Logo Search packages:      
Sourcecode: linux version File versions  Download package

elevator.c

/*
 *  Block device elevator/IO-scheduler.
 *
 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
 *
 * 30042000 Jens Axboe <axboe@kernel.dk> :
 *
 * Split the elevator a bit so that it is possible to choose a different
 * one or even write a new "plug in". There are three pieces:
 * - elevator_fn, inserts a new request in the queue list
 * - elevator_merge_fn, decides whether a new buffer can be merged with
 *   an existing request
 * - elevator_dequeue_fn, called when a request is taken off the active list
 *
 * 20082000 Dave Jones <davej@suse.de> :
 * Removed tests for max-bomb-segments, which was breaking elvtune
 *  when run without -bN
 *
 * Jens:
 * - Rework again to work with bio instead of buffer_heads
 * - loose bi_dev comparisons, partition handling is right now
 * - completely modularize elevator setup and teardown
 *
 */
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/delay.h>
#include <linux/blktrace_api.h>
#include <linux/hash.h>

#include <asm/uaccess.h>

static DEFINE_SPINLOCK(elv_list_lock);
static LIST_HEAD(elv_list);

/*
 * Merge hash stuff.
 */
static const int elv_hash_shift = 6;
#define ELV_HASH_BLOCK(sec)   ((sec) >> 3)
#define ELV_HASH_FN(sec)      (hash_long(ELV_HASH_BLOCK((sec)), elv_hash_shift))
#define ELV_HASH_ENTRIES      (1 << elv_hash_shift)
#define rq_hash_key(rq)       ((rq)->sector + (rq)->nr_sectors)
#define ELV_ON_HASH(rq)       (!hlist_unhashed(&(rq)->hash))

/*
 * Query io scheduler to see if the current process issuing bio may be
 * merged with rq.
 */
static int elv_iosched_allow_merge(struct request *rq, struct bio *bio)
{
      struct request_queue *q = rq->q;
      elevator_t *e = q->elevator;

      if (e->ops->elevator_allow_merge_fn)
            return e->ops->elevator_allow_merge_fn(q, rq, bio);

      return 1;
}

/*
 * can we safely merge with this request?
 */
inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
{
      if (!rq_mergeable(rq))
            return 0;

      /*
       * different data direction or already started, don't merge
       */
      if (bio_data_dir(bio) != rq_data_dir(rq))
            return 0;

      /*
       * must be same device and not a special request
       */
      if (rq->rq_disk != bio->bi_bdev->bd_disk || rq->special)
            return 0;

      if (!elv_iosched_allow_merge(rq, bio))
            return 0;

      return 1;
}
EXPORT_SYMBOL(elv_rq_merge_ok);

static inline int elv_try_merge(struct request *__rq, struct bio *bio)
{
      int ret = ELEVATOR_NO_MERGE;

      /*
       * we can merge and sequence is ok, check if it's possible
       */
      if (elv_rq_merge_ok(__rq, bio)) {
            if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
                  ret = ELEVATOR_BACK_MERGE;
            else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
                  ret = ELEVATOR_FRONT_MERGE;
      }

      return ret;
}

static struct elevator_type *elevator_find(const char *name)
{
      struct elevator_type *e;

      list_for_each_entry(e, &elv_list, list) {
            if (!strcmp(e->elevator_name, name))
                  return e;
      }

      return NULL;
}

static void elevator_put(struct elevator_type *e)
{
      module_put(e->elevator_owner);
}

static struct elevator_type *elevator_get(const char *name)
{
      struct elevator_type *e;

      spin_lock(&elv_list_lock);

      e = elevator_find(name);
      if (e && !try_module_get(e->elevator_owner))
            e = NULL;

      spin_unlock(&elv_list_lock);

      return e;
}

static void *elevator_init_queue(struct request_queue *q,
                         struct elevator_queue *eq)
{
      return eq->ops->elevator_init_fn(q);
}

static void elevator_attach(struct request_queue *q, struct elevator_queue *eq,
                     void *data)
{
      q->elevator = eq;
      eq->elevator_data = data;
}

static char chosen_elevator[16];

static int __init elevator_setup(char *str)
{
      /*
       * Be backwards-compatible with previous kernels, so users
       * won't get the wrong elevator.
       */
      if (!strcmp(str, "as"))
            strcpy(chosen_elevator, "anticipatory");
      else
            strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
      return 1;
}

