2.6.25

 block

diff --git a/block/blk-core.c b/block/blk-core.c
new file mode 100644
index 0000000..2a438a9
--- /dev/null
+++ b/block/blk-core.c
@@ -0,0 +1,2061 @@
+/*
+ * 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/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/completion.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/interrupt.h>
+#include <linux/cpu.h>
+#include <linux/blktrace_api.h>
+#include <linux/fault-inject.h>
+
+#include "blk.h"
+
+static int __make_request(struct request_queue *q, struct bio *bio);
+
+/*
+ * For the allocated request tables
+ */
+static struct kmem_cache *request_cachep;
+
+/*
+ * For queue allocation
+ */
+struct kmem_cache *blk_requestq_cachep;
+
+/*
+ * Controlling structure to kblockd
+ */
+static struct workqueue_struct *kblockd_workqueue;
+
+static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
+
+static void drive_stat_acct(struct request *rq, int new_io)
+{
+   int rw = rq_data_dir(rq);
+
+   if (!blk_fs_request(rq) || !rq->rq_disk)
+      return;
+
+   if (!new_io) {
+      __all_stat_inc(rq->rq_disk, merges[rw], rq->sector);
+   } else {
+      struct hd_struct *part = get_part(rq->rq_disk, rq->sector);
+      disk_round_stats(rq->rq_disk);
+      rq->rq_disk->in_flight++;
+      if (part) {
+         part_round_stats(part);
+         part->in_flight++;
+      }
+   }
+}
+
+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;
+}
+
+/**
+ * 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;
+   struct request_queue *q = bdev_get_queue(bdev);
+
+   if (q)
+      ret = &q->backing_dev_info;
+   return ret;
+}
+EXPORT_SYMBOL(blk_get_backing_dev_info);
+
+/*
+ * We can't just memset() the structure, since the allocation path
+ * already stored some information in the request.
+ */
+void rq_init(struct request_queue *q, struct request *rq)
+{
+   INIT_LIST_HEAD(&rq->queuelist);
+   INIT_LIST_HEAD(&rq->donelist);
+   rq->q = q;
+   rq->sector = rq->hard_sector = (sector_t) -1;
+   rq->nr_sectors = rq->hard_nr_sectors = 0;
+   rq->current_nr_sectors = rq->hard_cur_sectors = 0;
+   rq->bio = rq->biotail = NULL;
+   INIT_HLIST_NODE(&rq->hash);
+   RB_CLEAR_NODE(&rq->rb_node);
+   rq->rq_disk = NULL;
+   rq->nr_phys_segments = 0;
+   rq->nr_hw_segments = 0;
+   rq->ioprio = 0;
+   rq->special = NULL;
+   rq->buffer = NULL;
+   rq->tag = -1;
+   rq->errors = 0;
+   rq->ref_count = 1;
+   rq->cmd_len = 0;
+   memset(rq->cmd, 0, sizeof(rq->cmd));
+   rq->data_len = 0;
+   rq->extra_len = 0;
+   rq->sense_len = 0;
+   rq->data = NULL;
+   rq->sense = NULL;
+   rq->end_io = NULL;
+   rq->end_io_data = NULL;
+   rq->next_rq = NULL;
+}
+
+static void req_bio_endio(struct request *rq, struct bio *bio,
+           unsigned int nbytes, int error)
+{
+   struct request_queue *q = rq->q;
+
+   if (&q->bar_rq != rq) {
+      if (error)
+         clear_bit(BIO_UPTODATE, &bio->bi_flags);
+      else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+         error = -EIO;
+
+      if (unlikely(nbytes > bio->bi_size)) {
+         printk(KERN_ERR "%s: want %u bytes done, %u left\n",
+                __FUNCTION__, nbytes, bio->bi_size);
+         nbytes = bio->bi_size;
+      }
+
+      bio->bi_size -= nbytes;
+      bio->bi_sector += (nbytes >> 9);
+      if (bio->bi_size == 0)
+         bio_endio(bio, error);
+   } else {
+
+      /*
+       * Okay, this is the barrier request in progress, just
+       * record the error;
+       */
+      if (error && !q->orderr)
+         q->orderr = error;
+   }
+}
+
+void blk_dump_rq_flags(struct request *rq, char *msg)
+{
+   int bit;
+
+   printk(KERN_INFO "%s: dev %s: type=%x, flags=%x\n", msg,
+      rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->cmd_type,
+      rq->cmd_flags);
+
+   printk(KERN_INFO "  sector %llu, nr/cnr %lu/%u\n",
+                  (unsigned long long)rq->sector,
+                  rq->nr_sectors,
+                  rq->current_nr_sectors);
+   printk(KERN_INFO "  bio %p, biotail %p, buffer %p, data %p, len %u\n",
+                  rq->bio, rq->biotail,
+                  rq->buffer, rq->data,
+                  rq->data_len);
+
+   if (blk_pc_request(rq)) {
+      printk(KERN_INFO "  cdb: ");
+      for (bit = 0; bit < sizeof(rq->cmd); bit++)
