[BLOCK] Reimplement elevator switch
This patch reimplements elevator switch. This patch assumes generic dispatch queue patchset is applied. * Each request is tagged with REQ_ELVPRIV flag if it has its elevator private data set. * Requests which doesn't have REQ_ELVPRIV flag set never enter iosched. They are always directly back inserted to dispatch queue. Of course, elevator_put_req_fn is called only for requests which have its REQ_ELVPRIV set. * Request queue maintains the current number of requests which have its elevator data set (elevator_set_req_fn called) in q->rq->elvpriv. * If a request queue has QUEUE_FLAG_BYPASS set, elevator private data is not allocated for new requests. To switch to another iosched, we set QUEUE_FLAG_BYPASS and wait until elvpriv goes to zero; then, we attach the new iosched and clears QUEUE_FLAG_BYPASS. New implementation is much simpler and main code paths are less cluttered, IMHO. Signed-off-by: Tejun Heo <htejun@gmail.com> Signed-off-by: Jens Axboe <axboe@suse.de>
This commit is contained in:
Tejun Heo
Jens Axboe
parent
cb19833dcc
commit
cb98fc8bb9
3 changed files with 66 additions and 164 deletions
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@ -34,6 +34,7 @@
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#include <linux/slab.h>
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#include <linux/init.h>
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#include <linux/compiler.h>
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#include <linux/delay.h>
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#include <asm/uaccess.h>
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@ -131,11 +132,7 @@ static int elevator_attach(request_queue_t *q, struct elevator_type *e,
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eq->ops = &e->ops;
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eq->elevator_type = e;
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INIT_LIST_HEAD(&q->queue_head);
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q->last_merge = NULL;
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q->elevator = eq;
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q->end_sector = 0;
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q->boundary_rq = NULL;
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if (eq->ops->elevator_init_fn)
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ret = eq->ops->elevator_init_fn(q, eq);
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@ -184,6 +181,12 @@ int elevator_init(request_queue_t *q, char *name)
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struct elevator_queue *eq;
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int ret = 0;
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INIT_LIST_HEAD(&q->queue_head);
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q->last_merge = NULL;
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q->end_sector = 0;
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q->boundary_rq = NULL;
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q->max_back_kb = 0;
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elevator_setup_default();
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if (!name)
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@ -336,23 +339,14 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where,
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q->end_sector = rq_end_sector(rq);
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q->boundary_rq = rq;
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}
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}
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} else if (!(rq->flags & REQ_ELVPRIV) && where == ELEVATOR_INSERT_SORT)
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where = ELEVATOR_INSERT_BACK;
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if (plug)
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blk_plug_device(q);
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rq->q = q;
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if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
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/*
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* if drain is set, store the request "locally". when the drain
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* is finished, the requests will be handed ordered to the io
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* scheduler
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*/
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list_add_tail(&rq->queuelist, &q->drain_list);
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return;
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}
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switch (where) {
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case ELEVATOR_INSERT_FRONT:
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rq->flags |= REQ_SOFTBARRIER;
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@ -659,25 +653,36 @@ EXPORT_SYMBOL_GPL(elv_unregister);
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* switch to new_e io scheduler. be careful not to introduce deadlocks -
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* we don't free the old io scheduler, before we have allocated what we
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* need for the new one. this way we have a chance of going back to the old
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* one, if the new one fails init for some reason. we also do an intermediate
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* switch to noop to ensure safety with stack-allocated requests, since they
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* don't originate from the block layer allocator. noop is safe here, because
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* it never needs to touch the elevator itself for completion events. DRAIN
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* flags will make sure we don't touch it for additions either.
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* one, if the new one fails init for some reason.
