scsi_lib.c

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			return spnt;
		}
		/*
		 * I am still not entirely satisfied with this solution,
		 * but it is good enough for now.  Disks have a number of
		 * major numbers associated with them, the primary
		 * 8, which we test above, and a secondary range of 7
		 * different consecutive major numbers.   If this ever
		 * becomes insufficient, then we could add another function
		 * to the structure, and generalize this completely.
		 */
		if( spnt->min_major != 0 
		    && spnt->max_major != 0
		    && major >= spnt->min_major
		    && major <= spnt->max_major )
		{
			return spnt;
		}
	}
	return NULL;
}

/*
 * Function:    scsi_request_fn()
 *
 * Purpose:     Generic version of request function for SCSI hosts.
 *
 * Arguments:   q       - Pointer to actual queue.
 *
 * Returns:     Nothing
 *
 * Lock status: IO request lock assumed to be held when called.
 *
 * Notes:       The theory is that this function is something which individual
 *              drivers could also supply if they wished to.   The problem
 *              is that we have 30 some odd low-level drivers in the kernel
 *              tree already, and it would be most difficult to retrofit
 *              this crap into all of them.   Thus this function has the job
 *              of acting as a generic queue manager for all of those existing
 *              drivers.
 */
void scsi_request_fn(request_queue_t * q)
{
	struct request *req;
	Scsi_Cmnd *SCpnt;
	Scsi_Request *SRpnt;
	Scsi_Device *SDpnt;
	struct Scsi_Host *SHpnt;
	struct Scsi_Device_Template *STpnt;

	ASSERT_LOCK(&io_request_lock, 1);

	SDpnt = (Scsi_Device *) q->queuedata;
	if (!SDpnt) {
		panic("Missing device");
	}
	SHpnt = SDpnt->host;

	/*
	 * To start with, we keep looping until the queue is empty, or until
	 * the host is no longer able to accept any more requests.
	 */
	while (1 == 1) {
		/*
		 * Check this again - each time we loop through we will have
		 * released the lock and grabbed it again, so each time
		 * we need to check to see if the queue is plugged or not.
		 */
		if (SHpnt->in_recovery || q->plugged)
			return;

		/*
		 * If the device cannot accept another request, then quit.
		 */
		if (SDpnt->device_blocked) {
			break;
		}
		if ((SHpnt->can_queue > 0 && (SHpnt->host_busy >= SHpnt->can_queue))
		    || (SHpnt->host_blocked) 
		    || (SHpnt->host_self_blocked)) {
			/*
			 * If we are unable to process any commands at all for
			 * this device, then we consider it to be starved.
			 * What this means is that there are no outstanding
			 * commands for this device and hence we need a
			 * little help getting it started again
			 * once the host isn't quite so busy.
			 */
			if (SDpnt->device_busy == 0) {
				SDpnt->starved = 1;
				SHpnt->some_device_starved = 1;
			}
			break;
		} else {
			SDpnt->starved = 0;
		}

 		/*
		 * FIXME(eric)
		 * I am not sure where the best place to do this is.  We need
		 * to hook in a place where we are likely to come if in user
		 * space.   Technically the error handling thread should be
		 * doing this crap, but the error handler isn't used by
		 * most hosts.
		 */
		if (SDpnt->was_reset) {
			/*
			 * We need to relock the door, but we might
			 * be in an interrupt handler.  Only do this
			 * from user space, since we do not want to
			 * sleep from an interrupt.
			 *
			 * FIXME(eric) - have the error handler thread do
			 * this work.
			 */
			SDpnt->was_reset = 0;
			if (SDpnt->removable && !in_interrupt()) {
				spin_unlock_irq(&io_request_lock);
				scsi_ioctl(SDpnt, SCSI_IOCTL_DOORLOCK, 0);
				spin_lock_irq(&io_request_lock);
				continue;
			}
		}

		/*
		 * If we couldn't find a request that could be queued, then we
		 * can also quit.
		 */
		if (list_empty(&q->queue_head))
			break;

		/*
		 * Loop through all of the requests in this queue, and find
		 * one that is queueable.
		 */
		req = blkdev_entry_next_request(&q->queue_head);