+         printk("%02x ", rq->cmd[bit]);
+      printk("\n");
+   }
+}
+EXPORT_SYMBOL(blk_dump_rq_flags);
+
+/*
+ * "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(struct request_queue *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 (blk_queue_stopped(q))
+      return;
+
+   if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags)) {
+      mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
+      blk_add_trace_generic(q, NULL, 0, BLK_TA_PLUG);
+   }
+}
+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(struct request_queue *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(struct request_queue *q)
+{
+   if (unlikely(blk_queue_stopped(q)))
+      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 &struct request_queue 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(struct request_queue *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)
+{
+   struct request_queue *q = bdi->unplug_io_data;
+
+   blk_unplug(q);
+}
+
+void blk_unplug_work(struct work_struct *work)
+{
+   struct request_queue *q =
+      container_of(work, struct request_queue, unplug_work);
+
+   blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL,
+            q->rq.count[READ] + q->rq.count[WRITE]);
+
+   q->unplug_fn(q);
+}
+
+void blk_unplug_timeout(unsigned long data)
+{
+   struct request_queue *q = (struct request_queue *)data;
+
+   blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_TIMER, NULL,
+            q->rq.count[READ] + q->rq.count[WRITE]);
+
+   kblockd_schedule_work(&q->unplug_work);
+}
+
+void blk_unplug(struct request_queue *q)
+{
+   /*
+    * devices don't necessarily have an ->unplug_fn defined
+    */
+   if (q->unplug_fn) {
+      blk_add_trace_pdu_int(q, BLK_TA_UNPLUG_IO, NULL,
+               q->rq.count[READ] + q->rq.count[WRITE]);
+
+      q->unplug_fn(q);
+   }
+}
+EXPORT_SYMBOL(blk_unplug);
+
+/**
+ * blk_start_queue - restart a previously stopped queue
+ * @q:    The &struct request_queue 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(struct request_queue *q)
+{
+   WARN_ON(!irqs_disabled());
+
+   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 &struct request_queue 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(struct request_queue *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
+ *     that 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_work(&q->unplug_work);
+}
+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);
+
+   /*
+    * Only recurse once to avoid overrunning the stack, let the unplug
+    * handling reinvoke the handler shortly if we already got there.
+    */
+   if (!elv_queue_empty(q)) {
+      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);
+      }
+   }
+
+   spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_run_queue);
+
+void blk_put_queue(struct request_queue *q)
+{
+   kobject_put(&q->kobj);
+}
+
+void blk_cleanup_queue(struct request_queue *q)
+{
+   mutex_lock(&q->sysfs_lock);
+   set_bit(QUEUE_FLAG_DEAD, &q->queue_flags);
+   mutex_unlock(&q->sysfs_lock);
+
+   if (q->elevator)
+      elevator_exit(q->elevator);
+
+   blk_put_queue(q);
+}
+EXPORT_SYMBOL(blk_cleanup_queue);
+
+static int blk_init_free_list(struct request_queue *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;
+}
+
+struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
+{
+   return blk_alloc_queue_node(gfp_mask, -1);
+}
+EXPORT_SYMBOL(blk_alloc_queue);
+
+struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
+{
+   struct request_queue *q;
+   int err;
+
+   q = kmem_cache_alloc_node(blk_requestq_cachep,
+            gfp_mask | __GFP_ZERO, node_id);
+   if (!q)
+      return NULL;
+
+   q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
+   q->backing_dev_info.unplug_io_data = q;
+   err = bdi_init(&q->backing_dev_info);
+   if (err) {
+      kmem_cache_free(blk_requestq_cachep, q);
+      return NULL;
+   }
+
+   init_timer(&q->unplug_timer);
+
+   kobject_init(&q->kobj, &blk_queue_ktype);
+
+   mutex_init(&q->sysfs_lock);
+
+   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; this lock will be taken also from interrupt context, so irq
+ *    disabling is needed for it.
+ *
+ *    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).
