/*
   *  scsi.c Copyright (C) 1992 Drew Eckhardt
   *         Copyright (C) 1993, 1994, 1995, 1999 Eric Youngdale
   *         Copyright (C) 2002, 2003 Christoph Hellwig
   *
   *  generic mid-level SCSI driver
   *      Initial versions: Drew Eckhardt
   *      Subsequent revisions: Eric Youngdale
   *
   *  <drew@colorado.edu>
   *
   *  Bug correction thanks go to :
   *      Rik Faith <faith@cs.unc.edu>
   *      Tommy Thorn <tthorn>
   *      Thomas Wuensche <tw@fgb1.fgb.mw.tu-muenchen.de>
   *
   *  Modified by Eric Youngdale eric@andante.org or ericy@gnu.ai.mit.edu to
   *  add scatter-gather, multiple outstanding request, and other
   *  enhancements.
   *
   *  Native multichannel, wide scsi, /proc/scsi and hot plugging
   *  support added by Michael Neuffer <mike@i-connect.net>
   *
   *  Added request_module("scsi_hostadapter") for kerneld:
   *  (Put an "alias scsi_hostadapter your_hostadapter" in /etc/modprobe.conf)
   *  Bjorn Ekwall  <bj0rn@blox.se>
   *  (changed to kmod)
   *
   *  Major improvements to the timeout, abort, and reset processing,
   *  as well as performance modifications for large queue depths by
   *  Leonard N. Zubkoff <lnz@dandelion.com>
   *
   *  Converted cli() code to spinlocks, Ingo Molnar
   *
   *  Jiffies wrap fixes (host->resetting), 3 Dec 1998 Andrea Arcangeli
   *
   *  out_of_space hacks, D. Gilbert (dpg) 990608
   */
  
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/kernel.h>

  #include <linux/timer.h>
  #include <linux/string.h>
  #include <linux/slab.h>
  #include <linux/blkdev.h>
  #include <linux/delay.h>
  #include <linux/init.h>
  #include <linux/completion.h>

  #include <linux/unistd.h>
  #include <linux/spinlock.h>
  #include <linux/kmod.h>
  #include <linux/interrupt.h>
  #include <linux/notifier.h>
  #include <linux/cpu.h>

  #include <linux/mutex.h>

  #include <linux/async.h>

  #include <asm/unaligned.h>

  
  #include <scsi/scsi.h>
  #include <scsi/scsi_cmnd.h>
  #include <scsi/scsi_dbg.h>
  #include <scsi/scsi_device.h>

  #include <scsi/scsi_driver.h>

  #include <scsi/scsi_eh.h>
  #include <scsi/scsi_host.h>
  #include <scsi/scsi_tcq.h>

  
  #include "scsi_priv.h"
  #include "scsi_logging.h"

  #define CREATE_TRACE_POINTS
  #include <trace/events/scsi.h>

  /*
   * Definitions and constants.
   */

  /*

   * Note - the initial logging level can be set here to log events at boot time.
   * After the system is up, you may enable logging via the /proc interface.
   */
  unsigned int scsi_logging_level;
  #if defined(CONFIG_SCSI_LOGGING)
  EXPORT_SYMBOL(scsi_logging_level);
  #endif

  /* sd, scsi core and power management need to coordinate flushing async actions */

  ASYNC_DOMAIN(scsi_sd_probe_domain);

  EXPORT_SYMBOL(scsi_sd_probe_domain);

  /*
   * Separate domain (from scsi_sd_probe_domain) to maximize the benefit of
   * asynchronous system resume operations.  It is marked 'exclusive' to avoid
   * being included in the async_synchronize_full() that is invoked by
   * dpm_resume()
   */
  ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain);
  EXPORT_SYMBOL(scsi_sd_pm_domain);

  struct scsi_host_cmd_pool {

  	struct kmem_cache	*cmd_slab;
  	struct kmem_cache	*sense_slab;
  	unsigned int		users;
  	char			*cmd_name;
  	char			*sense_name;
  	unsigned int		slab_flags;
  	gfp_t			gfp_mask;

  };
  
  static struct scsi_host_cmd_pool scsi_cmd_pool = {

  	.cmd_name	= "scsi_cmd_cache",
  	.sense_name	= "scsi_sense_cache",

  	.slab_flags	= SLAB_HWCACHE_ALIGN,
  };
  
  static struct scsi_host_cmd_pool scsi_cmd_dma_pool = {

  	.cmd_name	= "scsi_cmd_cache(DMA)",
  	.sense_name	= "scsi_sense_cache(DMA)",

  	.slab_flags	= SLAB_HWCACHE_ALIGN|SLAB_CACHE_DMA,
  	.gfp_mask	= __GFP_DMA,
  };

  static DEFINE_MUTEX(host_cmd_pool_mutex);

  /**

   * scsi_host_free_command - internal function to release a command
   * @shost:	host to free the command for

   * @cmd:	command to release
   *
   * the command must previously have been allocated by

   * scsi_host_alloc_command.

