[BLOCK] Move all core block layer code to new block/ directory

drivers/block/ is right now a mix of core and driver parts. Lets move
the core parts to a new top level directory. Al will move the fs/
related block parts to block/ next.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 3613 insertions, 0 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
new file mode 100644
index 0000000..2747741
--- /dev/null
+++ b/block/ll_rw_blk.c
@@ -0,0 +1,3613 @@
+/*
+ *  linux/drivers/block/ll_rw_blk.c
+ *
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
+ * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
+ * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
+ * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au> -  July2000
+ * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
+ */
+
+/*
+ * This handles all read/write requests to block devices
+ */
+#include <linux/config.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/backing-dev.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/kernel_stat.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/bootmem.h>	/* for max_pfn/max_low_pfn */
+#include <linux/completion.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+
+/*
+ * for max sense size
+ */
+#include <scsi/scsi_cmnd.h>
+
+static void blk_unplug_work(void *data);
+static void blk_unplug_timeout(unsigned long data);
+static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io);
+
+/*
+ * For the allocated request tables
+ */
+static kmem_cache_t *request_cachep;
+
+/*
+ * For queue allocation
+ */
+static kmem_cache_t *requestq_cachep;
+
+/*
+ * For io context allocations
+ */
+static kmem_cache_t *iocontext_cachep;
+
+static wait_queue_head_t congestion_wqh[2] = {
+		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
+		__WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
+	};
+
+/*
+ * Controlling structure to kblockd
+ */
+static struct workqueue_struct *kblockd_workqueue; 
+
+unsigned long blk_max_low_pfn, blk_max_pfn;
+
+EXPORT_SYMBOL(blk_max_low_pfn);
+EXPORT_SYMBOL(blk_max_pfn);
+
+/* Amount of time in which a process may batch requests */
+#define BLK_BATCH_TIME	(HZ/50UL)
+
+/* Number of requests a "batching" process may submit */
+#define BLK_BATCH_REQ	32
+
+/*
+ * Return the threshold (number of used requests) at which the queue is
+ * considered to be congested.  It include a little hysteresis to keep the
+ * context switch rate down.
+ */
+static inline int queue_congestion_on_threshold(struct request_queue *q)
+{
+	return q->nr_congestion_on;
+}
+
+/*
+ * The threshold at which a queue is considered to be uncongested
+ */
+static inline int queue_congestion_off_threshold(struct request_queue *q)
+{
+	return q->nr_congestion_off;
+}
+
+static void blk_queue_congestion_threshold(struct request_queue *q)
+{
+	int nr;
+
+	nr = q->nr_requests - (q->nr_requests / 8) + 1;
+	if (nr > q->nr_requests)
+		nr = q->nr_requests;
+	q->nr_congestion_on = nr;
+
+	nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
+	if (nr < 1)
+		nr = 1;
+	q->nr_congestion_off = nr;
+}
+
+/*
+ * A queue has just exitted congestion.  Note this in the global counter of
+ * congested queues, and wake up anyone who was waiting for requests to be
+ * put back.
+ */
+static void clear_queue_congested(request_queue_t *q, int rw)
+{
+	enum bdi_state bit;
+	wait_queue_head_t *wqh = &congestion_wqh[rw];
+
+	bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+	clear_bit(bit, &q->backing_dev_info.state);
+	smp_mb__after_clear_bit();
+	if (waitqueue_active(wqh))
+		wake_up(wqh);
+}
+
+/*
+ * A queue has just entered congestion.  Flag that in the queue's VM-visible
+ * state flags and increment the global gounter of congested queues.
+ */
+static void set_queue_congested(request_queue_t *q, int rw)
+{
+	enum bdi_state bit;
+
+	bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
+	set_bit(bit, &q->backing_dev_info.state);
+}
+
+/**
+ * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
+ * @bdev:	device
+ *
+ * Locates the passed device's request queue and returns the address of its
+ * backing_dev_info
+ *
+ * Will return NULL if the request queue cannot be located.
+ */
+struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
+{
+	struct backing_dev_info *ret = NULL;
+	request_queue_t *q = bdev_get_queue(bdev);
+
+	if (q)
+		ret = &q->backing_dev_info;
+	return ret;
+}
+
+EXPORT_SYMBOL(blk_get_backing_dev_info);
+
+void blk_queue_activity_fn(request_queue_t *q, activity_fn *fn, void *data)
+{
+	q->activity_fn = fn;
+	q->activity_data = data;
+}
+
+EXPORT_SYMBOL(blk_queue_activity_fn);
+
+/**
+ * blk_queue_prep_rq - set a prepare_request function for queue
+ * @q:		queue
+ * @pfn:	prepare_request function
+ *
+ * It's possible for a queue to register a prepare_request callback which
+ * is invoked before the request is handed to the request_fn. The goal of
+ * the function is to prepare a request for I/O, it can be used to build a
+ * cdb from the request data for instance.
+ *
+ */
+void blk_queue_prep_rq(request_queue_t *q, prep_rq_fn *pfn)
+{
+	q->prep_rq_fn = pfn;
+}
+
+EXPORT_SYMBOL(blk_queue_prep_rq);
+
+/**
+ * blk_queue_merge_bvec - set a merge_bvec function for queue
+ * @q:		queue
+ * @mbfn:	merge_bvec_fn
+ *
+ * Usually queues have static limitations on the max sectors or segments that
+ * we can put in a request. Stacking drivers may have some settings that
+ * are dynamic, and thus we have to query the queue whether it is ok to
+ * add a new bio_vec to a bio at a given offset or not. If the block device
+ * has such limitations, it needs to register a merge_bvec_fn to control
+ * the size of bio's sent to it. Note that a block device *must* allow a
+ * single page to be added to an empty bio. The block device driver may want
+ * to use the bio_split() function to deal with these bio's. By default
+ * no merge_bvec_fn is defined for a queue, and only the fixed limits are
+ * honored.
+ */
+void blk_queue_merge_bvec(request_queue_t *q, merge_bvec_fn *mbfn)
+{
+	q->merge_bvec_fn = mbfn;
+}
+
+EXPORT_SYMBOL(blk_queue_merge_bvec);
+
+/**
+ * blk_queue_make_request - define an alternate make_request function for a device
+ * @q:  the request queue for the device to be affected
+ * @mfn: the alternate make_request function
+ *
+ * Description:
+ *    The normal way for &struct bios to be passed to a device
+ *    driver is for them to be collected into requests on a request
+ *    queue, and then to allow the device driver to select requests
+ *    off that queue when it is ready.  This works well for many block
+ *    devices. However some block devices (typically virtual devices
+ *    such as md or lvm) do not benefit from the processing on the
+ *    request queue, and are served best by having the requests passed
+ *    directly to them.  This can be achieved by providing a function
+ *    to blk_queue_make_request().
+ *
+ * Caveat:
+ *    The driver that does this *must* be able to deal appropriately
+ *    with buffers in "highmemory". This can be accomplished by either calling
+ *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
+ *    blk_queue_bounce() to create a buffer in normal memory.
+ **/
+void blk_queue_make_request(request_queue_t * q, make_request_fn * mfn)
+{
+	/*
+	 * set defaults
+	 */
+	q->nr_requests = BLKDEV_MAX_RQ;
+	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+	q->make_request_fn = mfn;
+	q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
+	q->backing_dev_info.state = 0;
+	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
+	blk_queue_max_sectors(q, MAX_SECTORS);
+	blk_queue_hardsect_size(q, 512);
+	blk_queue_dma_alignment(q, 511);
+	blk_queue_congestion_threshold(q);
+	q->nr_batching = BLK_BATCH_REQ;
+
+	q->unplug_thresh = 4;		/* hmm */
+	q->unplug_delay = (3 * HZ) / 1000;	/* 3 milliseconds */
+	if (q->unplug_delay == 0)
+		q->unplug_delay = 1;
+
+	INIT_WORK(&q->unplug_work, blk_unplug_work, q);
+
+	q->unplug_timer.function = blk_unplug_timeout;
+	q->unplug_timer.data = (unsigned long)q;
+
+	/*
+	 * by default assume old behaviour and bounce for any highmem page
+	 */
+	blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
+
+	blk_queue_activity_fn(q, NULL, NULL);
+}
+
+EXPORT_SYMBOL(blk_queue_make_request);
+
+static inline void rq_init(request_queue_t *q, struct request *rq)
+{
+	INIT_LIST_HEAD(&rq->queuelist);
+
+	rq->errors = 0;
+	rq->rq_status = RQ_ACTIVE;
+	rq->bio = rq->biotail = NULL;
+	rq->ioprio = 0;
+	rq->buffer = NULL;
+	rq->ref_count = 1;
+	rq->q = q;
+	rq->waiting = NULL;
+	rq->special = NULL;
+	rq->data_len = 0;
+	rq->data = NULL;
+	rq->nr_phys_segments = 0;
+	rq->sense = NULL;
+	rq->end_io = NULL;
+	rq->end_io_data = NULL;
+}
+
+/**
+ * blk_queue_ordered - does this queue support ordered writes
+ * @q:     the request queue
+ * @flag:  see below
+ *
+ * Description:
+ *   For journalled file systems, doing ordered writes on a commit
+ *   block instead of explicitly doing wait_on_buffer (which is bad
+ *   for performance) can be a big win. Block drivers supporting this
+ *   feature should call this function and indicate so.
+ *
+ **/
+void blk_queue_ordered(request_queue_t *q, int flag)
+{
+	switch (flag) {
+		case QUEUE_ORDERED_NONE:
+			if (q->flush_rq)
+				kmem_cache_free(request_cachep, q->flush_rq);
+			q->flush_rq = NULL;
+			q->ordered = flag;
+			break;
+		case QUEUE_ORDERED_TAG:
+			q->ordered = flag;
+			break;
+		case QUEUE_ORDERED_FLUSH:
+			q->ordered = flag;
+			if (!q->flush_rq)
+				q->flush_rq = kmem_cache_alloc(request_cachep,
+								GFP_KERNEL);
+			break;
+		default:
+			printk("blk_queue_ordered: bad value %d\n", flag);
+			break;
+	}
+}
+
+EXPORT_SYMBOL(blk_queue_ordered);
+
+/**
+ * blk_queue_issue_flush_fn - set function for issuing a flush
+ * @q:     the request queue
+ * @iff:   the function to be called issuing the flush
+ *
+ * Description:
+ *   If a driver supports issuing a flush command, the support is notified
+ *   to the block layer by defining it through this call.
+ *
+ **/
+void blk_queue_issue_flush_fn(request_queue_t *q, issue_flush_fn *iff)
+{
+	q->issue_flush_fn = iff;
+}
+
+EXPORT_SYMBOL(blk_queue_issue_flush_fn);
+
+/*
+ * Cache flushing for ordered writes handling
+ */
+static void blk_pre_flush_end_io(struct request *flush_rq)
+{
+	struct request *rq = flush_rq->end_io_data;
+	request_queue_t *q = rq->q;
+
+	elv_completed_request(q, flush_rq);
+
+	rq->flags |= REQ_BAR_PREFLUSH;
+
+	if (!flush_rq->errors)
+		elv_requeue_request(q, rq);
+	else {
+		q->end_flush_fn(q, flush_rq);
+		clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+		q->request_fn(q);
+	}
+}
+
+static void blk_post_flush_end_io(struct request *flush_rq)
+{
+	struct request *rq = flush_rq->end_io_data;
+	request_queue_t *q = rq->q;
+
+	elv_completed_request(q, flush_rq);
+
+	rq->flags |= REQ_BAR_POSTFLUSH;
+
+	q->end_flush_fn(q, flush_rq);
+	clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+	q->request_fn(q);
+}
+
+struct request *blk_start_pre_flush(request_queue_t *q, struct request *rq)
+{
+	struct request *flush_rq = q->flush_rq;
+
+	BUG_ON(!blk_barrier_rq(rq));
+
+	if (test_and_set_bit(QUEUE_FLAG_FLUSH, &q->queue_flags))
+		return NULL;
+
+	rq_init(q, flush_rq);
+	flush_rq->elevator_private = NULL;
+	flush_rq->flags = REQ_BAR_FLUSH;
+	flush_rq->rq_disk = rq->rq_disk;
+	flush_rq->rl = NULL;
+
+	/*
+	 * prepare_flush returns 0 if no flush is needed, just mark both
+	 * pre and post flush as done in that case
+	 */
+	if (!q->prepare_flush_fn(q, flush_rq)) {
+		rq->flags |= REQ_BAR_PREFLUSH | REQ_BAR_POSTFLUSH;
+		clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
+		return rq;
+	}
+
+	/*
+	 * some drivers dequeue requests right away, some only after io
+	 * completion. make sure the request is dequeued.
