/*
   * 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@ucw.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/mutex.h>
  #include <linux/compiler.h>
  #include <linux/err.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <net/sock.h>
  #include <linux/net.h>
  #include <linux/kthread.h>
  
  #include <asm/uaccess.h>
  #include <asm/types.h>
  
  #include <linux/nbd.h>
  
  #define NBD_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_SET_TIMEOUT: return "set-timeout";
  	case NBD_SET_FLAGS: return "set-flags";
  	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";
  	case NBD_CMD_FLUSH: return "flush";
  	case  NBD_CMD_TRIM: return "trim/discard";
  	}
  	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_all(req, error);
  	spin_unlock_irqrestore(q->queue_lock, flags);
  }
  
  static void sock_shutdown(struct nbd_device *nbd, 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(&nbd->tx_lock);
  	if (nbd->sock) {
  		dev_warn(disk_to_dev(nbd->disk), "shutting down socket
  ");
  		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
  		nbd->sock = NULL;
  	}
  	if (lock)
  		mutex_unlock(&nbd->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 *nbd, int send, void *buf, int size,
  		int msg_flags)
  {
  	struct socket *sock = nbd->sock;
  	int result;
  	struct msghdr msg;
  	struct kvec iov;
  	sigset_t blocked, oldset;
  	unsigned long pflags = current->flags;
  
  	if (unlikely(!sock)) {
  		dev_err(disk_to_dev(nbd->disk),
  			"Attempted %s on closed socket in sock_xmit
  ",
  			(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);
  
  	current->flags |= PF_MEMALLOC;
  	do {
  		sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
  		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 (nbd->xmit_timeout) {
  				init_timer(&ti);
  				ti.function = nbd_xmit_timeout;
  				ti.data = (unsigned long)current;
  				ti.expires = jiffies + nbd->xmit_timeout;
  				add_timer(&ti);
  			}
  			result = kernel_sendmsg(sock, &msg, &iov, 1, size);
  			if (nbd->xmit_timeout)
  				del_timer_sync(&ti);
  		} else
  			result = kernel_recvmsg(sock, &msg, &iov, 1, size,
  						msg.msg_flags);
  
  		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(nbd, !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);
  	tsk_restore_flags(current, pflags, PF_MEMALLOC);
  
  	return result;
  }
  
  static inline int sock_send_bvec(struct nbd_device *nbd, struct bio_vec *bvec,
  		int flags)
  {
  	int result;
  	void *kaddr = kmap(bvec->bv_page);
  	result = sock_xmit(nbd, 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 *nbd, struct request *req)
  {
  	int result, flags;
  	struct nbd_request request;
  	unsigned long size = blk_rq_bytes(req);
  
  	request.magic = htonl(NBD_REQUEST_MAGIC);
  	request.type = htonl(nbd_cmd(req));
  
  	if (nbd_cmd(req) == NBD_CMD_FLUSH) {
  		/* Other values are reserved for FLUSH requests.  */
  		request.from = 0;
  		request.len = 0;
  	} else {
  		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
  		request.len = htonl(size);
  	}
  	memcpy(request.handle, &req, sizeof(req));
  
  	dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%uB)
  ",
  			nbd->disk->disk_name, req,
  			nbdcmd_to_ascii(nbd_cmd(req)),
  			(unsigned long long)blk_rq_pos(req) << 9,
  			blk_rq_bytes(req));
  	result = sock_xmit(nbd, 1, &request, sizeof(request),
  			(nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);
  	if (result <= 0) {
  		dev_err(disk_to_dev(nbd->disk),
  			"Send control failed (result %d)
  ", 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(bvec, iter))
  				flags = MSG_MORE;
  			dprintk(DBG_TX, "%s: request %p: sending %d bytes data
  ",
  					nbd->disk->disk_name, req, bvec.bv_len);
  			result = sock_send_bvec(nbd, &bvec, flags);
  			if (result <= 0) {
  				dev_err(disk_to_dev(nbd->disk),
  					"Send data failed (result %d)
  ",
  					result);
  				goto error_out;
  			}
  		}
  	}
  	return 0;
  
  error_out:
  	return -EIO;
  }
  
  static struct request *nbd_find_request(struct nbd_device *nbd,
  					struct request *xreq)
  {
  	struct request *req, *tmp;
  	int err;
  
  	err = wait_event_interruptible(nbd->active_wq, nbd->active_req != xreq);
  	if (unlikely(err))
  		goto out;
  
  	spin_lock(&nbd->queue_lock);
  	list_for_each_entry_safe(req, tmp, &nbd->queue_head, queuelist) {
  		if (req != xreq)
  			continue;
  		list_del_init(&req->queuelist);
  		spin_unlock(&nbd->queue_lock);
  		return req;
  	}
  	spin_unlock(&nbd->queue_lock);
  