   */
  static void

  scsi_host_free_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd)

  {

  	struct scsi_host_cmd_pool *pool = shost->cmd_pool;

  	if (cmd->prot_sdb)
  		kmem_cache_free(scsi_sdb_cache, cmd->prot_sdb);

  	kmem_cache_free(pool->sense_slab, cmd->sense_buffer);
  	kmem_cache_free(pool->cmd_slab, cmd);
  }
  
  /**

   * scsi_host_alloc_command - internal function to allocate command
   * @shost:	SCSI host whose pool to allocate from
   * @gfp_mask:	mask for the allocation
   *
   * Returns a fully allocated command with sense buffer and protection
   * data buffer (where applicable) or NULL on failure
   */
  static struct scsi_cmnd *
  scsi_host_alloc_command(struct Scsi_Host *shost, gfp_t gfp_mask)
  {

  	struct scsi_host_cmd_pool *pool = shost->cmd_pool;

  	struct scsi_cmnd *cmd;

  	cmd = kmem_cache_zalloc(pool->cmd_slab, gfp_mask | pool->gfp_mask);

  	if (!cmd)

  		goto fail;
  
  	cmd->sense_buffer = kmem_cache_alloc(pool->sense_slab,
  					     gfp_mask | pool->gfp_mask);
  	if (!cmd->sense_buffer)
  		goto fail_free_cmd;

  
  	if (scsi_host_get_prot(shost) >= SHOST_DIX_TYPE0_PROTECTION) {
  		cmd->prot_sdb = kmem_cache_zalloc(scsi_sdb_cache, gfp_mask);

  		if (!cmd->prot_sdb)
  			goto fail_free_sense;

  	}
  
  	return cmd;

  
  fail_free_sense:
  	kmem_cache_free(pool->sense_slab, cmd->sense_buffer);
  fail_free_cmd:
  	kmem_cache_free(pool->cmd_slab, cmd);
  fail:
  	return NULL;

  }
  
  /**

   * __scsi_get_command - Allocate a struct scsi_cmnd
   * @shost: host to transmit command
   * @gfp_mask: allocation mask
   *
   * Description: allocate a struct scsi_cmd from host's slab, recycling from the
   *              host's free_list if necessary.
   */

  static struct scsi_cmnd *
  __scsi_get_command(struct Scsi_Host *shost, gfp_t gfp_mask)

  {

  	struct scsi_cmnd *cmd = scsi_host_alloc_command(shost, gfp_mask);

  	if (unlikely(!cmd)) {
  		unsigned long flags;
  
  		spin_lock_irqsave(&shost->free_list_lock, flags);
  		if (likely(!list_empty(&shost->free_list))) {
  			cmd = list_entry(shost->free_list.next,
  					 struct scsi_cmnd, list);
  			list_del_init(&cmd->list);
  		}
  		spin_unlock_irqrestore(&shost->free_list_lock, flags);

  
  		if (cmd) {

  			void *buf, *prot;

  			buf = cmd->sense_buffer;

  			prot = cmd->prot_sdb;

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

  			cmd->sense_buffer = buf;

  			cmd->prot_sdb = prot;

  		}

  	}
  
  	return cmd;
  }

  /**
   * scsi_get_command - Allocate and setup a scsi command block
   * @dev: parent scsi device
   * @gfp_mask: allocator flags

   *
   * Returns:	The allocated scsi command structure.
   */

  struct scsi_cmnd *scsi_get_command(struct scsi_device *dev, gfp_t gfp_mask)

  {

  	struct scsi_cmnd *cmd = __scsi_get_command(dev->host, gfp_mask);
  	unsigned long flags;

  	if (unlikely(cmd == NULL))

  		return NULL;

  	cmd->device = dev;
  	INIT_LIST_HEAD(&cmd->list);
  	INIT_DELAYED_WORK(&cmd->abort_work, scmd_eh_abort_handler);
  	spin_lock_irqsave(&dev->list_lock, flags);
  	list_add_tail(&cmd->list, &dev->cmd_list);
  	spin_unlock_irqrestore(&dev->list_lock, flags);
  	cmd->jiffies_at_alloc = jiffies;

  	return cmd;

  }

  /**
   * __scsi_put_command - Free a struct scsi_cmnd
   * @shost: dev->host
   * @cmd: Command to free

   */

  static void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd)

  {
  	unsigned long flags;

  	if (unlikely(list_empty(&shost->free_list))) {

  		spin_lock_irqsave(&shost->free_list_lock, flags);
  		if (list_empty(&shost->free_list)) {
  			list_add(&cmd->list, &shost->free_list);
  			cmd = NULL;
  		}
  		spin_unlock_irqrestore(&shost->free_list_lock, flags);

  	}

  	if (likely(cmd != NULL))

  		scsi_host_free_command(shost, cmd);

  }

  /**
   * scsi_put_command - Free a scsi command block
   * @cmd: command block to free

   *
   * Returns:	Nothing.
   *
   * Notes:	The command must not belong to any lists.
   */
  void scsi_put_command(struct scsi_cmnd *cmd)
  {

  	unsigned long flags;

  	/* serious error if the command hasn't come from a device list */
  	spin_lock_irqsave(&cmd->device->list_lock, flags);
  	BUG_ON(list_empty(&cmd->list));
  	list_del_init(&cmd->list);

  	spin_unlock_irqrestore(&cmd->device->list_lock, flags);

  	BUG_ON(delayed_work_pending(&cmd->abort_work));

  	__scsi_put_command(cmd->device->host, cmd);

  }

  static struct scsi_host_cmd_pool *
  scsi_find_host_cmd_pool(struct Scsi_Host *shost)

