scsi_lib.c

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/*
 *  scsi_lib.c Copyright (C) 1999 Eric Youngdale
 *
 *  SCSI queueing library.
 *      Initial versions: Eric Youngdale ([e-mail]).
 *                        Based upon conversations with large numbers
 *                        of people at Linux Expo.
 */

/*
 * The fundamental purpose of this file is to contain a library of utility
 * routines that can be used by low-level drivers.   Ultimately the idea
 * is that there should be a sufficiently rich number of functions that it
 * would be possible for a driver author to fashion a queueing function for
 * a low-level driver if they wished.   Note however that this file also
 * contains the "default" versions of these functions, as we don't want to
 * go through and retrofit queueing functions into all 30 some-odd drivers.
 */

#define __NO_VERSION__
#include <linux/module.h>

#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/malloc.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/stat.h>
#include <linux/blk.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/smp_lock.h>


#define __KERNEL_SYSCALLS__

#include <linux/unistd.h>

#include <asm/system.h>
#include <asm/irq.h>
#include <asm/dma.h>

#include "scsi.h"
#include "hosts.h"
#include "constants.h"
#include <scsi/scsi_ioctl.h>

/*
 * This entire source file deals with the new queueing code.
 */


/*
 * Function:    scsi_insert_special_cmd()
 *
 * Purpose:     Insert pre-formed command into request queue.
 *
 * Arguments:   SCpnt   - command that is ready to be queued.
 *              at_head - boolean.  True if we should insert at head
 *                        of queue, false if we should insert at tail.
 *
 * Lock status: Assumed that lock is not held upon entry.
 *
 * Returns:     Nothing
 *
 * Notes:       This function is called from character device and from
 *              ioctl types of functions where the caller knows exactly
 *              what SCSI command needs to be issued.   The idea is that
 *              we merely inject the command into the queue (at the head
 *              for now), and then call the queue request function to actually
 *              process it.
 */
int scsi_insert_special_cmd(Scsi_Cmnd * SCpnt, int at_head)
{
	unsigned long flags;
	request_queue_t *q;

	ASSERT_LOCK(&io_request_lock, 0);

	/*
	 * The SCpnt already contains a request structure - we will doctor the
	 * thing up with the appropriate values and use that in the actual
	 * request queue.
	 */
	q = &SCpnt->device->request_queue;
	SCpnt->request.cmd = SPECIAL;
	SCpnt->request.special = (void *) SCpnt;
	SCpnt->request.q = NULL;
	SCpnt->request.free_list = NULL;
	SCpnt->request.nr_segments = 0;

	/*
	 * We have the option of inserting the head or the tail of the queue.
	 * Typically we use the tail for new ioctls and so forth.  We use the
	 * head of the queue for things like a QUEUE_FULL message from a
	 * device, or a host that is unable to accept a particular command.
	 */
	spin_lock_irqsave(&io_request_lock, flags);

	if (at_head) {
		list_add(&SCpnt->request.queue, &q->queue_head);
	} else {
		/*
		 * FIXME(eric) - we always insert at the tail of the
		 * list.  Otherwise ioctl commands would always take
		 * precedence over normal I/O.  An ioctl on a busy
		 * disk might be delayed indefinitely because the
		 * request might not float high enough in the queue
		 * to be scheduled.
		 */
		list_add_tail(&SCpnt->request.queue, &q->queue_head);
	}

	/*
	 * Now hit the requeue function for the queue.  If the host is
	 * already busy, so be it - we have nothing special to do.  If
	 * the host can queue it, then send it off.  
	 */
	q->request_fn(q);
	spin_unlock_irqrestore(&io_request_lock, flags);
	return 0;
}

/*
 * Function:    scsi_insert_special_req()
 *
 * Purpose:     Insert pre-formed request into request queue.
 *
 * Arguments:   SRpnt   - request that is ready to be queued.
 *              at_head - boolean.  True if we should insert at head
 *                        of queue, false if we should insert at tail.
 *
 * Lock status: Assumed that lock is not held upon entry.
 *
 * Returns:     Nothing
 *
 * Notes:       This function is called from character device and from
 *              ioctl types of functions where the caller knows exactly
 *              what SCSI command needs to be issued.   The idea is that
 *              we merely inject the command into the queue (at the head
 *              for now), and then call the queue request function to actually
 *              process it.
 */
int scsi_insert_special_req(Scsi_Request * SRpnt, int at_head)
{
	unsigned long flags;
	request_queue_t *q;