  	err = -ENOENT;
  
  out:
  	return ERR_PTR(err);
  }
  
  static inline int sock_recv_bvec(struct nbd_device *nbd, struct bio_vec *bvec)
  {
  	int result;
  	void *kaddr = kmap(bvec->bv_page);
  	result = sock_xmit(nbd, 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 *nbd)
  {
  	int result;
  	struct nbd_reply reply;
  	struct request *req;
  
  	reply.magic = 0;
  	result = sock_xmit(nbd, 0, &reply, sizeof(reply), MSG_WAITALL);
  	if (result <= 0) {
  		dev_err(disk_to_dev(nbd->disk),
  			"Receive control failed (result %d)
  ", result);
  		goto harderror;
  	}
  
  	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
  		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)
  ",
  				(unsigned long)ntohl(reply.magic));
  		result = -EPROTO;
  		goto harderror;
  	}
  
  	req = nbd_find_request(nbd, *(struct request **)reply.handle);
  	if (IS_ERR(req)) {
  		result = PTR_ERR(req);
  		if (result != -ENOENT)
  			goto harderror;
  
  		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%p)
  ",
  			reply.handle);
  		result = -EBADR;
  		goto harderror;
  	}
  
  	if (ntohl(reply.error)) {
  		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)
  ",
  			ntohl(reply.error));
  		req->errors++;
  		return req;
  	}
  
  	dprintk(DBG_RX, "%s: request %p: got reply
  ",
  			nbd->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(nbd, &bvec);
  			if (result <= 0) {
  				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)
  ",
  					result);
  				req->errors++;
  				return req;
  			}
  			dprintk(DBG_RX, "%s: request %p: got %d bytes data
  ",
  				nbd->disk->disk_name, req, bvec.bv_len);
  		}
  	}
  	return req;
  harderror:
  	nbd->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 *nbd)
  {
  	struct request *req;
  	int ret;
  
  	BUG_ON(nbd->magic != NBD_MAGIC);
  
  	sk_set_memalloc(nbd->sock->sk);
  	nbd->pid = task_pid_nr(current);
  	ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
  	if (ret) {
  		dev_err(disk_to_dev(nbd->disk), "device_create_file failed!
  ");
  		nbd->pid = 0;
  		return ret;
  	}
  
  	while ((req = nbd_read_stat(nbd)) != NULL)
  		nbd_end_request(req);
  
  	device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
  	nbd->pid = 0;
  	return 0;
  }
  
  static void nbd_clear_que(struct nbd_device *nbd)
  {
  	struct request *req;
  
  	BUG_ON(nbd->magic != NBD_MAGIC);
  
  	/*
  	 * Because we have set nbd->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(nbd->sock);
  	BUG_ON(nbd->active_req);
  
  	while (!list_empty(&nbd->queue_head)) {
  		req = list_entry(nbd->queue_head.next, struct request,
  				 queuelist);
  		list_del_init(&req->queuelist);
  		req->errors++;
  		nbd_end_request(req);
  	}
  
  	while (!list_empty(&nbd->waiting_queue)) {
  		req = list_entry(nbd->waiting_queue.next, struct request,
  				 queuelist);
  		list_del_init(&req->queuelist);
  		req->errors++;
  		nbd_end_request(req);
  	}
  }
  
  
  static void nbd_handle_req(struct nbd_device *nbd, struct request *req)
  {
  	if (req->cmd_type != REQ_TYPE_FS)
  		goto error_out;
  
  	nbd_cmd(req) = NBD_CMD_READ;
  	if (rq_data_dir(req) == WRITE) {
  		if ((req->cmd_flags & REQ_DISCARD)) {
  			WARN_ON(!(nbd->flags & NBD_FLAG_SEND_TRIM));
  			nbd_cmd(req) = NBD_CMD_TRIM;
  		} else
  			nbd_cmd(req) = NBD_CMD_WRITE;
  		if (nbd->flags & NBD_FLAG_READ_ONLY) {
  			dev_err(disk_to_dev(nbd->disk),
  				"Write on read-only
  ");
  			goto error_out;
  		}
  	}
  
  	if (req->cmd_flags & REQ_FLUSH) {
  		BUG_ON(unlikely(blk_rq_sectors(req)));
  		nbd_cmd(req) = NBD_CMD_FLUSH;
  	}
  
  	req->errors = 0;
  
  	mutex_lock(&nbd->tx_lock);
  	if (unlikely(!nbd->sock)) {
  		mutex_unlock(&nbd->tx_lock);
  		dev_err(disk_to_dev(nbd->disk),
  			"Attempted send on closed socket
  ");
  		goto error_out;
  	}
  
  	nbd->active_req = req;
  