  {

  	if (shost->hostt->cmd_size)
  		return shost->hostt->cmd_pool;
  	if (shost->unchecked_isa_dma)
  		return &scsi_cmd_dma_pool;
  	return &scsi_cmd_pool;
  }
  
  static void
  scsi_free_host_cmd_pool(struct scsi_host_cmd_pool *pool)
  {
  	kfree(pool->sense_name);
  	kfree(pool->cmd_name);
  	kfree(pool);
  }
  
  static struct scsi_host_cmd_pool *
  scsi_alloc_host_cmd_pool(struct Scsi_Host *shost)
  {
  	struct scsi_host_template *hostt = shost->hostt;
  	struct scsi_host_cmd_pool *pool;
  
  	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
  	if (!pool)
  		return NULL;

  	pool->cmd_name = kasprintf(GFP_KERNEL, "%s_cmd", hostt->proc_name);
  	pool->sense_name = kasprintf(GFP_KERNEL, "%s_sense", hostt->proc_name);

  	if (!pool->cmd_name || !pool->sense_name) {
  		scsi_free_host_cmd_pool(pool);
  		return NULL;
  	}
  
  	pool->slab_flags = SLAB_HWCACHE_ALIGN;
  	if (shost->unchecked_isa_dma) {
  		pool->slab_flags |= SLAB_CACHE_DMA;
  		pool->gfp_mask = __GFP_DMA;
  	}

  
  	if (hostt->cmd_size)
  		hostt->cmd_pool = pool;

  	return pool;
  }
  
  static struct scsi_host_cmd_pool *
  scsi_get_host_cmd_pool(struct Scsi_Host *shost)
  {
  	struct scsi_host_template *hostt = shost->hostt;

  	struct scsi_host_cmd_pool *retval = NULL, *pool;

  	size_t cmd_size = sizeof(struct scsi_cmnd) + hostt->cmd_size;

  	/*
  	 * Select a command slab for this host and create it if not

  	 * yet existent.

  	 */

  	mutex_lock(&host_cmd_pool_mutex);

  	pool = scsi_find_host_cmd_pool(shost);
  	if (!pool) {
  		pool = scsi_alloc_host_cmd_pool(shost);
  		if (!pool)
  			goto out;
  	}

  	if (!pool->users) {

  		pool->cmd_slab = kmem_cache_create(pool->cmd_name, cmd_size, 0,

  						   pool->slab_flags, NULL);
  		if (!pool->cmd_slab)

  			goto out_free_pool;

  
  		pool->sense_slab = kmem_cache_create(pool->sense_name,
  						     SCSI_SENSE_BUFFERSIZE, 0,
  						     pool->slab_flags, NULL);

  		if (!pool->sense_slab)
  			goto out_free_slab;

  	}
  
  	pool->users++;

  	retval = pool;

  out:

  	mutex_unlock(&host_cmd_pool_mutex);

  	return retval;

  
  out_free_slab:
  	kmem_cache_destroy(pool->cmd_slab);
  out_free_pool:

  	if (hostt->cmd_size) {

  		scsi_free_host_cmd_pool(pool);

  		hostt->cmd_pool = NULL;
  	}

  	goto out;

  }

  static void scsi_put_host_cmd_pool(struct Scsi_Host *shost)

  {

  	struct scsi_host_template *hostt = shost->hostt;

  	struct scsi_host_cmd_pool *pool;

  	mutex_lock(&host_cmd_pool_mutex);

  	pool = scsi_find_host_cmd_pool(shost);

  	/*

  	 * This may happen if a driver has a mismatched get and put
  	 * of the command pool; the driver should be implicated in
  	 * the stack trace

  	 */

  	BUG_ON(pool->users == 0);

  	if (!--pool->users) {
  		kmem_cache_destroy(pool->cmd_slab);
  		kmem_cache_destroy(pool->sense_slab);

  		if (hostt->cmd_size) {

  			scsi_free_host_cmd_pool(pool);

  			hostt->cmd_pool = NULL;
  		}

  	}

  	mutex_unlock(&host_cmd_pool_mutex);

  }
  
  /**

   * scsi_setup_command_freelist - Setup the command freelist for a scsi host.
   * @shost: host to allocate the freelist for.
   *
   * Description: The command freelist protects against system-wide out of memory
   * deadlock by preallocating one SCSI command structure for each host, so the
   * system can always write to a swap file on a device associated with that host.
   *
   * Returns:	Nothing.
   */
  int scsi_setup_command_freelist(struct Scsi_Host *shost)
  {

  	const gfp_t gfp_mask = shost->unchecked_isa_dma ? GFP_DMA : GFP_KERNEL;

  	struct scsi_cmnd *cmd;

  
  	spin_lock_init(&shost->free_list_lock);
  	INIT_LIST_HEAD(&shost->free_list);

  	shost->cmd_pool = scsi_get_host_cmd_pool(shost);

  	if (!shost->cmd_pool)
  		return -ENOMEM;
  
  	/*
  	 * Get one backup command for this host.
  	 */

  	cmd = scsi_host_alloc_command(shost, gfp_mask);

  	if (!cmd) {

  		scsi_put_host_cmd_pool(shost);

  		shost->cmd_pool = NULL;

  		return -ENOMEM;
  	}
  	list_add(&cmd->list, &shost->free_list);
  	return 0;

