lo, 0, &reply, sizeof(reply), MSG_WAITALL);

  	if (result <= 0) {
  		printk(KERN_ERR "%s: Receive control failed (result %d)
  ",
  				lo->disk->disk_name, result);
  		goto harderror;
  	}

  
  	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
  		printk(KERN_ERR "%s: Wrong magic (0x%lx)
  ",
  				lo->disk->disk_name,
  				(unsigned long)ntohl(reply.magic));
  		result = -EPROTO;
  		goto harderror;
  	}

  	req = nbd_find_request(lo, *(struct request **)reply.handle);

  	if (IS_ERR(req)) {

  		result = PTR_ERR(req);
  		if (result != -ENOENT)
  			goto harderror;

  		printk(KERN_ERR "%s: Unexpected reply (%p)
  ",
  				lo->disk->disk_name, reply.handle);
  		result = -EBADR;
  		goto harderror;
  	}

  	if (ntohl(reply.error)) {
  		printk(KERN_ERR "%s: Other side returned error (%d)
  ",
  				lo->disk->disk_name, ntohl(reply.error));
  		req->errors++;
  		return req;
  	}
  
  	dprintk(DBG_RX, "%s: request %p: got reply
  ",
  			lo->disk->disk_name, req);
  	if (nbd_cmd(req) == NBD_CMD_READ) {

  		struct req_iterator iter;
  		struct bio_vec *bvec;
  
  		rq_for_each_segment(bvec, req, iter) {

  			result = sock_recv_bvec(lo, bvec);

  			if (result <= 0) {
  				printk(KERN_ERR "%s: Receive data failed (result %d)
  ",
  						lo->disk->disk_name, result);
  				req->errors++;
  				return req;
  			}
  			dprintk(DBG_RX, "%s: request %p: got %d bytes data
  ",
  				lo->disk->disk_name, req, bvec->bv_len);

  		}
  	}
  	return req;
  harderror:
  	lo->harderror = result;
  	return NULL;
  }

  static ssize_t pid_show(struct device *dev,
  			struct device_attribute *attr, char *buf)

  {

  	struct gendisk *disk = dev_to_disk(dev);
  
  	return sprintf(buf, "%ld
  ",

  		(long) ((struct nbd_device *)disk->private_data)->pid);
  }

  static struct device_attribute pid_attr = {

  	.attr = { .name = "pid", .mode = S_IRUGO},

  	.show = pid_show,
  };

  static int nbd_do_it(struct nbd_device *lo)

  {
  	struct request *req;

  	int ret;

  
  	BUG_ON(lo->magic != LO_MAGIC);

  	lo->pid = current->pid;

  	ret = sysfs_create_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);

  	if (ret) {
  		printk(KERN_ERR "nbd: sysfs_create_file failed!");

  		lo->pid = 0;

  		return ret;
  	}

  	while ((req = nbd_read_stat(lo)) != NULL)
  		nbd_end_request(req);

  	sysfs_remove_file(&disk_to_dev(lo->disk)->kobj, &pid_attr.attr);

  	lo->pid = 0;

  	return 0;

  }
  
  static void nbd_clear_que(struct nbd_device *lo)
  {
  	struct request *req;
  
  	BUG_ON(lo->magic != LO_MAGIC);

  	/*
  	 * Because we have set lo->sock to NULL under the tx_lock, all
  	 * modifications to the list must have completed by now.  For
  	 * the same reason, the active_req must be NULL.
  	 *
  	 * As a consequence, we don't need to take the spin lock while
  	 * purging the list here.
  	 */
  	BUG_ON(lo->sock);
  	BUG_ON(lo->active_req);
  
  	while (!list_empty(&lo->queue_head)) {
  		req = list_entry(lo->queue_head.next, struct request,
  				 queuelist);
  		list_del_init(&req->queuelist);
  		req->errors++;
  		nbd_end_request(req);
  	}