__setup("elevator=", elevator_setup);

static struct kobj_type elv_ktype;

static elevator_t *elevator_alloc(struct request_queue *q,
                          struct elevator_type *e)
{
      elevator_t *eq;
      int i;

      eq = kmalloc_node(sizeof(elevator_t), GFP_KERNEL | __GFP_ZERO, q->node);
      if (unlikely(!eq))
            goto err;

      eq->ops = &e->ops;
      eq->elevator_type = e;
      kobject_init(&eq->kobj);
      kobject_set_name(&eq->kobj, "%s", "iosched");
      eq->kobj.ktype = &elv_ktype;
      mutex_init(&eq->sysfs_lock);

      eq->hash = kmalloc_node(sizeof(struct hlist_head) * ELV_HASH_ENTRIES,
                              GFP_KERNEL, q->node);
      if (!eq->hash)
            goto err;

      for (i = 0; i < ELV_HASH_ENTRIES; i++)
            INIT_HLIST_HEAD(&eq->hash[i]);

      return eq;
err:
      kfree(eq);
      elevator_put(e);
      return NULL;
}

static void elevator_release(struct kobject *kobj)
{
      elevator_t *e = container_of(kobj, elevator_t, kobj);

      elevator_put(e->elevator_type);
      kfree(e->hash);
      kfree(e);
}

int elevator_init(struct request_queue *q, char *name)
{
      struct elevator_type *e = NULL;
      struct elevator_queue *eq;
      int ret = 0;
      void *data;

      INIT_LIST_HEAD(&q->queue_head);
      q->last_merge = NULL;
      q->end_sector = 0;
      q->boundary_rq = NULL;

      if (name && !(e = elevator_get(name)))
            return -EINVAL;

      if (!e && *chosen_elevator && !(e = elevator_get(chosen_elevator)))
            printk("I/O scheduler %s not found\n", chosen_elevator);

      if (!e && !(e = elevator_get(CONFIG_DEFAULT_IOSCHED))) {
            printk("Default I/O scheduler not found, using no-op\n");
            e = elevator_get("noop");
      }

      eq = elevator_alloc(q, e);
      if (!eq)
            return -ENOMEM;

      data = elevator_init_queue(q, eq);
      if (!data) {
            kobject_put(&eq->kobj);
            return -ENOMEM;
      }

      elevator_attach(q, eq, data);
      return ret;
}

EXPORT_SYMBOL(elevator_init);

void elevator_exit(elevator_t *e)
{
      mutex_lock(&e->sysfs_lock);
      if (e->ops->elevator_exit_fn)
            e->ops->elevator_exit_fn(e);
      e->ops = NULL;
      mutex_unlock(&e->sysfs_lock);

      kobject_put(&e->kobj);
}

EXPORT_SYMBOL(elevator_exit);

static void elv_activate_rq(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_activate_req_fn)
            e->ops->elevator_activate_req_fn(q, rq);
}

static void elv_deactivate_rq(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_deactivate_req_fn)
            e->ops->elevator_deactivate_req_fn(q, rq);
}

static inline void __elv_rqhash_del(struct request *rq)
{
      hlist_del_init(&rq->hash);
}

static void elv_rqhash_del(struct request_queue *q, struct request *rq)
{
      if (ELV_ON_HASH(rq))
            __elv_rqhash_del(rq);
}

static void elv_rqhash_add(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      BUG_ON(ELV_ON_HASH(rq));
      hlist_add_head(&rq->hash, &e->hash[ELV_HASH_FN(rq_hash_key(rq))]);
}

static void elv_rqhash_reposition(struct request_queue *q, struct request *rq)
{
      __elv_rqhash_del(rq);
      elv_rqhash_add(q, rq);
}

static struct request *elv_rqhash_find(struct request_queue *q, sector_t offset)
{
      elevator_t *e = q->elevator;
      struct hlist_head *hash_list = &e->hash[ELV_HASH_FN(offset)];
      struct hlist_node *entry, *next;
      struct request *rq;

      hlist_for_each_entry_safe(rq, entry, next, hash_list, hash) {
            BUG_ON(!ELV_ON_HASH(rq));

            if (unlikely(!rq_mergeable(rq))) {
                  __elv_rqhash_del(rq);
                  continue;
            }