  }

  /**
   * scsi_destroy_command_freelist - Release the command freelist for a scsi host.
   * @shost: host whose freelist is going to be destroyed

   */
  void scsi_destroy_command_freelist(struct Scsi_Host *shost)
  {

  	/*
  	 * If cmd_pool is NULL the free list was not initialized, so
  	 * do not attempt to release resources.
  	 */
  	if (!shost->cmd_pool)
  		return;

  	while (!list_empty(&shost->free_list)) {
  		struct scsi_cmnd *cmd;
  
  		cmd = list_entry(shost->free_list.next, struct scsi_cmnd, list);
  		list_del_init(&cmd->list);

  		scsi_host_free_command(shost, cmd);

  	}

  	shost->cmd_pool = NULL;

  	scsi_put_host_cmd_pool(shost);

  }

  #ifdef CONFIG_SCSI_LOGGING
  void scsi_log_send(struct scsi_cmnd *cmd)
  {
  	unsigned int level;

  
  	/*
  	 * If ML QUEUE log level is greater than or equal to:
  	 *
  	 * 1: nothing (match completion)
  	 *

  	 * 2: log opcode + command of all commands + cmd address

  	 *

  	 * 3: same as 2

  	 *

  	 * 4: same as 3

  	 */
  	if (unlikely(scsi_logging_level)) {
  		level = SCSI_LOG_LEVEL(SCSI_LOG_MLQUEUE_SHIFT,
  				       SCSI_LOG_MLQUEUE_BITS);
  		if (level > 1) {

  			scmd_printk(KERN_INFO, cmd,
  				    "Send: scmd 0x%p
  ", cmd);

  			scsi_print_command(cmd);

  		}
  	}
  }
  
  void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
  {
  	unsigned int level;

  
  	/*
  	 * If ML COMPLETE log level is greater than or equal to:
  	 *
  	 * 1: log disposition, result, opcode + command, and conditionally
  	 * sense data for failures or non SUCCESS dispositions.
  	 *
  	 * 2: same as 1 but for all command completions.
  	 *

  	 * 3: same as 2

  	 *
  	 * 4: same as 3 plus dump extra junk
  	 */
  	if (unlikely(scsi_logging_level)) {
  		level = SCSI_LOG_LEVEL(SCSI_LOG_MLCOMPLETE_SHIFT,
  				       SCSI_LOG_MLCOMPLETE_BITS);
  		if (((level > 0) && (cmd->result || disposition != SUCCESS)) ||
  		    (level > 1)) {

  			scsi_print_result(cmd, "Done", disposition);

  			scsi_print_command(cmd);

  			if (status_byte(cmd->result) & CHECK_CONDITION)

  				scsi_print_sense(cmd);

  			if (level > 3)
  				scmd_printk(KERN_INFO, cmd,
  					    "scsi host busy %d failed %d
  ",

  					    atomic_read(&cmd->device->host->host_busy),

  					    cmd->device->host->host_failed);

  		}
  	}
  }
  #endif

  /**
   * scsi_cmd_get_serial - Assign a serial number to a command
   * @host: the scsi host
   * @cmd: command to assign serial number to
   *
   * Description: a serial number identifies a request for error recovery

   * and debugging purposes.  Protected by the Host_Lock of host.
   */

  void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)

  {
  	cmd->serial_number = host->cmd_serial_number++;
  	if (cmd->serial_number == 0) 
  		cmd->serial_number = host->cmd_serial_number++;

  }

  EXPORT_SYMBOL(scsi_cmd_get_serial);

  /**

   * scsi_finish_command - cleanup and pass command back to upper layer
   * @cmd: the command

   *

   * Description: Pass command off to upper layer for finishing of I/O

   *              request, waking processes that are waiting on results,
   *              etc.
   */
  void scsi_finish_command(struct scsi_cmnd *cmd)
  {
  	struct scsi_device *sdev = cmd->device;

  	struct scsi_target *starget = scsi_target(sdev);

  	struct Scsi_Host *shost = sdev->host;

  	struct scsi_driver *drv;
  	unsigned int good_bytes;

  
  	scsi_device_unbusy(sdev);

  	/*
  	 * Clear the flags that say that the device/target/host is no longer
  	 * capable of accepting new commands.
  	 */
  	if (atomic_read(&shost->host_blocked))
  		atomic_set(&shost->host_blocked, 0);
  	if (atomic_read(&starget->target_blocked))
  		atomic_set(&starget->target_blocked, 0);
  	if (atomic_read(&sdev->device_blocked))
  		atomic_set(&sdev->device_blocked, 0);

  
  	/*
  	 * If we have valid sense information, then some kind of recovery
  	 * must have taken place.  Make a note of this.
  	 */
  	if (SCSI_SENSE_VALID(cmd))
  		cmd->result |= (DRIVER_SENSE << 24);

  	SCSI_LOG_MLCOMPLETE(4, sdev_printk(KERN_INFO, sdev,
  				"Notifying upper driver of completion "
  				"(result %x)
  ", cmd->result));

  	good_bytes = scsi_bufflen(cmd);

          if (cmd->request->cmd_type != REQ_TYPE_BLOCK_PC) {

  		int old_good_bytes = good_bytes;

  		drv = scsi_cmd_to_driver(cmd);
  		if (drv->done)
  			good_bytes = drv->done(cmd);

  		/*
  		 * USB may not give sense identifying bad sector and
  		 * simply return a residue instead, so subtract off the
  		 * residue if drv->done() error processing indicates no
  		 * change to the completion length.
  		 */
  		if (good_bytes == old_good_bytes)
  			good_bytes -= scsi_get_resid(cmd);

  	}
  	scsi_io_completion(cmd, good_bytes);

  }

  /**

   * scsi_change_queue_depth - change a device's queue depth

   * @sdev: SCSI Device in question

   * @depth: number of commands allowed to be queued to the driver

   *

   * Sets the device queue depth and returns the new value.