+	 */
+	if (!list_empty(&rq->queuelist))
+		blkdev_dequeue_request(rq);
+
+	flush_rq->end_io_data = rq;
+	flush_rq->end_io = blk_pre_flush_end_io;
+
+	__elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+	return flush_rq;
+}
+
+static void blk_start_post_flush(request_queue_t *q, struct request *rq)
+{
+	struct request *flush_rq = q->flush_rq;
+
+	BUG_ON(!blk_barrier_rq(rq));
+
+	rq_init(q, flush_rq);
+	flush_rq->elevator_private = NULL;
+	flush_rq->flags = REQ_BAR_FLUSH;
+	flush_rq->rq_disk = rq->rq_disk;
+	flush_rq->rl = NULL;
+
+	if (q->prepare_flush_fn(q, flush_rq)) {
+		flush_rq->end_io_data = rq;
+		flush_rq->end_io = blk_post_flush_end_io;
+
+		__elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
+		q->request_fn(q);
+	}
+}
+
+static inline int blk_check_end_barrier(request_queue_t *q, struct request *rq,
+					int sectors)
+{
+	if (sectors > rq->nr_sectors)
+		sectors = rq->nr_sectors;
+
+	rq->nr_sectors -= sectors;
+	return rq->nr_sectors;
+}
+
+static int __blk_complete_barrier_rq(request_queue_t *q, struct request *rq,
+				     int sectors, int queue_locked)
+{
+	if (q->ordered != QUEUE_ORDERED_FLUSH)
+		return 0;
+	if (!blk_fs_request(rq) || !blk_barrier_rq(rq))
+		return 0;
+	if (blk_barrier_postflush(rq))
+		return 0;
+
+	if (!blk_check_end_barrier(q, rq, sectors)) {
+		unsigned long flags = 0;
+
+		if (!queue_locked)
+			spin_lock_irqsave(q->queue_lock, flags);
+
+		blk_start_post_flush(q, rq);
+
+		if (!queue_locked)
+			spin_unlock_irqrestore(q->queue_lock, flags);
+	}
+
+	return 1;
+}
+
+/**
+ * blk_complete_barrier_rq - complete possible barrier request
+ * @q:  the request queue for the device
+ * @rq:  the request
+ * @sectors:  number of sectors to complete
+ *
+ * Description:
+ *   Used in driver end_io handling to determine whether to postpone
+ *   completion of a barrier request until a post flush has been done. This
+ *   is the unlocked variant, used if the caller doesn't already hold the
+ *   queue lock.
+ **/
+int blk_complete_barrier_rq(request_queue_t *q, struct request *rq, int sectors)
+{
+	return __blk_complete_barrier_rq(q, rq, sectors, 0);
+}
+EXPORT_SYMBOL(blk_complete_barrier_rq);
+
+/**
+ * blk_complete_barrier_rq_locked - complete possible barrier request
+ * @q:  the request queue for the device
+ * @rq:  the request
+ * @sectors:  number of sectors to complete
+ *
+ * Description:
+ *   See blk_complete_barrier_rq(). This variant must be used if the caller
+ *   holds the queue lock.
+ **/
+int blk_complete_barrier_rq_locked(request_queue_t *q, struct request *rq,
+				   int sectors)
+{
+	return __blk_complete_barrier_rq(q, rq, sectors, 1);
+}
+EXPORT_SYMBOL(blk_complete_barrier_rq_locked);
+
+/**
+ * blk_queue_bounce_limit - set bounce buffer limit for queue
+ * @q:  the request queue for the device
+ * @dma_addr:   bus address limit
+ *
+ * Description:
+ *    Different hardware can have different requirements as to what pages
+ *    it can do I/O directly to. A low level driver can call
+ *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
+ *    buffers for doing I/O to pages residing above @page. By default
+ *    the block layer sets this to the highest numbered "low" memory page.
+ **/
+void blk_queue_bounce_limit(request_queue_t *q, u64 dma_addr)
+{
+	unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
+
+	/*
+	 * set appropriate bounce gfp mask -- unfortunately we don't have a
+	 * full 4GB zone, so we have to resort to low memory for any bounces.
+	 * ISA has its own < 16MB zone.
+	 */
+	if (bounce_pfn < blk_max_low_pfn) {
+		BUG_ON(dma_addr < BLK_BOUNCE_ISA);
+		init_emergency_isa_pool();
+		q->bounce_gfp = GFP_NOIO | GFP_DMA;
+	} else
+		q->bounce_gfp = GFP_NOIO;
+
+	q->bounce_pfn = bounce_pfn;
+}
+
+EXPORT_SYMBOL(blk_queue_bounce_limit);
+
+/**
+ * blk_queue_max_sectors - set max sectors for a request for this queue
+ * @q:  the request queue for the device
+ * @max_sectors:  max sectors in the usual 512b unit
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the size of
+ *    received requests.
+ **/
+void blk_queue_max_sectors(request_queue_t *q, unsigned short max_sectors)
+{
+	if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
+		max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
+		printk("%s: set to minimum %d\n", __FUNCTION__, max_sectors);
+	}
+
+	q->max_sectors = q->max_hw_sectors = max_sectors;
+}
+
+EXPORT_SYMBOL(blk_queue_max_sectors);
+
+/**
+ * blk_queue_max_phys_segments - set max phys segments for a request for this queue
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    physical data segments in a request.  This would be the largest sized
+ *    scatter list the driver could handle.
+ **/
+void blk_queue_max_phys_segments(request_queue_t *q, unsigned short max_segments)
+{
+	if (!max_segments) {
+		max_segments = 1;
+		printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+	}
+
+	q->max_phys_segments = max_segments;
+}
+
+EXPORT_SYMBOL(blk_queue_max_phys_segments);
+
+/**
+ * blk_queue_max_hw_segments - set max hw segments for a request for this queue
+ * @q:  the request queue for the device
+ * @max_segments:  max number of segments
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the number of
+ *    hw data segments in a request.  This would be the largest number of
+ *    address/length pairs the host adapter can actually give as once
+ *    to the device.
+ **/
+void blk_queue_max_hw_segments(request_queue_t *q, unsigned short max_segments)
+{
+	if (!max_segments) {
+		max_segments = 1;
+		printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
+	}
+
+	q->max_hw_segments = max_segments;
+}
+
+EXPORT_SYMBOL(blk_queue_max_hw_segments);
+
+/**
+ * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
+ * @q:  the request queue for the device
+ * @max_size:  max size of segment in bytes
+ *
+ * Description:
+ *    Enables a low level driver to set an upper limit on the size of a
+ *    coalesced segment
+ **/
+void blk_queue_max_segment_size(request_queue_t *q, unsigned int max_size)
+{
+	if (max_size < PAGE_CACHE_SIZE) {
+		max_size = PAGE_CACHE_SIZE;
+		printk("%s: set to minimum %d\n", __FUNCTION__, max_size);
+	}
+
+	q->max_segment_size = max_size;
+}
+
+EXPORT_SYMBOL(blk_queue_max_segment_size);
+
+/**
+ * blk_queue_hardsect_size - set hardware sector size for the queue
+ * @q:  the request queue for the device
+ * @size:  the hardware sector size, in bytes
+ *
+ * Description:
+ *   This should typically be set to the lowest possible sector size
+ *   that the hardware can operate on (possible without reverting to
+ *   even internal read-modify-write operations). Usually the default
+ *   of 512 covers most hardware.
+ **/
+void blk_queue_hardsect_size(request_queue_t *q, unsigned short size)
+{
+	q->hardsect_size = size;
+}
+
+EXPORT_SYMBOL(blk_queue_hardsect_size);
+
+/*
+ * Returns the minimum that is _not_ zero, unless both are zero.
+ */
+#define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
+
+/**
+ * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
+ * @t:	the stacking driver (top)
+ * @b:  the underlying device (bottom)
+ **/
+void blk_queue_stack_limits(request_queue_t *t, request_queue_t *b)
+{
+	/* zero is "infinity" */
+	t->max_sectors = t->max_hw_sectors =
+		min_not_zero(t->max_sectors,b->max_sectors);
+
+	t->max_phys_segments = min(t->max_phys_segments,b->max_phys_segments);
+	t->max_hw_segments = min(t->max_hw_segments,b->max_hw_segments);
+	t->max_segment_size = min(t->max_segment_size,b->max_segment_size);
+	t->hardsect_size = max(t->hardsect_size,b->hardsect_size);
+}
+
+EXPORT_SYMBOL(blk_queue_stack_limits);
+
+/**
+ * blk_queue_segment_boundary - set boundary rules for segment merging
+ * @q:  the request queue for the device
+ * @mask:  the memory boundary mask
+ **/
+void blk_queue_segment_boundary(request_queue_t *q, unsigned long mask)
+{
+	if (mask < PAGE_CACHE_SIZE - 1) {
+		mask = PAGE_CACHE_SIZE - 1;
+		printk("%s: set to minimum %lx\n", __FUNCTION__, mask);
+	}
+
+	q->seg_boundary_mask = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_segment_boundary);
+
+/**
+ * blk_queue_dma_alignment - set dma length and memory alignment
+ * @q:     the request queue for the device
+ * @mask:  alignment mask
+ *
+ * description:
+ *    set required memory and length aligment for direct dma transactions.
+ *    this is used when buiding direct io requests for the queue.
+ *
+ **/
+void blk_queue_dma_alignment(request_queue_t *q, int mask)
+{
+	q->dma_alignment = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_dma_alignment);
+
+/**
+ * blk_queue_find_tag - find a request by its tag and queue
+ *
+ * @q:	 The request queue for the device
+ * @tag: The tag of the request
+ *
+ * Notes:
+ *    Should be used when a device returns a tag and you want to match
+ *    it with a request.
+ *
+ *    no locks need be held.
+ **/
+struct request *blk_queue_find_tag(request_queue_t *q, int tag)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+
+	if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
+		return NULL;
+
+	return bqt->tag_index[tag];
+}
+
+EXPORT_SYMBOL(blk_queue_find_tag);
+
+/**
+ * __blk_queue_free_tags - release tag maintenance info
+ * @q:  the request queue for the device
+ *
+ *  Notes:
+ *    blk_cleanup_queue() will take care of calling this function, if tagging
+ *    has been used. So there's no need to call this directly.
+ **/
+static void __blk_queue_free_tags(request_queue_t *q)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+
+	if (!bqt)
+		return;
+
+	if (atomic_dec_and_test(&bqt->refcnt)) {
+		BUG_ON(bqt->busy);
+		BUG_ON(!list_empty(&bqt->busy_list));
+
+		kfree(bqt->tag_index);
+		bqt->tag_index = NULL;
+
+		kfree(bqt->tag_map);
+		bqt->tag_map = NULL;
+
+		kfree(bqt);
+	}
+
+	q->queue_tags = NULL;
+	q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
+}
+
+/**
+ * blk_queue_free_tags - release tag maintenance info
+ * @q:  the request queue for the device
+ *
+ *  Notes:
+ *	This is used to disabled tagged queuing to a device, yet leave
+ *	queue in function.
+ **/
+void blk_queue_free_tags(request_queue_t *q)
+{
+	clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+}
+
+EXPORT_SYMBOL(blk_queue_free_tags);
+
+static int
+init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
+{
+	struct request **tag_index;
+	unsigned long *tag_map;
+	int nr_ulongs;
+
+	if (depth > q->nr_requests * 2) {
+		depth = q->nr_requests * 2;
+		printk(KERN_ERR "%s: adjusted depth to %d\n",
+				__FUNCTION__, depth);
+	}
+
+	tag_index = kmalloc(depth * sizeof(struct request *), GFP_ATOMIC);
+	if (!tag_index)
+		goto fail;
+
+	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
+	tag_map = kmalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
+	if (!tag_map)
+		goto fail;
+
+	memset(tag_index, 0, depth * sizeof(struct request *));
+	memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
+	tags->real_max_depth = depth;
+	tags->max_depth = depth;
+	tags->tag_index = tag_index;
+	tags->tag_map = tag_map;
+
+	return 0;
+fail:
+	kfree(tag_index);
+	return -ENOMEM;
+}
+
+/**
+ * blk_queue_init_tags - initialize the queue tag info
+ * @q:  the request queue for the device
+ * @depth:  the maximum queue depth supported
+ * @tags: the tag to use
+ **/
+int blk_queue_init_tags(request_queue_t *q, int depth,
+			struct blk_queue_tag *tags)
+{
+	int rc;
+
+	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
+
+	if (!tags && !q->queue_tags) {
+		tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
+		if (!tags)
+			goto fail;
+
+		if (init_tag_map(q, tags, depth))
+			goto fail;
+
+		INIT_LIST_HEAD(&tags->busy_list);
+		tags->busy = 0;
+		atomic_set(&tags->refcnt, 1);
+	} else if (q->queue_tags) {
+		if ((rc = blk_queue_resize_tags(q, depth)))
+			return rc;
+		set_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
+		return 0;
+	} else
+		atomic_inc(&tags->refcnt);
+
+	/*
+	 * assign it, all done
+	 */
+	q->queue_tags = tags;
+	q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
+	return 0;
+fail:
+	kfree(tags);
+	return -ENOMEM;
+}
+
+EXPORT_SYMBOL(blk_queue_init_tags);
+
+/**
+ * blk_queue_resize_tags - change the queueing depth
+ * @q:  the request queue for the device
+ * @new_depth: the new max command queueing depth
+ *
+ *  Notes:
+ *    Must be called with the queue lock held.
+ **/
+int blk_queue_resize_tags(request_queue_t *q, int new_depth)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+	struct request **tag_index;
+	unsigned long *tag_map;
+	int max_depth, nr_ulongs;
+
+	if (!bqt)
+		return -ENXIO;
+
+	/*
+	 * if we already have large enough real_max_depth.  just
+	 * adjust max_depth.  *NOTE* as requests with tag value
+	 * between new_depth and real_max_depth can be in-flight, tag
+	 * map can not be shrunk blindly here.