+ **/
+
+struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+{
+   return blk_init_queue_node(rfn, lock, -1);
+}
+EXPORT_SYMBOL(blk_init_queue);
+
+struct request_queue *
+blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+{
+   struct request_queue *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
+
+   if (!q)
+      return NULL;
+
+   q->node = node_id;
+   if (blk_init_free_list(q)) {
+      kmem_cache_free(blk_requestq_cachep, q);
+      return NULL;
+   }
+
+   /*
+    * 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->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);
+
+   q->sg_reserved_size = INT_MAX;
+
+   /*
+    * all done
+    */
+   if (!elevator_init(q, NULL)) {
+      blk_queue_congestion_threshold(q);
+      return q;
+   }
+
+   blk_put_queue(q);
+   return NULL;
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+int blk_get_queue(struct request_queue *q)
+{
+   if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
+      kobject_get(&q->kobj);
+      return 0;
+   }
+
+   return 1;
+}
+
+static inline void blk_free_request(struct request_queue *q, struct request *rq)
+{
+   if (rq->cmd_flags & REQ_ELVPRIV)
+      elv_put_request(q, rq);
+   mempool_free(rq, q->rq.rq_pool);
+}
+
+static struct request *
+blk_alloc_request(struct request_queue *q, int rw, 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->cmd_flags and bio->bi_rw,
+    * see bio.h and blkdev.h
+    */
+   rq->cmd_flags = rw | REQ_ALLOCED;
+
+   if (priv) {
+      if (unlikely(elv_set_request(q, rq, gfp_mask))) {
+         mempool_free(rq, q->rq.rq_pool);
+         return NULL;
+      }
+      rq->cmd_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(struct request_queue *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(struct request_queue *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(struct request_queue *q, int rw)
+{
+   struct request_list *rl = &q->rq;
+
+   if (rl->count[rw] < queue_congestion_off_threshold(q))
+      blk_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(struct request_queue *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(struct request_queue *q, int rw_flags,
+               struct bio *bio, gfp_t gfp_mask)
+{
+   struct request *rq = NULL;
+   struct request_list *rl = &q->rq;
+   struct io_context *ioc = NULL;
+   const int rw = rw_flags & 0x01;
+   int may_queue, priv;
+
+   may_queue = elv_may_queue(q, rw_flags);
+   if (may_queue == ELV_MQUEUE_NO)
+      goto rq_starved;
+
+   if (rl->count[rw]+1 >= queue_congestion_on_threshold(q)) {
+      if (rl->count[rw]+1 >= q->nr_requests) {
+         ioc = current_io_context(GFP_ATOMIC, q->node);
+         /*
+          * 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);
+         } else {
+            if (may_queue != ELV_MQUEUE_MUST
+                  && !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;
+            }
+         }
+      }
+      blk_set_queue_congested(q, rw);
+   }
+
+   /*
+    * 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;
+
+   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_flags, priv, gfp_mask);
+   if (unlikely(!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;
+   }
+
+   /*
+    * ioc may be NULL here, and ioc_batching will be false. That's
+    * OK, if the queue is under the request limit then requests need
+    * not count toward the nr_batch_requests limit. There will always
+    * be some limit enforced by BLK_BATCH_TIME.
+    */
+   if (ioc_batching(q, ioc))
+      ioc->nr_batch_requests--;
+
+   rq_init(q, rq);
+
+   blk_add_trace_generic(q, bio, rw, BLK_TA_GETRQ);
+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(struct request_queue *q, int rw_flags,
+               struct bio *bio)
+{
+   const int rw = rw_flags & 0x01;
+   struct request *rq;
+
+   rq = get_request(q, rw_flags, 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_flags, bio, GFP_NOIO);
+
+      if (!rq) {
+         struct io_context *ioc;
+
+         blk_add_trace_generic(q, bio, rw, BLK_TA_SLEEPRQ);
+
+         __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, q->node);
+         ioc_set_batching(q, ioc);
+
+         spin_lock_irq(q->queue_lock);
+      }
+      finish_wait(&rl->wait[rw], &wait);
+   }
+
+   return rq;
+}
+
+struct request *blk_get_request(struct request_queue *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_start_queueing - initiate dispatch of requests to device
+ * @q:      request queue to kick into gear
+ *
+ * This is basically a helper to remove the need to know whether a queue
+ * is plugged or not if someone just wants to initiate dispatch of requests
+ * for this queue.
+ *
+ * The queue lock must be held with interrupts disabled.
