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Subject[PATCH 05/16] block: implement blk_queue_bypass_start/end()
Date
From: Tejun Heo <tejun@google.com>

Rename and extend elv_queisce_start/end() to
blk_queue_bypass_start/end() which are exported and supports nesting
via @q->bypass_depth. Also add blk_queue_bypass() to test bypass
state.

This will be further extended and used for blkio_group management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
block/blk-core.c | 39 +++++++++++++++++++++++++++++++++++++--
block/blk.h | 6 ++----
block/elevator.c | 25 +++----------------------
include/linux/blkdev.h | 5 ++++-
4 files changed, 46 insertions(+), 29 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index e6c05a9..c2e39de 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -403,6 +403,42 @@ void blk_drain_queue(struct request_queue *q, bool drain_all)
}

/**
+ * blk_queue_bypass_start - enter queue bypass mode
+ * @q: queue of interest
+ *
+ * In bypass mode, only the dispatch FIFO queue of @q is used. This
+ * function makes @q enter bypass mode and drains all requests which were
+ * issued before. On return, it's guaranteed that no request has ELVPRIV
+ * set.
+ */
+void blk_queue_bypass_start(struct request_queue *q)
+{
+ spin_lock_irq(q->queue_lock);
+ q->bypass_depth++;
+ queue_flag_set(QUEUE_FLAG_BYPASS, q);
+ spin_unlock_irq(q->queue_lock);
+
+ blk_drain_queue(q, false);
+}
+EXPORT_SYMBOL_GPL(blk_queue_bypass_start);
+
+/**
+ * blk_queue_bypass_end - leave queue bypass mode
+ * @q: queue of interest
+ *
+ * Leave bypass mode and restore the normal queueing behavior.
+ */
+void blk_queue_bypass_end(struct request_queue *q)
+{
+ spin_lock_irq(q->queue_lock);
+ if (!--q->bypass_depth)
+ queue_flag_clear(QUEUE_FLAG_BYPASS, q);
+ WARN_ON_ONCE(q->bypass_depth < 0);
+ spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL_GPL(blk_queue_bypass_end);
+
+/**
* blk_cleanup_queue - shutdown a request queue
* @q: request queue to shutdown
*
@@ -859,8 +895,7 @@ retry:
* Also, lookup icq while holding queue_lock. If it doesn't exist,
* it will be created after releasing queue_lock.
*/
- if (blk_rq_should_init_elevator(bio) &&
- !test_bit(QUEUE_FLAG_ELVSWITCH, &q->queue_flags)) {
+ if (blk_rq_should_init_elevator(bio) && !blk_queue_bypass(q)) {
rw_flags |= REQ_ELVPRIV;
rl->elvpriv++;
if (et->icq_cache && ioc)
diff --git a/block/blk.h b/block/blk.h
index 7efd772..33897f6 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -23,7 +23,8 @@ void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
struct bio *bio);
int blk_rq_append_bio(struct request_queue *q, struct request *rq,
struct bio *bio);
-void blk_drain_queue(struct request_queue *q, bool drain_all);
+void blk_queue_bypass_start(struct request_queue *q);
+void blk_queue_bypass_end(struct request_queue *q);
void blk_dequeue_request(struct request *rq);
void __blk_queue_free_tags(struct request_queue *q);
bool __blk_end_bidi_request(struct request *rq, int error,
@@ -142,9 +143,6 @@ void blk_queue_congestion_threshold(struct request_queue *q);

int blk_dev_init(void);

-void elv_quiesce_start(struct request_queue *q);
-void elv_quiesce_end(struct request_queue *q);
-

/*
* Return the threshold (number of used requests) at which the queue is
diff --git a/block/elevator.c b/block/elevator.c
index 8dc65b1..078a491 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -600,25 +600,6 @@ void elv_drain_elevator(struct request_queue *q)
}
}

-void elv_quiesce_start(struct request_queue *q)
-{
- if (!q->elevator)
- return;
-
- spin_lock_irq(q->queue_lock);
- queue_flag_set(QUEUE_FLAG_ELVSWITCH, q);
- spin_unlock_irq(q->queue_lock);
-
- blk_drain_queue(q, false);
-}
-
-void elv_quiesce_end(struct request_queue *q)
-{
- spin_lock_irq(q->queue_lock);
- queue_flag_clear(QUEUE_FLAG_ELVSWITCH, q);
- spin_unlock_irq(q->queue_lock);
-}
-
void __elv_add_request(struct request_queue *q, struct request *rq, int where)
{
trace_block_rq_insert(q, rq);
@@ -950,7 +931,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
* using INSERT_BACK. All requests have SOFTBARRIER set and no
* merge happens either.
*/
- elv_quiesce_start(q);
+ blk_queue_bypass_start(q);

/* unregister and clear all auxiliary data of the old elevator */
if (registered)
@@ -980,7 +961,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)

/* done, kill the old one and finish */
elevator_exit(old);
- elv_quiesce_end(q);
+ blk_queue_bypass_end(q);

blk_add_trace_msg(q, "elv switch: %s", e->type->elevator_name);

@@ -992,7 +973,7 @@ fail_init:
/* switch failed, restore and re-register old elevator */
q->elevator = old;
elv_register_queue(q);
- elv_quiesce_end(q);
+ blk_queue_bypass_end(q);

return err;
}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6c6a1f0..f10958b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -389,6 +389,8 @@ struct request_queue {

struct mutex sysfs_lock;

+ int bypass_depth;
+
#if defined(CONFIG_BLK_DEV_BSG)
bsg_job_fn *bsg_job_fn;
int bsg_job_size;
@@ -409,7 +411,7 @@ struct request_queue {
#define QUEUE_FLAG_SYNCFULL 3 /* read queue has been filled */
#define QUEUE_FLAG_ASYNCFULL 4 /* write queue has been filled */
#define QUEUE_FLAG_DEAD 5 /* queue being torn down */
-#define QUEUE_FLAG_ELVSWITCH 6 /* don't use elevator, just do FIFO */
+#define QUEUE_FLAG_BYPASS 6 /* act as dumb FIFO queue */
#define QUEUE_FLAG_BIDI 7 /* queue supports bidi requests */
#define QUEUE_FLAG_NOMERGES 8 /* disable merge attempts */
#define QUEUE_FLAG_SAME_COMP 9 /* complete on same CPU-group */
@@ -497,6 +499,7 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
#define blk_queue_tagged(q) test_bit(QUEUE_FLAG_QUEUED, &(q)->queue_flags)
#define blk_queue_stopped(q) test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
#define blk_queue_dead(q) test_bit(QUEUE_FLAG_DEAD, &(q)->queue_flags)
+#define blk_queue_bypass(q) test_bit(QUEUE_FLAG_BYPASS, &(q)->queue_flags)
#define blk_queue_nomerges(q) test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)
#define blk_queue_noxmerges(q) \
test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)
--
1.7.7.3


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