+	 */
+	if (new_depth <= bqt->real_max_depth) {
+		bqt->max_depth = new_depth;
+		return 0;
+	}
+
+	/*
+	 * save the old state info, so we can copy it back
+	 */
+	tag_index = bqt->tag_index;
+	tag_map = bqt->tag_map;
+	max_depth = bqt->real_max_depth;
+
+	if (init_tag_map(q, bqt, new_depth))
+		return -ENOMEM;
+
+	memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
+	nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
+	memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
+
+	kfree(tag_index);
+	kfree(tag_map);
+	return 0;
+}
+
+EXPORT_SYMBOL(blk_queue_resize_tags);
+
+/**
+ * blk_queue_end_tag - end tag operations for a request
+ * @q:  the request queue for the device
+ * @rq: the request that has completed
+ *
+ *  Description:
+ *    Typically called when end_that_request_first() returns 0, meaning
+ *    all transfers have been done for a request. It's important to call
+ *    this function before end_that_request_last(), as that will put the
+ *    request back on the free list thus corrupting the internal tag list.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+void blk_queue_end_tag(request_queue_t *q, struct request *rq)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+	int tag = rq->tag;
+
+	BUG_ON(tag == -1);
+
+	if (unlikely(tag >= bqt->real_max_depth))
+		/*
+		 * This can happen after tag depth has been reduced.
+		 * FIXME: how about a warning or info message here?
+		 */
+		return;
+
+	if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
+		printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
+		       __FUNCTION__, tag);
+		return;
+	}
+
+	list_del_init(&rq->queuelist);
+	rq->flags &= ~REQ_QUEUED;
+	rq->tag = -1;
+
+	if (unlikely(bqt->tag_index[tag] == NULL))
+		printk(KERN_ERR "%s: tag %d is missing\n",
+		       __FUNCTION__, tag);
+
+	bqt->tag_index[tag] = NULL;
+	bqt->busy--;
+}
+
+EXPORT_SYMBOL(blk_queue_end_tag);
+
+/**
+ * blk_queue_start_tag - find a free tag and assign it
+ * @q:  the request queue for the device
+ * @rq:  the block request that needs tagging
+ *
+ *  Description:
+ *    This can either be used as a stand-alone helper, or possibly be
+ *    assigned as the queue &prep_rq_fn (in which case &struct request
+ *    automagically gets a tag assigned). Note that this function
+ *    assumes that any type of request can be queued! if this is not
+ *    true for your device, you must check the request type before
+ *    calling this function.  The request will also be removed from
+ *    the request queue, so it's the drivers responsibility to readd
+ *    it if it should need to be restarted for some reason.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+int blk_queue_start_tag(request_queue_t *q, struct request *rq)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+	int tag;
+
+	if (unlikely((rq->flags & REQ_QUEUED))) {
+		printk(KERN_ERR 
+		       "%s: request %p for device [%s] already tagged %d",
+		       __FUNCTION__, rq,
+		       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
+		BUG();
+	}
+
+	tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
+	if (tag >= bqt->max_depth)
+		return 1;
+
+	__set_bit(tag, bqt->tag_map);
+
+	rq->flags |= REQ_QUEUED;
+	rq->tag = tag;
+	bqt->tag_index[tag] = rq;
+	blkdev_dequeue_request(rq);
+	list_add(&rq->queuelist, &bqt->busy_list);
+	bqt->busy++;
+	return 0;
+}
+
+EXPORT_SYMBOL(blk_queue_start_tag);
+
+/**
+ * blk_queue_invalidate_tags - invalidate all pending tags
+ * @q:  the request queue for the device
+ *
+ *  Description:
+ *   Hardware conditions may dictate a need to stop all pending requests.
+ *   In this case, we will safely clear the block side of the tag queue and
+ *   readd all requests to the request queue in the right order.
+ *
+ *  Notes:
+ *   queue lock must be held.
+ **/
+void blk_queue_invalidate_tags(request_queue_t *q)
+{
+	struct blk_queue_tag *bqt = q->queue_tags;
+	struct list_head *tmp, *n;
+	struct request *rq;
+
+	list_for_each_safe(tmp, n, &bqt->busy_list) {
+		rq = list_entry_rq(tmp);
+
+		if (rq->tag == -1) {
+			printk(KERN_ERR
+			       "%s: bad tag found on list\n", __FUNCTION__);
+			list_del_init(&rq->queuelist);
+			rq->flags &= ~REQ_QUEUED;
+		} else
+			blk_queue_end_tag(q, rq);
+
+		rq->flags &= ~REQ_STARTED;
+		__elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
+	}
+}
+
+EXPORT_SYMBOL(blk_queue_invalidate_tags);
+
+static char *rq_flags[] = {
+	"REQ_RW",
+	"REQ_FAILFAST",
+	"REQ_SORTED",
+	"REQ_SOFTBARRIER",
+	"REQ_HARDBARRIER",
+	"REQ_CMD",
+	"REQ_NOMERGE",
+	"REQ_STARTED",
+	"REQ_DONTPREP",
+	"REQ_QUEUED",
+	"REQ_ELVPRIV",
+	"REQ_PC",
+	"REQ_BLOCK_PC",
+	"REQ_SENSE",
+	"REQ_FAILED",
+	"REQ_QUIET",
+	"REQ_SPECIAL",
+	"REQ_DRIVE_CMD",
+	"REQ_DRIVE_TASK",
+	"REQ_DRIVE_TASKFILE",
+	"REQ_PREEMPT",
+	"REQ_PM_SUSPEND",
+	"REQ_PM_RESUME",
+	"REQ_PM_SHUTDOWN",
+};
+
+void blk_dump_rq_flags(struct request *rq, char *msg)
+{
+	int bit;
+
+	printk("%s: dev %s: flags = ", msg,
+		rq->rq_disk ? rq->rq_disk->disk_name : "?");
+	bit = 0;
+	do {
+		if (rq->flags & (1 << bit))
+			printk("%s ", rq_flags[bit]);
+		bit++;
+	} while (bit < __REQ_NR_BITS);
+
+	printk("\nsector %llu, nr/cnr %lu/%u\n", (unsigned long long)rq->sector,
+						       rq->nr_sectors,
+						       rq->current_nr_sectors);
+	printk("bio %p, biotail %p, buffer %p, data %p, len %u\n", rq->bio, rq->biotail, rq->buffer, rq->data, rq->data_len);
+
+	if (rq->flags & (REQ_BLOCK_PC | REQ_PC)) {
+		printk("cdb: ");
+		for (bit = 0; bit < sizeof(rq->cmd); bit++)
+			printk("%02x ", rq->cmd[bit]);
+		printk("\n");
+	}
+}
+
+EXPORT_SYMBOL(blk_dump_rq_flags);
+
+void blk_recount_segments(request_queue_t *q, struct bio *bio)
+{
+	struct bio_vec *bv, *bvprv = NULL;
+	int i, nr_phys_segs, nr_hw_segs, seg_size, hw_seg_size, cluster;
+	int high, highprv = 1;
+
+	if (unlikely(!bio->bi_io_vec))
+		return;
+
+	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+	hw_seg_size = seg_size = nr_phys_segs = nr_hw_segs = 0;
+	bio_for_each_segment(bv, bio, i) {
+		/*
+		 * the trick here is making sure that a high page is never
+		 * considered part of another segment, since that might
+		 * change with the bounce page.
+		 */
+		high = page_to_pfn(bv->bv_page) >= q->bounce_pfn;
+		if (high || highprv)
+			goto new_hw_segment;
+		if (cluster) {
+			if (seg_size + bv->bv_len > q->max_segment_size)
+				goto new_segment;
+			if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
+				goto new_segment;
+			if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
+				goto new_segment;
+			if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
+				goto new_hw_segment;
+
+			seg_size += bv->bv_len;
+			hw_seg_size += bv->bv_len;
+			bvprv = bv;
+			continue;
+		}
+new_segment:
+		if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
+		    !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len)) {
+			hw_seg_size += bv->bv_len;
+		} else {
+new_hw_segment:
+			if (hw_seg_size > bio->bi_hw_front_size)
+				bio->bi_hw_front_size = hw_seg_size;
+			hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
+			nr_hw_segs++;
+		}
+
+		nr_phys_segs++;
+		bvprv = bv;
+		seg_size = bv->bv_len;
+		highprv = high;
+	}
+	if (hw_seg_size > bio->bi_hw_back_size)
+		bio->bi_hw_back_size = hw_seg_size;
+	if (nr_hw_segs == 1 && hw_seg_size > bio->bi_hw_front_size)
+		bio->bi_hw_front_size = hw_seg_size;
+	bio->bi_phys_segments = nr_phys_segs;
+	bio->bi_hw_segments = nr_hw_segs;
+	bio->bi_flags |= (1 << BIO_SEG_VALID);
+}
+
+
+static int blk_phys_contig_segment(request_queue_t *q, struct bio *bio,
+				   struct bio *nxt)
+{
+	if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
+		return 0;
+
+	if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
+		return 0;
+	if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+		return 0;
+
+	/*
+	 * bio and nxt are contigous in memory, check if the queue allows
+	 * these two to be merged into one
+	 */
+	if (BIO_SEG_BOUNDARY(q, bio, nxt))
+		return 1;
+
+	return 0;
+}
+
+static int blk_hw_contig_segment(request_queue_t *q, struct bio *bio,
+				 struct bio *nxt)
+{
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
+		blk_recount_segments(q, nxt);
+	if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
+	    BIOVEC_VIRT_OVERSIZE(bio->bi_hw_front_size + bio->bi_hw_back_size))
+		return 0;
+	if (bio->bi_size + nxt->bi_size > q->max_segment_size)
+		return 0;
+
+	return 1;
+}
+
+/*
+ * map a request to scatterlist, return number of sg entries setup. Caller
+ * must make sure sg can hold rq->nr_phys_segments entries
+ */
+int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg)
+{
+	struct bio_vec *bvec, *bvprv;
+	struct bio *bio;
+	int nsegs, i, cluster;
+
+	nsegs = 0;
+	cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
+
+	/*
+	 * for each bio in rq
+	 */
+	bvprv = NULL;
+	rq_for_each_bio(bio, rq) {
+		/*
+		 * for each segment in bio
+		 */
+		bio_for_each_segment(bvec, bio, i) {
+			int nbytes = bvec->bv_len;
+
+			if (bvprv && cluster) {
+				if (sg[nsegs - 1].length + nbytes > q->max_segment_size)
+					goto new_segment;
+
+				if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
+					goto new_segment;
+				if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
+					goto new_segment;
+
+				sg[nsegs - 1].length += nbytes;
+			} else {
+new_segment:
+				memset(&sg[nsegs],0,sizeof(struct scatterlist));
+				sg[nsegs].page = bvec->bv_page;
+				sg[nsegs].length = nbytes;
+				sg[nsegs].offset = bvec->bv_offset;
+
+				nsegs++;
+			}
+			bvprv = bvec;
+		} /* segments in bio */
+	} /* bios in rq */
+
+	return nsegs;
+}
+
+EXPORT_SYMBOL(blk_rq_map_sg);
+
+/*
+ * the standard queue merge functions, can be overridden with device
+ * specific ones if so desired
+ */
+
+static inline int ll_new_mergeable(request_queue_t *q,
+				   struct request *req,
+				   struct bio *bio)
+{
+	int nr_phys_segs = bio_phys_segments(q, bio);
+
+	if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+		req->flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+
+	/*
+	 * A hw segment is just getting larger, bump just the phys
+	 * counter.
+	 */
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+}
+
+static inline int ll_new_hw_segment(request_queue_t *q,
+				    struct request *req,
+				    struct bio *bio)
+{
+	int nr_hw_segs = bio_hw_segments(q, bio);
+	int nr_phys_segs = bio_phys_segments(q, bio);
+
+	if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
+	    || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
+		req->flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+
+	/*
+	 * This will form the start of a new hw segment.  Bump both
+	 * counters.
+	 */
+	req->nr_hw_segments += nr_hw_segs;
+	req->nr_phys_segments += nr_phys_segs;
+	return 1;
+}
+
+static int ll_back_merge_fn(request_queue_t *q, struct request *req, 
+			    struct bio *bio)
+{
+	int len;
+
+	if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+		req->flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
+		blk_recount_segments(q, req->biotail);
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
+	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
+	    !BIOVEC_VIRT_OVERSIZE(len)) {
+		int mergeable =  ll_new_mergeable(q, req, bio);
+
+		if (mergeable) {
+			if (req->nr_hw_segments == 1)
+				req->bio->bi_hw_front_size = len;
+			if (bio->bi_hw_segments == 1)
+				bio->bi_hw_back_size = len;
+		}
+		return mergeable;
+	}
+
+	return ll_new_hw_segment(q, req, bio);
+}
+
+static int ll_front_merge_fn(request_queue_t *q, struct request *req, 
+			     struct bio *bio)
+{
+	int len;
+
+	if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
+		req->flags |= REQ_NOMERGE;
+		if (req == q->last_merge)
+			q->last_merge = NULL;
+		return 0;
+	}
+	len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
+	if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, bio);
+	if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
+		blk_recount_segments(q, req->bio);
+	if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
+	    !BIOVEC_VIRT_OVERSIZE(len)) {
+		int mergeable =  ll_new_mergeable(q, req, bio);
+
+		if (mergeable) {
+			if (bio->bi_hw_segments == 1)
+				bio->bi_hw_front_size = len;
+			if (req->nr_hw_segments == 1)
+				req->biotail->bi_hw_back_size = len;
+		}
+		return mergeable;
+	}
+
+	return ll_new_hw_segment(q, req, bio);
+}
+
+static int ll_merge_requests_fn(request_queue_t *q, struct request *req,
+				struct request *next)
+{
+	int total_phys_segments;
+	int total_hw_segments;
+
+	/*
+	 * First check if the either of the requests are re-queued
+	 * requests.  Can't merge them if they are.
