/*
   * 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 <linux/types.h>

  #include <linux/debugfs.h>

  #include <asm/uaccess.h>
  #include <asm/types.h>
  
  #include <linux/nbd.h>

  struct nbd_device {

  	u32 flags;

  	struct socket * sock;	/* If == NULL, device is not ready, yet	*/
  	int magic;
  
  	spinlock_t queue_lock;
  	struct list_head queue_head;	/* Requests waiting result */
  	struct request *active_req;
  	wait_queue_head_t active_wq;
  	struct list_head waiting_queue;	/* Requests to be sent */
  	wait_queue_head_t waiting_wq;
  
  	struct mutex tx_lock;
  	struct gendisk *disk;
  	int blksize;

  	loff_t bytesize;

  	int xmit_timeout;

  	bool timedout;

  	bool disconnect; /* a disconnect has been requested by user */

  
  	struct timer_list timeout_timer;

  	/* protects initialization and shutdown of the socket */
  	spinlock_t sock_lock;

  	struct task_struct *task_recv;
  	struct task_struct *task_send;

  
  #if IS_ENABLED(CONFIG_DEBUG_FS)
  	struct dentry *dbg_dir;
  #endif

  };

  #if IS_ENABLED(CONFIG_DEBUG_FS)
  static struct dentry *nbd_dbg_dir;
  #endif
  
  #define nbd_name(nbd) ((nbd)->disk->disk_name)

  #define NBD_MAGIC 0x68797548

  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);

  static inline struct device *nbd_to_dev(struct nbd_device *nbd)

  {

  	return disk_to_dev(nbd->disk);

  }

  static bool nbd_is_connected(struct nbd_device *nbd)
  {
  	return !!nbd->task_recv;
  }

  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";
  }

  static int nbd_size_clear(struct nbd_device *nbd, struct block_device *bdev)
  {
  	bdev->bd_inode->i_size = 0;
  	set_capacity(nbd->disk, 0);
  	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
  
  	return 0;
  }
  
  static void nbd_size_update(struct nbd_device *nbd, struct block_device *bdev)
  {
  	if (!nbd_is_connected(nbd))
  		return;
  
  	bdev->bd_inode->i_size = nbd->bytesize;
  	set_capacity(nbd->disk, nbd->bytesize >> 9);
  	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
  }
  
  static int nbd_size_set(struct nbd_device *nbd, struct block_device *bdev,
  			int blocksize, int nr_blocks)
  {
  	int ret;
  
  	ret = set_blocksize(bdev, blocksize);
  	if (ret)
  		return ret;
  
  	nbd->blksize = blocksize;
  	nbd->bytesize = (loff_t)blocksize * (loff_t)nr_blocks;
  
  	nbd_size_update(nbd, bdev);
  
  	return 0;
  }

  static void nbd_end_request(struct nbd_device *nbd, struct request *req)

  {

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

  	struct request_queue *q = req->q;

  	unsigned long flags;

  	dev_dbg(nbd_to_dev(nbd), "request %p: %s
  ", req,
  		error ? "failed" : "done");

  
  	spin_lock_irqsave(q->queue_lock, flags);

  	__blk_end_request_all(req, error);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }

  /*
   * Forcibly shutdown the socket causing all listeners to error
   */

  static void sock_shutdown(struct nbd_device *nbd)

  {

  	spin_lock_irq(&nbd->sock_lock);
  
  	if (!nbd->sock) {
  		spin_unlock_irq(&nbd->sock_lock);

  		return;

  	}

  
  	dev_warn(disk_to_dev(nbd->disk), "shutting down socket
  ");
  	kernel_sock_shutdown(nbd->sock, SHUT_RDWR);

  	sockfd_put(nbd->sock);

  	nbd->sock = NULL;

  	spin_unlock_irq(&nbd->sock_lock);
  
  	del_timer(&nbd->timeout_timer);