            if (rq_hash_key(rq) == offset)
                  return rq;
      }

      return NULL;
}

/*
 * RB-tree support functions for inserting/lookup/removal of requests
 * in a sorted RB tree.
 */
struct request *elv_rb_add(struct rb_root *root, struct request *rq)
{
      struct rb_node **p = &root->rb_node;
      struct rb_node *parent = NULL;
      struct request *__rq;

      while (*p) {
            parent = *p;
            __rq = rb_entry(parent, struct request, rb_node);

            if (rq->sector < __rq->sector)
                  p = &(*p)->rb_left;
            else if (rq->sector > __rq->sector)
                  p = &(*p)->rb_right;
            else
                  return __rq;
      }

      rb_link_node(&rq->rb_node, parent, p);
      rb_insert_color(&rq->rb_node, root);
      return NULL;
}

EXPORT_SYMBOL(elv_rb_add);

void elv_rb_del(struct rb_root *root, struct request *rq)
{
      BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
      rb_erase(&rq->rb_node, root);
      RB_CLEAR_NODE(&rq->rb_node);
}

EXPORT_SYMBOL(elv_rb_del);

struct request *elv_rb_find(struct rb_root *root, sector_t sector)
{
      struct rb_node *n = root->rb_node;
      struct request *rq;

      while (n) {
            rq = rb_entry(n, struct request, rb_node);

            if (sector < rq->sector)
                  n = n->rb_left;
            else if (sector > rq->sector)
                  n = n->rb_right;
            else
                  return rq;
      }

      return NULL;
}

EXPORT_SYMBOL(elv_rb_find);

/*
 * Insert rq into dispatch queue of q.  Queue lock must be held on
 * entry.  rq is sort instead into the dispatch queue. To be used by
 * specific elevators.
 */
void elv_dispatch_sort(struct request_queue *q, struct request *rq)
{
      sector_t boundary;
      struct list_head *entry;

      if (q->last_merge == rq)
            q->last_merge = NULL;

      elv_rqhash_del(q, rq);

      q->nr_sorted--;

      boundary = q->end_sector;

      list_for_each_prev(entry, &q->queue_head) {
            struct request *pos = list_entry_rq(entry);

            if (rq_data_dir(rq) != rq_data_dir(pos))
                  break;
            if (pos->cmd_flags & (REQ_SOFTBARRIER|REQ_HARDBARRIER|REQ_STARTED))
                  break;
            if (rq->sector >= boundary) {
                  if (pos->sector < boundary)
                        continue;
            } else {
                  if (pos->sector >= boundary)
                        break;
            }
            if (rq->sector >= pos->sector)
                  break;
      }

      list_add(&rq->queuelist, entry);
}

EXPORT_SYMBOL(elv_dispatch_sort);

/*
 * Insert rq into dispatch queue of q.  Queue lock must be held on
 * entry.  rq is added to the back of the dispatch queue. To be used by
 * specific elevators.
 */
void elv_dispatch_add_tail(struct request_queue *q, struct request *rq)
{
      if (q->last_merge == rq)
            q->last_merge = NULL;

      elv_rqhash_del(q, rq);

      q->nr_sorted--;

      q->end_sector = rq_end_sector(rq);
      q->boundary_rq = rq;
      list_add_tail(&rq->queuelist, &q->queue_head);
}

EXPORT_SYMBOL(elv_dispatch_add_tail);

int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
{
      elevator_t *e = q->elevator;
      struct request *__rq;
      int ret;

      /*
       * First try one-hit cache.
       */
      if (q->last_merge) {
            ret = elv_try_merge(q->last_merge, bio);
            if (ret != ELEVATOR_NO_MERGE) {
                  *req = q->last_merge;
                  return ret;
            }
      }

      /*
       * See if our hash lookup can find a potential backmerge.
       */
      __rq = elv_rqhash_find(q, bio->bi_sector);
      if (__rq && elv_rq_merge_ok(__rq, bio)) {
            *req = __rq;
            return ELEVATOR_BACK_MERGE;
      }

      if (e->ops->elevator_merge_fn)
            return e->ops->elevator_merge_fn(q, req, bio);

      return ELEVATOR_NO_MERGE;
}

void elv_merged_request(struct request_queue *q, struct request *rq, int type)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_merged_fn)
            e->ops->elevator_merged_fn(q, rq, type);

      if (type == ELEVATOR_BACK_MERGE)
            elv_rqhash_reposition(q, rq);