+ */
+void blk_start_queueing(struct request_queue *q)
+{
+   if (!blk_queue_plugged(q))
+      q->request_fn(q);
+   else
+      __generic_unplug_device(q);
+}
+EXPORT_SYMBOL(blk_start_queueing);
+
+/**
+ * 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(struct request_queue *q, struct request *rq)
+{
+   blk_add_trace_rq(q, rq, BLK_TA_REQUEUE);
+
+   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(struct request_queue *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->cmd_type = REQ_TYPE_SPECIAL;
+   rq->cmd_flags |= 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, 1);
+   __elv_add_request(q, rq, where, 0);
+   blk_start_queueing(q);
+   spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_insert_request);
+
+/*
+ * 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(struct request_queue *q, struct request *req)
+{
+   drive_stat_acct(req, 1);
+
+   /*
+    * 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;
+}
+EXPORT_SYMBOL_GPL(disk_round_stats);
+
+void part_round_stats(struct hd_struct *part)
+{
+   unsigned long now = jiffies;
+
+   if (now == part->stamp)
+      return;
+
+   if (part->in_flight) {
+      __part_stat_add(part, time_in_queue,
+            part->in_flight * (now - part->stamp));
+      __part_stat_add(part, io_ticks, (now - part->stamp));
+   }
+   part->stamp = now;
+}
+
+/*
+ * queue lock must be held
+ */
+void __blk_put_request(struct request_queue *q, struct request *req)
+{
+   if (unlikely(!q))
+      return;
+   if (unlikely(--req->ref_count))
+      return;
+
+   elv_completed_request(q, req);
+
+   /*
+    * Request may not have originated from ll_rw_blk. if not,
+    * it didn't come out of our reserved rq pools
+    */
+   if (req->cmd_flags & REQ_ALLOCED) {
+      int rw = rq_data_dir(req);
+      int priv = req->cmd_flags & REQ_ELVPRIV;
+
+      BUG_ON(!list_empty(&req->queuelist));
+      BUG_ON(!hlist_unhashed(&req->hash));
+
+      blk_free_request(q, req);
+      freed_request(q, rw, priv);
+   }
+}
+EXPORT_SYMBOL_GPL(__blk_put_request);
+
+void blk_put_request(struct request *req)
+{
+   unsigned long flags;
+   struct request_queue *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);
+
+void init_request_from_bio(struct request *req, struct bio *bio)
+{
+   req->cmd_type = REQ_TYPE_FS;
+
+   /*
+    * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
+    */
+   if (bio_rw_ahead(bio) || bio_failfast(bio))
+      req->cmd_flags |= REQ_FAILFAST;
+
+   /*
+    * REQ_BARRIER implies no merging, but lets make it explicit
+    */
+   if (unlikely(bio_barrier(bio)))
+      req->cmd_flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
+
+   if (bio_sync(bio))
+      req->cmd_flags |= REQ_RW_SYNC;
+   if (bio_rw_meta(bio))
+      req->cmd_flags |= REQ_RW_META;
+
+   req->errors = 0;
+   req->hard_sector = req->sector = bio->bi_sector;
+   req->ioprio = bio_prio(bio);
+   req->start_time = jiffies;
+   blk_rq_bio_prep(req->q, req, bio);
+}
+
+static int __make_request(struct request_queue *q, struct bio *bio)
+{
+   struct request *req;
+   int el_ret, nr_sectors, barrier, err;
+   const unsigned short prio = bio_prio(bio);
+   const int sync = bio_sync(bio);
+   int rw_flags;
+
+   nr_sectors = bio_sectors(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);
+
+   barrier = bio_barrier(bio);
+   if (unlikely(barrier) && (q->next_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 (!ll_back_merge_fn(q, req, bio))
+         break;
+
+      blk_add_trace_bio(q, bio, BLK_TA_BACKMERGE);
+
+      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, 0);
+      if (!attempt_back_merge(q, req))
+         elv_merged_request(q, req, el_ret);
+      goto out;
+
+   case ELEVATOR_FRONT_MERGE:
+      BUG_ON(!rq_mergeable(req));
+
+      if (!ll_front_merge_fn(q, req, bio))
+         break;
+
+      blk_add_trace_bio(q, bio, BLK_TA_FRONTMERGE);
+
+      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 = bio_cur_sectors(bio);
+      req->hard_cur_sectors = req->current_nr_sectors;
+      req->sector = req->hard_sector = bio->bi_sector;
+      req->nr_sectors = req->hard_nr_sectors += nr_sectors;
+      req->ioprio = ioprio_best(req->ioprio, prio);
+      drive_stat_acct(req, 0);
+      if (!attempt_front_merge(q, req))
+         elv_merged_request(q, req, el_ret);
+      goto out;
+
+   /* ELV_NO_MERGE: elevator says don't/can't merge. */
+   default:
+      ;
+   }
+
+get_rq:
+   /*
+    * This sync check and mask will be re-done in init_request_from_bio(),
+    * but we need to set it earlier to expose the sync flag to the
+    * rq allocator and io schedulers.
+    */
+   rw_flags = bio_data_dir(bio);
+   if (sync)
+      rw_flags |= REQ_RW_SYNC;
+
+   /*
+    * Grab a free request. This is might sleep but can not fail.
+    * Returns with the queue unlocked.
+    */
+   req = get_request_wait(q, rw_flags, 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.
