/*

   * bsg.c - block layer implementation of the sg v4 interface

   *
   * Copyright (C) 2004 Jens Axboe <axboe@suse.de> SUSE Labs
   * Copyright (C) 2004 Peter M. Jones <pjones@redhat.com>
   *
   *  This file is subject to the terms and conditions of the GNU General Public
   *  License version 2.  See the file "COPYING" in the main directory of this
   *  archive for more details.
   *
   */

  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/file.h>
  #include <linux/blkdev.h>
  #include <linux/poll.h>
  #include <linux/cdev.h>
  #include <linux/percpu.h>
  #include <linux/uio.h>

  #include <linux/idr.h>

  #include <linux/bsg.h>

  #include <linux/smp_lock.h>

  
  #include <scsi/scsi.h>
  #include <scsi/scsi_ioctl.h>
  #include <scsi/scsi_cmnd.h>

  #include <scsi/scsi_device.h>
  #include <scsi/scsi_driver.h>

  #include <scsi/sg.h>

  #define BSG_DESCRIPTION	"Block layer SCSI generic (bsg) driver"
  #define BSG_VERSION	"0.4"

  struct bsg_device {

  	struct request_queue *queue;

  	spinlock_t lock;
  	struct list_head busy_list;
  	struct list_head done_list;
  	struct hlist_node dev_list;
  	atomic_t ref_count;

  	int queued_cmds;
  	int done_cmds;

  	wait_queue_head_t wq_done;
  	wait_queue_head_t wq_free;

  	char name[20];

  	int max_queue;
  	unsigned long flags;
  };
  
  enum {
  	BSG_F_BLOCK		= 1,

  };

  #define BSG_DEFAULT_CMDS	64

  #define BSG_MAX_DEVS		32768

  
  #undef BSG_DEBUG
  
  #ifdef BSG_DEBUG

  #define dprintk(fmt, args...) printk(KERN_ERR "%s: " fmt, __func__, ##args)

  #else
  #define dprintk(fmt, args...)
  #endif

  static DEFINE_MUTEX(bsg_mutex);

  static DEFINE_IDR(bsg_minor_idr);

  #define BSG_LIST_ARRAY_SIZE	8

  static struct hlist_head bsg_device_list[BSG_LIST_ARRAY_SIZE];

  
  static struct class *bsg_class;

  static int bsg_major;

  static struct kmem_cache *bsg_cmd_cachep;

  /*
   * our internal command type
   */
  struct bsg_command {
  	struct bsg_device *bd;
  	struct list_head list;
  	struct request *rq;
  	struct bio *bio;

  	struct bio *bidi_bio;

  	int err;

  	struct sg_io_v4 hdr;

  	char sense[SCSI_SENSE_BUFFERSIZE];
  };
  
  static void bsg_free_command(struct bsg_command *bc)
  {
  	struct bsg_device *bd = bc->bd;

  	unsigned long flags;

  	kmem_cache_free(bsg_cmd_cachep, bc);

  
  	spin_lock_irqsave(&bd->lock, flags);
  	bd->queued_cmds--;

  	spin_unlock_irqrestore(&bd->lock, flags);
  
  	wake_up(&bd->wq_free);
  }

  static struct bsg_command *bsg_alloc_command(struct bsg_device *bd)

  {

  	struct bsg_command *bc = ERR_PTR(-EINVAL);

  
  	spin_lock_irq(&bd->lock);
  
  	if (bd->queued_cmds >= bd->max_queue)
  		goto out;

  	bd->queued_cmds++;

  	spin_unlock_irq(&bd->lock);

  	bc = kmem_cache_zalloc(bsg_cmd_cachep, GFP_KERNEL);

  	if (unlikely(!bc)) {
  		spin_lock_irq(&bd->lock);

  		bd->queued_cmds--;

  		bc = ERR_PTR(-ENOMEM);

  		goto out;

  	}

  	bc->bd = bd;
  	INIT_LIST_HEAD(&bc->list);

  	dprintk("%s: returning free cmd %p
  ", bd->name, bc);

  	return bc;
  out:

  	spin_unlock_irq(&bd->lock);
  	return bc;
  }

  static inline struct hlist_head *bsg_dev_idx_hash(int index)

  {

  	return &bsg_device_list[index & (BSG_LIST_ARRAY_SIZE - 1)];

  }

  static int bsg_io_schedule(struct bsg_device *bd)

  {
  	DEFINE_WAIT(wait);
  	int ret = 0;
  
  	spin_lock_irq(&bd->lock);
  