+	 */
+	if (req->special || next->special)
+		return 0;
+
+	/*
+	 * Will it become too large?
+	 */
+	if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
+		return 0;
+
+	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
+	if (blk_phys_contig_segment(q, req->biotail, next->bio))
+		total_phys_segments--;
+
+	if (total_phys_segments > q->max_phys_segments)
+		return 0;
+
+	total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
+	if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
+		int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
+		/*
+		 * propagate the combined length to the end of the requests
+		 */
+		if (req->nr_hw_segments == 1)
+			req->bio->bi_hw_front_size = len;
+		if (next->nr_hw_segments == 1)
+			next->biotail->bi_hw_back_size = len;
+		total_hw_segments--;
+	}
+
+	if (total_hw_segments > q->max_hw_segments)
+		return 0;
+
+	/* Merge is OK... */
+	req->nr_phys_segments = total_phys_segments;
+	req->nr_hw_segments = total_hw_segments;
+	return 1;
+}
+
+/*
+ * "plug" the device if there are no outstanding requests: this will
+ * force the transfer to start only after we have put all the requests
+ * on the list.
+ *
+ * This is called with interrupts off and no requests on the queue and
+ * with the queue lock held.
+ */
+void blk_plug_device(request_queue_t *q)
+{
+	WARN_ON(!irqs_disabled());
+
+	/*
+	 * don't plug a stopped queue, it must be paired with blk_start_queue()
+	 * which will restart the queueing
+	 */
+	if (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags))
+		return;
+
+	if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+		mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
+}
+
+EXPORT_SYMBOL(blk_plug_device);
+
+/*
+ * remove the queue from the plugged list, if present. called with
+ * queue lock held and interrupts disabled.
+ */
+int blk_remove_plug(request_queue_t *q)
+{
+	WARN_ON(!irqs_disabled());
+
+	if (!test_and_clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
+		return 0;
+
+	del_timer(&q->unplug_timer);
+	return 1;
+}
+
+EXPORT_SYMBOL(blk_remove_plug);
+
+/*
+ * remove the plug and let it rip..
+ */
+void __generic_unplug_device(request_queue_t *q)
+{
+	if (unlikely(test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)))
+		return;
+
+	if (!blk_remove_plug(q))
+		return;
+
+	q->request_fn(q);
+}
+EXPORT_SYMBOL(__generic_unplug_device);
+
+/**
+ * generic_unplug_device - fire a request queue
+ * @q:    The &request_queue_t in question
+ *
+ * Description:
+ *   Linux uses plugging to build bigger requests queues before letting
+ *   the device have at them. If a queue is plugged, the I/O scheduler
+ *   is still adding and merging requests on the queue. Once the queue
+ *   gets unplugged, the request_fn defined for the queue is invoked and
+ *   transfers started.
+ **/
+void generic_unplug_device(request_queue_t *q)
+{
+	spin_lock_irq(q->queue_lock);
+	__generic_unplug_device(q);
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(generic_unplug_device);
+
+static void blk_backing_dev_unplug(struct backing_dev_info *bdi,
+				   struct page *page)
+{
+	request_queue_t *q = bdi->unplug_io_data;
+
+	/*
+	 * devices don't necessarily have an ->unplug_fn defined
+	 */
+	if (q->unplug_fn)
+		q->unplug_fn(q);
+}
+
+static void blk_unplug_work(void *data)
+{
+	request_queue_t *q = data;
+
+	q->unplug_fn(q);
+}
+
+static void blk_unplug_timeout(unsigned long data)
+{
+	request_queue_t *q = (request_queue_t *)data;
+
+	kblockd_schedule_work(&q->unplug_work);
+}
+
+/**
+ * blk_start_queue - restart a previously stopped queue
+ * @q:    The &request_queue_t in question
+ *
+ * Description:
+ *   blk_start_queue() will clear the stop flag on the queue, and call
+ *   the request_fn for the queue if it was in a stopped state when
+ *   entered. Also see blk_stop_queue(). Queue lock must be held.
+ **/
+void blk_start_queue(request_queue_t *q)
+{
+	clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+
+	/*
+	 * one level of recursion is ok and is much faster than kicking
+	 * the unplug handling
+	 */
+	if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
+		q->request_fn(q);
+		clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
+	} else {
+		blk_plug_device(q);
+		kblockd_schedule_work(&q->unplug_work);
+	}
+}
+
+EXPORT_SYMBOL(blk_start_queue);
+
+/**
+ * blk_stop_queue - stop a queue
+ * @q:    The &request_queue_t in question
+ *
+ * Description:
+ *   The Linux block layer assumes that a block driver will consume all
+ *   entries on the request queue when the request_fn strategy is called.
+ *   Often this will not happen, because of hardware limitations (queue
+ *   depth settings). If a device driver gets a 'queue full' response,
+ *   or if it simply chooses not to queue more I/O at one point, it can
+ *   call this function to prevent the request_fn from being called until
+ *   the driver has signalled it's ready to go again. This happens by calling
+ *   blk_start_queue() to restart queue operations. Queue lock must be held.
+ **/
+void blk_stop_queue(request_queue_t *q)
+{
+	blk_remove_plug(q);
+	set_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
+}
+EXPORT_SYMBOL(blk_stop_queue);
+
+/**
+ * blk_sync_queue - cancel any pending callbacks on a queue
+ * @q: the queue
+ *
+ * Description:
+ *     The block layer may perform asynchronous callback activity
+ *     on a queue, such as calling the unplug function after a timeout.
+ *     A block device may call blk_sync_queue to ensure that any
+ *     such activity is cancelled, thus allowing it to release resources
+ *     the the callbacks might use. The caller must already have made sure
+ *     that its ->make_request_fn will not re-add plugging prior to calling
+ *     this function.
+ *
+ */
+void blk_sync_queue(struct request_queue *q)
+{
+	del_timer_sync(&q->unplug_timer);
+	kblockd_flush();
+}
+EXPORT_SYMBOL(blk_sync_queue);
+
+/**
+ * blk_run_queue - run a single device queue
+ * @q:	The queue to run
+ */
+void blk_run_queue(struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	blk_remove_plug(q);
+	if (!elv_queue_empty(q))
+		q->request_fn(q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_run_queue);
+
+/**
+ * blk_cleanup_queue: - release a &request_queue_t when it is no longer needed
+ * @q:    the request queue to be released
+ *
+ * Description:
+ *     blk_cleanup_queue is the pair to blk_init_queue() or
+ *     blk_queue_make_request().  It should be called when a request queue is
+ *     being released; typically when a block device is being de-registered.
+ *     Currently, its primary task it to free all the &struct request
+ *     structures that were allocated to the queue and the queue itself.
+ *
+ * Caveat:
+ *     Hopefully the low level driver will have finished any
+ *     outstanding requests first...
+ **/
+void blk_cleanup_queue(request_queue_t * q)
+{
+	struct request_list *rl = &q->rq;
+
+	if (!atomic_dec_and_test(&q->refcnt))
+		return;
+
+	if (q->elevator)
+		elevator_exit(q->elevator);
+
+	blk_sync_queue(q);
+
+	if (rl->rq_pool)
+		mempool_destroy(rl->rq_pool);
+
+	if (q->queue_tags)
+		__blk_queue_free_tags(q);
+
+	blk_queue_ordered(q, QUEUE_ORDERED_NONE);
+
+	kmem_cache_free(requestq_cachep, q);
+}
+
+EXPORT_SYMBOL(blk_cleanup_queue);
+
+static int blk_init_free_list(request_queue_t *q)
+{
+	struct request_list *rl = &q->rq;
+
+	rl->count[READ] = rl->count[WRITE] = 0;
+	rl->starved[READ] = rl->starved[WRITE] = 0;
+	rl->elvpriv = 0;
+	init_waitqueue_head(&rl->wait[READ]);
+	init_waitqueue_head(&rl->wait[WRITE]);
+
+	rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
+				mempool_free_slab, request_cachep, q->node);
+
+	if (!rl->rq_pool)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int __make_request(request_queue_t *, struct bio *);
+
+request_queue_t *blk_alloc_queue(gfp_t gfp_mask)
+{
+	return blk_alloc_queue_node(gfp_mask, -1);
+}
+EXPORT_SYMBOL(blk_alloc_queue);
+
+request_queue_t *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
+{
+	request_queue_t *q;
+
+	q = kmem_cache_alloc_node(requestq_cachep, gfp_mask, node_id);
+	if (!q)
+		return NULL;
+
+	memset(q, 0, sizeof(*q));
+	init_timer(&q->unplug_timer);
+	atomic_set(&q->refcnt, 1);
+
+	q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
+	q->backing_dev_info.unplug_io_data = q;
+
+	return q;
+}
+EXPORT_SYMBOL(blk_alloc_queue_node);
+
+/**
+ * blk_init_queue  - prepare a request queue for use with a block device
+ * @rfn:  The function to be called to process requests that have been
+ *        placed on the queue.
+ * @lock: Request queue spin lock
+ *
+ * Description:
+ *    If a block device wishes to use the standard request handling procedures,
+ *    which sorts requests and coalesces adjacent requests, then it must
+ *    call blk_init_queue().  The function @rfn will be called when there
+ *    are requests on the queue that need to be processed.  If the device
+ *    supports plugging, then @rfn may not be called immediately when requests
+ *    are available on the queue, but may be called at some time later instead.
+ *    Plugged queues are generally unplugged when a buffer belonging to one
+ *    of the requests on the queue is needed, or due to memory pressure.
+ *
+ *    @rfn is not required, or even expected, to remove all requests off the
+ *    queue, but only as many as it can handle at a time.  If it does leave
+ *    requests on the queue, it is responsible for arranging that the requests
+ *    get dealt with eventually.
+ *
+ *    The queue spin lock must be held while manipulating the requests on the
+ *    request queue.
+ *
+ *    Function returns a pointer to the initialized request queue, or NULL if
+ *    it didn't succeed.
+ *
+ * Note:
+ *    blk_init_queue() must be paired with a blk_cleanup_queue() call
+ *    when the block device is deactivated (such as at module unload).
+ **/
+
+request_queue_t *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+{
+	return blk_init_queue_node(rfn, lock, -1);
+}
+EXPORT_SYMBOL(blk_init_queue);
+
+request_queue_t *
+blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+{
+	request_queue_t *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
+
+	if (!q)
+		return NULL;
+
+	q->node = node_id;
+	if (blk_init_free_list(q))
+		goto out_init;
+
+	/*
+	 * if caller didn't supply a lock, they get per-queue locking with
+	 * our embedded lock
+	 */
+	if (!lock) {
+		spin_lock_init(&q->__queue_lock);
+		lock = &q->__queue_lock;
+	}
+
+	q->request_fn		= rfn;
+	q->back_merge_fn       	= ll_back_merge_fn;
+	q->front_merge_fn      	= ll_front_merge_fn;
+	q->merge_requests_fn	= ll_merge_requests_fn;
+	q->prep_rq_fn		= NULL;
+	q->unplug_fn		= generic_unplug_device;
+	q->queue_flags		= (1 << QUEUE_FLAG_CLUSTER);
+	q->queue_lock		= lock;
+
+	blk_queue_segment_boundary(q, 0xffffffff);
+
+	blk_queue_make_request(q, __make_request);
+	blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
+
+	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
+	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
+
+	/*
+	 * all done
+	 */
+	if (!elevator_init(q, NULL)) {
+		blk_queue_congestion_threshold(q);
+		return q;
+	}
+
+	blk_cleanup_queue(q);
+out_init:
+	kmem_cache_free(requestq_cachep, q);
+	return NULL;
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+int blk_get_queue(request_queue_t *q)
+{
+	if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
+		atomic_inc(&q->refcnt);
+		return 0;
+	}
+
+	return 1;
+}
+
+EXPORT_SYMBOL(blk_get_queue);
+
+static inline void blk_free_request(request_queue_t *q, struct request *rq)
+{
+	if (rq->flags & REQ_ELVPRIV)
+		elv_put_request(q, rq);
+	mempool_free(rq, q->rq.rq_pool);
+}
+
+static inline struct request *
+blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
+		  int priv, gfp_t gfp_mask)
+{
+	struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
+
+	if (!rq)
+		return NULL;
+
+	/*
+	 * first three bits are identical in rq->flags and bio->bi_rw,
+	 * see bio.h and blkdev.h
+	 */
+	rq->flags = rw;
+
+	if (priv) {
+		if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
+			mempool_free(rq, q->rq.rq_pool);
+			return NULL;
+		}
+		rq->flags |= REQ_ELVPRIV;
+	}
+
+	return rq;
+}
+
+/*
+ * ioc_batching returns true if the ioc is a valid batching request and
+ * should be given priority access to a request.
+ */
+static inline int ioc_batching(request_queue_t *q, struct io_context *ioc)
+{
+	if (!ioc)
+		return 0;
+
+	/*
+	 * Make sure the process is able to allocate at least 1 request
+	 * even if the batch times out, otherwise we could theoretically
+	 * lose wakeups.
+	 */
+	return ioc->nr_batch_requests == q->nr_batching ||
+		(ioc->nr_batch_requests > 0
+		&& time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
+}
+
+/*
+ * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
+ * will cause the process to be a "batcher" on all queues in the system. This
+ * is the behaviour we want though - once it gets a wakeup it should be given
+ * a nice run.