      q->last_merge = rq;
}

void elv_merge_requests(struct request_queue *q, struct request *rq,
                       struct request *next)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_merge_req_fn)
            e->ops->elevator_merge_req_fn(q, rq, next);

      elv_rqhash_reposition(q, rq);
      elv_rqhash_del(q, next);

      q->nr_sorted--;
      q->last_merge = rq;
}

void elv_requeue_request(struct request_queue *q, struct request *rq)
{
      /*
       * it already went through dequeue, we need to decrement the
       * in_flight count again
       */
      if (blk_account_rq(rq)) {
            q->in_flight--;
            if (blk_sorted_rq(rq))
                  elv_deactivate_rq(q, rq);
      }

      rq->cmd_flags &= ~REQ_STARTED;

      elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
}

static void elv_drain_elevator(struct request_queue *q)
{
      static int printed;
      while (q->elevator->ops->elevator_dispatch_fn(q, 1))
            ;
      if (q->nr_sorted == 0)
            return;
      if (printed++ < 10) {
            printk(KERN_ERR "%s: forced dispatching is broken "
                   "(nr_sorted=%u), please report this\n",
                   q->elevator->elevator_type->elevator_name, q->nr_sorted);
      }
}

void elv_insert(struct request_queue *q, struct request *rq, int where)
{
      struct list_head *pos;
      unsigned ordseq;
      int unplug_it = 1;

      blk_add_trace_rq(q, rq, BLK_TA_INSERT);

      rq->q = q;

      switch (where) {
      case ELEVATOR_INSERT_FRONT:
            rq->cmd_flags |= REQ_SOFTBARRIER;

            list_add(&rq->queuelist, &q->queue_head);
            break;

      case ELEVATOR_INSERT_BACK:
            rq->cmd_flags |= REQ_SOFTBARRIER;
            elv_drain_elevator(q);
            list_add_tail(&rq->queuelist, &q->queue_head);
            /*
             * We kick the queue here for the following reasons.
             * - The elevator might have returned NULL previously
             *   to delay requests and returned them now.  As the
             *   queue wasn't empty before this request, ll_rw_blk
             *   won't run the queue on return, resulting in hang.
             * - Usually, back inserted requests won't be merged
             *   with anything.  There's no point in delaying queue
             *   processing.
             */
            blk_remove_plug(q);
            q->request_fn(q);
            break;

      case ELEVATOR_INSERT_SORT:
            BUG_ON(!blk_fs_request(rq));
            rq->cmd_flags |= REQ_SORTED;
            q->nr_sorted++;
            if (rq_mergeable(rq)) {
                  elv_rqhash_add(q, rq);
                  if (!q->last_merge)
                        q->last_merge = rq;
            }

            /*
             * Some ioscheds (cfq) run q->request_fn directly, so
             * rq cannot be accessed after calling
             * elevator_add_req_fn.
             */
            q->elevator->ops->elevator_add_req_fn(q, rq);
            break;

      case ELEVATOR_INSERT_REQUEUE:
            /*
             * If ordered flush isn't in progress, we do front
             * insertion; otherwise, requests should be requeued
             * in ordseq order.
             */
            rq->cmd_flags |= REQ_SOFTBARRIER;

            /*
             * Most requeues happen because of a busy condition,
             * don't force unplug of the queue for that case.
             */
            unplug_it = 0;

            if (q->ordseq == 0) {
                  list_add(&rq->queuelist, &q->queue_head);
                  break;
            }

            ordseq = blk_ordered_req_seq(rq);

            list_for_each(pos, &q->queue_head) {
                  struct request *pos_rq = list_entry_rq(pos);
                  if (ordseq <= blk_ordered_req_seq(pos_rq))
                        break;
            }

            list_add_tail(&rq->queuelist, pos);
            break;

      default:
            printk(KERN_ERR "%s: bad insertion point %d\n",
                   __FUNCTION__, where);
            BUG();
      }

      if (unplug_it && blk_queue_plugged(q)) {
            int nrq = q->rq.count[READ] + q->rq.count[WRITE]
                  - q->in_flight;

            if (nrq >= q->unplug_thresh)
                  __generic_unplug_device(q);
      }
}

void __elv_add_request(struct request_queue *q, struct request *rq, int where,
                   int plug)
{
      if (q->ordcolor)
            rq->cmd_flags |= REQ_ORDERED_COLOR;

      if (rq->cmd_flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
            /*
             * toggle ordered color
             */
            if (blk_barrier_rq(rq))
                  q->ordcolor ^= 1;