+    */
+   init_request_from_bio(req, bio);
+
+   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, 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 (bio_sectors(bio) && bdev != bdev->bd_contains) {
+      struct hd_struct *p = bdev->bd_part;
+
+      bio->bi_sector += p->start_sect;
+      bio->bi_bdev = bdev->bd_contains;
+
+      blk_add_trace_remap(bdev_get_queue(bio->bi_bdev), bio,
+                bdev->bd_dev, bio->bi_sector,
+                bio->bi_sector - p->start_sect);
+   }
+}
+
+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);
+}
+
+#ifdef CONFIG_FAIL_MAKE_REQUEST
+
+static DECLARE_FAULT_ATTR(fail_make_request);
+
+static int __init setup_fail_make_request(char *str)
+{
+   return setup_fault_attr(&fail_make_request, str);
+}
+__setup("fail_make_request=", setup_fail_make_request);
+
+static int should_fail_request(struct bio *bio)
+{
+   if ((bio->bi_bdev->bd_disk->flags & GENHD_FL_FAIL) ||
+       (bio->bi_bdev->bd_part && bio->bi_bdev->bd_part->make_it_fail))
+      return should_fail(&fail_make_request, bio->bi_size);
+
+   return 0;
+}
+
+static int __init fail_make_request_debugfs(void)
+{
+   return init_fault_attr_dentries(&fail_make_request,
+               "fail_make_request");
+}
+
+late_initcall(fail_make_request_debugfs);
+
+#else /* CONFIG_FAIL_MAKE_REQUEST */
+
+static inline int should_fail_request(struct bio *bio)
+{
+   return 0;
+}
+
+#endif /* CONFIG_FAIL_MAKE_REQUEST */
+
+/*
+ * Check whether this bio extends beyond the end of the device.
+ */
+static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
+{
+   sector_t maxsector;
+
+   if (!nr_sectors)
+      return 0;
+
+   /* 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);
+         return 1;
+      }
+   }
+
+   return 0;
+}
+
+/**
+ * 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.
+ */
+static inline void __generic_make_request(struct bio *bio)
+{
+   struct request_queue *q;
+   sector_t old_sector;
+   int ret, nr_sectors = bio_sectors(bio);
+   dev_t old_dev;
+   int err = -EIO;
+
+   might_sleep();
+
+   if (bio_check_eod(bio, nr_sectors))
+      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.
+    */
+   old_sector = -1;
+   old_dev = 0;
+   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, err);
+         break;
+      }
+
+      if (unlikely(nr_sectors > q->max_hw_sectors)) {
+         printk(KERN_ERR "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 (should_fail_request(bio))
+         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);
+
+      if (old_sector != -1)
+         blk_add_trace_remap(q, bio, old_dev, bio->bi_sector,
+                   old_sector);
+
+      blk_add_trace_bio(q, bio, BLK_TA_QUEUE);
+
+      old_sector = bio->bi_sector;
+      old_dev = bio->bi_bdev->bd_dev;
+
+      if (bio_check_eod(bio, nr_sectors))
+         goto end_io;
+      if (bio_empty_barrier(bio) && !q->prepare_flush_fn) {
+         err = -EOPNOTSUPP;
+         goto end_io;
+      }
+
+      ret = q->make_request_fn(q, bio);
+   } while (ret);
+}
+
+/*
+ * We only want one ->make_request_fn to be active at a time,
+ * else stack usage with stacked devices could be a problem.
+ * So use current->bio_{list,tail} to keep a list of requests
+ * submited by a make_request_fn function.
+ * current->bio_tail is also used as a flag to say if
+ * generic_make_request is currently active in this task or not.
+ * If it is NULL, then no make_request is active.  If it is non-NULL,
+ * then a make_request is active, and new requests should be added
+ * at the tail
+ */
+void generic_make_request(struct bio *bio)
+{
+   if (current->bio_tail) {
+      /* make_request is active */
+      *(current->bio_tail) = bio;
+      bio->bi_next = NULL;
+      current->bio_tail = &bio->bi_next;
+      return;
+   }
+   /* following loop may be a bit non-obvious, and so deserves some
+    * explanation.
+    * Before entering the loop, bio->bi_next is NULL (as all callers
+    * ensure that) so we have a list with a single bio.
+    * We pretend that we have just taken it off a longer list, so
+    * we assign bio_list to the next (which is NULL) and bio_tail
+    * to &bio_list, thus initialising the bio_list of new bios to be
+    * added.  __generic_make_request may indeed add some more bios
+    * through a recursive call to generic_make_request.  If it
+    * did, we find a non-NULL value in bio_list and re-enter the loop
+    * from the top.  In this case we really did just take the bio
+    * of the top of the list (no pretending) and so fixup bio_list and
+    * bio_tail or bi_next, and call into __generic_make_request again.
+    *
+    * The loop was structured like this to make only one call to
+    * __generic_make_request (which is important as it is large and
+    * inlined) and to keep the structure simple.
+    */
+   BUG_ON(bio->bi_next);
+   do {
+      current->bio_list = bio->bi_next;
+      if (bio->bi_next == NULL)
+         current->bio_tail = ¤t->bio_list;
+      else
+         bio->bi_next = NULL;
+      __generic_make_request(bio);
+      bio = current->bio_list;
+   } while (bio);
+   current->bio_tail = NULL; /* deactivate */
+}
+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->bi_rw |= rw;
+
+   /*
+    * If it's a regular read/write or a barrier with data attached,
+    * go through the normal accounting stuff before submission.