  	BUG_ON(bd->done_cmds > bd->queued_cmds);
  
  	/*
  	 * -ENOSPC or -ENODATA?  I'm going for -ENODATA, meaning "I have no
  	 * work to do", even though we return -ENOSPC after this same test
  	 * during bsg_write() -- there, it means our buffer can't have more
  	 * bsg_commands added to it, thus has no space left.
  	 */
  	if (bd->done_cmds == bd->queued_cmds) {
  		ret = -ENODATA;
  		goto unlock;
  	}
  
  	if (!test_bit(BSG_F_BLOCK, &bd->flags)) {
  		ret = -EAGAIN;
  		goto unlock;
  	}

  	prepare_to_wait(&bd->wq_done, &wait, TASK_UNINTERRUPTIBLE);

  	spin_unlock_irq(&bd->lock);
  	io_schedule();
  	finish_wait(&bd->wq_done, &wait);

  	return ret;
  unlock:
  	spin_unlock_irq(&bd->lock);
  	return ret;
  }

  static int blk_fill_sgv4_hdr_rq(struct request_queue *q, struct request *rq,

  				struct sg_io_v4 *hdr, struct bsg_device *bd,

  				fmode_t has_write_perm)

  {

  	if (hdr->request_len > BLK_MAX_CDB) {
  		rq->cmd = kzalloc(hdr->request_len, GFP_KERNEL);
  		if (!rq->cmd)
  			return -ENOMEM;
  	}

  
  	if (copy_from_user(rq->cmd, (void *)(unsigned long)hdr->request,
  			   hdr->request_len))
  		return -EFAULT;

  
  	if (hdr->subprotocol == BSG_SUB_PROTOCOL_SCSI_CMD) {

  		if (blk_verify_command(rq->cmd, has_write_perm))

  			return -EPERM;
  	} else if (!capable(CAP_SYS_RAWIO))

  		return -EPERM;
  
  	/*
  	 * fill in request structure
  	 */
  	rq->cmd_len = hdr->request_len;
  	rq->cmd_type = REQ_TYPE_BLOCK_PC;
  
  	rq->timeout = (hdr->timeout * HZ) / 1000;
  	if (!rq->timeout)
  		rq->timeout = q->sg_timeout;
  	if (!rq->timeout)
  		rq->timeout = BLK_DEFAULT_SG_TIMEOUT;

  	if (rq->timeout < BLK_MIN_SG_TIMEOUT)
  		rq->timeout = BLK_MIN_SG_TIMEOUT;

  
  	return 0;
  }

  /*

   * Check if sg_io_v4 from user is allowed and valid

   */
  static int

  bsg_validate_sgv4_hdr(struct request_queue *q, struct sg_io_v4 *hdr, int *rw)

  {

  	int ret = 0;

  	if (hdr->guard != 'Q')

  		return -EINVAL;

  	switch (hdr->protocol) {
  	case BSG_PROTOCOL_SCSI:
  		switch (hdr->subprotocol) {
  		case BSG_SUB_PROTOCOL_SCSI_CMD:
  		case BSG_SUB_PROTOCOL_SCSI_TRANSPORT:
  			break;
  		default:
  			ret = -EINVAL;
  		}
  		break;
  	default:
  		ret = -EINVAL;
  	}

  	*rw = hdr->dout_xfer_len ? WRITE : READ;

  	return ret;

  }
  
  /*

   * map sg_io_v4 to a request.

   */
  static struct request *

  bsg_map_hdr(struct bsg_device *bd, struct sg_io_v4 *hdr, fmode_t has_write_perm,
  	    u8 *sense)

  {

  	struct request_queue *q = bd->queue;

  	struct request *rq, *next_rq = NULL;

  	int ret, rw;

  	unsigned int dxfer_len;
  	void *dxferp = NULL;

  	dprintk("map hdr %llx/%u %llx/%u
  ", (unsigned long long) hdr->dout_xferp,
  		hdr->dout_xfer_len, (unsigned long long) hdr->din_xferp,
  		hdr->din_xfer_len);

  	ret = bsg_validate_sgv4_hdr(q, hdr, &rw);

  	if (ret)
  		return ERR_PTR(ret);
  