   */

  int scsi_change_queue_depth(struct scsi_device *sdev, int depth)

  {

  	if (depth > 0) {
  		sdev->queue_depth = depth;
  		wmb();

  	}

  	return sdev->queue_depth;

  }

  EXPORT_SYMBOL(scsi_change_queue_depth);

  /**
   * scsi_track_queue_full - track QUEUE_FULL events to adjust queue depth
   * @sdev: SCSI Device in question
   * @depth: Current number of outstanding SCSI commands on this device,
   *         not counting the one returned as QUEUE_FULL.

   *

   * Description:	This function will track successive QUEUE_FULL events on a

   * 		specific SCSI device to determine if and when there is a
   * 		need to adjust the queue depth on the device.
   *

   * Returns:	0 - No change needed, >0 - Adjust queue depth to this new depth,

   * 		-1 - Drop back to untagged operation using host->cmd_per_lun
   * 			as the untagged command depth
   *
   * Lock Status:	None held on entry
   *
   * Notes:	Low level drivers may call this at any time and we will do
   * 		"The Right Thing."  We are interrupt context safe.
   */
  int scsi_track_queue_full(struct scsi_device *sdev, int depth)
  {

  
  	/*
  	 * Don't let QUEUE_FULLs on the same
  	 * jiffies count, they could all be from
  	 * same event.
  	 */
  	if ((jiffies >> 4) == (sdev->last_queue_full_time >> 4))

  		return 0;

  	sdev->last_queue_full_time = jiffies;

  	if (sdev->last_queue_full_depth != depth) {
  		sdev->last_queue_full_count = 1;
  		sdev->last_queue_full_depth = depth;
  	} else {
  		sdev->last_queue_full_count++;
  	}
  
  	if (sdev->last_queue_full_count <= 10)
  		return 0;

  	return scsi_change_queue_depth(sdev, depth);

  }
  EXPORT_SYMBOL(scsi_track_queue_full);
  
  /**

   * scsi_vpd_inquiry - Request a device provide us with a VPD page
   * @sdev: The device to ask
   * @buffer: Where to put the result
   * @page: Which Vital Product Data to return
   * @len: The length of the buffer
   *
   * This is an internal helper function.  You probably want to use
   * scsi_get_vpd_page instead.
   *

   * Returns size of the vpd page on success or a negative error number.

   */
  static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
  							u8 page, unsigned len)
  {
  	int result;
  	unsigned char cmd[16];

  	if (len < 4)
  		return -EINVAL;

  	cmd[0] = INQUIRY;
  	cmd[1] = 1;		/* EVPD */
  	cmd[2] = page;
  	cmd[3] = len >> 8;
  	cmd[4] = len & 0xff;
  	cmd[5] = 0;		/* Control byte */
  
  	/*
  	 * I'm not convinced we need to try quite this hard to get VPD, but
  	 * all the existing users tried this hard.
  	 */
  	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,

  				  len, NULL, 30 * HZ, 3, NULL);

  	if (result)

  		return -EIO;

  
  	/* Sanity check that we got the page back that we asked for */
  	if (buffer[1] != page)
  		return -EIO;

  	return get_unaligned_be16(&buffer[2]) + 4;

  }
  
  /**
   * scsi_get_vpd_page - Get Vital Product Data from a SCSI device
   * @sdev: The device to ask
   * @page: Which Vital Product Data to return

   * @buf: where to store the VPD
   * @buf_len: number of bytes in the VPD buffer area

   *
   * SCSI devices may optionally supply Vital Product Data.  Each 'page'
   * of VPD is defined in the appropriate SCSI document (eg SPC, SBC).
   * If the device supports this VPD page, this routine returns a pointer
   * to a buffer containing the data from that page.  The caller is
   * responsible for calling kfree() on this pointer when it is no longer
   * needed.  If we cannot retrieve the VPD page this routine returns %NULL.
   */

  int scsi_get_vpd_page(struct scsi_device *sdev, u8 page, unsigned char *buf,
  		      int buf_len)

  {
  	int i, result;

  	if (sdev->skip_vpd_pages)
  		goto fail;

  	/* Ask for all the pages supported by this device */

  	result = scsi_vpd_inquiry(sdev, buf, 0, buf_len);

  	if (result < 4)

  		goto fail;
  
  	/* If the user actually wanted this page, we can skip the rest */
  	if (page == 0)

  		return 0;

  	for (i = 4; i < min(result, buf_len); i++)
  		if (buf[i] == page)

  			goto found;

  	if (i < result && i >= buf_len)

  		/* ran off the end of the buffer, give us benefit of doubt */
  		goto found;