            /*
             * barriers implicitly indicate back insertion
             */
            if (where == ELEVATOR_INSERT_SORT)
                  where = ELEVATOR_INSERT_BACK;

            /*
             * this request is scheduling boundary, update
             * end_sector
             */
            if (blk_fs_request(rq)) {
                  q->end_sector = rq_end_sector(rq);
                  q->boundary_rq = rq;
            }
      } else if (!(rq->cmd_flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
            where = ELEVATOR_INSERT_BACK;

      if (plug)
            blk_plug_device(q);

      elv_insert(q, rq, where);
}

EXPORT_SYMBOL(__elv_add_request);

void elv_add_request(struct request_queue *q, struct request *rq, int where,
                 int plug)
{
      unsigned long flags;

      spin_lock_irqsave(q->queue_lock, flags);
      __elv_add_request(q, rq, where, plug);
      spin_unlock_irqrestore(q->queue_lock, flags);
}

EXPORT_SYMBOL(elv_add_request);

static inline struct request *__elv_next_request(struct request_queue *q)
{
      struct request *rq;

      while (1) {
            while (!list_empty(&q->queue_head)) {
                  rq = list_entry_rq(q->queue_head.next);
                  if (blk_do_ordered(q, &rq))
                        return rq;
            }

            if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
                  return NULL;
      }
}

struct request *elv_next_request(struct request_queue *q)
{
      struct request *rq;
      int ret;

      while ((rq = __elv_next_request(q)) != NULL) {
            /*
             * Kill the empty barrier place holder, the driver must
             * not ever see it.
             */
            if (blk_empty_barrier(rq)) {
                  end_queued_request(rq, 1);
                  continue;
            }
            if (!(rq->cmd_flags & REQ_STARTED)) {
                  /*
                   * This is the first time the device driver
                   * sees this request (possibly after
                   * requeueing).  Notify IO scheduler.
                   */
                  if (blk_sorted_rq(rq))
                        elv_activate_rq(q, rq);

                  /*
                   * just mark as started even if we don't start
                   * it, a request that has been delayed should
                   * not be passed by new incoming requests
                   */
                  rq->cmd_flags |= REQ_STARTED;
                  blk_add_trace_rq(q, rq, BLK_TA_ISSUE);
            }

            if (!q->boundary_rq || q->boundary_rq == rq) {
                  q->end_sector = rq_end_sector(rq);
                  q->boundary_rq = NULL;
            }

            if ((rq->cmd_flags & REQ_DONTPREP) || !q->prep_rq_fn)
                  break;

            ret = q->prep_rq_fn(q, rq);
            if (ret == BLKPREP_OK) {
                  break;
            } else if (ret == BLKPREP_DEFER) {
                  /*
                   * the request may have been (partially) prepped.
                   * we need to keep this request in the front to
                   * avoid resource deadlock.  REQ_STARTED will
                   * prevent other fs requests from passing this one.
                   */
                  rq = NULL;
                  break;
            } else if (ret == BLKPREP_KILL) {
                  rq->cmd_flags |= REQ_QUIET;
                  end_queued_request(rq, 0);
            } else {
                  printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
                                                ret);
                  break;
            }
      }

      return rq;
}

EXPORT_SYMBOL(elv_next_request);

void elv_dequeue_request(struct request_queue *q, struct request *rq)
{
      BUG_ON(list_empty(&rq->queuelist));
      BUG_ON(ELV_ON_HASH(rq));

      list_del_init(&rq->queuelist);

      /*
       * the time frame between a request being removed from the lists
       * and to it is freed is accounted as io that is in progress at
       * the driver side.
       */
      if (blk_account_rq(rq))
            q->in_flight++;
}