  }

  static void nbd_handle_req(struct nbd_device *lo, struct request *req)
  {
  	if (!blk_fs_request(req))
  		goto error_out;
  
  	nbd_cmd(req) = NBD_CMD_READ;
  	if (rq_data_dir(req) == WRITE) {
  		nbd_cmd(req) = NBD_CMD_WRITE;
  		if (lo->flags & NBD_READ_ONLY) {
  			printk(KERN_ERR "%s: Write on read-only
  ",
  					lo->disk->disk_name);
  			goto error_out;
  		}
  	}
  
  	req->errors = 0;
  
  	mutex_lock(&lo->tx_lock);
  	if (unlikely(!lo->sock)) {
  		mutex_unlock(&lo->tx_lock);
  		printk(KERN_ERR "%s: Attempted send on closed socket
  ",
  		       lo->disk->disk_name);

  		goto error_out;

  	}
  
  	lo->active_req = req;
  
  	if (nbd_send_req(lo, req) != 0) {
  		printk(KERN_ERR "%s: Request send failed
  ",
  				lo->disk->disk_name);
  		req->errors++;
  		nbd_end_request(req);
  	} else {
  		spin_lock(&lo->queue_lock);
  		list_add(&req->queuelist, &lo->queue_head);
  		spin_unlock(&lo->queue_lock);
  	}
  
  	lo->active_req = NULL;
  	mutex_unlock(&lo->tx_lock);
  	wake_up_all(&lo->active_wq);
  
  	return;
  
  error_out:
  	req->errors++;
  	nbd_end_request(req);
  }
  
  static int nbd_thread(void *data)
  {
  	struct nbd_device *lo = data;
  	struct request *req;
  
  	set_user_nice(current, -20);
  	while (!kthread_should_stop() || !list_empty(&lo->waiting_queue)) {
  		/* wait for something to do */
  		wait_event_interruptible(lo->waiting_wq,
  					 kthread_should_stop() ||
  					 !list_empty(&lo->waiting_queue));
  
  		/* extract request */
  		if (list_empty(&lo->waiting_queue))
  			continue;
  
  		spin_lock_irq(&lo->queue_lock);
  		req = list_entry(lo->waiting_queue.next, struct request,
  				 queuelist);
  		list_del_init(&req->queuelist);
  		spin_unlock_irq(&lo->queue_lock);
  
  		/* handle request */
  		nbd_handle_req(lo, req);
  	}
  	return 0;
  }

  /*
   * We always wait for result of write, for now. It would be nice to make it optional
   * in future

   * if ((rq_data_dir(req) == WRITE) && (lo->flags & NBD_WRITE_NOCHK))

   *   { printk( "Warning: Ignoring result!
  "); nbd_end_request( req ); }
   */

  static void do_nbd_request(struct request_queue *q)

  {
  	struct request *req;
  	
  	while ((req = elv_next_request(q)) != NULL) {
  		struct nbd_device *lo;
  
  		blkdev_dequeue_request(req);

  
  		spin_unlock_irq(q->queue_lock);

  		dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%x)
  ",
  				req->rq_disk->disk_name, req, req->cmd_type);

  		lo = req->rq_disk->private_data;
  
  		BUG_ON(lo->magic != LO_MAGIC);

  		if (unlikely(!lo->sock)) {
  			printk(KERN_ERR "%s: Attempted send on closed socket
  ",
  				lo->disk->disk_name);
  			req->errors++;
  			nbd_end_request(req);
  			spin_lock_irq(q->queue_lock);
  			continue;
  		}

  		spin_lock_irq(&lo->queue_lock);
  		list_add_tail(&req->queuelist, &lo->waiting_queue);
  		spin_unlock_irq(&lo->queue_lock);

  		wake_up(&lo->waiting_wq);

  		spin_lock_irq(q->queue_lock);

  	}

  }

  /* Must be called with tx_lock held */

  static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
  		       unsigned int cmd, unsigned long arg)
  {

  	switch (cmd) {

  	case NBD_DISCONNECT: {
  		struct request sreq;

  	        printk(KERN_INFO "%s: NBD_DISCONNECT
  ", lo->disk->disk_name);

  		blk_rq_init(NULL, &sreq);

  		sreq.cmd_type = REQ_TYPE_SPECIAL;

  		nbd_cmd(&sreq) = NBD_CMD_DISC;
  		/*
  		 * Set these to sane values in case server implementation
  		 * fails to check the request type first and also to keep
  		 * debugging output cleaner.
  		 */
  		sreq.sector = 0;
  		sreq.nr_sectors = 0;

  		if (!lo->sock)

  			return -EINVAL;

  		nbd_send_req(lo, &sreq);

                  return 0;