+ */
+static void ioc_set_batching(request_queue_t *q, struct io_context *ioc)
+{
+	if (!ioc || ioc_batching(q, ioc))
+		return;
+
+	ioc->nr_batch_requests = q->nr_batching;
+	ioc->last_waited = jiffies;
+}
+
+static void __freed_request(request_queue_t *q, int rw)
+{
+	struct request_list *rl = &q->rq;
+
+	if (rl->count[rw] < queue_congestion_off_threshold(q))
+		clear_queue_congested(q, rw);
+
+	if (rl->count[rw] + 1 <= q->nr_requests) {
+		if (waitqueue_active(&rl->wait[rw]))
+			wake_up(&rl->wait[rw]);
+
+		blk_clear_queue_full(q, rw);
+	}
+}
+
+/*
+ * A request has just been released.  Account for it, update the full and
+ * congestion status, wake up any waiters.   Called under q->queue_lock.
+ */
+static void freed_request(request_queue_t *q, int rw, int priv)
+{
+	struct request_list *rl = &q->rq;
+
+	rl->count[rw]--;
+	if (priv)
+		rl->elvpriv--;
+
+	__freed_request(q, rw);
+
+	if (unlikely(rl->starved[rw ^ 1]))
+		__freed_request(q, rw ^ 1);
+}
+
+#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
+/*
+ * Get a free request, queue_lock must be held.
+ * Returns NULL on failure, with queue_lock held.
+ * Returns !NULL on success, with queue_lock *not held*.
+ */
+static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
+				   gfp_t gfp_mask)
+{
+	struct request *rq = NULL;
+	struct request_list *rl = &q->rq;
+	struct io_context *ioc = current_io_context(GFP_ATOMIC);
+	int priv;
+
+	if (rl->count[rw]+1 >= q->nr_requests) {
+		/*
+		 * The queue will fill after this allocation, so set it as
+		 * full, and mark this process as "batching". This process
+		 * will be allowed to complete a batch of requests, others
+		 * will be blocked.
+		 */
+		if (!blk_queue_full(q, rw)) {
+			ioc_set_batching(q, ioc);
+			blk_set_queue_full(q, rw);
+		}
+	}
+
+	switch (elv_may_queue(q, rw, bio)) {
+		case ELV_MQUEUE_NO:
+			goto rq_starved;
+		case ELV_MQUEUE_MAY:
+			break;
+		case ELV_MQUEUE_MUST:
+			goto get_rq;
+	}
+
+	if (blk_queue_full(q, rw) && !ioc_batching(q, ioc)) {
+		/*
+		 * The queue is full and the allocating process is not a
+		 * "batcher", and not exempted by the IO scheduler
+		 */
+		goto out;
+	}
+
+get_rq:
+	/*
+	 * Only allow batching queuers to allocate up to 50% over the defined
+	 * limit of requests, otherwise we could have thousands of requests
+	 * allocated with any setting of ->nr_requests
+	 */
+	if (rl->count[rw] >= (3 * q->nr_requests / 2))
+		goto out;
+
+	rl->count[rw]++;
+	rl->starved[rw] = 0;
+	if (rl->count[rw] >= queue_congestion_on_threshold(q))
+		set_queue_congested(q, rw);
+
+	priv = !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
+	if (priv)
+		rl->elvpriv++;
+
+	spin_unlock_irq(q->queue_lock);
+
+	rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
+	if (!rq) {
+		/*
+		 * Allocation failed presumably due to memory. Undo anything
+		 * we might have messed up.
+		 *
+		 * Allocating task should really be put onto the front of the
+		 * wait queue, but this is pretty rare.
+		 */
+		spin_lock_irq(q->queue_lock);
+		freed_request(q, rw, priv);
+
+		/*
+		 * in the very unlikely event that allocation failed and no
+		 * requests for this direction was pending, mark us starved
+		 * so that freeing of a request in the other direction will
+		 * notice us. another possible fix would be to split the
+		 * rq mempool into READ and WRITE
+		 */
+rq_starved:
+		if (unlikely(rl->count[rw] == 0))
+			rl->starved[rw] = 1;
+
+		goto out;
+	}
+
+	if (ioc_batching(q, ioc))
+		ioc->nr_batch_requests--;
+	
+	rq_init(q, rq);
+	rq->rl = rl;
+out:
+	return rq;
+}
+
+/*
+ * No available requests for this queue, unplug the device and wait for some
+ * requests to become available.
+ *
+ * Called with q->queue_lock held, and returns with it unlocked.
+ */
+static struct request *get_request_wait(request_queue_t *q, int rw,
+					struct bio *bio)
+{
+	struct request *rq;
+
+	rq = get_request(q, rw, bio, GFP_NOIO);
+	while (!rq) {
+		DEFINE_WAIT(wait);
+		struct request_list *rl = &q->rq;
+
+		prepare_to_wait_exclusive(&rl->wait[rw], &wait,
+				TASK_UNINTERRUPTIBLE);
+
+		rq = get_request(q, rw, bio, GFP_NOIO);
+
+		if (!rq) {
+			struct io_context *ioc;
+
+			__generic_unplug_device(q);
+			spin_unlock_irq(q->queue_lock);
+			io_schedule();
+
+			/*
+			 * After sleeping, we become a "batching" process and
+			 * will be able to allocate at least one request, and
+			 * up to a big batch of them for a small period time.
+			 * See ioc_batching, ioc_set_batching
+			 */
+			ioc = current_io_context(GFP_NOIO);
+			ioc_set_batching(q, ioc);
+
+			spin_lock_irq(q->queue_lock);
+		}
+		finish_wait(&rl->wait[rw], &wait);
+	}
+
+	return rq;
+}
+
+struct request *blk_get_request(request_queue_t *q, int rw, gfp_t gfp_mask)
+{
+	struct request *rq;
+
+	BUG_ON(rw != READ && rw != WRITE);
+
+	spin_lock_irq(q->queue_lock);
+	if (gfp_mask & __GFP_WAIT) {
+		rq = get_request_wait(q, rw, NULL);
+	} else {
+		rq = get_request(q, rw, NULL, gfp_mask);
+		if (!rq)
+			spin_unlock_irq(q->queue_lock);
+	}
+	/* q->queue_lock is unlocked at this point */
+
+	return rq;
+}
+EXPORT_SYMBOL(blk_get_request);
+
+/**
+ * blk_requeue_request - put a request back on queue
+ * @q:		request queue where request should be inserted
+ * @rq:		request to be inserted
+ *
+ * Description:
+ *    Drivers often keep queueing requests until the hardware cannot accept
+ *    more, when that condition happens we need to put the request back
+ *    on the queue. Must be called with queue lock held.
+ */
+void blk_requeue_request(request_queue_t *q, struct request *rq)
+{
+	if (blk_rq_tagged(rq))
+		blk_queue_end_tag(q, rq);
+
+	elv_requeue_request(q, rq);
+}
+
+EXPORT_SYMBOL(blk_requeue_request);
+
+/**
+ * blk_insert_request - insert a special request in to a request queue
+ * @q:		request queue where request should be inserted
+ * @rq:		request to be inserted
+ * @at_head:	insert request at head or tail of queue
+ * @data:	private data
+ *
+ * Description:
+ *    Many block devices need to execute commands asynchronously, so they don't
+ *    block the whole kernel from preemption during request execution.  This is
+ *    accomplished normally by inserting aritficial requests tagged as
+ *    REQ_SPECIAL in to the corresponding request queue, and letting them be
+ *    scheduled for actual execution by the request queue.
+ *
+ *    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.
+ */
+void blk_insert_request(request_queue_t *q, struct request *rq,
+			int at_head, void *data)
+{
+	int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+	unsigned long flags;
+
+	/*
+	 * tell I/O scheduler that this isn't a regular read/write (ie it
+	 * must not attempt merges on this) and that it acts as a soft
+	 * barrier
+	 */
+	rq->flags |= REQ_SPECIAL | REQ_SOFTBARRIER;
+
+	rq->special = data;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+
+	/*
+	 * If command is tagged, release the tag
+	 */
+	if (blk_rq_tagged(rq))
+		blk_queue_end_tag(q, rq);
+
+	drive_stat_acct(rq, rq->nr_sectors, 1);
+	__elv_add_request(q, rq, where, 0);
+
+	if (blk_queue_plugged(q))
+		__generic_unplug_device(q);
+	else
+		q->request_fn(q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+EXPORT_SYMBOL(blk_insert_request);
+
+/**
+ * blk_rq_map_user - map user data to a request, for REQ_BLOCK_PC usage
+ * @q:		request queue where request should be inserted
+ * @rq:		request structure to fill
+ * @ubuf:	the user buffer
+ * @len:	length of user data
+ *
+ * Description:
+ *    Data will be mapped directly for zero copy io, if possible. Otherwise
+ *    a kernel bounce buffer is used.
+ *
+ *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+ *    still in process context.
+ *
+ *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+ *    before being submitted to the device, as pages mapped may be out of
+ *    reach. It's the callers responsibility to make sure this happens. The
+ *    original bio must be passed back in to blk_rq_unmap_user() for proper
+ *    unmapping.
+ */
+int blk_rq_map_user(request_queue_t *q, struct request *rq, void __user *ubuf,
+		    unsigned int len)
+{
+	unsigned long uaddr;
+	struct bio *bio;
+	int reading;
+
+	if (len > (q->max_sectors << 9))
+		return -EINVAL;
+	if (!len || !ubuf)
+		return -EINVAL;
+
+	reading = rq_data_dir(rq) == READ;
+
+	/*
+	 * if alignment requirement is satisfied, map in user pages for
+	 * direct dma. else, set up kernel bounce buffers
+	 */
+	uaddr = (unsigned long) ubuf;
+	if (!(uaddr & queue_dma_alignment(q)) && !(len & queue_dma_alignment(q)))
+		bio = bio_map_user(q, NULL, uaddr, len, reading);
+	else
+		bio = bio_copy_user(q, uaddr, len, reading);
+
+	if (!IS_ERR(bio)) {
+		rq->bio = rq->biotail = bio;
+		blk_rq_bio_prep(q, rq, bio);
+
+		rq->buffer = rq->data = NULL;
+		rq->data_len = len;
+		return 0;
+	}
+
+	/*
+	 * bio is the err-ptr
+	 */
+	return PTR_ERR(bio);
+}
+
+EXPORT_SYMBOL(blk_rq_map_user);
+
+/**
+ * blk_rq_map_user_iov - map user data to a request, for REQ_BLOCK_PC usage
+ * @q:		request queue where request should be inserted
+ * @rq:		request to map data to
+ * @iov:	pointer to the iovec
+ * @iov_count:	number of elements in the iovec
+ *
+ * Description:
+ *    Data will be mapped directly for zero copy io, if possible. Otherwise
+ *    a kernel bounce buffer is used.
+ *
+ *    A matching blk_rq_unmap_user() must be issued at the end of io, while
+ *    still in process context.
+ *
+ *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
+ *    before being submitted to the device, as pages mapped may be out of
+ *    reach. It's the callers responsibility to make sure this happens. The
+ *    original bio must be passed back in to blk_rq_unmap_user() for proper
+ *    unmapping.
+ */
+int blk_rq_map_user_iov(request_queue_t *q, struct request *rq,
+			struct sg_iovec *iov, int iov_count)
+{
+	struct bio *bio;
+
+	if (!iov || iov_count <= 0)
+		return -EINVAL;
+
+	/* we don't allow misaligned data like bio_map_user() does.  If the
+	 * user is using sg, they're expected to know the alignment constraints
+	 * and respect them accordingly */
+	bio = bio_map_user_iov(q, NULL, iov, iov_count, rq_data_dir(rq)== READ);
+	if (IS_ERR(bio))
+		return PTR_ERR(bio);
+
+	rq->bio = rq->biotail = bio;
+	blk_rq_bio_prep(q, rq, bio);
+	rq->buffer = rq->data = NULL;
+	rq->data_len = bio->bi_size;
+	return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_user_iov);
+
+/**
+ * blk_rq_unmap_user - unmap a request with user data
+ * @bio:	bio to be unmapped
+ * @ulen:	length of user buffer
+ *
+ * Description:
+ *    Unmap a bio previously mapped by blk_rq_map_user().
+ */
+int blk_rq_unmap_user(struct bio *bio, unsigned int ulen)
+{
+	int ret = 0;
+
+	if (bio) {
+		if (bio_flagged(bio, BIO_USER_MAPPED))
+			bio_unmap_user(bio);
+		else
+			ret = bio_uncopy_user(bio);
+	}
+
+	return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_unmap_user);
+
+/**
+ * blk_rq_map_kern - map kernel data to a request, for REQ_BLOCK_PC usage
+ * @q:		request queue where request should be inserted
+ * @rq:		request to fill
+ * @kbuf:	the kernel buffer
+ * @len:	length of user data
+ * @gfp_mask:	memory allocation flags
+ */
+int blk_rq_map_kern(request_queue_t *q, struct request *rq, void *kbuf,
+		    unsigned int len, gfp_t gfp_mask)
+{
+	struct bio *bio;
+
+	if (len > (q->max_sectors << 9))
+		return -EINVAL;
+	if (!len || !kbuf)
+		return -EINVAL;
+
+	bio = bio_map_kern(q, kbuf, len, gfp_mask);
+	if (IS_ERR(bio))
+		return PTR_ERR(bio);
+
+	if (rq_data_dir(rq) == WRITE)
+		bio->bi_rw |= (1 << BIO_RW);
+
+	rq->bio = rq->biotail = bio;
+	blk_rq_bio_prep(q, rq, bio);
+
+	rq->buffer = rq->data = NULL;
+	rq->data_len = len;
+	return 0;
+}
+
+EXPORT_SYMBOL(blk_rq_map_kern);
+
+/**
+ * blk_execute_rq_nowait - insert a request into queue for execution
+ * @q:		queue to insert the request in
+ * @bd_disk:	matching gendisk
+ * @rq:		request to insert
+ * @at_head:    insert request at head or tail of queue
+ * @done:	I/O completion handler
+ *
+ * Description:
+ *    Insert a fully prepared request at the back of the io scheduler queue
+ *    for execution.  Don't wait for completion.