		/*
		 * Find the actual device driver associated with this command.
		 * The SPECIAL requests are things like character device or
		 * ioctls, which did not originate from ll_rw_blk.  Note that
		 * the special field is also used to indicate the SCpnt for
		 * the remainder of a partially fulfilled request that can 
		 * come up when there is a medium error.  We have to treat
		 * these two cases differently.  We differentiate by looking
		 * at request.cmd, as this tells us the real story.
		 */
		if (req->cmd == SPECIAL) {
			STpnt = NULL;
			SCpnt = (Scsi_Cmnd *) req->special;
			SRpnt = (Scsi_Request *) req->special;

			if( SRpnt->sr_magic == SCSI_REQ_MAGIC ) {
				SCpnt = scsi_allocate_device(SRpnt->sr_device, 
							     FALSE, FALSE);
				if( !SCpnt ) {
					break;
				}
				scsi_init_cmd_from_req(SCpnt, SRpnt);
			}

		} else {
			SRpnt = NULL;
			STpnt = scsi_get_request_dev(req);
			if (!STpnt) {
				panic("Unable to find device associated with request");
			}
			/*
			 * Now try and find a command block that we can use.
			 */
			if( req->special != NULL ) {
				SCpnt = (Scsi_Cmnd *) req->special;
				/*
				 * We need to recount the number of
				 * scatter-gather segments here - the
				 * normal case code assumes this to be
				 * correct, as it would be a performance
				 * lose to always recount.  Handling
				 * errors is always unusual, of course.
				 */
				recount_segments(SCpnt);
			} else {
				SCpnt = scsi_allocate_device(SDpnt, FALSE, FALSE);
			}
			/*
			 * If so, we are ready to do something.  Bump the count
			 * while the queue is locked and then break out of the
			 * loop. Otherwise loop around and try another request.
			 */
			if (!SCpnt) {
				break;
			}
		}

		/*
		 * Now bump the usage count for both the host and the
		 * device.
		 */
		SHpnt->host_busy++;
		SDpnt->device_busy++;

		/*
		 * Finally, before we release the lock, we copy the
		 * request to the command block, and remove the
		 * request from the request list.   Note that we always
		 * operate on the queue head - there is absolutely no
		 * reason to search the list, because all of the commands
		 * in this queue are for the same device.
		 */
		blkdev_dequeue_request(req);

		if (req != &SCpnt->request && req != &SRpnt->sr_request ) {
			memcpy(&SCpnt->request, req, sizeof(struct request));

			/*
			 * We have copied the data out of the request block -
			 * it is now in a field in SCpnt.  Release the request
			 * block.
			 */
			blkdev_release_request(req);
		}
		/*
		 * Now it is finally safe to release the lock.  We are
		 * not going to noodle the request list until this
		 * request has been queued and we loop back to queue
		 * another.  
		 */
		req = NULL;
		spin_unlock_irq(&io_request_lock);

		if (SCpnt->request.cmd != SPECIAL) {
			/*
			 * This will do a couple of things:
			 *  1) Fill in the actual SCSI command.
			 *  2) Fill in any other upper-level specific fields
			 * (timeout).
			 *
			 * If this returns 0, it means that the request failed
			 * (reading past end of disk, reading offline device,
			 * etc).   This won't actually talk to the device, but
			 * some kinds of consistency checking may cause the	
			 * request to be rejected immediately.
			 */
			if (STpnt == NULL) {
				STpnt = scsi_get_request_dev(req);
			}
			/* 
			 * This sets up the scatter-gather table (allocating if
			 * required).  Hosts that need bounce buffers will also
			 * get those allocated here.  
			 */
			if (!SDpnt->scsi_init_io_fn(SCpnt)) {
				SCpnt = __scsi_end_request(SCpnt, 0, 
							   SCpnt->request.nr_sectors, 0, 0);
				if( SCpnt != NULL )
				{
					panic("Should not have leftover blocks\n");
				}
				spin_lock_irq(&io_request_lock);
				SHpnt->host_busy--;
				SDpnt->device_busy--;
				continue;
			}
			/*
			 * Initialize the actual SCSI command for this request.
			 */
			if (!STpnt->init_command(SCpnt)) {
				scsi_release_buffers(SCpnt);
				SCpnt = __scsi_end_request(SCpnt, 0, 
							   SCpnt->request.nr_sectors, 0, 0);
				if( SCpnt != NULL )
				{
					panic("Should not have leftover blocks\n");
				}
				spin_lock_irq(&io_request_lock);
				SHpnt->host_busy--;
				SDpnt->device_busy--;
				continue;
			}
		}
		/*
		 * Finally, initialize any error handling parameters, and set up
		 * the timers for timeouts.
		 */
		scsi_init_cmd_errh(SCpnt);