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*/
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static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
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{
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elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
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struct elevator_type *noop_elevator = NULL;
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elevator_t *old_elevator;
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elevator_t *old_elevator, *e;
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/*
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* Allocate new elevator
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*/
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e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
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if (!e)
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goto error;
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/*
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* first step, drain requests from the block freelist
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* Turn on BYPASS and drain all requests w/ elevator private data
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*/
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blk_wait_queue_drained(q, 0);
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spin_lock_irq(q->queue_lock);
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set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
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while (q->elevator->ops->elevator_dispatch_fn(q, 1))
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;
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while (q->rq.elvpriv) {
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spin_unlock_irq(q->queue_lock);
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msleep(100);
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spin_lock_irq(q->queue_lock);
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}
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spin_unlock_irq(q->queue_lock);
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/*
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* unregister old elevator data
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@ -685,18 +690,6 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
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elv_unregister_queue(q);
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old_elevator = q->elevator;
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/*
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* next step, switch to noop since it uses no private rq structures
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* and doesn't allocate any memory for anything. then wait for any
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* non-fs requests in-flight
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*/
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noop_elevator = elevator_get("noop");
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spin_lock_irq(q->queue_lock);
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elevator_attach(q, noop_elevator, e);
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spin_unlock_irq(q->queue_lock);
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blk_wait_queue_drained(q, 1);
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/*
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* attach and start new elevator
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*/
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@ -707,11 +700,10 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
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goto fail_register;
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/*
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* finally exit old elevator and start queue again
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* finally exit old elevator and turn off BYPASS.
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*/
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elevator_exit(old_elevator);
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blk_finish_queue_drain(q);
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elevator_put(noop_elevator);
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clear_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
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return;
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fail_register:
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@ -720,13 +712,13 @@ static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
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* one again (along with re-adding the sysfs dir)
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*/
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elevator_exit(e);
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e = NULL;
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fail:
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q->elevator = old_elevator;
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elv_register_queue(q);
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blk_finish_queue_drain(q);
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clear_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
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kfree(e);
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error:
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if (noop_elevator)
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elevator_put(noop_elevator);
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elevator_put(new_e);
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printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
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}
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@ -263,8 +263,6 @@ void blk_queue_make_request(request_queue_t * q, make_request_fn * mfn)
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blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
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blk_queue_activity_fn(q, NULL, NULL);
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INIT_LIST_HEAD(&q->drain_list);
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}
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EXPORT_SYMBOL(blk_queue_make_request);
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@ -1050,6 +1048,7 @@ static char *rq_flags[] = {
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"REQ_STARTED",
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"REQ_DONTPREP",
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"REQ_QUEUED",
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"REQ_ELVPRIV",
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"REQ_PC",
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"REQ_BLOCK_PC",
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"REQ_SENSE",
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@ -1640,9 +1639,9 @@ static int blk_init_free_list(request_queue_t *q)
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rl->count[READ] = rl->count[WRITE] = 0;
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rl->starved[READ] = rl->starved[WRITE] = 0;
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rl->elvpriv = 0;
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init_waitqueue_head(&rl->wait[READ]);
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init_waitqueue_head(&rl->wait[WRITE]);
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init_waitqueue_head(&rl->drain);
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rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
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mempool_free_slab, request_cachep, q->node);
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@ -1785,12 +1784,14 @@ EXPORT_SYMBOL(blk_get_queue);
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static inline void blk_free_request(request_queue_t *q, struct request *rq)
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{
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elv_put_request(q, rq);
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if (rq->flags & REQ_ELVPRIV)
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elv_put_request(q, rq);
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mempool_free(rq, q->rq.rq_pool);
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}
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static inline struct request *
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blk_alloc_request(request_queue_t *q, int rw, struct bio *bio, int gfp_mask)
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blk_alloc_request(request_queue_t *q, int rw, struct bio *bio,
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int priv, int gfp_mask)
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{
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struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
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@ -1803,11 +1804,15 @@ blk_alloc_request(request_queue_t *q, int rw, struct bio *bio, int gfp_mask)
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*/
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rq->flags = rw;
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if (!elv_set_request(q, rq, bio, gfp_mask))
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return rq;
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if (priv) {
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if (unlikely(elv_set_request(q, rq, bio, gfp_mask))) {
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mempool_free(rq, q->rq.rq_pool);
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return NULL;
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}
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rq->flags |= REQ_ELVPRIV;
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}
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mempool_free(rq, q->rq.rq_pool);
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return NULL;
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return rq;
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}
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/*
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@ -1863,22 +1868,18 @@ static void __freed_request(request_queue_t *q, int rw)
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* A request has just been released. Account for it, update the full and
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* congestion status, wake up any waiters. Called under q->queue_lock.