  	/* The device claims it doesn't support the requested page */
  	goto fail;
  
   found:

  	result = scsi_vpd_inquiry(sdev, buf, page, buf_len);

  	if (result < 0)

  		goto fail;

  	return 0;

  
   fail:

  	return -EINVAL;

  }
  EXPORT_SYMBOL_GPL(scsi_get_vpd_page);
  
  /**

   * scsi_attach_vpd - Attach Vital Product Data to a SCSI device structure
   * @sdev: The device to ask
   *
   * Attach the 'Device Identification' VPD page (0x83) and the
   * 'Unit Serial Number' VPD page (0x80) to a SCSI device
   * structure. This information can be used to identify the device
   * uniquely.
   */
  void scsi_attach_vpd(struct scsi_device *sdev)
  {
  	int result, i;
  	int vpd_len = SCSI_VPD_PG_LEN;
  	int pg80_supported = 0;
  	int pg83_supported = 0;

  	unsigned char __rcu *vpd_buf, *orig_vpd_buf = NULL;

  
  	if (sdev->skip_vpd_pages)
  		return;
  retry_pg0:
  	vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
  	if (!vpd_buf)
  		return;
  
  	/* Ask for all the pages supported by this device */
  	result = scsi_vpd_inquiry(sdev, vpd_buf, 0, vpd_len);
  	if (result < 0) {
  		kfree(vpd_buf);
  		return;
  	}
  	if (result > vpd_len) {
  		vpd_len = result;
  		kfree(vpd_buf);
  		goto retry_pg0;
  	}
  
  	for (i = 4; i < result; i++) {
  		if (vpd_buf[i] == 0x80)
  			pg80_supported = 1;
  		if (vpd_buf[i] == 0x83)
  			pg83_supported = 1;
  	}
  	kfree(vpd_buf);
  	vpd_len = SCSI_VPD_PG_LEN;
  
  	if (pg80_supported) {
  retry_pg80:
  		vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
  		if (!vpd_buf)
  			return;
  
  		result = scsi_vpd_inquiry(sdev, vpd_buf, 0x80, vpd_len);
  		if (result < 0) {
  			kfree(vpd_buf);
  			return;
  		}
  		if (result > vpd_len) {
  			vpd_len = result;
  			kfree(vpd_buf);
  			goto retry_pg80;
  		}

  		mutex_lock(&sdev->inquiry_mutex);
  		orig_vpd_buf = sdev->vpd_pg80;

  		sdev->vpd_pg80_len = result;

  		rcu_assign_pointer(sdev->vpd_pg80, vpd_buf);
  		mutex_unlock(&sdev->inquiry_mutex);
  		synchronize_rcu();
  		if (orig_vpd_buf) {
  			kfree(orig_vpd_buf);
  			orig_vpd_buf = NULL;
  		}

  		vpd_len = SCSI_VPD_PG_LEN;
  	}
  
  	if (pg83_supported) {
  retry_pg83:
  		vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
  		if (!vpd_buf)
  			return;
  
  		result = scsi_vpd_inquiry(sdev, vpd_buf, 0x83, vpd_len);
  		if (result < 0) {
  			kfree(vpd_buf);
  			return;
  		}
  		if (result > vpd_len) {
  			vpd_len = result;
  			kfree(vpd_buf);
  			goto retry_pg83;
  		}

  		mutex_lock(&sdev->inquiry_mutex);
  		orig_vpd_buf = sdev->vpd_pg83;

  		sdev->vpd_pg83_len = result;

  		rcu_assign_pointer(sdev->vpd_pg83, vpd_buf);
  		mutex_unlock(&sdev->inquiry_mutex);
  		synchronize_rcu();
  		if (orig_vpd_buf)
  			kfree(orig_vpd_buf);

  	}
  }
  
  /**

   * scsi_report_opcode - Find out if a given command opcode is supported
   * @sdev:	scsi device to query
   * @buffer:	scratch buffer (must be at least 20 bytes long)
   * @len:	length of buffer
   * @opcode:	opcode for command to look up
   *
   * Uses the REPORT SUPPORTED OPERATION CODES to look up the given

   * opcode. Returns -EINVAL if RSOC fails, 0 if the command opcode is
   * unsupported and 1 if the device claims to support the command.

   */
  int scsi_report_opcode(struct scsi_device *sdev, unsigned char *buffer,
  		       unsigned int len, unsigned char opcode)
  {
  	unsigned char cmd[16];
  	struct scsi_sense_hdr sshdr;
  	int result;
  
  	if (sdev->no_report_opcodes || sdev->scsi_level < SCSI_SPC_3)

  		return -EINVAL;

  
  	memset(cmd, 0, 16);
  	cmd[0] = MAINTENANCE_IN;
  	cmd[1] = MI_REPORT_SUPPORTED_OPERATION_CODES;
  	cmd[2] = 1;		/* One command format */
  	cmd[3] = opcode;
  	put_unaligned_be32(len, &cmd[6]);
  	memset(buffer, 0, len);
  
  	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer, len,
  				  &sshdr, 30 * HZ, 3, NULL);
  
  	if (result && scsi_sense_valid(&sshdr) &&
  	    sshdr.sense_key == ILLEGAL_REQUEST &&
  	    (sshdr.asc == 0x20 || sshdr.asc == 0x24) && sshdr.ascq == 0x00)

  		return -EINVAL;

  
  	if ((buffer[1] & 3) == 3) /* Command supported */
  		return 1;
  
  	return 0;
  }
  EXPORT_SYMBOL(scsi_report_opcode);
  
  /**

   * scsi_device_get  -  get an additional reference to a scsi_device

   * @sdev:	device to get a reference to
   *

   * Description: Gets a reference to the scsi_device and increments the use count

   * of the underlying LLDD module.  You must hold host_lock of the
   * parent Scsi_Host or already have a reference when calling this.