  	/*
  	 * map scatter-gather elements seperately and string them to request
  	 */
  	rq = blk_get_request(q, rw, GFP_KERNEL);

  	if (!rq)
  		return ERR_PTR(-ENOMEM);

  	ret = blk_fill_sgv4_hdr_rq(q, rq, hdr, bd, has_write_perm);

  	if (ret)
  		goto out;
  
  	if (rw == WRITE && hdr->din_xfer_len) {
  		if (!test_bit(QUEUE_FLAG_BIDI, &q->queue_flags)) {
  			ret = -EOPNOTSUPP;
  			goto out;
  		}
  
  		next_rq = blk_get_request(q, READ, GFP_KERNEL);
  		if (!next_rq) {
  			ret = -ENOMEM;
  			goto out;
  		}
  		rq->next_rq = next_rq;

  		next_rq->cmd_type = rq->cmd_type;

  
  		dxferp = (void*)(unsigned long)hdr->din_xferp;

  		ret =  blk_rq_map_user(q, next_rq, NULL, dxferp,
  				       hdr->din_xfer_len, GFP_KERNEL);

  		if (ret)
  			goto out;

  	}

  	if (hdr->dout_xfer_len) {
  		dxfer_len = hdr->dout_xfer_len;
  		dxferp = (void*)(unsigned long)hdr->dout_xferp;
  	} else if (hdr->din_xfer_len) {
  		dxfer_len = hdr->din_xfer_len;
  		dxferp = (void*)(unsigned long)hdr->din_xferp;
  	} else
  		dxfer_len = 0;
  
  	if (dxfer_len) {

  		ret = blk_rq_map_user(q, rq, NULL, dxferp, dxfer_len,
  				      GFP_KERNEL);

  		if (ret)
  			goto out;

  	}

  
  	rq->sense = sense;
  	rq->sense_len = 0;

  	return rq;

  out:

  	if (rq->cmd != rq->__cmd)
  		kfree(rq->cmd);

  	blk_put_request(rq);
  	if (next_rq) {
  		blk_rq_unmap_user(next_rq->bio);
  		blk_put_request(next_rq);
  	}
  	return ERR_PTR(ret);

  }
  
  /*
   * async completion call-back from the block layer, when scsi/ide/whatever
   * calls end_that_request_last() on a request
   */
  static void bsg_rq_end_io(struct request *rq, int uptodate)
  {
  	struct bsg_command *bc = rq->end_io_data;
  	struct bsg_device *bd = bc->bd;
  	unsigned long flags;

  	dprintk("%s: finished rq %p bc %p, bio %p stat %d
  ",
  		bd->name, rq, bc, bc->bio, uptodate);

  
  	bc->hdr.duration = jiffies_to_msecs(jiffies - bc->hdr.duration);
  
  	spin_lock_irqsave(&bd->lock, flags);

  	list_move_tail(&bc->list, &bd->done_list);
  	bd->done_cmds++;

  	spin_unlock_irqrestore(&bd->lock, flags);

  
  	wake_up(&bd->wq_done);

  }
  
  /*
   * do final setup of a 'bc' and submit the matching 'rq' to the block
   * layer for io
   */

  static void bsg_add_command(struct bsg_device *bd, struct request_queue *q,

  			    struct bsg_command *bc, struct request *rq)
  {

  	int at_head = (0 == (bc->hdr.flags & BSG_FLAG_Q_AT_TAIL));

  	/*
  	 * add bc command to busy queue and submit rq for io
  	 */
  	bc->rq = rq;
  	bc->bio = rq->bio;

  	if (rq->next_rq)
  		bc->bidi_bio = rq->next_rq->bio;

  	bc->hdr.duration = jiffies;
  	spin_lock_irq(&bd->lock);
  	list_add_tail(&bc->list, &bd->busy_list);
  	spin_unlock_irq(&bd->lock);
  
  	dprintk("%s: queueing rq %p, bc %p
  ", bd->name, rq, bc);
  
  	rq->end_io_data = bc;

  	blk_execute_rq_nowait(q, NULL, rq, at_head, bsg_rq_end_io);

  }

  static struct bsg_command *bsg_next_done_cmd(struct bsg_device *bd)

  {
  	struct bsg_command *bc = NULL;
  
  	spin_lock_irq(&bd->lock);
  	if (bd->done_cmds) {

  		bc = list_first_entry(&bd->done_list, struct bsg_command, list);

  		list_del(&bc->list);
  		bd->done_cmds--;

  	}
  	spin_unlock_irq(&bd->lock);
  
  	return bc;
  }
  
  /*
   * Get a finished command from the done list
   */

  static struct bsg_command *bsg_get_done_cmd(struct bsg_device *bd)