  	if (nbd_send_req(nbd, req) != 0) {
  		dev_err(disk_to_dev(nbd->disk), "Request send failed
  ");
  		req->errors++;
  		nbd_end_request(req);
  	} else {
  		spin_lock(&nbd->queue_lock);
  		list_add_tail(&req->queuelist, &nbd->queue_head);
  		spin_unlock(&nbd->queue_lock);
  	}
  
  	nbd->active_req = NULL;
  	mutex_unlock(&nbd->tx_lock);
  	wake_up_all(&nbd->active_wq);
  
  	return;
  
  error_out:
  	req->errors++;
  	nbd_end_request(req);
  }
  
  static int nbd_thread(void *data)
  {
  	struct nbd_device *nbd = data;
  	struct request *req;
  
  	set_user_nice(current, -20);
  	while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) {
  		/* wait for something to do */
  		wait_event_interruptible(nbd->waiting_wq,
  					 kthread_should_stop() ||
  					 !list_empty(&nbd->waiting_queue));
  
  		/* extract request */
  		if (list_empty(&nbd->waiting_queue))
  			continue;
  
  		spin_lock_irq(&nbd->queue_lock);
  		req = list_entry(nbd->waiting_queue.next, struct request,
  				 queuelist);
  		list_del_init(&req->queuelist);
  		spin_unlock_irq(&nbd->queue_lock);
  
  		/* handle request */
  		nbd_handle_req(nbd, 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) && (nbd->flags & NBD_WRITE_NOCHK))
   *   { printk( "Warning: Ignoring result!
  "); nbd_end_request( req ); }
   */
  
  static void do_nbd_request(struct request_queue *q)
  		__releases(q->queue_lock) __acquires(q->queue_lock)
  {
  	struct request *req;
  	
  	while ((req = blk_fetch_request(q)) != NULL) {
  		struct nbd_device *nbd;
  
  		spin_unlock_irq(q->queue_lock);
  
  		dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%x)
  ",
  				req->rq_disk->disk_name, req, req->cmd_type);
  
  		nbd = req->rq_disk->private_data;
  
  		BUG_ON(nbd->magic != NBD_MAGIC);
  
  		if (unlikely(!nbd->sock)) {
  			dev_err(disk_to_dev(nbd->disk),
  				"Attempted send on closed socket
  ");
  			req->errors++;
  			nbd_end_request(req);
  			spin_lock_irq(q->queue_lock);
  			continue;
  		}
  
  		spin_lock_irq(&nbd->queue_lock);
  		list_add_tail(&req->queuelist, &nbd->waiting_queue);
  		spin_unlock_irq(&nbd->queue_lock);
  
  		wake_up(&nbd->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 *nbd,
  		       unsigned int cmd, unsigned long arg)
  {
  	switch (cmd) {
  	case NBD_DISCONNECT: {
  		struct request sreq;
  
  		dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT
  ");
  		if (!nbd->sock)
  			return -EINVAL;
  
  		mutex_unlock(&nbd->tx_lock);
  		fsync_bdev(bdev);
  		mutex_lock(&nbd->tx_lock);
  		blk_rq_init(NULL, &sreq);
  		sreq.cmd_type = REQ_TYPE_SPECIAL;
  		nbd_cmd(&sreq) = NBD_CMD_DISC;
  
  		/* Check again after getting mutex back.  */
  		if (!nbd->sock)
  			return -EINVAL;
  
  		nbd->disconnect = 1;
  
  		nbd_send_req(nbd, &sreq);
  		return 0;
  	}
   
  	case NBD_CLEAR_SOCK: {
  		struct file *file;
  
  		nbd->sock = NULL;
  		file = nbd->file;
  		nbd->file = NULL;
  		nbd_clear_que(nbd);
  		BUG_ON(!list_empty(&nbd->queue_head));
  		BUG_ON(!list_empty(&nbd->waiting_queue));
  		kill_bdev(bdev);
  		if (file)
  			fput(file);
  		return 0;
  	}
  
  	case NBD_SET_SOCK: {
  		struct file *file;
  		if (nbd->file)
  			return -EBUSY;
  		file = fget(arg);
  		if (file) {
  			struct inode *inode = file_inode(file);
  			if (S_ISSOCK(inode->i_mode)) {
  				nbd->file = file;
  				nbd->sock = SOCKET_I(inode);
  				if (max_part > 0)
  					bdev->bd_invalidated = 1;
  				nbd->disconnect = 0; /* we're connected now */
  				return 0;
  			} else {
  				fput(file);
  			}
  		}
  		return -EINVAL;
  	}
  
  	case NBD_SET_BLKSIZE:
  		nbd->blksize = arg;
  		nbd->bytesize &= ~(nbd->blksize-1);
  		bdev->bd_inode->i_size = nbd->bytesize;
  		set_blocksize(bdev, nbd->blksize);
  		set_capacity(nbd->disk, nbd->bytesize >> 9);
  		return 0;
  