   *
   * This will fail if a device is deleted or cancelled, or when the LLD module
   * is in the process of being unloaded.

   */
  int scsi_device_get(struct scsi_device *sdev)
  {

  	if (sdev->sdev_state == SDEV_DEL || sdev->sdev_state == SDEV_CANCEL)
  		goto fail;

  	if (!get_device(&sdev->sdev_gendev))

  		goto fail;
  	if (!try_module_get(sdev->host->hostt->module))
  		goto fail_put_device;

  	return 0;

  
  fail_put_device:
  	put_device(&sdev->sdev_gendev);
  fail:
  	return -ENXIO;

  }
  EXPORT_SYMBOL(scsi_device_get);
  
  /**
   * scsi_device_put  -  release a reference to a scsi_device
   * @sdev:	device to release a reference on.
   *

   * Description: Release a reference to the scsi_device and decrements the use
   * count of the underlying LLDD module.  The device is freed once the last

   * user vanishes.
   */
  void scsi_device_put(struct scsi_device *sdev)
  {

  	module_put(sdev->host->hostt->module);

  	put_device(&sdev->sdev_gendev);
  }
  EXPORT_SYMBOL(scsi_device_put);

  /* helper for shost_for_each_device, see that for documentation */

  struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
  					   struct scsi_device *prev)
  {
  	struct list_head *list = (prev ? &prev->siblings : &shost->__devices);
  	struct scsi_device *next = NULL;
  	unsigned long flags;
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	while (list->next != &shost->__devices) {
  		next = list_entry(list->next, struct scsi_device, siblings);
  		/* skip devices that we can't get a reference to */
  		if (!scsi_device_get(next))
  			break;
  		next = NULL;
  		list = list->next;
  	}
  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	if (prev)
  		scsi_device_put(prev);
  	return next;
  }
  EXPORT_SYMBOL(__scsi_iterate_devices);
  
  /**
   * starget_for_each_device  -  helper to walk all devices of a target
   * @starget:	target whose devices we want to iterate over.

   * @data:	Opaque passed to each function call.
   * @fn:		Function to call on each device

   *

   * This traverses over each device of @starget.  The devices have

   * a reference that must be released by scsi_host_put when breaking
   * out of the loop.
   */

  void starget_for_each_device(struct scsi_target *starget, void *data,

  		     void (*fn)(struct scsi_device *, void *))
  {
  	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
  	struct scsi_device *sdev;
  
  	shost_for_each_device(sdev, shost) {
  		if ((sdev->channel == starget->channel) &&
  		    (sdev->id == starget->id))
  			fn(sdev, data);
  	}
  }
  EXPORT_SYMBOL(starget_for_each_device);
  
  /**

   * __starget_for_each_device - helper to walk all devices of a target (UNLOCKED)

   * @starget:	target whose devices we want to iterate over.

   * @data:	parameter for callback @fn()
   * @fn:		callback function that is invoked for each device

   *
   * This traverses over each device of @starget.  It does _not_
   * take a reference on the scsi_device, so the whole loop must be
   * protected by shost->host_lock.
   *
   * Note:  The only reason why drivers would want to use this is because
   * they need to access the device list in irq context.  Otherwise you
   * really want to use starget_for_each_device instead.
   **/
  void __starget_for_each_device(struct scsi_target *starget, void *data,
  			       void (*fn)(struct scsi_device *, void *))
  {
  	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
  	struct scsi_device *sdev;
  
  	__shost_for_each_device(sdev, shost) {
  		if ((sdev->channel == starget->channel) &&
  		    (sdev->id == starget->id))
  			fn(sdev, data);
  	}
  }
  EXPORT_SYMBOL(__starget_for_each_device);
  
  /**

   * __scsi_device_lookup_by_target - find a device given the target (UNLOCKED)
   * @starget:	SCSI target pointer
   * @lun:	SCSI Logical Unit Number
   *

   * Description: Looks up the scsi_device with the specified @lun for a given
   * @starget.  The returned scsi_device does not have an additional

   * reference.  You must hold the host's host_lock over this call and

   * any access to the returned scsi_device. A scsi_device in state
   * SDEV_DEL is skipped.

   *

   * Note:  The only reason why drivers should use this is because

   * they need to access the device list in irq context.  Otherwise you

   * really want to use scsi_device_lookup_by_target instead.
   **/
  struct scsi_device *__scsi_device_lookup_by_target(struct scsi_target *starget,

  						   u64 lun)

  {
  	struct scsi_device *sdev;
  
  	list_for_each_entry(sdev, &starget->devices, same_target_siblings) {

  		if (sdev->sdev_state == SDEV_DEL)
  			continue;

  		if (sdev->lun ==lun)
  			return sdev;
  	}
  
  	return NULL;
  }
  EXPORT_SYMBOL(__scsi_device_lookup_by_target);
  
  /**
   * scsi_device_lookup_by_target - find a device given the target
   * @starget:	SCSI target pointer
   * @lun:	SCSI Logical Unit Number
   *

   * Description: Looks up the scsi_device with the specified @lun for a given
   * @starget.  The returned scsi_device has an additional reference that

   * needs to be released with scsi_device_put once you're done with it.