+    */
+   if (!bio_empty_barrier(bio)) {
+
+      BIO_BUG_ON(!bio->bi_size);
+      BIO_BUG_ON(!bio->bi_io_vec);
+
+      if (rw & WRITE) {
+         count_vm_events(PGPGOUT, count);
+      } else {
+         task_io_account_read(bio->bi_size);
+         count_vm_events(PGPGIN, count);
+      }
+
+      if (unlikely(block_dump)) {
+         char b[BDEVNAME_SIZE];
+         printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
+         current->comm, task_pid_nr(current),
+            (rw & WRITE) ? "WRITE" : "READ",
+            (unsigned long long)bio->bi_sector,
+            bdevname(bio->bi_bdev, b));
+      }
+   }
+
+   generic_make_request(bio);
+}
+EXPORT_SYMBOL(submit_bio);
+
+/**
+ * __end_that_request_first - end I/O on a request
+ * @req:      the request being processed
+ * @error:    0 for success, < 0 for 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) in the cluster.
+ *
+ * Return:
+ *     0 - we are done with this request, call end_that_request_last()
+ *     1 - still buffers pending for this request
+ **/
+static int __end_that_request_first(struct request *req, int error,
+                int nr_bytes)
+{
+   int total_bytes, bio_nbytes, next_idx = 0;
+   struct bio *bio;
+
+   blk_add_trace_rq(req->q, req, BLK_TA_COMPLETE);
+
+   /*
+    * 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 (error && (blk_fs_request(req) && !(req->cmd_flags & REQ_QUIET))) {
+      printk(KERN_ERR "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);
+
+      all_stat_add(req->rq_disk, sectors[rw],
+              nr_bytes >> 9, req->sector);
+   }
+
+   total_bytes = bio_nbytes = 0;
+   while ((bio = req->bio) != NULL) {
+      int nbytes;
+
+      /*
+       * For an empty barrier request, the low level driver must
+       * store a potential error location in ->sector. We pass
+       * that back up in ->bi_sector.
+       */
+      if (blk_empty_barrier(req))
+         bio->bi_sector = req->sector;
+
+      if (nr_bytes >= bio->bi_size) {
+         req->bio = bio->bi_next;
+         nbytes = bio->bi_size;
+         req_bio_endio(req, 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(KERN_ERR "%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;
+
+      bio = req->bio;
+      if (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) {
+      req_bio_endio(req, 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;
+}
+
+/*
+ * splice the completion data to a local structure and hand off to
+ * process_completion_queue() to complete the requests
+ */
+static void blk_done_softirq(struct softirq_action *h)
+{
+   struct list_head *cpu_list, local_list;
+
+   local_irq_disable();
+   cpu_list = &__get_cpu_var(blk_cpu_done);
+   list_replace_init(cpu_list, &local_list);
+   local_irq_enable();
+
+   while (!list_empty(&local_list)) {
+      struct request *rq;
+
+      rq = list_entry(local_list.next, struct request, donelist);
+      list_del_init(&rq->donelist);
+      rq->q->softirq_done_fn(rq);
+   }
+}
+
+static int __cpuinit blk_cpu_notify(struct notifier_block *self,
+                unsigned long action, void *hcpu)
+{
+   /*
+    * If a CPU goes away, splice its entries to the current CPU
+    * and trigger a run of the softirq
+    */
+   if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
+      int cpu = (unsigned long) hcpu;
+
+      local_irq_disable();
+      list_splice_init(&per_cpu(blk_cpu_done, cpu),
+             &__get_cpu_var(blk_cpu_done));
+      raise_softirq_irqoff(BLOCK_SOFTIRQ);
+      local_irq_enable();
+   }
+
+   return NOTIFY_OK;
+}
+
+
+static struct notifier_block blk_cpu_notifier __cpuinitdata = {
+   .notifier_call   = blk_cpu_notify,
+};
+
+/**
+ * blk_complete_request - end I/O on a request
+ * @req:      the request being processed
+ *
+ * Description:
+ *     Ends all I/O on a request. It does not handle partial completions,
+ *     unless the driver actually implements this in its completion callback
+ *     through requeueing. The actual completion happens out-of-order,
+ *     through a softirq handler. The user must have registered a completion
+ *     callback through blk_queue_softirq_done().
+ **/
+
+void blk_complete_request(struct request *req)
+{
+   struct list_head *cpu_list;
+   unsigned long flags;
+
+   BUG_ON(!req->q->softirq_done_fn);
+
+   local_irq_save(flags);
+
+   cpu_list = &__get_cpu_var(blk_cpu_done);
+   list_add_tail(&req->donelist, cpu_list);
+   raise_softirq_irqoff(BLOCK_SOFTIRQ);
+
+   local_irq_restore(flags);
+}
+EXPORT_SYMBOL(blk_complete_request);
+
+/*
+ * queue lock must be held
+ */
+static void end_that_request_last(struct request *req, int error)
+{
+   struct gendisk *disk = req->rq_disk;
+
+   if (blk_rq_tagged(req))
+      blk_queue_end_tag(req->q, req);
+
+   if (blk_queued_rq(req))
+      blkdev_dequeue_request(req);
+
+   if (unlikely(laptop_mode) && blk_fs_request(req))
+      laptop_io_completion();
+
+   /*
+    * Account IO completion.  bar_rq isn't accounted as a normal
+    * IO on queueing nor completion.  Accounting the containing
+    * request is enough.