	ASSERT_LOCK(&io_request_lock, 0);

	/*
	 * The SCpnt already contains a request structure - we will doctor the
	 * thing up with the appropriate values and use that in the actual
	 * request queue.
	 */
	q = &SRpnt->sr_device->request_queue;
	SRpnt->sr_request.cmd = SPECIAL;
	SRpnt->sr_request.special = (void *) SRpnt;
	SRpnt->sr_request.q = NULL;
	SRpnt->sr_request.nr_segments = 0;

	/*
	 * We have the option of inserting the head or the tail of the queue.
	 * Typically we use the tail for new ioctls and so forth.  We use the
	 * head of the queue for things like a QUEUE_FULL message from a
	 * device, or a host that is unable to accept a particular command.
	 */
	spin_lock_irqsave(&io_request_lock, flags);

	if (at_head) {
		list_add(&SRpnt->sr_request.queue, &q->queue_head);
	} else {
		/*
		 * FIXME(eric) - we always insert at the tail of the
		 * list.  Otherwise ioctl commands would always take
		 * precedence over normal I/O.  An ioctl on a busy
		 * disk might be delayed indefinitely because the
		 * request might not float high enough in the queue
		 * to be scheduled.
		 */
		list_add_tail(&SRpnt->sr_request.queue, &q->queue_head);
	}

	/*
	 * Now hit the requeue function for the queue.  If the host is
	 * already busy, so be it - we have nothing special to do.  If
	 * the host can queue it, then send it off.  
	 */
	q->request_fn(q);
	spin_unlock_irqrestore(&io_request_lock, flags);
	return 0;
}

/*
 * Function:    scsi_init_cmd_errh()
 *
 * Purpose:     Initialize SCpnt fields related to error handling.
 *
 * Arguments:   SCpnt   - command that is ready to be queued.
 *
 * Returns:     Nothing
 *
 * Notes:       This function has the job of initializing a number of
 *              fields related to error handling.   Typically this will
 *              be called once for each command, as required.
 */
int scsi_init_cmd_errh(Scsi_Cmnd * SCpnt)
{
	ASSERT_LOCK(&io_request_lock, 0);

	SCpnt->owner = SCSI_OWNER_MIDLEVEL;
	SCpnt->reset_chain = NULL;
	SCpnt->serial_number = 0;
	SCpnt->serial_number_at_timeout = 0;
	SCpnt->flags = 0;
	SCpnt->retries = 0;

	SCpnt->abort_reason = 0;

	memset((void *) SCpnt->sense_buffer, 0, sizeof SCpnt->sense_buffer);

	if (SCpnt->cmd_len == 0)
		SCpnt->cmd_len = COMMAND_SIZE(SCpnt->cmnd[0]);

	/*
	 * We need saved copies of a number of fields - this is because
	 * error handling may need to overwrite these with different values
	 * to run different commands, and once error handling is complete,
	 * we will need to restore these values prior to running the actual
	 * command.
	 */
	SCpnt->old_use_sg = SCpnt->use_sg;
	SCpnt->old_cmd_len = SCpnt->cmd_len;
	SCpnt->sc_old_data_direction = SCpnt->sc_data_direction;
	SCpnt->old_underflow = SCpnt->underflow;
	memcpy((void *) SCpnt->data_cmnd,
	       (const void *) SCpnt->cmnd, sizeof(SCpnt->cmnd));
	SCpnt->buffer = SCpnt->request_buffer;
	SCpnt->bufflen = SCpnt->request_bufflen;

	SCpnt->reset_chain = NULL;

	SCpnt->internal_timeout = NORMAL_TIMEOUT;
	SCpnt->abort_reason = 0;

	return 1;
}

/*
 * Function:    scsi_queue_next_request()
 *
 * Purpose:     Handle post-processing of completed commands.
 *
 * Arguments:   SCpnt   - command that may need to be requeued.
 *
 * Returns:     Nothing
 *
 * Notes:       After command completion, there may be blocks left
 *              over which weren't finished by the previous command
 *              this can be for a number of reasons - the main one is
 *              that a medium error occurred, and the sectors after
 *              the bad block need to be re-read.
 *
 *              If SCpnt is NULL, it means that the previous command
 *              was completely finished, and we should simply start
 *              a new command, if possible.
 *
 *		This is where a lot of special case code has begun to
 *		accumulate.  It doesn't really affect readability or
 *		anything, but it might be considered architecturally
 *		inelegant.  If more of these special cases start to
 *		accumulate, I am thinking along the lines of implementing
 *		an atexit() like technology that gets run when commands
 *		complete.  I am not convinced that it is worth the
 *		added overhead, however.  Right now as things stand,
 *		there are simple conditional checks, and most hosts
 *		would skip past.
 *
 *		Another possible solution would be to tailor different
 *		handler functions, sort of like what we did in scsi_merge.c.
 *		This is probably a better solution, but the number of different
 *		permutations grows as 2**N, and if too many more special cases
 *		get added, we start to get screwed.
 */
void scsi_queue_next_request(request_queue_t * q, Scsi_Cmnd * SCpnt)
{
	int all_clear;
	unsigned long flags;
	Scsi_Device *SDpnt;
	struct Scsi_Host *SHpnt;