  }
  
  static void nbd_xmit_timeout(unsigned long arg)
  {

  	struct nbd_device *nbd = (struct nbd_device *)arg;

  	unsigned long flags;

  
  	if (list_empty(&nbd->queue_head))
  		return;

  	spin_lock_irqsave(&nbd->sock_lock, flags);

  	nbd->timedout = true;

  	if (nbd->sock)
  		kernel_sock_shutdown(nbd->sock, SHUT_RDWR);

  	spin_unlock_irqrestore(&nbd->sock_lock, flags);

  	dev_err(nbd_to_dev(nbd), "Connection timed out, shutting down connection
  ");

  }

  /*
   *  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;

  	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;
  	}

  	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)

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

  		else

  			result = kernel_recvmsg(sock, &msg, &iov, 1, size,
  						msg.msg_flags);

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

  	tsk_restore_flags(current, pflags, PF_MEMALLOC);

  	if (!send && nbd->xmit_timeout)
  		mod_timer(&nbd->timeout_timer, jiffies + nbd->xmit_timeout);

  	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);

  	u32 type;
  
  	if (req->cmd_type == REQ_TYPE_DRV_PRIV)
  		type = NBD_CMD_DISC;

  	else if (req_op(req) == REQ_OP_DISCARD)

  		type = NBD_CMD_TRIM;

  	else if (req_op(req) == REQ_OP_FLUSH)

  		type = NBD_CMD_FLUSH;
  	else if (rq_data_dir(req) == WRITE)
  		type = NBD_CMD_WRITE;
  	else
  		type = NBD_CMD_READ;

  	memset(&request, 0, sizeof(request));

  	request.magic = htonl(NBD_REQUEST_MAGIC);

  	request.type = htonl(type);
  	if (type != NBD_CMD_FLUSH && type != NBD_CMD_DISC) {

  		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
  		request.len = htonl(size);
  	}

  	memcpy(request.handle, &req, sizeof(req));

  	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)
  ",

  		req, nbdcmd_to_ascii(type),

  		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));

  	result = sock_xmit(nbd, 1, &request, sizeof(request),

  			(type == NBD_CMD_WRITE) ? MSG_MORE : 0);

  	if (result <= 0) {

  		dev_err(disk_to_dev(nbd->disk),

  			"Send control failed (result %d)
  ", result);

  		return -EIO;

  	}

  	if (type == 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;

  			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data
  ",
  				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);

  				return -EIO;

  			}

  		}
  	}

  	return 0;

  }

  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))

  		return ERR_PTR(err);

  	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);

  	return ERR_PTR(-ENOENT);

  }

  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);

  		return ERR_PTR(result);

  	}

  
  	if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {

  		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)
  ",

  				(unsigned long)ntohl(reply.magic));

  		return ERR_PTR(-EPROTO);

  	}

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

  	if (IS_ERR(req)) {

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

  			return ERR_PTR(result);

  		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%p)
  ",

  			reply.handle);

  		return ERR_PTR(-EBADR);

  	}

  	if (ntohl(reply.error)) {

  		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)
  ",

  			ntohl(reply.error));

  		req->errors++;
  		return req;
  	}

  	dev_dbg(nbd_to_dev(nbd), "request %p: got reply
  ", req);

  	if (rq_data_dir(req) != WRITE) {

  		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;
  			}

  			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data
  ",
  				req, bvec.bv_len);

  		}
  	}
  	return req;

  }

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

  {

  	struct gendisk *disk = dev_to_disk(dev);

  	struct nbd_device *nbd = (struct nbd_device *)disk->private_data;

  	return sprintf(buf, "%d
  ", task_pid_nr(nbd->task_recv));

  }

  static struct device_attribute pid_attr = {

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

  	.show = pid_show,
  };

  static int nbd_thread_recv(struct nbd_device *nbd, struct block_device *bdev)

  {
  	struct request *req;

  	int ret;