  {
  	struct bsg_command *bc;
  	int ret;
  
  	do {
  		bc = bsg_next_done_cmd(bd);
  		if (bc)
  			break;

  		if (!test_bit(BSG_F_BLOCK, &bd->flags)) {
  			bc = ERR_PTR(-EAGAIN);
  			break;
  		}
  
  		ret = wait_event_interruptible(bd->wq_done, bd->done_cmds);

  		if (ret) {

  			bc = ERR_PTR(-ERESTARTSYS);

  			break;
  		}
  	} while (1);
  
  	dprintk("%s: returning done %p
  ", bd->name, bc);
  
  	return bc;
  }

  static int blk_complete_sgv4_hdr_rq(struct request *rq, struct sg_io_v4 *hdr,

  				    struct bio *bio, struct bio *bidi_bio)

  {
  	int ret = 0;

  	dprintk("rq %p bio %p 0x%x
  ", rq, bio, rq->errors);

  	/*
  	 * fill in all the output members
  	 */
  	hdr->device_status = status_byte(rq->errors);
  	hdr->transport_status = host_byte(rq->errors);
  	hdr->driver_status = driver_byte(rq->errors);
  	hdr->info = 0;
  	if (hdr->device_status || hdr->transport_status || hdr->driver_status)
  		hdr->info |= SG_INFO_CHECK;

  	hdr->response_len = 0;
  
  	if (rq->sense_len && hdr->response) {

  		int len = min_t(unsigned int, hdr->max_response_len,
  					rq->sense_len);

  
  		ret = copy_to_user((void*)(unsigned long)hdr->response,
  				   rq->sense, len);
  		if (!ret)
  			hdr->response_len = len;
  		else
  			ret = -EFAULT;
  	}

  	if (rq->next_rq) {

  		hdr->dout_resid = rq->resid_len;
  		hdr->din_resid = rq->next_rq->resid_len;

  		blk_rq_unmap_user(bidi_bio);
  		blk_put_request(rq->next_rq);

  	} else if (rq_data_dir(rq) == READ)

  		hdr->din_resid = rq->resid_len;

  	else

  		hdr->dout_resid = rq->resid_len;

  	/*
  	 * If the request generated a negative error number, return it
  	 * (providing we aren't already returning an error); if it's
  	 * just a protocol response (i.e. non negative), that gets
  	 * processed above.
  	 */
  	if (!ret && rq->errors < 0)
  		ret = rq->errors;

  	blk_rq_unmap_user(bio);

  	if (rq->cmd != rq->__cmd)
  		kfree(rq->cmd);

  	blk_put_request(rq);
  
  	return ret;
  }

  static int bsg_complete_all_commands(struct bsg_device *bd)
  {
  	struct bsg_command *bc;
  	int ret, tret;
  
  	dprintk("%s: entered
  ", bd->name);

  	/*
  	 * wait for all commands to complete
  	 */
  	ret = 0;
  	do {

  		ret = bsg_io_schedule(bd);

  		/*
  		 * look for -ENODATA specifically -- we'll sometimes get
  		 * -ERESTARTSYS when we've taken a signal, but we can't
  		 * return until we're done freeing the queue, so ignore
  		 * it.  The signal will get handled when we're done freeing
  		 * the bsg_device.
  		 */
  	} while (ret != -ENODATA);
  
  	/*
  	 * discard done commands
  	 */
  	ret = 0;
  	do {

  		spin_lock_irq(&bd->lock);
  		if (!bd->queued_cmds) {
  			spin_unlock_irq(&bd->lock);

  			break;
  		}

  		spin_unlock_irq(&bd->lock);

  		bc = bsg_get_done_cmd(bd);
  		if (IS_ERR(bc))
  			break;

  		tret = blk_complete_sgv4_hdr_rq(bc->rq, &bc->hdr, bc->bio,
  						bc->bidi_bio);

  		if (!ret)
  			ret = tret;
  
  		bsg_free_command(bc);
  	} while (1);
  
  	return ret;
  }

  static int

  __bsg_read(char __user *buf, size_t count, struct bsg_device *bd,
  	   const struct iovec *iov, ssize_t *bytes_read)

  {
  	struct bsg_command *bc;
  	int nr_commands, ret;

  	if (count % sizeof(struct sg_io_v4))

  		return -EINVAL;
  
  	ret = 0;

  	nr_commands = count / sizeof(struct sg_io_v4);

  	while (nr_commands) {

  		bc = bsg_get_done_cmd(bd);

  		if (IS_ERR(bc)) {
  			ret = PTR_ERR(bc);
  			break;
  		}
  
  		/*
  		 * this is the only case where we need to copy data back
  		 * after completing the request. so do that here,
  		 * bsg_complete_work() cannot do that for us
  		 */