  	case NBD_SET_SIZE:
  		nbd->bytesize = arg & ~(nbd->blksize-1);
  		bdev->bd_inode->i_size = nbd->bytesize;
  		set_blocksize(bdev, nbd->blksize);
  		set_capacity(nbd->disk, nbd->bytesize >> 9);
  		return 0;
  
  	case NBD_SET_TIMEOUT:
  		nbd->xmit_timeout = arg * HZ;
  		return 0;
  
  	case NBD_SET_FLAGS:
  		nbd->flags = arg;
  		return 0;
  
  	case NBD_SET_SIZE_BLOCKS:
  		nbd->bytesize = ((u64) arg) * nbd->blksize;
  		bdev->bd_inode->i_size = nbd->bytesize;
  		set_blocksize(bdev, nbd->blksize);
  		set_capacity(nbd->disk, nbd->bytesize >> 9);
  		return 0;
  
  	case NBD_DO_IT: {
  		struct task_struct *thread;
  		struct file *file;
  		int error;
  
  		if (nbd->pid)
  			return -EBUSY;
  		if (!nbd->file)
  			return -EINVAL;
  
  		mutex_unlock(&nbd->tx_lock);
  
  		if (nbd->flags & NBD_FLAG_READ_ONLY)
  			set_device_ro(bdev, true);
  		if (nbd->flags & NBD_FLAG_SEND_TRIM)
  			queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
  				nbd->disk->queue);
  		if (nbd->flags & NBD_FLAG_SEND_FLUSH)
  			blk_queue_flush(nbd->disk->queue, REQ_FLUSH);
  		else
  			blk_queue_flush(nbd->disk->queue, 0);
  
  		thread = kthread_create(nbd_thread, nbd, "%s",
  					nbd->disk->disk_name);
  		if (IS_ERR(thread)) {
  			mutex_lock(&nbd->tx_lock);
  			return PTR_ERR(thread);
  		}
  		wake_up_process(thread);
  		error = nbd_do_it(nbd);
  		kthread_stop(thread);
  
  		mutex_lock(&nbd->tx_lock);
  		if (error)
  			return error;
  		sock_shutdown(nbd, 0);
  		file = nbd->file;
  		nbd->file = NULL;
  		nbd_clear_que(nbd);
  		dev_warn(disk_to_dev(nbd->disk), "queue cleared
  ");
  		kill_bdev(bdev);
  		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
  		set_device_ro(bdev, false);
  		if (file)
  			fput(file);
  		nbd->flags = 0;
  		nbd->bytesize = 0;
  		bdev->bd_inode->i_size = 0;
  		set_capacity(nbd->disk, 0);
  		if (max_part > 0)
  			ioctl_by_bdev(bdev, BLKRRPART, 0);
  		if (nbd->disconnect) /* user requested, ignore socket errors */
  			return 0;
  		return nbd->harderror;
  	}
  
  	case NBD_CLEAR_QUE:
  		/*
  		 * This is for compatibility only.  The queue is always cleared
  		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
  		 */
  		return 0;
  
  	case NBD_PRINT_DEBUG:
  		dev_info(disk_to_dev(nbd->disk),
  			"next = %p, prev = %p, head = %p
  ",
  			nbd->queue_head.next, nbd->queue_head.prev,
  			&nbd->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 *nbd = bdev->bd_disk->private_data;
  	int error;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return -EPERM;
  
  	BUG_ON(nbd->magic != NBD_MAGIC);
  
  	/* Anyone capable of this syscall can do *real bad* things */
  	dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu
  ",
  		nbd->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);
  
  	mutex_lock(&nbd->tx_lock);
  	error = __nbd_ioctl(bdev, nbd, cmd, arg);
  	mutex_unlock(&nbd->tx_lock);
  
  	return error;
  }
  
  static const struct block_device_operations nbd_fops =
  {
  	.owner =	THIS_MODULE,
  	.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_ERR "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);
  
  		/*
  		 * Adjust max_part according to part_shift as it is exported
  		 * to user space so that user can know the max number of
  		 * partition kernel should be able to manage.
  		 *
  		 * Note that -1 is required because partition 0 is reserved
  		 * for the whole disk.
  		 */
  		max_part = (1UL << part_shift) - 1;
  	}
  
  	if ((1UL << part_shift) > DISK_MAX_PARTS)
  		return -EINVAL;
  
  	if (nbds_max > 1UL << (MINORBITS - part_shift))
  		return -EINVAL;
  
  	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);
  		disk->queue->limits.discard_granularity = 512;
  		disk->queue->limits.max_discard_sectors = UINT_MAX;
  		disk->queue->limits.discard_zeroes_data = 0;
  		blk_queue_max_hw_sectors(disk->queue, 65536);
  		disk->queue->limits.max_sectors = 256;
  	}
  
  	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 = NBD_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