  	}

  	case NBD_CLEAR_SOCK: {
  		struct file *file;

  		lo->sock = NULL;

  		file = lo->file;
  		lo->file = NULL;

  		nbd_clear_que(lo);

  		BUG_ON(!list_empty(&lo->queue_head));

  		if (file)
  			fput(file);

  		return 0;
  	}
  
  	case NBD_SET_SOCK: {
  		struct file *file;

  		if (lo->file)
  			return -EBUSY;

  		file = fget(arg);
  		if (file) {

  			struct inode *inode = file->f_path.dentry->d_inode;

  			if (S_ISSOCK(inode->i_mode)) {
  				lo->file = file;
  				lo->sock = SOCKET_I(inode);

  				if (max_part > 0)
  					bdev->bd_invalidated = 1;

  				return 0;

  			} else {
  				fput(file);
  			}
  		}

  		return -EINVAL;
  	}

  	case NBD_SET_BLKSIZE:
  		lo->blksize = arg;
  		lo->bytesize &= ~(lo->blksize-1);

  		bdev->bd_inode->i_size = lo->bytesize;
  		set_blocksize(bdev, lo->blksize);

  		set_capacity(lo->disk, lo->bytesize >> 9);
  		return 0;

  	case NBD_SET_SIZE:
  		lo->bytesize = arg & ~(lo->blksize-1);

  		bdev->bd_inode->i_size = lo->bytesize;
  		set_blocksize(bdev, lo->blksize);

  		set_capacity(lo->disk, lo->bytesize >> 9);
  		return 0;

  	case NBD_SET_TIMEOUT:
  		lo->xmit_timeout = arg * HZ;
  		return 0;

  	case NBD_SET_SIZE_BLOCKS:
  		lo->bytesize = ((u64) arg) * lo->blksize;

  		bdev->bd_inode->i_size = lo->bytesize;
  		set_blocksize(bdev, lo->blksize);

  		set_capacity(lo->disk, lo->bytesize >> 9);
  		return 0;

  
  	case NBD_DO_IT: {
  		struct task_struct *thread;
  		struct file *file;
  		int error;

  		if (lo->pid)
  			return -EBUSY;

  		if (!lo->file)
  			return -EINVAL;

  
  		mutex_unlock(&lo->tx_lock);

  		thread = kthread_create(nbd_thread, lo, lo->disk->disk_name);

  		if (IS_ERR(thread)) {
  			mutex_lock(&lo->tx_lock);

  			return PTR_ERR(thread);

  		}

  		wake_up_process(thread);

  		error = nbd_do_it(lo);

  		kthread_stop(thread);

  
  		mutex_lock(&lo->tx_lock);

  		if (error)
  			return error;

  		sock_shutdown(lo, 0);

  		file = lo->file;
  		lo->file = NULL;

  		nbd_clear_que(lo);
  		printk(KERN_WARNING "%s: queue cleared
  ", lo->disk->disk_name);
  		if (file)
  			fput(file);

  		lo->bytesize = 0;

  		bdev->bd_inode->i_size = 0;

  		set_capacity(lo->disk, 0);

  		if (max_part > 0)

  			ioctl_by_bdev(bdev, BLKRRPART, 0);

  		return lo->harderror;

  	}

  	case NBD_CLEAR_QUE:

  		/*
  		 * This is for compatibility only.  The queue is always cleared
  		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
  		 */
  		BUG_ON(!lo->sock && !list_empty(&lo->queue_head));

  		return 0;

  	case NBD_PRINT_DEBUG:
  		printk(KERN_INFO "%s: next = %p, prev = %p, head = %p
  ",

  			bdev->bd_disk->disk_name,

  			lo->queue_head.next, lo->queue_head.prev,
  			&lo->queue_head);
  		return 0;
  	}

  	return -ENOTTY;
  }
  
  static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
  		     unsigned int cmd, unsigned long arg)
  {
  	struct nbd_device *lo = bdev->bd_disk->private_data;
  	int error;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;
  
  	BUG_ON(lo->magic != LO_MAGIC);
  
  	/* Anyone capable of this syscall can do *real bad* things */
  	dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu
  ",
  			lo->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);
  
  	mutex_lock(&lo->tx_lock);
  	error = __nbd_ioctl(bdev, lo, cmd, arg);
  	mutex_unlock(&lo->tx_lock);
  
  	return error;