+ */
+void blk_execute_rq_nowait(request_queue_t *q, struct gendisk *bd_disk,
+			   struct request *rq, int at_head,
+			   void (*done)(struct request *))
+{
+	int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
+
+	rq->rq_disk = bd_disk;
+	rq->flags |= REQ_NOMERGE;
+	rq->end_io = done;
+	elv_add_request(q, rq, where, 1);
+	generic_unplug_device(q);
+}
+
+/**
+ * blk_execute_rq - insert a request into queue for execution
+ * @q:		queue to insert the request in
+ * @bd_disk:	matching gendisk
+ * @rq:		request to insert
+ * @at_head:    insert request at head or tail of queue
+ *
+ * Description:
+ *    Insert a fully prepared request at the back of the io scheduler queue
+ *    for execution and wait for completion.
+ */
+int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
+		   struct request *rq, int at_head)
+{
+	DECLARE_COMPLETION(wait);
+	char sense[SCSI_SENSE_BUFFERSIZE];
+	int err = 0;
+
+	/*
+	 * we need an extra reference to the request, so we can look at
+	 * it after io completion
+	 */
+	rq->ref_count++;
+
+	if (!rq->sense) {
+		memset(sense, 0, sizeof(sense));
+		rq->sense = sense;
+		rq->sense_len = 0;
+	}
+
+	rq->waiting = &wait;
+	blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);
+	wait_for_completion(&wait);
+	rq->waiting = NULL;
+
+	if (rq->errors)
+		err = -EIO;
+
+	return err;
+}
+
+EXPORT_SYMBOL(blk_execute_rq);
+
+/**
+ * blkdev_issue_flush - queue a flush
+ * @bdev:	blockdev to issue flush for
+ * @error_sector:	error sector
+ *
+ * Description:
+ *    Issue a flush for the block device in question. Caller can supply
+ *    room for storing the error offset in case of a flush error, if they
+ *    wish to.  Caller must run wait_for_completion() on its own.
+ */
+int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
+{
+	request_queue_t *q;
+
+	if (bdev->bd_disk == NULL)
+		return -ENXIO;
+
+	q = bdev_get_queue(bdev);
+	if (!q)
+		return -ENXIO;
+	if (!q->issue_flush_fn)
+		return -EOPNOTSUPP;
+
+	return q->issue_flush_fn(q, bdev->bd_disk, error_sector);
+}
+
+EXPORT_SYMBOL(blkdev_issue_flush);
+
+static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io)
+{
+	int rw = rq_data_dir(rq);
+
+	if (!blk_fs_request(rq) || !rq->rq_disk)
+		return;
+
+	if (!new_io) {
+		__disk_stat_inc(rq->rq_disk, merges[rw]);
+	} else {
+		disk_round_stats(rq->rq_disk);
+		rq->rq_disk->in_flight++;
+	}
+}
+
+/*
+ * add-request adds a request to the linked list.
+ * queue lock is held and interrupts disabled, as we muck with the
+ * request queue list.
+ */
+static inline void add_request(request_queue_t * q, struct request * req)
+{
+	drive_stat_acct(req, req->nr_sectors, 1);
+
+	if (q->activity_fn)
+		q->activity_fn(q->activity_data, rq_data_dir(req));
+
+	/*
+	 * elevator indicated where it wants this request to be
+	 * inserted at elevator_merge time
+	 */
+	__elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
+}
+ 
+/*
+ * disk_round_stats()	- Round off the performance stats on a struct
+ * disk_stats.
+ *
+ * The average IO queue length and utilisation statistics are maintained
+ * by observing the current state of the queue length and the amount of
+ * time it has been in this state for.
+ *
+ * Normally, that accounting is done on IO completion, but that can result
+ * in more than a second's worth of IO being accounted for within any one
+ * second, leading to >100% utilisation.  To deal with that, we call this
+ * function to do a round-off before returning the results when reading
+ * /proc/diskstats.  This accounts immediately for all queue usage up to
+ * the current jiffies and restarts the counters again.
+ */
+void disk_round_stats(struct gendisk *disk)
+{
+	unsigned long now = jiffies;
+
+	if (now == disk->stamp)
+		return;
+
+	if (disk->in_flight) {
+		__disk_stat_add(disk, time_in_queue,
+				disk->in_flight * (now - disk->stamp));
+		__disk_stat_add(disk, io_ticks, (now - disk->stamp));
+	}
+	disk->stamp = now;
+}
+
+/*
+ * queue lock must be held
+ */
+static void __blk_put_request(request_queue_t *q, struct request *req)
+{
+	struct request_list *rl = req->rl;
+
+	if (unlikely(!q))
+		return;
+	if (unlikely(--req->ref_count))
+		return;
+
+	elv_completed_request(q, req);
+
+	req->rq_status = RQ_INACTIVE;
+	req->rl = NULL;
+
+	/*
+	 * Request may not have originated from ll_rw_blk. if not,
+	 * it didn't come out of our reserved rq pools
+	 */
+	if (rl) {
+		int rw = rq_data_dir(req);
+		int priv = req->flags & REQ_ELVPRIV;
+
+		BUG_ON(!list_empty(&req->queuelist));
+
+		blk_free_request(q, req);
+		freed_request(q, rw, priv);
+	}
+}
+
+void blk_put_request(struct request *req)
+{
+	unsigned long flags;
+	request_queue_t *q = req->q;
+
+	/*
+	 * Gee, IDE calls in w/ NULL q.  Fix IDE and remove the
+	 * following if (q) test.
+	 */
+	if (q) {
+		spin_lock_irqsave(q->queue_lock, flags);
+		__blk_put_request(q, req);
+		spin_unlock_irqrestore(q->queue_lock, flags);
+	}
+}
+
+EXPORT_SYMBOL(blk_put_request);
+
+/**
+ * blk_end_sync_rq - executes a completion event on a request
+ * @rq: request to complete
+ */
+void blk_end_sync_rq(struct request *rq)
+{
+	struct completion *waiting = rq->waiting;
+
+	rq->waiting = NULL;
+	__blk_put_request(rq->q, rq);
+
+	/*
+	 * complete last, if this is a stack request the process (and thus
+	 * the rq pointer) could be invalid right after this complete()
+	 */
+	complete(waiting);
+}
+EXPORT_SYMBOL(blk_end_sync_rq);
+
+/**
+ * blk_congestion_wait - wait for a queue to become uncongested
+ * @rw: READ or WRITE
+ * @timeout: timeout in jiffies
+ *
+ * Waits for up to @timeout jiffies for a queue (any queue) to exit congestion.
+ * If no queues are congested then just wait for the next request to be
+ * returned.
+ */
+long blk_congestion_wait(int rw, long timeout)
+{
+	long ret;
+	DEFINE_WAIT(wait);
+	wait_queue_head_t *wqh = &congestion_wqh[rw];
+
+	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
+	ret = io_schedule_timeout(timeout);
+	finish_wait(wqh, &wait);
+	return ret;
+}
+
+EXPORT_SYMBOL(blk_congestion_wait);
+
+/*
+ * Has to be called with the request spinlock acquired
+ */
+static int attempt_merge(request_queue_t *q, struct request *req,
+			  struct request *next)
+{
+	if (!rq_mergeable(req) || !rq_mergeable(next))
+		return 0;
+
+	/*
+	 * not contigious
+	 */
+	if (req->sector + req->nr_sectors != next->sector)
+		return 0;
+
+	if (rq_data_dir(req) != rq_data_dir(next)
+	    || req->rq_disk != next->rq_disk
+	    || next->waiting || next->special)
+		return 0;
+
+	/*
+	 * If we are allowed to merge, then append bio list
+	 * from next to rq and release next. merge_requests_fn
+	 * will have updated segment counts, update sector
+	 * counts here.
+	 */
+	if (!q->merge_requests_fn(q, req, next))
+		return 0;
+
+	/*
+	 * At this point we have either done a back merge
+	 * or front merge. We need the smaller start_time of
+	 * the merged requests to be the current request
+	 * for accounting purposes.
+	 */
+	if (time_after(req->start_time, next->start_time))
+		req->start_time = next->start_time;
+
+	req->biotail->bi_next = next->bio;
+	req->biotail = next->biotail;
+
+	req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
+
+	elv_merge_requests(q, req, next);
+
+	if (req->rq_disk) {
+		disk_round_stats(req->rq_disk);
+		req->rq_disk->in_flight--;
+	}
+
+	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
+
+	__blk_put_request(q, next);
+	return 1;
+}
+
+static inline int attempt_back_merge(request_queue_t *q, struct request *rq)
+{
+	struct request *next = elv_latter_request(q, rq);
+
+	if (next)
+		return attempt_merge(q, rq, next);
+
+	return 0;
+}
+
+static inline int attempt_front_merge(request_queue_t *q, struct request *rq)
+{
+	struct request *prev = elv_former_request(q, rq);
+
+	if (prev)
+		return attempt_merge(q, prev, rq);
+
+	return 0;
+}
+
+/**
+ * blk_attempt_remerge  - attempt to remerge active head with next request
+ * @q:    The &request_queue_t belonging to the device
+ * @rq:   The head request (usually)
+ *
+ * Description:
+ *    For head-active devices, the queue can easily be unplugged so quickly
+ *    that proper merging is not done on the front request. This may hurt
+ *    performance greatly for some devices. The block layer cannot safely
+ *    do merging on that first request for these queues, but the driver can
+ *    call this function and make it happen any way. Only the driver knows
+ *    when it is safe to do so.
+ **/
+void blk_attempt_remerge(request_queue_t *q, struct request *rq)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	attempt_back_merge(q, rq);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+EXPORT_SYMBOL(blk_attempt_remerge);
+
+static int __make_request(request_queue_t *q, struct bio *bio)
+{
+	struct request *req;
+	int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
+	unsigned short prio;
+	sector_t sector;
+
+	sector = bio->bi_sector;
+	nr_sectors = bio_sectors(bio);
+	cur_nr_sectors = bio_cur_sectors(bio);
+	prio = bio_prio(bio);
+
+	rw = bio_data_dir(bio);
+	sync = bio_sync(bio);
+
+	/*
+	 * low level driver can indicate that it wants pages above a
+	 * certain limit bounced to low memory (ie for highmem, or even
+	 * ISA dma in theory)
+	 */
+	blk_queue_bounce(q, &bio);
+
+	spin_lock_prefetch(q->queue_lock);
+
+	barrier = bio_barrier(bio);
+	if (unlikely(barrier) && (q->ordered == QUEUE_ORDERED_NONE)) {
+		err = -EOPNOTSUPP;
+		goto end_io;
+	}
+
+	spin_lock_irq(q->queue_lock);
+
+	if (unlikely(barrier) || elv_queue_empty(q))
+		goto get_rq;
+
+	el_ret = elv_merge(q, &req, bio);
+	switch (el_ret) {
+		case ELEVATOR_BACK_MERGE:
+			BUG_ON(!rq_mergeable(req));
+
+			if (!q->back_merge_fn(q, req, bio))
+				break;
+
+			req->biotail->bi_next = bio;
+			req->biotail = bio;
+			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+			req->ioprio = ioprio_best(req->ioprio, prio);
+			drive_stat_acct(req, nr_sectors, 0);
+			if (!attempt_back_merge(q, req))
+				elv_merged_request(q, req);
+			goto out;
+
+		case ELEVATOR_FRONT_MERGE:
+			BUG_ON(!rq_mergeable(req));
+
+			if (!q->front_merge_fn(q, req, bio))
+				break;
+
+			bio->bi_next = req->bio;
+			req->bio = bio;
+
+			/*
+			 * may not be valid. if the low level driver said
+			 * it didn't need a bounce buffer then it better
+			 * not touch req->buffer either...
+			 */
+			req->buffer = bio_data(bio);
+			req->current_nr_sectors = cur_nr_sectors;
+			req->hard_cur_sectors = cur_nr_sectors;
+			req->sector = req->hard_sector = sector;
+			req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+			req->ioprio = ioprio_best(req->ioprio, prio);
+			drive_stat_acct(req, nr_sectors, 0);
+			if (!attempt_front_merge(q, req))
+				elv_merged_request(q, req);
+			goto out;
+
+		/* ELV_NO_MERGE: elevator says don't/can't merge. */
+		default:
+			;
+	}
+
+get_rq:
+	/*
+	 * Grab a free request. This is might sleep but can not fail.
+	 * Returns with the queue unlocked.
+	 */
+	req = get_request_wait(q, rw, bio);
+
+	/*
+	 * After dropping the lock and possibly sleeping here, our request
+	 * may now be mergeable after it had proven unmergeable (above).
+	 * We don't worry about that case for efficiency. It won't happen
+	 * often, and the elevators are able to handle it.