EXPORT_SYMBOL(elv_dequeue_request);

int elv_queue_empty(struct request_queue *q)
{
      elevator_t *e = q->elevator;

      if (!list_empty(&q->queue_head))
            return 0;

      if (e->ops->elevator_queue_empty_fn)
            return e->ops->elevator_queue_empty_fn(q);

      return 1;
}

EXPORT_SYMBOL(elv_queue_empty);

struct request *elv_latter_request(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_latter_req_fn)
            return e->ops->elevator_latter_req_fn(q, rq);
      return NULL;
}

struct request *elv_former_request(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_former_req_fn)
            return e->ops->elevator_former_req_fn(q, rq);
      return NULL;
}

int elv_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_set_req_fn)
            return e->ops->elevator_set_req_fn(q, rq, gfp_mask);

      rq->elevator_private = NULL;
      return 0;
}

void elv_put_request(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_put_req_fn)
            e->ops->elevator_put_req_fn(rq);
}

int elv_may_queue(struct request_queue *q, int rw)
{
      elevator_t *e = q->elevator;

      if (e->ops->elevator_may_queue_fn)
            return e->ops->elevator_may_queue_fn(q, rw);

      return ELV_MQUEUE_MAY;
}

void elv_completed_request(struct request_queue *q, struct request *rq)
{
      elevator_t *e = q->elevator;

      /*
       * request is released from the driver, io must be done
       */
      if (blk_account_rq(rq)) {
            q->in_flight--;
            if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
                  e->ops->elevator_completed_req_fn(q, rq);
      }

      /*
       * Check if the queue is waiting for fs requests to be
       * drained for flush sequence.
       */
      if (unlikely(q->ordseq)) {
            struct request *first_rq = list_entry_rq(q->queue_head.next);
            if (q->in_flight == 0 &&
                blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
                blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
                  blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
                  q->request_fn(q);
            }
      }
}

#define to_elv(atr) container_of((atr), struct elv_fs_entry, attr)

static ssize_t
elv_attr_show(struct kobject *kobj, struct attribute *attr, char *page)
{
      elevator_t *e = container_of(kobj, elevator_t, kobj);
      struct elv_fs_entry *entry = to_elv(attr);
      ssize_t error;

      if (!entry->show)
            return -EIO;

      mutex_lock(&e->sysfs_lock);
      error = e->ops ? entry->show(e, page) : -ENOENT;
      mutex_unlock(&e->sysfs_lock);
      return error;
}

static ssize_t
elv_attr_store(struct kobject *kobj, struct attribute *attr,
             const char *page, size_t length)
{
      elevator_t *e = container_of(kobj, elevator_t, kobj);
      struct elv_fs_entry *entry = to_elv(attr);
      ssize_t error;

      if (!entry->store)
            return -EIO;

      mutex_lock(&e->sysfs_lock);
      error = e->ops ? entry->store(e, page, length) : -ENOENT;
      mutex_unlock(&e->sysfs_lock);
      return error;
}

static struct sysfs_ops elv_sysfs_ops = {
      .show = elv_attr_show,
      .store      = elv_attr_store,
};

static struct kobj_type elv_ktype = {
      .sysfs_ops  = &elv_sysfs_ops,
      .release    = elevator_release,
};

int elv_register_queue(struct request_queue *q)
{
      elevator_t *e = q->elevator;
      int error;

      e->kobj.parent = &q->kobj;

      error = kobject_add(&e->kobj);
      if (!error) {
            struct elv_fs_entry *attr = e->elevator_type->elevator_attrs;
            if (attr) {
                  while (attr->attr.name) {
                        if (sysfs_create_file(&e->kobj, &attr->attr))
                              break;
                        attr++;
                  }
            }
            kobject_uevent(&e->kobj, KOBJ_ADD);
      }
      return error;
}

static void __elv_unregister_queue(elevator_t *e)
{
      kobject_uevent(&e->kobj, KOBJ_REMOVE);
      kobject_del(&e->kobj);
}

void elv_unregister_queue(struct request_queue *q)
{
      if (q)
            __elv_unregister_queue(q->elevator);
}

void elv_register(struct elevator_type *e)
{
      char *def = "";

      spin_lock(&elv_list_lock);
      BUG_ON(elevator_find(e->elevator_name));
      list_add_tail(&e->list, &elv_list);
      spin_unlock(&elv_list_lock);

      if (!strcmp(e->elevator_name, chosen_elevator) ||
                  (!*chosen_elevator &&
                   !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
                        def = " (default)";

      printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name, def);
}
EXPORT_SYMBOL_GPL(elv_register);

void elv_unregister(struct elevator_type *e)
{
      struct task_struct *g, *p;