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*/
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static void freed_request(request_queue_t *q, int rw)
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static void freed_request(request_queue_t *q, int rw, int priv)
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{
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struct request_list *rl = &q->rq;
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rl->count[rw]--;
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if (priv)
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rl->elvpriv--;
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__freed_request(q, rw);
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if (unlikely(rl->starved[rw ^ 1]))
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__freed_request(q, rw ^ 1);
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if (!rl->count[READ] && !rl->count[WRITE]) {
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smp_mb();
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if (unlikely(waitqueue_active(&rl->drain)))
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wake_up(&rl->drain);
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}
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}
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#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
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@ -1893,9 +1894,7 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
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struct request *rq = NULL;
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struct request_list *rl = &q->rq;
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struct io_context *ioc = current_io_context(GFP_ATOMIC);
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if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
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goto out;
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int priv;
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if (rl->count[rw]+1 >= q->nr_requests) {
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/*
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@ -1940,9 +1939,14 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
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rl->starved[rw] = 0;
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if (rl->count[rw] >= queue_congestion_on_threshold(q))
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set_queue_congested(q, rw);
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priv = !test_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);
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if (priv)
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rl->elvpriv++;
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spin_unlock_irq(q->queue_lock);
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rq = blk_alloc_request(q, rw, bio, gfp_mask);
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rq = blk_alloc_request(q, rw, bio, priv, gfp_mask);
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if (!rq) {
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/*
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* Allocation failed presumably due to memory. Undo anything
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@ -1952,7 +1956,7 @@ static struct request *get_request(request_queue_t *q, int rw, struct bio *bio,
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* wait queue, but this is pretty rare.
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*/
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spin_lock_irq(q->queue_lock);
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freed_request(q, rw);
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freed_request(q, rw, priv);
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/*
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* in the very unlikely event that allocation failed and no
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@ -2470,11 +2474,12 @@ static void __blk_put_request(request_queue_t *q, struct request *req)
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*/
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if (rl) {
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int rw = rq_data_dir(req);
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int priv = req->flags & REQ_ELVPRIV;
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BUG_ON(!list_empty(&req->queuelist));
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blk_free_request(q, req);
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freed_request(q, rw);
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freed_request(q, rw, priv);
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}
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}
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@ -2802,97 +2807,6 @@ static inline void blk_partition_remap(struct bio *bio)
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}
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}
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void blk_finish_queue_drain(request_queue_t *q)
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{
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struct request_list *rl = &q->rq;
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struct request *rq;
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int requeued = 0;
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spin_lock_irq(q->queue_lock);
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clear_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
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while (!list_empty(&q->drain_list)) {
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rq = list_entry_rq(q->drain_list.next);
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list_del_init(&rq->queuelist);
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elv_requeue_request(q, rq);
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requeued++;
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}
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if (requeued)
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q->request_fn(q);
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spin_unlock_irq(q->queue_lock);
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wake_up(&rl->wait[0]);
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wake_up(&rl->wait[1]);
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wake_up(&rl->drain);
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}
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static int wait_drain(request_queue_t *q, struct request_list *rl, int dispatch)
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{
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int wait = rl->count[READ] + rl->count[WRITE];
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if (dispatch)
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wait += !list_empty(&q->queue_head);
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return wait;
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}
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/*
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* We rely on the fact that only requests allocated through blk_alloc_request()
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* have io scheduler private data structures associated with them. Any other
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* type of request (allocated on stack or through kmalloc()) should not go
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* to the io scheduler core, but be attached to the queue head instead.
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*/
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void blk_wait_queue_drained(request_queue_t *q, int wait_dispatch)
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{
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struct request_list *rl = &q->rq;
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DEFINE_WAIT(wait);
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spin_lock_irq(q->queue_lock);
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set_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
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while (wait_drain(q, rl, wait_dispatch)) {
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prepare_to_wait(&rl->drain, &wait, TASK_UNINTERRUPTIBLE);
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if (wait_drain(q, rl, wait_dispatch)) {
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__generic_unplug_device(q);
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spin_unlock_irq(q->queue_lock);
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io_schedule();
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spin_lock_irq(q->queue_lock);
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}
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finish_wait(&rl->drain, &wait);
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}
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spin_unlock_irq(q->queue_lock);
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}
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/*
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* block waiting for the io scheduler being started again.