  		ret = blk_complete_sgv4_hdr_rq(bc->rq, &bc->hdr, bc->bio,
  					       bc->bidi_bio);

  		if (copy_to_user(buf, &bc->hdr, sizeof(bc->hdr)))

  			ret = -EFAULT;
  
  		bsg_free_command(bc);
  
  		if (ret)
  			break;

  		buf += sizeof(struct sg_io_v4);
  		*bytes_read += sizeof(struct sg_io_v4);

  		nr_commands--;
  	}
  
  	return ret;
  }
  
  static inline void bsg_set_block(struct bsg_device *bd, struct file *file)
  {
  	if (file->f_flags & O_NONBLOCK)
  		clear_bit(BSG_F_BLOCK, &bd->flags);
  	else
  		set_bit(BSG_F_BLOCK, &bd->flags);
  }

  /*
   * Check if the error is a "real" error that we should return.
   */

  static inline int err_block_err(int ret)
  {
  	if (ret && ret != -ENOSPC && ret != -ENODATA && ret != -EAGAIN)
  		return 1;
  
  	return 0;
  }
  
  static ssize_t
  bsg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
  {
  	struct bsg_device *bd = file->private_data;
  	int ret;
  	ssize_t bytes_read;

  	dprintk("%s: read %Zd bytes
  ", bd->name, count);

  
  	bsg_set_block(bd, file);

  	bytes_read = 0;

  	ret = __bsg_read(buf, count, bd, NULL, &bytes_read);

  	*ppos = bytes_read;
  
  	if (!bytes_read || (bytes_read && err_block_err(ret)))
  		bytes_read = ret;
  
  	return bytes_read;
  }

  static int __bsg_write(struct bsg_device *bd, const char __user *buf,

  		       size_t count, ssize_t *bytes_written,
  		       fmode_t has_write_perm)

  {
  	struct bsg_command *bc;
  	struct request *rq;
  	int ret, nr_commands;

  	if (count % sizeof(struct sg_io_v4))

  		return -EINVAL;

  	nr_commands = count / sizeof(struct sg_io_v4);

  	rq = NULL;
  	bc = NULL;
  	ret = 0;
  	while (nr_commands) {

  		struct request_queue *q = bd->queue;

  		bc = bsg_alloc_command(bd);

  		if (IS_ERR(bc)) {
  			ret = PTR_ERR(bc);
  			bc = NULL;
  			break;
  		}

  		if (copy_from_user(&bc->hdr, buf, sizeof(bc->hdr))) {
  			ret = -EFAULT;
  			break;
  		}
  
  		/*
  		 * get a request, fill in the blanks, and add to request queue
  		 */

  		rq = bsg_map_hdr(bd, &bc->hdr, has_write_perm, bc->sense);

  		if (IS_ERR(rq)) {
  			ret = PTR_ERR(rq);
  			rq = NULL;
  			break;
  		}
  
  		bsg_add_command(bd, q, bc, rq);
  		bc = NULL;
  		rq = NULL;
  		nr_commands--;

  		buf += sizeof(struct sg_io_v4);

  		*bytes_written += sizeof(struct sg_io_v4);

  	}

  	if (bc)
  		bsg_free_command(bc);
  
  	return ret;
  }
  
  static ssize_t
  bsg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
  {
  	struct bsg_device *bd = file->private_data;

  	ssize_t bytes_written;

  	int ret;

  	dprintk("%s: write %Zd bytes
  ", bd->name, count);

  
  	bsg_set_block(bd, file);

  	bytes_written = 0;

  	ret = __bsg_write(bd, buf, count, &bytes_written,
  			  file->f_mode & FMODE_WRITE);

  	*ppos = bytes_written;

  
  	/*
  	 * return bytes written on non-fatal errors
  	 */

  	if (!bytes_written || (bytes_written && err_block_err(ret)))
  		bytes_written = ret;

  	dprintk("%s: returning %Zd
  ", bd->name, bytes_written);
  	return bytes_written;

  }

  static struct bsg_device *bsg_alloc_device(void)
  {

  	struct bsg_device *bd;

  
  	bd = kzalloc(sizeof(struct bsg_device), GFP_KERNEL);
  	if (unlikely(!bd))
  		return NULL;
  
  	spin_lock_init(&bd->lock);

  	bd->max_queue = BSG_DEFAULT_CMDS;