      /*
       * Iterate every thread in the process to remove the io contexts.
       */
      if (e->ops.trim) {
            read_lock(&tasklist_lock);
            do_each_thread(g, p) {
                  task_lock(p);
                  if (p->io_context)
                        e->ops.trim(p->io_context);
                  task_unlock(p);
            } while_each_thread(g, p);
            read_unlock(&tasklist_lock);
      }

      spin_lock(&elv_list_lock);
      list_del_init(&e->list);
      spin_unlock(&elv_list_lock);
}
EXPORT_SYMBOL_GPL(elv_unregister);

/*
 * switch to new_e io scheduler. be careful not to introduce deadlocks -
 * we don't free the old io scheduler, before we have allocated what we
 * need for the new one. this way we have a chance of going back to the old
 * one, if the new one fails init for some reason.
 */
static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
{
      elevator_t *old_elevator, *e;
      void *data;

      /*
       * Allocate new elevator
       */
      e = elevator_alloc(q, new_e);
      if (!e)
            return 0;

      data = elevator_init_queue(q, e);
      if (!data) {
            kobject_put(&e->kobj);
            return 0;
      }

      /*
       * Turn on BYPASS and drain all requests w/ elevator private data
       */
      spin_lock_irq(q->queue_lock);

      set_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);

      elv_drain_elevator(q);

      while (q->rq.elvpriv) {
            blk_remove_plug(q);
            q->request_fn(q);
            spin_unlock_irq(q->queue_lock);
            msleep(10);
            spin_lock_irq(q->queue_lock);
            elv_drain_elevator(q);
      }

      /*
       * Remember old elevator.
       */
      old_elevator = q->elevator;

      /*
       * attach and start new elevator
       */
      elevator_attach(q, e, data);

      spin_unlock_irq(q->queue_lock);

      __elv_unregister_queue(old_elevator);

      if (elv_register_queue(q))
            goto fail_register;

      /*
       * finally exit old elevator and turn off BYPASS.
       */
      elevator_exit(old_elevator);
      clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
      return 1;

fail_register:
      /*
       * switch failed, exit the new io scheduler and reattach the old
       * one again (along with re-adding the sysfs dir)
       */
      elevator_exit(e);
      q->elevator = old_elevator;
      elv_register_queue(q);
      clear_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags);
      return 0;
}

ssize_t elv_iosched_store(struct request_queue *q, const char *name,
                    size_t count)
{
      char elevator_name[ELV_NAME_MAX];
      size_t len;
      struct elevator_type *e;

      elevator_name[sizeof(elevator_name) - 1] = '\0';
      strncpy(elevator_name, name, sizeof(elevator_name) - 1);
      len = strlen(elevator_name);

      if (len && elevator_name[len - 1] == '\n')
            elevator_name[len - 1] = '\0';

      e = elevator_get(elevator_name);
      if (!e) {
            printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
            return -EINVAL;
      }

      if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name)) {
            elevator_put(e);
            return count;
      }

      if (!elevator_switch(q, e))
            printk(KERN_ERR "elevator: switch to %s failed\n",elevator_name);
      return count;
}

ssize_t elv_iosched_show(struct request_queue *q, char *name)
{
      elevator_t *e = q->elevator;
      struct elevator_type *elv = e->elevator_type;
      struct elevator_type *__e;
      int len = 0;

      spin_lock(&elv_list_lock);
      list_for_each_entry(__e, &elv_list, list) {
            if (!strcmp(elv->elevator_name, __e->elevator_name))
                  len += sprintf(name+len, "[%s] ", elv->elevator_name);
            else
                  len += sprintf(name+len, "%s ", __e->elevator_name);
      }
      spin_unlock(&elv_list_lock);

      len += sprintf(len+name, "\n");
      return len;
}

struct request *elv_rb_former_request(struct request_queue *q,
                              struct request *rq)
{
      struct rb_node *rbprev = rb_prev(&rq->rb_node);

      if (rbprev)
            return rb_entry_rq(rbprev);

      return NULL;
}

EXPORT_SYMBOL(elv_rb_former_request);

struct request *elv_rb_latter_request(struct request_queue *q,
                              struct request *rq)
{
      struct rb_node *rbnext = rb_next(&rq->rb_node);

      if (rbnext)
            return rb_entry_rq(rbnext);

      return NULL;
}

EXPORT_SYMBOL(elv_rb_latter_request);

Generated by  Doxygen 1.6.0   Back to index