  	BUG_ON(nbd->magic != NBD_MAGIC);

  	sk_set_memalloc(nbd->sock->sk);

  
  	nbd->task_recv = 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->task_recv = NULL;

  		return ret;
  	}

  	nbd_size_update(nbd, bdev);

  	while (1) {
  		req = nbd_read_stat(nbd);
  		if (IS_ERR(req)) {
  			ret = PTR_ERR(req);
  			break;
  		}

  		nbd_end_request(nbd, req);

  	}

  	nbd_size_clear(nbd, bdev);

  	device_remove_file(disk_to_dev(nbd->disk), &pid_attr);

  	nbd->task_recv = NULL;

  	return ret;

  }

  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(nbd, 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(nbd, req);

  	}

  	dev_dbg(disk_to_dev(nbd->disk), "queue cleared
  ");

  }

  static void nbd_handle_req(struct nbd_device *nbd, struct request *req)

  {

  	if (req->cmd_type != REQ_TYPE_FS)

  		goto error_out;

  	if (rq_data_dir(req) == WRITE &&
  	    (nbd->flags & NBD_FLAG_READ_ONLY)) {
  		dev_err(disk_to_dev(nbd->disk),
  			"Write on read-only
  ");
  		goto error_out;

  	}

  	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->xmit_timeout && list_empty_careful(&nbd->queue_head))
  		mod_timer(&nbd->timeout_timer, jiffies + nbd->xmit_timeout);

  	if (nbd_send_req(nbd, req) != 0) {
  		dev_err(disk_to_dev(nbd->disk), "Request send failed
  ");

  		req->errors++;

  		nbd_end_request(nbd, 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(nbd, req);

  }

  static int nbd_thread_send(void *data)

  {

  	struct nbd_device *nbd = data;

  	struct request *req;

  	nbd->task_send = current;

  	set_user_nice(current, MIN_NICE);

  	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);

  	}

  
  	nbd->task_send = NULL;

  	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 nbd_request_handler(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);

  		nbd = req->rq_disk->private_data;

  		BUG_ON(nbd->magic != NBD_MAGIC);

  		dev_dbg(nbd_to_dev(nbd), "request %p: dequeued (flags=%x)
  ",
  			req, req->cmd_type);

  		if (unlikely(!nbd->sock)) {

  			dev_err_ratelimited(disk_to_dev(nbd->disk),
  					    "Attempted send on closed socket
  ");

  			req->errors++;

  			nbd_end_request(nbd, 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);

  	}

  }

  static int nbd_set_socket(struct nbd_device *nbd, struct socket *sock)
  {
  	int ret = 0;
  
  	spin_lock_irq(&nbd->sock_lock);
  
  	if (nbd->sock) {
  		ret = -EBUSY;
  		goto out;
  	}
  
  	nbd->sock = sock;
  
  out:
  	spin_unlock_irq(&nbd->sock_lock);
  
  	return ret;
  }

  /* Reset all properties of an NBD device */
  static void nbd_reset(struct nbd_device *nbd)
  {
  	nbd->disconnect = false;
  	nbd->timedout = false;
  	nbd->blksize = 1024;
  	nbd->bytesize = 0;
  	set_capacity(nbd->disk, 0);
  	nbd->flags = 0;
  	nbd->xmit_timeout = 0;
  	queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
  	del_timer_sync(&nbd->timeout_timer);
  }
  
  static void nbd_bdev_reset(struct block_device *bdev)
  {
  	set_device_ro(bdev, false);
  	bdev->bd_inode->i_size = 0;
  	if (max_part > 0) {
  		blkdev_reread_part(bdev);
  		bdev->bd_invalidated = 1;
  	}
  }

  static void nbd_parse_flags(struct nbd_device *nbd, struct block_device *bdev)
  {
  	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_write_cache(nbd->disk->queue, true, false);

  	else

  		blk_queue_write_cache(nbd->disk->queue, false, false);

  }

  static int nbd_dev_dbg_init(struct nbd_device *nbd);
  static void nbd_dev_dbg_close(struct nbd_device *nbd);

  /* 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_DRV_PRIV;