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*/
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static inline void block_wait_queue_running(request_queue_t *q)
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{
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DEFINE_WAIT(wait);
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while (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
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struct request_list *rl = &q->rq;
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prepare_to_wait_exclusive(&rl->drain, &wait,
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TASK_UNINTERRUPTIBLE);
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/*
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* re-check the condition. avoids using prepare_to_wait()
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* in the fast path (queue is running)
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*/
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if (test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))
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io_schedule();
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finish_wait(&rl->drain, &wait);
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}
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}
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static void handle_bad_sector(struct bio *bio)
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{
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char b[BDEVNAME_SIZE];
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@ -2988,8 +2902,6 @@ void generic_make_request(struct bio *bio)
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if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
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goto end_io;
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block_wait_queue_running(q);
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/*
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* If this device has partitions, remap block n
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* of partition p to block n+start(p) of the disk.
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@ -107,9 +107,9 @@ typedef void (rq_end_io_fn)(struct request *);
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struct request_list {
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int count[2];
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int starved[2];
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int elvpriv;
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mempool_t *rq_pool;
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wait_queue_head_t wait[2];
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wait_queue_head_t drain;
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};
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#define BLK_MAX_CDB 16
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@ -211,6 +211,7 @@ enum rq_flag_bits {
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__REQ_STARTED, /* drive already may have started this one */
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__REQ_DONTPREP, /* don't call prep for this one */
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__REQ_QUEUED, /* uses queueing */
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__REQ_ELVPRIV, /* elevator private data attached */
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/*
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* for ATA/ATAPI devices
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*/
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@ -244,6 +245,7 @@ enum rq_flag_bits {
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#define REQ_STARTED (1 << __REQ_STARTED)
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#define REQ_DONTPREP (1 << __REQ_DONTPREP)
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#define REQ_QUEUED (1 << __REQ_QUEUED)
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#define REQ_ELVPRIV (1 << __REQ_ELVPRIV)
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#define REQ_PC (1 << __REQ_PC)
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#define REQ_BLOCK_PC (1 << __REQ_BLOCK_PC)
|
||||
#define REQ_SENSE (1 << __REQ_SENSE)
|
||||
|
|
@ -413,8 +415,6 @@ struct request_queue
|
|||
unsigned int sg_reserved_size;
|
||||
int node;
|
||||
|
||||
struct list_head drain_list;
|
||||
|
||||
/*
|
||||
* reserved for flush operations
|
||||
*/
|
||||
|
|
@ -442,7 +442,7 @@ enum {
|
|||
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
|
||||
#define QUEUE_FLAG_REENTER 6 /* Re-entrancy avoidance */
|
||||
#define QUEUE_FLAG_PLUGGED 7 /* queue is plugged */
|
||||
#define QUEUE_FLAG_DRAIN 8 /* draining queue for sched switch */
|
||||
#define QUEUE_FLAG_BYPASS 8 /* don't use elevator, just do FIFO */
|
||||
#define QUEUE_FLAG_FLUSH 9 /* doing barrier flush sequence */
|
||||
|
||||
#define blk_queue_plugged(q) test_bit(QUEUE_FLAG_PLUGGED, &(q)->queue_flags)
|
||||
|
|
@ -668,8 +668,6 @@ extern void blk_dump_rq_flags(struct request *, char *);
|
|||
extern void generic_unplug_device(request_queue_t *);
|
||||
extern void __generic_unplug_device(request_queue_t *);
|
||||
extern long nr_blockdev_pages(void);
|
||||
extern void blk_wait_queue_drained(request_queue_t *, int);
|
||||
extern void blk_finish_queue_drain(request_queue_t *);
|
||||
|
||||
int blk_get_queue(request_queue_t *);
|
||||
request_queue_t *blk_alloc_queue(int gfp_mask);
|
||||
|
|
|
|||
Loading…
Reference in a new issue