   **/
  struct scsi_device *scsi_device_lookup_by_target(struct scsi_target *starget,

  						 u64 lun)

  {
  	struct scsi_device *sdev;
  	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
  	unsigned long flags;
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	sdev = __scsi_device_lookup_by_target(starget, lun);
  	if (sdev && scsi_device_get(sdev))
  		sdev = NULL;
  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	return sdev;
  }
  EXPORT_SYMBOL(scsi_device_lookup_by_target);
  
  /**

   * __scsi_device_lookup - find a device given the host (UNLOCKED)

   * @shost:	SCSI host pointer
   * @channel:	SCSI channel (zero if only one channel)

   * @id:		SCSI target number (physical unit number)

   * @lun:	SCSI Logical Unit Number
   *

   * Description: Looks up the scsi_device with the specified @channel, @id, @lun
   * for a given host. The returned scsi_device does not have an additional
   * reference.  You must hold the host's host_lock over this call and any access
   * to the returned scsi_device.

   *
   * Note:  The only reason why drivers would want to use this is because

   * they need to access the device list in irq context.  Otherwise you

   * really want to use scsi_device_lookup instead.
   **/
  struct scsi_device *__scsi_device_lookup(struct Scsi_Host *shost,

  		uint channel, uint id, u64 lun)

  {
  	struct scsi_device *sdev;
  
  	list_for_each_entry(sdev, &shost->__devices, siblings) {
  		if (sdev->channel == channel && sdev->id == id &&
  				sdev->lun ==lun)
  			return sdev;
  	}
  
  	return NULL;
  }
  EXPORT_SYMBOL(__scsi_device_lookup);
  
  /**
   * scsi_device_lookup - find a device given the host
   * @shost:	SCSI host pointer
   * @channel:	SCSI channel (zero if only one channel)
   * @id:		SCSI target number (physical unit number)
   * @lun:	SCSI Logical Unit Number
   *

   * Description: Looks up the scsi_device with the specified @channel, @id, @lun
   * for a given host.  The returned scsi_device has an additional reference that
   * needs to be released with scsi_device_put once you're done with it.

   **/
  struct scsi_device *scsi_device_lookup(struct Scsi_Host *shost,

  		uint channel, uint id, u64 lun)

  {
  	struct scsi_device *sdev;
  	unsigned long flags;
  
  	spin_lock_irqsave(shost->host_lock, flags);
  	sdev = __scsi_device_lookup(shost, channel, id, lun);
  	if (sdev && scsi_device_get(sdev))
  		sdev = NULL;
  	spin_unlock_irqrestore(shost->host_lock, flags);
  
  	return sdev;
  }
  EXPORT_SYMBOL(scsi_device_lookup);

  MODULE_DESCRIPTION("SCSI core");
  MODULE_LICENSE("GPL");
  
  module_param(scsi_logging_level, int, S_IRUGO|S_IWUSR);
  MODULE_PARM_DESC(scsi_logging_level, "a bit mask of logging levels");

  #ifdef CONFIG_SCSI_MQ_DEFAULT
  bool scsi_use_blk_mq = true;
  #else

  bool scsi_use_blk_mq = false;

  #endif

  module_param_named(use_blk_mq, scsi_use_blk_mq, bool, S_IWUSR | S_IRUGO);

  static int __init init_scsi(void)
  {

  	int error;

  
  	error = scsi_init_queue();
  	if (error)
  		return error;
  	error = scsi_init_procfs();
  	if (error)
  		goto cleanup_queue;
  	error = scsi_init_devinfo();
  	if (error)
  		goto cleanup_procfs;
  	error = scsi_init_hosts();
  	if (error)
  		goto cleanup_devlist;
  	error = scsi_init_sysctl();
  	if (error)
  		goto cleanup_hosts;
  	error = scsi_sysfs_register();
  	if (error)
  		goto cleanup_sysctl;

  	scsi_netlink_init();

  	printk(KERN_NOTICE "SCSI subsystem initialized
  ");
  	return 0;
  
  cleanup_sysctl:
  	scsi_exit_sysctl();
  cleanup_hosts:
  	scsi_exit_hosts();
  cleanup_devlist:
  	scsi_exit_devinfo();
  cleanup_procfs:
  	scsi_exit_procfs();
  cleanup_queue:
  	scsi_exit_queue();
  	printk(KERN_ERR "SCSI subsystem failed to initialize, error = %d
  ",
  	       -error);
  	return error;
  }
  
  static void __exit exit_scsi(void)
  {

  	scsi_netlink_exit();

  	scsi_sysfs_unregister();
  	scsi_exit_sysctl();
  	scsi_exit_hosts();
  	scsi_exit_devinfo();

  	scsi_exit_procfs();
  	scsi_exit_queue();

  	async_unregister_domain(&scsi_sd_probe_domain);

  }
  
  subsys_initcall(init_scsi);
  module_exit(exit_scsi);