  
  	INIT_LIST_HEAD(&bd->busy_list);
  	INIT_LIST_HEAD(&bd->done_list);
  	INIT_HLIST_NODE(&bd->dev_list);
  
  	init_waitqueue_head(&bd->wq_free);
  	init_waitqueue_head(&bd->wq_done);
  	return bd;

  }

  static void bsg_kref_release_function(struct kref *kref)
  {
  	struct bsg_class_device *bcd =
  		container_of(kref, struct bsg_class_device, ref);

  	struct device *parent = bcd->parent;

  
  	if (bcd->release)
  		bcd->release(bcd->parent);

  	put_device(parent);

  }

  static int bsg_put_device(struct bsg_device *bd)
  {

  	int ret = 0, do_free;
  	struct request_queue *q = bd->queue;

  
  	mutex_lock(&bsg_mutex);

  	do_free = atomic_dec_and_test(&bd->ref_count);

  	if (!do_free) {
  		mutex_unlock(&bsg_mutex);

  		goto out;

  	}
  
  	hlist_del(&bd->dev_list);
  	mutex_unlock(&bsg_mutex);

  
  	dprintk("%s: tearing down
  ", bd->name);
  
  	/*
  	 * close can always block
  	 */
  	set_bit(BSG_F_BLOCK, &bd->flags);
  
  	/*
  	 * correct error detection baddies here again. it's the responsibility
  	 * of the app to properly reap commands before close() if it wants
  	 * fool-proof error detection
  	 */
  	ret = bsg_complete_all_commands(bd);

  	kfree(bd);

  out:

  	kref_put(&q->bsg_dev.ref, bsg_kref_release_function);
  	if (do_free)
  		blk_put_queue(q);

  	return ret;
  }
  
  static struct bsg_device *bsg_add_device(struct inode *inode,

  					 struct request_queue *rq,

  					 struct file *file)
  {

  	struct bsg_device *bd;

  	int ret;

  #ifdef BSG_DEBUG
  	unsigned char buf[32];
  #endif

  	ret = blk_get_queue(rq);
  	if (ret)
  		return ERR_PTR(-ENXIO);

  
  	bd = bsg_alloc_device();

  	if (!bd) {
  		blk_put_queue(rq);

  		return ERR_PTR(-ENOMEM);

  	}

  	bd->queue = rq;

  	bsg_set_block(bd, file);
  
  	atomic_set(&bd->ref_count, 1);

  	mutex_lock(&bsg_mutex);

  	hlist_add_head(&bd->dev_list, bsg_dev_idx_hash(iminor(inode)));

  	strncpy(bd->name, dev_name(rq->bsg_dev.class_dev), sizeof(bd->name) - 1);

  	dprintk("bound to <%s>, max queue %d
  ",

  		format_dev_t(buf, inode->i_rdev), bd->max_queue);

  
  	mutex_unlock(&bsg_mutex);
  	return bd;
  }

  static struct bsg_device *__bsg_get_device(int minor, struct request_queue *q)

  {

  	struct bsg_device *bd;

  	struct hlist_node *entry;
  
  	mutex_lock(&bsg_mutex);

  	hlist_for_each_entry(bd, entry, bsg_dev_idx_hash(minor), dev_list) {

  		if (bd->queue == q) {

  			atomic_inc(&bd->ref_count);

  			goto found;

  		}

  	}

  	bd = NULL;
  found:

  	mutex_unlock(&bsg_mutex);
  	return bd;
  }
  
  static struct bsg_device *bsg_get_device(struct inode *inode, struct file *file)
  {

  	struct bsg_device *bd;
  	struct bsg_class_device *bcd;

  	/*
  	 * find the class device
  	 */

  	mutex_lock(&bsg_mutex);

  	bcd = idr_find(&bsg_minor_idr, iminor(inode));

  	if (bcd)

  		kref_get(&bcd->ref);

  	mutex_unlock(&bsg_mutex);
  
  	if (!bcd)
  		return ERR_PTR(-ENODEV);

  	bd = __bsg_get_device(iminor(inode), bcd->queue);

  	if (bd)
  		return bd;
  
  	bd = bsg_add_device(inode, bcd->queue, file);
  	if (IS_ERR(bd))

  		kref_put(&bcd->ref, bsg_kref_release_function);

  
  	return bd;