  
  		/* Check again after getting mutex back.  */

  		if (!nbd->sock)

  			return -EINVAL;

  		nbd->disconnect = true;

  		nbd_send_req(nbd, &sreq);

  		return 0;

  	}

  	case NBD_CLEAR_SOCK:
  		sock_shutdown(nbd);

  		nbd_clear_que(nbd);
  		BUG_ON(!list_empty(&nbd->queue_head));

  		BUG_ON(!list_empty(&nbd->waiting_queue));

  		kill_bdev(bdev);

  		return 0;

  
  	case NBD_SET_SOCK: {

  		int err;

  		struct socket *sock = sockfd_lookup(arg, &err);
  
  		if (!sock)
  			return err;
  
  		err = nbd_set_socket(nbd, sock);
  		if (!err && max_part)
  			bdev->bd_invalidated = 1;
  
  		return err;

  	}

  	case NBD_SET_BLKSIZE: {

  		loff_t bsize = div_s64(nbd->bytesize, arg);

  
  		return nbd_size_set(nbd, bdev, arg, bsize);
  	}

  	case NBD_SET_SIZE:

  		return nbd_size_set(nbd, bdev, nbd->blksize,
  				    arg / nbd->blksize);
  
  	case NBD_SET_SIZE_BLOCKS:
  		return nbd_size_set(nbd, bdev, nbd->blksize, arg);

  	case NBD_SET_TIMEOUT:

  		nbd->xmit_timeout = arg * HZ;

  		if (arg)
  			mod_timer(&nbd->timeout_timer,
  				  jiffies + nbd->xmit_timeout);
  		else
  			del_timer_sync(&nbd->timeout_timer);

  		return 0;

  	case NBD_SET_FLAGS:
  		nbd->flags = arg;
  		return 0;

  	case NBD_DO_IT: {
  		struct task_struct *thread;

  		int error;

  		if (nbd->task_recv)

  			return -EBUSY;

  		if (!nbd->sock)

  			return -EINVAL;

  		mutex_unlock(&nbd->tx_lock);

  		nbd_parse_flags(nbd, bdev);

  		thread = kthread_run(nbd_thread_send, nbd, "%s",

  				     nbd_name(nbd));

  		if (IS_ERR(thread)) {

  			mutex_lock(&nbd->tx_lock);

  			return PTR_ERR(thread);

  		}

  		nbd_dev_dbg_init(nbd);

  		error = nbd_thread_recv(nbd, bdev);

  		nbd_dev_dbg_close(nbd);

  		kthread_stop(thread);

  		mutex_lock(&nbd->tx_lock);

  		sock_shutdown(nbd);

  		nbd_clear_que(nbd);

  		kill_bdev(bdev);

  		nbd_bdev_reset(bdev);

  		if (nbd->disconnect) /* user requested, ignore socket errors */

  			error = 0;
  		if (nbd->timedout)
  			error = -ETIMEDOUT;

  		nbd_reset(nbd);

  		return error;

  	}

  	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);

  	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,

  	.compat_ioctl =	nbd_ioctl,

  };

  #if IS_ENABLED(CONFIG_DEBUG_FS)
  
  static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
  {
  	struct nbd_device *nbd = s->private;
  
  	if (nbd->task_recv)
  		seq_printf(s, "recv: %d
  ", task_pid_nr(nbd->task_recv));
  	if (nbd->task_send)
  		seq_printf(s, "send: %d
  ", task_pid_nr(nbd->task_send));
  
  	return 0;
  }
  
  static int nbd_dbg_tasks_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, nbd_dbg_tasks_show, inode->i_private);
  }
  
  static const struct file_operations nbd_dbg_tasks_ops = {
  	.open = nbd_dbg_tasks_open,
  	.read = seq_read,
  	.llseek = seq_lseek,
  	.release = single_release,
  };
  
  static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
  {
  	struct nbd_device *nbd = s->private;
  	u32 flags = nbd->flags;
  
  	seq_printf(s, "Hex: 0x%08x
  
  ", flags);
  