  }
  
  static struct block_device_operations nbd_fops =
  {
  	.owner =	THIS_MODULE,

  	.locked_ioctl =	nbd_ioctl,

  };
  
  /*
   * And here should be modules and kernel interface 
   *  (Just smiley confuses emacs :-)
   */
  
  static int __init nbd_init(void)
  {
  	int err = -ENOMEM;
  	int i;

  	int part_shift;

  	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

  	if (max_part < 0) {
  		printk(KERN_CRIT "nbd: max_part must be >= 0
  ");
  		return -EINVAL;
  	}

  	nbd_dev = kcalloc(nbds_max, sizeof(*nbd_dev), GFP_KERNEL);
  	if (!nbd_dev)
  		return -ENOMEM;

  	part_shift = 0;
  	if (max_part > 0)
  		part_shift = fls(max_part);

  	for (i = 0; i < nbds_max; i++) {

  		struct gendisk *disk = alloc_disk(1 << part_shift);

  		if (!disk)
  			goto out;
  		nbd_dev[i].disk = disk;
  		/*
  		 * The new linux 2.5 block layer implementation requires
  		 * every gendisk to have its very own request_queue struct.
  		 * These structs are big so we dynamically allocate them.
  		 */
  		disk->queue = blk_init_queue(do_nbd_request, &nbd_lock);
  		if (!disk->queue) {
  			put_disk(disk);
  			goto out;
  		}

  		/*
  		 * Tell the block layer that we are not a rotational device
  		 */
  		queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);

  	}
  
  	if (register_blkdev(NBD_MAJOR, "nbd")) {
  		err = -EIO;
  		goto out;
  	}
  
  	printk(KERN_INFO "nbd: registered device at major %d
  ", NBD_MAJOR);
  	dprintk(DBG_INIT, "nbd: debugflags=0x%x
  ", debugflags);

  	for (i = 0; i < nbds_max; i++) {

  		struct gendisk *disk = nbd_dev[i].disk;
  		nbd_dev[i].file = NULL;
  		nbd_dev[i].magic = LO_MAGIC;
  		nbd_dev[i].flags = 0;

  		INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);

  		spin_lock_init(&nbd_dev[i].queue_lock);
  		INIT_LIST_HEAD(&nbd_dev[i].queue_head);

  		mutex_init(&nbd_dev[i].tx_lock);

  		init_waitqueue_head(&nbd_dev[i].active_wq);

  		init_waitqueue_head(&nbd_dev[i].waiting_wq);

  		nbd_dev[i].blksize = 1024;

  		nbd_dev[i].bytesize = 0;

  		disk->major = NBD_MAJOR;

  		disk->first_minor = i << part_shift;

  		disk->fops = &nbd_fops;
  		disk->private_data = &nbd_dev[i];

  		sprintf(disk->disk_name, "nbd%d", i);

  		set_capacity(disk, 0);

  		add_disk(disk);
  	}
  
  	return 0;
  out:
  	while (i--) {
  		blk_cleanup_queue(nbd_dev[i].disk->queue);
  		put_disk(nbd_dev[i].disk);
  	}

  	kfree(nbd_dev);

  	return err;
  }
  
  static void __exit nbd_cleanup(void)
  {
  	int i;

  	for (i = 0; i < nbds_max; i++) {

  		struct gendisk *disk = nbd_dev[i].disk;

  		nbd_dev[i].magic = 0;

  		if (disk) {
  			del_gendisk(disk);
  			blk_cleanup_queue(disk->queue);
  			put_disk(disk);
  		}
  	}

  	unregister_blkdev(NBD_MAJOR, "nbd");

  	kfree(nbd_dev);

  	printk(KERN_INFO "nbd: unregistered device at major %d
  ", NBD_MAJOR);
  }
  
  module_init(nbd_init);
  module_exit(nbd_cleanup);
  
  MODULE_DESCRIPTION("Network Block Device");
  MODULE_LICENSE("GPL");

  module_param(nbds_max, int, 0444);

  MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
  module_param(max_part, int, 0444);
  MODULE_PARM_DESC(max_part, "number of partitions per device (default: 0)");

  #ifndef NDEBUG
  module_param(debugflags, int, 0644);
  MODULE_PARM_DESC(debugflags, "flags for controlling debug output");
  #endif