+	 */
+
+	req->flags |= REQ_CMD;
+
+	/*
+	 * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+	 */
+	if (bio_rw_ahead(bio) || bio_failfast(bio))
+		req->flags |= REQ_FAILFAST;
+
+	/*
+	 * REQ_BARRIER implies no merging, but lets make it explicit
+	 */
+	if (unlikely(barrier))
+		req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+
+	req->errors = 0;
+	req->hard_sector = req->sector = sector;
+	req->hard_nr_sectors = req->nr_sectors = nr_sectors;
+	req->current_nr_sectors = req->hard_cur_sectors = cur_nr_sectors;
+	req->nr_phys_segments = bio_phys_segments(q, bio);
+	req->nr_hw_segments = bio_hw_segments(q, bio);
+	req->buffer = bio_data(bio);	/* see ->buffer comment above */
+	req->waiting = NULL;
+	req->bio = req->biotail = bio;
+	req->ioprio = prio;
+	req->rq_disk = bio->bi_bdev->bd_disk;
+	req->start_time = jiffies;
+
+	spin_lock_irq(q->queue_lock);
+	if (elv_queue_empty(q))
+		blk_plug_device(q);
+	add_request(q, req);
+out:
+	if (sync)
+		__generic_unplug_device(q);
+
+	spin_unlock_irq(q->queue_lock);
+	return 0;
+
+end_io:
+	bio_endio(bio, nr_sectors << 9, err);
+	return 0;
+}
+
+/*
+ * If bio->bi_dev is a partition, remap the location
+ */
+static inline void blk_partition_remap(struct bio *bio)
+{
+	struct block_device *bdev = bio->bi_bdev;
+
+	if (bdev != bdev->bd_contains) {
+		struct hd_struct *p = bdev->bd_part;
+		const int rw = bio_data_dir(bio);
+
+		p->sectors[rw] += bio_sectors(bio);
+		p->ios[rw]++;
+
+		bio->bi_sector += p->start_sect;
+		bio->bi_bdev = bdev->bd_contains;
+	}
+}
+
+static void handle_bad_sector(struct bio *bio)
+{
+	char b[BDEVNAME_SIZE];
+
+	printk(KERN_INFO "attempt to access beyond end of device\n");
+	printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
+			bdevname(bio->bi_bdev, b),
+			bio->bi_rw,
+			(unsigned long long)bio->bi_sector + bio_sectors(bio),
+			(long long)(bio->bi_bdev->bd_inode->i_size >> 9));
+
+	set_bit(BIO_EOF, &bio->bi_flags);
+}
+
+/**
+ * generic_make_request: hand a buffer to its device driver for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * generic_make_request() is used to make I/O requests of block
+ * devices. It is passed a &struct bio, which describes the I/O that needs
+ * to be done.
+ *
+ * generic_make_request() does not return any status.  The
+ * success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the bio->bi_end_io
+ * function described (one day) else where.
+ *
+ * The caller of generic_make_request must make sure that bi_io_vec
+ * are set to describe the memory buffer, and that bi_dev and bi_sector are
+ * set to describe the device address, and the
+ * bi_end_io and optionally bi_private are set to describe how
+ * completion notification should be signaled.
+ *
+ * generic_make_request and the drivers it calls may use bi_next if this
+ * bio happens to be merged with someone else, and may change bi_dev and
+ * bi_sector for remaps as it sees fit.  So the values of these fields
+ * should NOT be depended on after the call to generic_make_request.
+ */
+void generic_make_request(struct bio *bio)
+{
+	request_queue_t *q;
+	sector_t maxsector;
+	int ret, nr_sectors = bio_sectors(bio);
+
+	might_sleep();
+	/* Test device or partition size, when known. */
+	maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
+	if (maxsector) {
+		sector_t sector = bio->bi_sector;
+
+		if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
+			/*
+			 * This may well happen - the kernel calls bread()
+			 * without checking the size of the device, e.g., when
+			 * mounting a device.
+			 */
+			handle_bad_sector(bio);
+			goto end_io;
+		}
+	}
+
+	/*
+	 * Resolve the mapping until finished. (drivers are
+	 * still free to implement/resolve their own stacking
+	 * by explicitly returning 0)
+	 *
+	 * NOTE: we don't repeat the blk_size check for each new device.
+	 * Stacking drivers are expected to know what they are doing.
+	 */
+	do {
+		char b[BDEVNAME_SIZE];
+
+		q = bdev_get_queue(bio->bi_bdev);
+		if (!q) {
+			printk(KERN_ERR
+			       "generic_make_request: Trying to access "
+				"nonexistent block-device %s (%Lu)\n",
+				bdevname(bio->bi_bdev, b),
+				(long long) bio->bi_sector);
+end_io:
+			bio_endio(bio, bio->bi_size, -EIO);
+			break;
+		}
+
+		if (unlikely(bio_sectors(bio) > q->max_hw_sectors)) {
+			printk("bio too big device %s (%u > %u)\n", 
+				bdevname(bio->bi_bdev, b),
+				bio_sectors(bio),
+				q->max_hw_sectors);
+			goto end_io;
+		}
+
+		if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
+			goto end_io;
+
+		/*
+		 * If this device has partitions, remap block n
+		 * of partition p to block n+start(p) of the disk.
+		 */
+		blk_partition_remap(bio);
+
+		ret = q->make_request_fn(q, bio);
+	} while (ret);
+}
+
+EXPORT_SYMBOL(generic_make_request);
+
+/**
+ * submit_bio: submit a bio to the block device layer for I/O
+ * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
+ * @bio: The &struct bio which describes the I/O
+ *
+ * submit_bio() is very similar in purpose to generic_make_request(), and
+ * uses that function to do most of the work. Both are fairly rough
+ * interfaces, @bio must be presetup and ready for I/O.
+ *
+ */
+void submit_bio(int rw, struct bio *bio)
+{
+	int count = bio_sectors(bio);
+
+	BIO_BUG_ON(!bio->bi_size);
+	BIO_BUG_ON(!bio->bi_io_vec);
+	bio->bi_rw |= rw;
+	if (rw & WRITE)
+		mod_page_state(pgpgout, count);
+	else
+		mod_page_state(pgpgin, count);
+
+	if (unlikely(block_dump)) {
+		char b[BDEVNAME_SIZE];
+		printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+			current->comm, current->pid,
+			(rw & WRITE) ? "WRITE" : "READ",
+			(unsigned long long)bio->bi_sector,
+			bdevname(bio->bi_bdev,b));
+	}
+
+	generic_make_request(bio);
+}
+
+EXPORT_SYMBOL(submit_bio);
+
+static void blk_recalc_rq_segments(struct request *rq)
+{
+	struct bio *bio, *prevbio = NULL;
+	int nr_phys_segs, nr_hw_segs;
+	unsigned int phys_size, hw_size;
+	request_queue_t *q = rq->q;
+
+	if (!rq->bio)
+		return;
+
+	phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
+	rq_for_each_bio(bio, rq) {
+		/* Force bio hw/phys segs to be recalculated. */
+		bio->bi_flags &= ~(1 << BIO_SEG_VALID);
+
+		nr_phys_segs += bio_phys_segments(q, bio);
+		nr_hw_segs += bio_hw_segments(q, bio);
+		if (prevbio) {
+			int pseg = phys_size + prevbio->bi_size + bio->bi_size;
+			int hseg = hw_size + prevbio->bi_size + bio->bi_size;
+
+			if (blk_phys_contig_segment(q, prevbio, bio) &&
+			    pseg <= q->max_segment_size) {
+				nr_phys_segs--;
+				phys_size += prevbio->bi_size + bio->bi_size;
+			} else
+				phys_size = 0;
+
+			if (blk_hw_contig_segment(q, prevbio, bio) &&
+			    hseg <= q->max_segment_size) {
+				nr_hw_segs--;
+				hw_size += prevbio->bi_size + bio->bi_size;
+			} else
+				hw_size = 0;
+		}
+		prevbio = bio;
+	}
+
+	rq->nr_phys_segments = nr_phys_segs;
+	rq->nr_hw_segments = nr_hw_segs;
+}
+
+static void blk_recalc_rq_sectors(struct request *rq, int nsect)
+{
+	if (blk_fs_request(rq)) {
+		rq->hard_sector += nsect;
+		rq->hard_nr_sectors -= nsect;
+
+		/*
+		 * Move the I/O submission pointers ahead if required.
+		 */
+		if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
+		    (rq->sector <= rq->hard_sector)) {
+			rq->sector = rq->hard_sector;
+			rq->nr_sectors = rq->hard_nr_sectors;
+			rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
+			rq->current_nr_sectors = rq->hard_cur_sectors;
+			rq->buffer = bio_data(rq->bio);
+		}
+
+		/*
+		 * if total number of sectors is less than the first segment
+		 * size, something has gone terribly wrong
+		 */
+		if (rq->nr_sectors < rq->current_nr_sectors) {
+			printk("blk: request botched\n");
+			rq->nr_sectors = rq->current_nr_sectors;
+		}
+	}
+}
+
+static int __end_that_request_first(struct request *req, int uptodate,
+				    int nr_bytes)
+{
+	int total_bytes, bio_nbytes, error, next_idx = 0;
+	struct bio *bio;
+
+	/*
+	 * extend uptodate bool to allow < 0 value to be direct io error
+	 */
+	error = 0;
+	if (end_io_error(uptodate))
+		error = !uptodate ? -EIO : uptodate;
+
+	/*
+	 * for a REQ_BLOCK_PC request, we want to carry any eventual
+	 * sense key with us all the way through
+	 */
+	if (!blk_pc_request(req))
+		req->errors = 0;
+
+	if (!uptodate) {
+		if (blk_fs_request(req) && !(req->flags & REQ_QUIET))
+			printk("end_request: I/O error, dev %s, sector %llu\n",
+				req->rq_disk ? req->rq_disk->disk_name : "?",
+				(unsigned long long)req->sector);
+	}
+
+	if (blk_fs_request(req) && req->rq_disk) {
+		const int rw = rq_data_dir(req);
+
+		__disk_stat_add(req->rq_disk, sectors[rw], nr_bytes >> 9);
+	}
+
+	total_bytes = bio_nbytes = 0;
+	while ((bio = req->bio) != NULL) {
+		int nbytes;
+
+		if (nr_bytes >= bio->bi_size) {
+			req->bio = bio->bi_next;
+			nbytes = bio->bi_size;
+			bio_endio(bio, nbytes, error);
+			next_idx = 0;
+			bio_nbytes = 0;
+		} else {
+			int idx = bio->bi_idx + next_idx;
+
+			if (unlikely(bio->bi_idx >= bio->bi_vcnt)) {
+				blk_dump_rq_flags(req, "__end_that");
+				printk("%s: bio idx %d >= vcnt %d\n",
+						__FUNCTION__,
+						bio->bi_idx, bio->bi_vcnt);
+				break;
+			}
+
+			nbytes = bio_iovec_idx(bio, idx)->bv_len;
+			BIO_BUG_ON(nbytes > bio->bi_size);
+
+			/*
+			 * not a complete bvec done
+			 */
+			if (unlikely(nbytes > nr_bytes)) {
+				bio_nbytes += nr_bytes;
+				total_bytes += nr_bytes;
+				break;
+			}
+
+			/*
+			 * advance to the next vector
+			 */
+			next_idx++;
+			bio_nbytes += nbytes;
+		}
+
+		total_bytes += nbytes;
+		nr_bytes -= nbytes;
+
+		if ((bio = req->bio)) {
+			/*
+			 * end more in this run, or just return 'not-done'
+			 */
+			if (unlikely(nr_bytes <= 0))
+				break;
+		}
+	}
+
+	/*
+	 * completely done
+	 */
+	if (!req->bio)
+		return 0;
+
+	/*
+	 * if the request wasn't completed, update state
+	 */
+	if (bio_nbytes) {
+		bio_endio(bio, bio_nbytes, error);
+		bio->bi_idx += next_idx;
+		bio_iovec(bio)->bv_offset += nr_bytes;
+		bio_iovec(bio)->bv_len -= nr_bytes;
+	}
+
+	blk_recalc_rq_sectors(req, total_bytes >> 9);
+	blk_recalc_rq_segments(req);
+	return 1;
+}
+
+/**
+ * end_that_request_first - end I/O on a request
+ * @req:      the request being processed
+ * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
+ * @nr_sectors: number of sectors to end I/O on
+ *
+ * Description:
+ *     Ends I/O on a number of sectors attached to @req, and sets it up
+ *     for the next range of segments (if any) in the cluster.
+ *
+ * Return:
+ *     0 - we are done with this request, call end_that_request_last()
+ *     1 - still buffers pending for this request
+ **/
+int end_that_request_first(struct request *req, int uptodate, int nr_sectors)
+{
+	return __end_that_request_first(req, uptodate, nr_sectors << 9);
+}
+
+EXPORT_SYMBOL(end_that_request_first);
+
+/**
+ * end_that_request_chunk - end I/O on a request
+ * @req:      the request being processed
+ * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @req, and sets it up
+ *     for the next range of segments (if any). Like end_that_request_first(),
+ *     but deals with bytes instead of sectors.