	ASSERT_LOCK(&io_request_lock, 0);

	spin_lock_irqsave(&io_request_lock, flags);
	if (SCpnt != NULL) {

		/*
		 * For some reason, we are not done with this request.
		 * This happens for I/O errors in the middle of the request,
		 * in which case we need to request the blocks that come after
		 * the bad sector.
		 */
		SCpnt->request.special = (void *) SCpnt;
		list_add(&SCpnt->request.queue, &q->queue_head);
	}

	/*
	 * Just hit the requeue function for the queue.
	 */
	q->request_fn(q);

	SDpnt = (Scsi_Device *) q->queuedata;
	SHpnt = SDpnt->host;

	/*
	 * If this is a single-lun device, and we are currently finished
	 * with this device, then see if we need to get another device
	 * started.  FIXME(eric) - if this function gets too cluttered
	 * with special case code, then spin off separate versions and
	 * use function pointers to pick the right one.
	 */
	if (SDpnt->single_lun
	    && list_empty(&q->queue_head)
	    && SDpnt->device_busy == 0) {
		request_queue_t *q;

		for (SDpnt = SHpnt->host_queue;
		     SDpnt;
		     SDpnt = SDpnt->next) {
			if (((SHpnt->can_queue > 0)
			     && (SHpnt->host_busy >= SHpnt->can_queue))
			    || (SHpnt->host_blocked)
			    || (SHpnt->host_self_blocked)
			    || (SDpnt->device_blocked)) {
				break;
			}
			q = &SDpnt->request_queue;
			q->request_fn(q);
		}
	}

	/*
	 * Now see whether there are other devices on the bus which
	 * might be starved.  If so, hit the request function.  If we
	 * don't find any, then it is safe to reset the flag.  If we
	 * find any device that it is starved, it isn't safe to reset the
	 * flag as the queue function releases the lock and thus some
	 * other device might have become starved along the way.
	 */
	all_clear = 1;
	if (SHpnt->some_device_starved) {
		for (SDpnt = SHpnt->host_queue; SDpnt; SDpnt = SDpnt->next) {
			request_queue_t *q;
			if ((SHpnt->can_queue > 0 && (SHpnt->host_busy >= SHpnt->can_queue))
			    || (SHpnt->host_blocked) 
			    || (SHpnt->host_self_blocked)) {
				break;
			}
			if (SDpnt->device_blocked || !SDpnt->starved) {
				continue;
			}
			q = &SDpnt->request_queue;
			q->request_fn(q);
			all_clear = 0;
		}
		if (SDpnt == NULL && all_clear) {
			SHpnt->some_device_starved = 0;
		}
	}
	spin_unlock_irqrestore(&io_request_lock, flags);
}

/*
 * Function:    scsi_end_request()
 *
 * Purpose:     Post-processing of completed commands called from interrupt
 *              handler or a bottom-half handler.
 *
 * Arguments:   SCpnt    - command that is complete.
 *              uptodate - 1 if I/O indicates success, 0 for I/O error.
 *              sectors  - number of sectors we want to mark.
 *		requeue  - indicates whether we should requeue leftovers.
 *		frequeue - indicates that if we release the command block
 *			   that the queue request function should be called.
 *
 * Lock status: Assumed that lock is not held upon entry.
 *
 * Returns:     Nothing
 *
 * Notes:       This is called for block device requests in order to
 *              mark some number of sectors as complete.
 * 
 *		We are guaranteeing that the request queue will be goosed
 *		at some point during this call.
 */
static Scsi_Cmnd *__scsi_end_request(Scsi_Cmnd * SCpnt, 
				     int uptodate, 
				     int sectors,
				     int requeue,
				     int frequeue)
{
	struct request *req;