		/*
		 * Dispatch the command to the low-level driver.
		 */
		scsi_dispatch_cmd(SCpnt);

		/*
		 * Now we need to grab the lock again.  We are about to mess
		 * with the request queue and try to find another command.
		 */
		spin_lock_irq(&io_request_lock);
	}
}

/*
 * Function:    scsi_block_requests()
 *
 * Purpose:     Utility function used by low-level drivers to prevent further
 *		commands from being queued to the device.
 *
 * Arguments:   SHpnt       - Host in question
 *
 * Returns:     Nothing
 *
 * Lock status: No locks are assumed held.
 *
 * Notes:       There is no timer nor any other means by which the requests
 *		get unblocked other than the low-level driver calling
 *		scsi_unblock_requests().
 */
void scsi_block_requests(struct Scsi_Host * SHpnt)
{
	SHpnt->host_self_blocked = TRUE;
}

/*
 * Function:    scsi_unblock_requests()
 *
 * Purpose:     Utility function used by low-level drivers to allow further
 *		commands from being queued to the device.
 *
 * Arguments:   SHpnt       - Host in question
 *
 * Returns:     Nothing
 *
 * Lock status: No locks are assumed held.
 *
 * Notes:       There is no timer nor any other means by which the requests
 *		get unblocked other than the low-level driver calling
 *		scsi_unblock_requests().
 *
 *		This is done as an API function so that changes to the
 *		internals of the scsi mid-layer won't require wholesale
 *		changes to drivers that use this feature.
 */
void scsi_unblock_requests(struct Scsi_Host * SHpnt)
{
	Scsi_Device *SDloop;

	SHpnt->host_self_blocked = FALSE;
	/* Now that we are unblocked, try to start the queues. */
	for (SDloop = SHpnt->host_queue; SDloop; SDloop = SDloop->next)
		scsi_queue_next_request(&SDloop->request_queue, NULL);
}

/*
 * Function:    scsi_report_bus_reset()
 *
 * Purpose:     Utility function used by low-level drivers to report that
 *		they have observed a bus reset on the bus being handled.
 *
 * Arguments:   SHpnt       - Host in question
 *		channel     - channel on which reset was observed.
 *
 * Returns:     Nothing
 *
 * Lock status: No locks are assumed held.
 *
 * Notes:       This only needs to be called if the reset is one which
 *		originates from an unknown location.  Resets originated
 *		by the mid-level itself don't need to call this, but there
 *		should be no harm.
 *
 *		The main purpose of this is to make sure that a CHECK_CONDITION
 *		is properly treated.
 */
void scsi_report_bus_reset(struct Scsi_Host * SHpnt, int channel)
{
	Scsi_Device *SDloop;
	for (SDloop = SHpnt->host_queue; SDloop; SDloop = SDloop->next) {
		if (channel == SDloop->channel) {
			SDloop->was_reset = 1;
			SDloop->expecting_cc_ua = 1;
		}
	}
}

/*
 * FIXME(eric) - these are empty stubs for the moment.  I need to re-implement
 * host blocking from scratch. The theory is that hosts that wish to block
 * will register/deregister using these functions instead of the old way
 * of setting the wish_block flag.
 *
 * The details of the implementation remain to be settled, however the
 * stubs are here now so that the actual drivers will properly compile.
 */
void scsi_register_blocked_host(struct Scsi_Host * SHpnt)
{
}

void scsi_deregister_blocked_host(struct Scsi_Host * SHpnt)
{
}