+ *
+ * Return:
+ *     0 - we are done with this request, call end_that_request_last()
+ *     1 - still buffers pending for this request
+ **/
+int end_that_request_chunk(struct request *req, int uptodate, int nr_bytes)
+{
+	return __end_that_request_first(req, uptodate, nr_bytes);
+}
+
+EXPORT_SYMBOL(end_that_request_chunk);
+
+/*
+ * queue lock must be held
+ */
+void end_that_request_last(struct request *req)
+{
+	struct gendisk *disk = req->rq_disk;
+
+	if (unlikely(laptop_mode) && blk_fs_request(req))
+		laptop_io_completion();
+
+	if (disk && blk_fs_request(req)) {
+		unsigned long duration = jiffies - req->start_time;
+		const int rw = rq_data_dir(req);
+
+		__disk_stat_inc(disk, ios[rw]);
+		__disk_stat_add(disk, ticks[rw], duration);
+		disk_round_stats(disk);
+		disk->in_flight--;
+	}
+	if (req->end_io)
+		req->end_io(req);
+	else
+		__blk_put_request(req->q, req);
+}
+
+EXPORT_SYMBOL(end_that_request_last);
+
+void end_request(struct request *req, int uptodate)
+{
+	if (!end_that_request_first(req, uptodate, req->hard_cur_sectors)) {
+		add_disk_randomness(req->rq_disk);
+		blkdev_dequeue_request(req);
+		end_that_request_last(req);
+	}
+}
+
+EXPORT_SYMBOL(end_request);
+
+void blk_rq_bio_prep(request_queue_t *q, struct request *rq, struct bio *bio)
+{
+	/* first three bits are identical in rq->flags and bio->bi_rw */
+	rq->flags |= (bio->bi_rw & 7);
+
+	rq->nr_phys_segments = bio_phys_segments(q, bio);
+	rq->nr_hw_segments = bio_hw_segments(q, bio);
+	rq->current_nr_sectors = bio_cur_sectors(bio);
+	rq->hard_cur_sectors = rq->current_nr_sectors;
+	rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
+	rq->buffer = bio_data(bio);
+
+	rq->bio = rq->biotail = bio;
+}
+
+EXPORT_SYMBOL(blk_rq_bio_prep);
+
+int kblockd_schedule_work(struct work_struct *work)
+{
+	return queue_work(kblockd_workqueue, work);
+}
+
+EXPORT_SYMBOL(kblockd_schedule_work);
+
+void kblockd_flush(void)
+{
+	flush_workqueue(kblockd_workqueue);
+}
+EXPORT_SYMBOL(kblockd_flush);
+
+int __init blk_dev_init(void)
+{
+	kblockd_workqueue = create_workqueue("kblockd");
+	if (!kblockd_workqueue)
+		panic("Failed to create kblockd\n");
+
+	request_cachep = kmem_cache_create("blkdev_requests",
+			sizeof(struct request), 0, SLAB_PANIC, NULL, NULL);
+
+	requestq_cachep = kmem_cache_create("blkdev_queue",
+			sizeof(request_queue_t), 0, SLAB_PANIC, NULL, NULL);
+
+	iocontext_cachep = kmem_cache_create("blkdev_ioc",
+			sizeof(struct io_context), 0, SLAB_PANIC, NULL, NULL);
+
+	blk_max_low_pfn = max_low_pfn;
+	blk_max_pfn = max_pfn;
+
+	return 0;
+}
+
+/*
+ * IO Context helper functions
+ */
+void put_io_context(struct io_context *ioc)
+{
+	if (ioc == NULL)
+		return;
+
+	BUG_ON(atomic_read(&ioc->refcount) == 0);
+
+	if (atomic_dec_and_test(&ioc->refcount)) {
+		if (ioc->aic && ioc->aic->dtor)
+			ioc->aic->dtor(ioc->aic);
+		if (ioc->cic && ioc->cic->dtor)
+			ioc->cic->dtor(ioc->cic);
+
+		kmem_cache_free(iocontext_cachep, ioc);
+	}
+}
+EXPORT_SYMBOL(put_io_context);
+
+/* Called by the exitting task */
+void exit_io_context(void)
+{
+	unsigned long flags;
+	struct io_context *ioc;
+
+	local_irq_save(flags);
+	task_lock(current);
+	ioc = current->io_context;
+	current->io_context = NULL;
+	ioc->task = NULL;
+	task_unlock(current);
+	local_irq_restore(flags);
+
+	if (ioc->aic && ioc->aic->exit)
+		ioc->aic->exit(ioc->aic);
+	if (ioc->cic && ioc->cic->exit)
+		ioc->cic->exit(ioc->cic);
+
+	put_io_context(ioc);
+}
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * Otherwise, return its existing IO context.
+ *
+ * This returned IO context doesn't have a specifically elevated refcount,
+ * but since the current task itself holds a reference, the context can be
+ * used in general code, so long as it stays within `current` context.
+ */
+struct io_context *current_io_context(gfp_t gfp_flags)
+{
+	struct task_struct *tsk = current;
+	struct io_context *ret;
+
+	ret = tsk->io_context;
+	if (likely(ret))
+		return ret;
+
+	ret = kmem_cache_alloc(iocontext_cachep, gfp_flags);
+	if (ret) {
+		atomic_set(&ret->refcount, 1);
+		ret->task = current;
+		ret->set_ioprio = NULL;
+		ret->last_waited = jiffies; /* doesn't matter... */
+		ret->nr_batch_requests = 0; /* because this is 0 */
+		ret->aic = NULL;
+		ret->cic = NULL;
+		tsk->io_context = ret;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(current_io_context);
+
+/*
+ * If the current task has no IO context then create one and initialise it.
+ * If it does have a context, take a ref on it.
+ *
+ * This is always called in the context of the task which submitted the I/O.
+ */
+struct io_context *get_io_context(gfp_t gfp_flags)
+{
+	struct io_context *ret;
+	ret = current_io_context(gfp_flags);
+	if (likely(ret))
+		atomic_inc(&ret->refcount);
+	return ret;
+}
+EXPORT_SYMBOL(get_io_context);
+
+void copy_io_context(struct io_context **pdst, struct io_context **psrc)
+{
+	struct io_context *src = *psrc;
+	struct io_context *dst = *pdst;
+
+	if (src) {
+		BUG_ON(atomic_read(&src->refcount) == 0);
+		atomic_inc(&src->refcount);
+		put_io_context(dst);
+		*pdst = src;
+	}
+}
+EXPORT_SYMBOL(copy_io_context);
+
+void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
+{
+	struct io_context *temp;
+	temp = *ioc1;
+	*ioc1 = *ioc2;
+	*ioc2 = temp;
+}
+EXPORT_SYMBOL(swap_io_context);
+
+/*
+ * sysfs parts below
+ */
+struct queue_sysfs_entry {
+	struct attribute attr;
+	ssize_t (*show)(struct request_queue *, char *);
+	ssize_t (*store)(struct request_queue *, const char *, size_t);
+};
+
+static ssize_t
+queue_var_show(unsigned int var, char *page)
+{
+	return sprintf(page, "%d\n", var);
+}
+
+static ssize_t
+queue_var_store(unsigned long *var, const char *page, size_t count)
+{
+	char *p = (char *) page;
+
+	*var = simple_strtoul(p, &p, 10);
+	return count;
+}
+
+static ssize_t queue_requests_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(q->nr_requests, (page));
+}
+
+static ssize_t
+queue_requests_store(struct request_queue *q, const char *page, size_t count)
+{
+	struct request_list *rl = &q->rq;
+
+	int ret = queue_var_store(&q->nr_requests, page, count);
+	if (q->nr_requests < BLKDEV_MIN_RQ)
+		q->nr_requests = BLKDEV_MIN_RQ;
+	blk_queue_congestion_threshold(q);
+
+	if (rl->count[READ] >= queue_congestion_on_threshold(q))
+		set_queue_congested(q, READ);
+	else if (rl->count[READ] < queue_congestion_off_threshold(q))
+		clear_queue_congested(q, READ);
+
+	if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
+		set_queue_congested(q, WRITE);
+	else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
+		clear_queue_congested(q, WRITE);
+
+	if (rl->count[READ] >= q->nr_requests) {
+		blk_set_queue_full(q, READ);
+	} else if (rl->count[READ]+1 <= q->nr_requests) {
+		blk_clear_queue_full(q, READ);
+		wake_up(&rl->wait[READ]);
+	}
+
+	if (rl->count[WRITE] >= q->nr_requests) {
+		blk_set_queue_full(q, WRITE);
+	} else if (rl->count[WRITE]+1 <= q->nr_requests) {
+		blk_clear_queue_full(q, WRITE);
+		wake_up(&rl->wait[WRITE]);
+	}
+	return ret;
+}
+
+static ssize_t queue_ra_show(struct request_queue *q, char *page)
+{
+	int ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+
+	return queue_var_show(ra_kb, (page));
+}
+
+static ssize_t
+queue_ra_store(struct request_queue *q, const char *page, size_t count)
+{
+	unsigned long ra_kb;
+	ssize_t ret = queue_var_store(&ra_kb, page, count);
+
+	spin_lock_irq(q->queue_lock);
+	if (ra_kb > (q->max_sectors >> 1))
+		ra_kb = (q->max_sectors >> 1);
+
+	q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
+static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
+{
+	int max_sectors_kb = q->max_sectors >> 1;
+
+	return queue_var_show(max_sectors_kb, (page));
+}
+
+static ssize_t
+queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
+{
+	unsigned long max_sectors_kb,
+			max_hw_sectors_kb = q->max_hw_sectors >> 1,
+			page_kb = 1 << (PAGE_CACHE_SHIFT - 10);
+	ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
+	int ra_kb;
+
+	if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
+		return -EINVAL;
+	/*
+	 * Take the queue lock to update the readahead and max_sectors
+	 * values synchronously:
+	 */
+	spin_lock_irq(q->queue_lock);
+	/*
+	 * Trim readahead window as well, if necessary:
+	 */
+	ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
+	if (ra_kb > max_sectors_kb)
+		q->backing_dev_info.ra_pages =
+				max_sectors_kb >> (PAGE_CACHE_SHIFT - 10);
+
+	q->max_sectors = max_sectors_kb << 1;
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
+static ssize_t queue_max_hw_sectors_show(struct request_queue *q, char *page)
+{
+	int max_hw_sectors_kb = q->max_hw_sectors >> 1;
+
+	return queue_var_show(max_hw_sectors_kb, (page));
+}
+
+
+static struct queue_sysfs_entry queue_requests_entry = {
+	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_requests_show,
+	.store = queue_requests_store,
+};
+
+static struct queue_sysfs_entry queue_ra_entry = {
+	.attr = {.name = "read_ahead_kb", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_ra_show,
+	.store = queue_ra_store,
+};
+
+static struct queue_sysfs_entry queue_max_sectors_entry = {
+	.attr = {.name = "max_sectors_kb", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_max_sectors_show,
+	.store = queue_max_sectors_store,
+};
+
+static struct queue_sysfs_entry queue_max_hw_sectors_entry = {
+	.attr = {.name = "max_hw_sectors_kb", .mode = S_IRUGO },
+	.show = queue_max_hw_sectors_show,
+};
+
+static struct queue_sysfs_entry queue_iosched_entry = {
+	.attr = {.name = "scheduler", .mode = S_IRUGO | S_IWUSR },
+	.show = elv_iosched_show,
+	.store = elv_iosched_store,
+};
+
+static struct attribute *default_attrs[] = {
+	&queue_requests_entry.attr,
+	&queue_ra_entry.attr,
+	&queue_max_hw_sectors_entry.attr,
+	&queue_max_sectors_entry.attr,
+	&queue_iosched_entry.attr,
+	NULL,
+};
+
+#define to_queue(atr) container_of((atr), struct queue_sysfs_entry, attr)
+
+static ssize_t
+queue_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
+{
+	struct queue_sysfs_entry *entry = to_queue(attr);
+	struct request_queue *q;
+
+	q = container_of(kobj, struct request_queue, kobj);
+	if (!entry->show)
+		return -EIO;
+
+	return entry->show(q, page);
+}
+
+static ssize_t
+queue_attr_store(struct kobject *kobj, struct attribute *attr,
+		    const char *page, size_t length)
+{
+	struct queue_sysfs_entry *entry = to_queue(attr);
+	struct request_queue *q;
+
+	q = container_of(kobj, struct request_queue, kobj);
+	if (!entry->store)
+		return -EIO;
+
+	return entry->store(q, page, length);
+}
+
+static struct sysfs_ops queue_sysfs_ops = {
+	.show	= queue_attr_show,
+	.store	= queue_attr_store,
+};
+
+static struct kobj_type queue_ktype = {
+	.sysfs_ops	= &queue_sysfs_ops,
+	.default_attrs	= default_attrs,
+};
+
+int blk_register_queue(struct gendisk *disk)
+{
+	int ret;
+
+	request_queue_t *q = disk->queue;
+
+	if (!q || !q->request_fn)
+		return -ENXIO;
+
+	q->kobj.parent = kobject_get(&disk->kobj);
+	if (!q->kobj.parent)
+		return -EBUSY;
+
+	snprintf(q->kobj.name, KOBJ_NAME_LEN, "%s", "queue");
+	q->kobj.ktype = &queue_ktype;
+
+	ret = kobject_register(&q->kobj);
+	if (ret < 0)
+		return ret;
+
+	ret = elv_register_queue(q);
+	if (ret) {
+		kobject_unregister(&q->kobj);
+		return ret;
+	}
+
+	return 0;
+}
+
+void blk_unregister_queue(struct gendisk *disk)
+{
+	request_queue_t *q = disk->queue;
+
+	if (q && q->request_fn) {
+		elv_unregister_queue(q);
+
+		kobject_unregister(&q->kobj);
+		kobject_put(&disk->kobj);
+	}
+}