+    */
+   if (disk && blk_fs_request(req) && req != &req->q->bar_rq) {
+      unsigned long duration = jiffies - req->start_time;
+      const int rw = rq_data_dir(req);
+      struct hd_struct *part = get_part(disk, req->sector);
+
+      __all_stat_inc(disk, ios[rw], req->sector);
+      __all_stat_add(disk, ticks[rw], duration, req->sector);
+      disk_round_stats(disk);
+      disk->in_flight--;
+      if (part) {
+         part_round_stats(part);
+         part->in_flight--;
+      }
+   }
+
+   if (req->end_io)
+      req->end_io(req, error);
+   else {
+      if (blk_bidi_rq(req))
+         __blk_put_request(req->next_rq->q, req->next_rq);
+
+      __blk_put_request(req->q, req);
+   }
+}
+
+static inline void __end_request(struct request *rq, int uptodate,
+             unsigned int nr_bytes)
+{
+   int error = 0;
+
+   if (uptodate <= 0)
+      error = uptodate ? uptodate : -EIO;
+
+   __blk_end_request(rq, error, nr_bytes);
+}
+
+/**
+ * blk_rq_bytes - Returns bytes left to complete in the entire request
+ * @rq: the request being processed
+ **/
+unsigned int blk_rq_bytes(struct request *rq)
+{
+   if (blk_fs_request(rq))
+      return rq->hard_nr_sectors << 9;
+
+   return rq->data_len;
+}
+EXPORT_SYMBOL_GPL(blk_rq_bytes);
+
+/**
+ * blk_rq_cur_bytes - Returns bytes left to complete in the current segment
+ * @rq: the request being processed
+ **/
+unsigned int blk_rq_cur_bytes(struct request *rq)
+{
+   if (blk_fs_request(rq))
+      return rq->current_nr_sectors << 9;
+
+   if (rq->bio)
+      return rq->bio->bi_size;
+
+   return rq->data_len;
+}
+EXPORT_SYMBOL_GPL(blk_rq_cur_bytes);
+
+/**
+ * end_queued_request - end all I/O on a queued request
+ * @rq:      the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends all I/O on a request, and removes it from the block layer queues.
+ *     Not suitable for normal IO completion, unless the driver still has
+ *     the request attached to the block layer.
+ *
+ **/
+void end_queued_request(struct request *rq, int uptodate)
+{
+   __end_request(rq, uptodate, blk_rq_bytes(rq));
+}
+EXPORT_SYMBOL(end_queued_request);
+
+/**
+ * end_dequeued_request - end all I/O on a dequeued request
+ * @rq:      the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends all I/O on a request. The request must already have been
+ *     dequeued using blkdev_dequeue_request(), as is normally the case
+ *     for most drivers.
+ *
+ **/
+void end_dequeued_request(struct request *rq, int uptodate)
+{
+   __end_request(rq, uptodate, blk_rq_bytes(rq));
+}
+EXPORT_SYMBOL(end_dequeued_request);
+
+
+/**
+ * end_request - end I/O on the current segment of the request
+ * @req:   the request being processed
+ * @uptodate:   error value or 0/1 uptodate flag
+ *
+ * Description:
+ *     Ends I/O on the current segment of a request. If that is the only
+ *     remaining segment, the request is also completed and freed.
+ *
+ *     This is a remnant of how older block drivers handled IO completions.
+ *     Modern drivers typically end IO on the full request in one go, unless
+ *     they have a residual value to account for. For that case this function
+ *     isn't really useful, unless the residual just happens to be the
+ *     full current segment. In other words, don't use this function in new
+ *     code. Either use end_request_completely(), or the
+ *     end_that_request_chunk() (along with end_that_request_last()) for
+ *     partial completions.
+ *
+ **/
+void end_request(struct request *req, int uptodate)
+{
+   __end_request(req, uptodate, req->hard_cur_sectors << 9);
+}
+EXPORT_SYMBOL(end_request);
+
+/**
+ * blk_end_io - Generic end_io function to complete a request.
+ * @rq:           the request being processed
+ * @error:        0 for success, < 0 for error
+ * @nr_bytes:     number of bytes to complete @rq
+ * @bidi_bytes:   number of bytes to complete @rq->next_rq
+ * @drv_callback: function called between completion of bios in the request
+ *                and completion of the request.
