drivers/block/noop-iosched.c

   1 /*
   2  * elevator noop
   3  */
   4 #include <linux/kernel.h>
   5 #include <linux/fs.h>
   6 #include <linux/blkdev.h>
   7 #include <linux/elevator.h>
   8 #include <linux/bio.h>
   9 #include <linux/config.h>
  10 #include <linux/module.h>
  11 #include <linux/slab.h>
  12 #include <linux/init.h>
  13 #include <linux/compiler.h>
  14
  15 #include <asm/uaccess.h>
  16
  17 /*
  18  * See if we can find a request that this buffer can be coalesced with.
  19  */
  20 int elevator_noop_merge(request_queue_t *q, struct request **req,
  21                         struct bio *bio)
  22 {
  23         struct list_head *entry = &q->queue_head;
  24         struct request *__rq;
  25         int ret;
  26
  27         if ((ret = elv_try_last_merge(q, bio))) {
  28                 *req = q->last_merge;
  29                 return ret;
  30         }
  31
  32         while ((entry = entry->prev) != &q->queue_head) {
  33                 __rq = list_entry_rq(entry);
  34
  35                 if (__rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER))
  36                         break;
  37                 else if (__rq->flags & REQ_STARTED)
  38                         break;
  39
  40                 if (!blk_fs_request(__rq))
  41                         continue;
  42
  43                 if ((ret = elv_try_merge(__rq, bio))) {
  44                         *req = __rq;
  45                         q->last_merge = __rq;
  46                         return ret;
  47                 }
  48         }
  49
  50         return ELEVATOR_NO_MERGE;
  51 }
  52
  53 void elevator_noop_merge_requests(request_queue_t *q, struct request *req,
  54                                   struct request *next)
  55 {
  56         list_del_init(&next->queuelist);
  57 }
  58
  59 void elevator_noop_add_request(request_queue_t *q, struct request *rq,
  60                                int where)
  61 {
  62         struct list_head *insert = q->queue_head.prev;
  63
  64         if (where == ELEVATOR_INSERT_FRONT)
  65                 insert = &q->queue_head;
  66
  67         list_add_tail(&rq->queuelist, &q->queue_head);
  68
  69         /*
  70          * new merges must not precede this barrier
  71          */
  72         if (rq->flags & REQ_HARDBARRIER)
  73                 q->last_merge = NULL;
  74         else if (!q->last_merge)
  75                 q->last_merge = rq;
  76 }
  77
  78 struct request *elevator_noop_next_request(request_queue_t *q)
  79 {
  80         if (!list_empty(&q->queue_head))
  81                 return list_entry_rq(q->queue_head.next);
  82
  83         return NULL;
  84 }
  85
  86 elevator_t elevator_noop = {
  87         .elevator_merge_fn              = elevator_noop_merge,
  88         .elevator_merge_req_fn          = elevator_noop_merge_requests,
  89         .elevator_next_req_fn           = elevator_noop_next_request,
  90         .elevator_add_req_fn            = elevator_noop_add_request,
  91         .elevator_name                  = "noop",
  92 };
  93
  94 EXPORT_SYMBOL(elevator_noop);