  }
  
  static int bsg_open(struct inode *inode, struct file *file)
  {

  	struct bsg_device *bd;
  
  	lock_kernel();
  	bd = bsg_get_device(inode, file);
  	unlock_kernel();

  
  	if (IS_ERR(bd))
  		return PTR_ERR(bd);
  
  	file->private_data = bd;
  	return 0;
  }
  
  static int bsg_release(struct inode *inode, struct file *file)
  {
  	struct bsg_device *bd = file->private_data;
  
  	file->private_data = NULL;
  	return bsg_put_device(bd);
  }
  
  static unsigned int bsg_poll(struct file *file, poll_table *wait)
  {
  	struct bsg_device *bd = file->private_data;
  	unsigned int mask = 0;
  
  	poll_wait(file, &bd->wq_done, wait);
  	poll_wait(file, &bd->wq_free, wait);
  
  	spin_lock_irq(&bd->lock);
  	if (!list_empty(&bd->done_list))
  		mask |= POLLIN | POLLRDNORM;
  	if (bd->queued_cmds >= bd->max_queue)
  		mask |= POLLOUT;
  	spin_unlock_irq(&bd->lock);
  
  	return mask;
  }

  static long bsg_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

  {
  	struct bsg_device *bd = file->private_data;
  	int __user *uarg = (int __user *) arg;

  	int ret;

  	switch (cmd) {
  		/*
  		 * our own ioctls
  		 */
  	case SG_GET_COMMAND_Q:
  		return put_user(bd->max_queue, uarg);

  	case SG_SET_COMMAND_Q: {

  		int queue;
  
  		if (get_user(queue, uarg))
  			return -EFAULT;

  		if (queue < 1)

  			return -EINVAL;

  		spin_lock_irq(&bd->lock);

  		bd->max_queue = queue;

  		spin_unlock_irq(&bd->lock);

  		return 0;
  	}
  
  	/*
  	 * SCSI/sg ioctls
  	 */
  	case SG_GET_VERSION_NUM:
  	case SCSI_IOCTL_GET_IDLUN:
  	case SCSI_IOCTL_GET_BUS_NUMBER:
  	case SG_SET_TIMEOUT:
  	case SG_GET_TIMEOUT:
  	case SG_GET_RESERVED_SIZE:
  	case SG_SET_RESERVED_SIZE:
  	case SG_EMULATED_HOST:

  	case SCSI_IOCTL_SEND_COMMAND: {
  		void __user *uarg = (void __user *) arg;

  		return scsi_cmd_ioctl(bd->queue, NULL, file->f_mode, cmd, uarg);

  	}

  	case SG_IO: {
  		struct request *rq;

  		struct bio *bio, *bidi_bio = NULL;

  		struct sg_io_v4 hdr;

  		int at_head;

  		u8 sense[SCSI_SENSE_BUFFERSIZE];

  
  		if (copy_from_user(&hdr, uarg, sizeof(hdr)))
  			return -EFAULT;

  		rq = bsg_map_hdr(bd, &hdr, file->f_mode & FMODE_WRITE, sense);

  		if (IS_ERR(rq))
  			return PTR_ERR(rq);
  
  		bio = rq->bio;

  		if (rq->next_rq)
  			bidi_bio = rq->next_rq->bio;

  
  		at_head = (0 == (hdr.flags & BSG_FLAG_Q_AT_TAIL));
  		blk_execute_rq(bd->queue, NULL, rq, at_head);

  		ret = blk_complete_sgv4_hdr_rq(rq, &hdr, bio, bidi_bio);

  
  		if (copy_to_user(uarg, &hdr, sizeof(hdr)))
  			return -EFAULT;

  		return ret;

  	}

  	/*
  	 * block device ioctls
  	 */
  	default:
  #if 0
  		return ioctl_by_bdev(bd->bdev, cmd, arg);
  #else
  		return -ENOTTY;
  #endif
  	}
  }

  static const struct file_operations bsg_fops = {

  	.read		=	bsg_read,
  	.write		=	bsg_write,
  	.poll		=	bsg_poll,
  	.open		=	bsg_open,
  	.release	=	bsg_release,

  	.unlocked_ioctl	=	bsg_ioctl,

  	.owner		=	THIS_MODULE,
  };

  void bsg_unregister_queue(struct request_queue *q)

  {

  	struct bsg_class_device *bcd = &q->bsg_dev;

  	if (!bcd->class_dev)
  		return;

  
  	mutex_lock(&bsg_mutex);

  	idr_remove(&bsg_minor_idr, bcd->minor);

  	sysfs_remove_link(&q->kobj, "bsg");

  	device_unregister(bcd->class_dev);

  	bcd->class_dev = NULL;

  	kref_put(&bcd->ref, bsg_kref_release_function);

  	mutex_unlock(&bsg_mutex);
  }

  EXPORT_SYMBOL_GPL(bsg_unregister_queue);

  int bsg_register_queue(struct request_queue *q, struct device *parent,
  		       const char *name, void (*release)(struct device *))