+ *                If the callback returns non 0, this helper returns without
+ *                completion of the request.
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - this request is not freed yet, it still has pending buffers.
+ **/
+static int blk_end_io(struct request *rq, int error, unsigned int nr_bytes,
+            unsigned int bidi_bytes,
+            int (drv_callback)(struct request *))
+{
+   struct request_queue *q = rq->q;
+   unsigned long flags = 0UL;
+
+   if (blk_fs_request(rq) || blk_pc_request(rq)) {
+      if (__end_that_request_first(rq, error, nr_bytes))
+         return 1;
+
+      /* Bidi request must be completed as a whole */
+      if (blk_bidi_rq(rq) &&
+          __end_that_request_first(rq->next_rq, error, bidi_bytes))
+         return 1;
+   }
+
+   /* Special feature for tricky drivers */
+   if (drv_callback && drv_callback(rq))
+      return 1;
+
+   add_disk_randomness(rq->rq_disk);
+
+   spin_lock_irqsave(q->queue_lock, flags);
+   end_that_request_last(rq, error);
+   spin_unlock_irqrestore(q->queue_lock, flags);
+
+   return 0;
+}
+
+/**
+ * blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    0 for success, < 0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
+{
+   return blk_end_io(rq, error, nr_bytes, 0, NULL);
+}
+EXPORT_SYMBOL_GPL(blk_end_request);
+
+/**
+ * __blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    0 for success, < 0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Must be called with queue lock held unlike blk_end_request().
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int __blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
+{
+   if (blk_fs_request(rq) || blk_pc_request(rq)) {
+      if (__end_that_request_first(rq, error, nr_bytes))
+         return 1;
+   }
+
+   add_disk_randomness(rq->rq_disk);
+
+   end_that_request_last(rq, error);
+
+   return 0;
+}
+EXPORT_SYMBOL_GPL(__blk_end_request);
+
+/**
+ * blk_end_bidi_request - Helper function for drivers to complete bidi request.
+ * @rq:         the bidi request being processed
+ * @error:      0 for success, < 0 for error
+ * @nr_bytes:   number of bytes to complete @rq
+ * @bidi_bytes: number of bytes to complete @rq->next_rq
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - still buffers pending for this request
+ **/
+int blk_end_bidi_request(struct request *rq, int error, unsigned int nr_bytes,
+          unsigned int bidi_bytes)
+{
+   return blk_end_io(rq, error, nr_bytes, bidi_bytes, NULL);
+}
+EXPORT_SYMBOL_GPL(blk_end_bidi_request);
+
+/**
+ * blk_end_request_callback - Special helper function for tricky drivers
+ * @rq:           the request being processed
+ * @error:        0 for success, < 0 for error
+ * @nr_bytes:     number of bytes to complete
+ * @drv_callback: function called between completion of bios in the request
+ *                and completion of the request.
+ *                If the callback returns non 0, this helper returns without
+ *                completion of the request.
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ *     This special helper function is used only for existing tricky drivers.
+ *     (e.g. cdrom_newpc_intr() of ide-cd)
+ *     This interface will be removed when such drivers are rewritten.
+ *     Don't use this interface in other places anymore.
+ *
+ * Return:
+ *     0 - we are done with this request
+ *     1 - this request is not freed yet.
+ *         this request still has pending buffers or
+ *         the driver doesn't want to finish this request yet.
+ **/
+int blk_end_request_callback(struct request *rq, int error,
+              unsigned int nr_bytes,
+              int (drv_callback)(struct request *))
+{
+   return blk_end_io(rq, error, nr_bytes, 0, drv_callback);
+}
+EXPORT_SYMBOL_GPL(blk_end_request_callback);
+
+void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
+           struct bio *bio)
+{
+   /* first two bits are identical in rq->cmd_flags and bio->bi_rw */
+   rq->cmd_flags |= (bio->bi_rw & 3);
+
+   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->data_len = bio->bi_size;
+
+   rq->bio = rq->biotail = bio;
+
+   if (bio->bi_bdev)
+      rq->rq_disk = bio->bi_bdev->bd_disk;
+}
+
+int kblockd_schedule_work(struct work_struct *work)
+{
+   return queue_work(kblockd_workqueue, work);
+}
+EXPORT_SYMBOL(kblockd_schedule_work);
+
+void kblockd_flush_work(struct work_struct *work)
+{
+   cancel_work_sync(work);
+}
+EXPORT_SYMBOL(kblockd_flush_work);
+
+int __init blk_dev_init(void)
+{
+   int i;
+
+   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);
+
+   blk_requestq_cachep = kmem_cache_create("blkdev_queue",
+         sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
+
+   for_each_possible_cpu(i)
+      INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
+
+   open_softirq(BLOCK_SOFTIRQ, blk_done_softirq, NULL);
+   register_hotcpu_notifier(&blk_cpu_notifier);
+
+   return 0;
+}
+