  	seq_puts(s, "Known flags:
  ");
  
  	if (flags & NBD_FLAG_HAS_FLAGS)
  		seq_puts(s, "NBD_FLAG_HAS_FLAGS
  ");
  	if (flags & NBD_FLAG_READ_ONLY)
  		seq_puts(s, "NBD_FLAG_READ_ONLY
  ");
  	if (flags & NBD_FLAG_SEND_FLUSH)
  		seq_puts(s, "NBD_FLAG_SEND_FLUSH
  ");
  	if (flags & NBD_FLAG_SEND_TRIM)
  		seq_puts(s, "NBD_FLAG_SEND_TRIM
  ");
  
  	return 0;
  }
  
  static int nbd_dbg_flags_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, nbd_dbg_flags_show, inode->i_private);
  }
  
  static const struct file_operations nbd_dbg_flags_ops = {
  	.open = nbd_dbg_flags_open,
  	.read = seq_read,
  	.llseek = seq_lseek,
  	.release = single_release,
  };
  
  static int nbd_dev_dbg_init(struct nbd_device *nbd)
  {
  	struct dentry *dir;

  
  	if (!nbd_dbg_dir)
  		return -EIO;

  
  	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);

  	if (!dir) {
  		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'
  ",
  			nbd_name(nbd));
  		return -EIO;

  	}
  	nbd->dbg_dir = dir;

  	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_ops);
  	debugfs_create_u64("size_bytes", 0444, dir, &nbd->bytesize);
  	debugfs_create_u32("timeout", 0444, dir, &nbd->xmit_timeout);
  	debugfs_create_u32("blocksize", 0444, dir, &nbd->blksize);

  	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_ops);

  
  	return 0;
  }
  
  static void nbd_dev_dbg_close(struct nbd_device *nbd)
  {
  	debugfs_remove_recursive(nbd->dbg_dir);
  }
  
  static int nbd_dbg_init(void)
  {
  	struct dentry *dbg_dir;
  
  	dbg_dir = debugfs_create_dir("nbd", NULL);

  	if (!dbg_dir)
  		return -EIO;

  
  	nbd_dbg_dir = dbg_dir;
  
  	return 0;
  }
  
  static void nbd_dbg_close(void)
  {
  	debugfs_remove_recursive(nbd_dbg_dir);
  }
  
  #else  /* IS_ENABLED(CONFIG_DEBUG_FS) */
  
  static int nbd_dev_dbg_init(struct nbd_device *nbd)
  {
  	return 0;
  }
  
  static void nbd_dev_dbg_close(struct nbd_device *nbd)
  {
  }
  
  static int nbd_dbg_init(void)
  {
  	return 0;
  }
  
  static void nbd_dbg_close(void)
  {
  }
  
  #endif

  /*
   * 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;
  	}
  
  	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;

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

  	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(nbd_request_handler, &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);

  		queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, disk->queue);

  		disk->queue->limits.discard_granularity = 512;

  		blk_queue_max_discard_sectors(disk->queue, 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);

  	nbd_dbg_init();

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

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

  		nbd_dev[i].magic = NBD_MAGIC;

  		INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);

  		spin_lock_init(&nbd_dev[i].queue_lock);

  		spin_lock_init(&nbd_dev[i].sock_lock);

  		INIT_LIST_HEAD(&nbd_dev[i].queue_head);

  		mutex_init(&nbd_dev[i].tx_lock);

  		init_timer(&nbd_dev[i].timeout_timer);
  		nbd_dev[i].timeout_timer.function = nbd_xmit_timeout;
  		nbd_dev[i].timeout_timer.data = (unsigned long)&nbd_dev[i];

  		init_waitqueue_head(&nbd_dev[i].active_wq);

  		init_waitqueue_head(&nbd_dev[i].waiting_wq);

  		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);

  		nbd_reset(&nbd_dev[i]);

  		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;

  
  	nbd_dbg_close();

  	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)");