  {

  	struct bsg_class_device *bcd;

  	dev_t dev;

  	int ret, minor;

  	struct device *class_dev = NULL;

  	const char *devname;
  
  	if (name)
  		devname = name;
  	else

  		devname = dev_name(parent);

  
  	/*
  	 * we need a proper transport to send commands, not a stacked device
  	 */
  	if (!q->request_fn)
  		return 0;

  	bcd = &q->bsg_dev;

  	memset(bcd, 0, sizeof(*bcd));

  
  	mutex_lock(&bsg_mutex);

  	ret = idr_pre_get(&bsg_minor_idr, GFP_KERNEL);
  	if (!ret) {
  		ret = -ENOMEM;
  		goto unlock;

  	}

  	ret = idr_get_new(&bsg_minor_idr, bcd, &minor);
  	if (ret < 0)
  		goto unlock;

  	if (minor >= BSG_MAX_DEVS) {
  		printk(KERN_ERR "bsg: too many bsg devices
  ");
  		ret = -EINVAL;
  		goto remove_idr;
  	}
  
  	bcd->minor = minor;

  	bcd->queue = q;

  	bcd->parent = get_device(parent);
  	bcd->release = release;
  	kref_init(&bcd->ref);

  	dev = MKDEV(bsg_major, bcd->minor);

  	class_dev = device_create(bsg_class, parent, dev, NULL, "%s", devname);

  	if (IS_ERR(class_dev)) {
  		ret = PTR_ERR(class_dev);

  		goto put_dev;

  	}
  	bcd->class_dev = class_dev;

  	if (q->kobj.sd) {

  		ret = sysfs_create_link(&q->kobj, &bcd->class_dev->kobj, "bsg");
  		if (ret)

  			goto unregister_class_dev;

  	}

  	mutex_unlock(&bsg_mutex);
  	return 0;

  unregister_class_dev:

  	device_unregister(class_dev);

  put_dev:

  	put_device(parent);

  remove_idr:
  	idr_remove(&bsg_minor_idr, minor);
  unlock:

  	mutex_unlock(&bsg_mutex);

  	return ret;
  }

  EXPORT_SYMBOL_GPL(bsg_register_queue);

  static struct cdev bsg_cdev;

  static char *bsg_nodename(struct device *dev)
  {
  	return kasprintf(GFP_KERNEL, "bsg/%s", dev_name(dev));
  }

  static int __init bsg_init(void)
  {
  	int ret, i;

  	dev_t devid;

  	bsg_cmd_cachep = kmem_cache_create("bsg_cmd",

  				sizeof(struct bsg_command), 0, 0, NULL);

  	if (!bsg_cmd_cachep) {
  		printk(KERN_ERR "bsg: failed creating slab cache
  ");
  		return -ENOMEM;
  	}

  	for (i = 0; i < BSG_LIST_ARRAY_SIZE; i++)

  		INIT_HLIST_HEAD(&bsg_device_list[i]);
  
  	bsg_class = class_create(THIS_MODULE, "bsg");

  	if (IS_ERR(bsg_class)) {

  		ret = PTR_ERR(bsg_class);
  		goto destroy_kmemcache;

  	}

  	bsg_class->nodename = bsg_nodename;

  	ret = alloc_chrdev_region(&devid, 0, BSG_MAX_DEVS, "bsg");

  	if (ret)
  		goto destroy_bsg_class;

  	bsg_major = MAJOR(devid);

  	cdev_init(&bsg_cdev, &bsg_fops);

  	ret = cdev_add(&bsg_cdev, MKDEV(bsg_major, 0), BSG_MAX_DEVS);

  	if (ret)
  		goto unregister_chrdev;

  	printk(KERN_INFO BSG_DESCRIPTION " version " BSG_VERSION

  	       " loaded (major %d)
  ", bsg_major);

  	return 0;

  unregister_chrdev:
  	unregister_chrdev_region(MKDEV(bsg_major, 0), BSG_MAX_DEVS);
  destroy_bsg_class:
  	class_destroy(bsg_class);
  destroy_kmemcache:
  	kmem_cache_destroy(bsg_cmd_cachep);
  	return ret;

  }
  
  MODULE_AUTHOR("Jens Axboe");

  MODULE_DESCRIPTION(BSG_DESCRIPTION);

  MODULE_LICENSE("GPL");

  device_initcall(bsg_init);