blk_queue_enter

Name:lk_queue_enter() - try to increase q->q_usage_counter*@q: request queue pointer*@flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PREEMPT

Proto:int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)

Type:int

Parameter:

Type	Parameter	Name
struct request_queue *	q
blk_mq_req_flags_t	flags

405

pm = flags & BLK_MQ_REQ_PREEMPT

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When (true) cycle

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bool success = false

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_read_lock() - mark the beginning of an RCU read-side critical section* When synchronize_rcu() is invoked on one CPU while other CPUs* are within RCU read-side critical sections, then the* synchronize_rcu() is guaranteed to block until after all the other

411

If percpu_ref_tryget_live - try to increment a live percpu refcount*@ref: percpu_ref to try-get* Increment a percpu refcount unless it has already been killed Then

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If pm || Not blk_queue_pm_only(q) Then

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success = true

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Else

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percpu_ref_put - decrement a percpu refcount*@ref: percpu_ref to put* Decrement the refcount, and if 0, call the release function (which was passed* to percpu_ref_init())* This function is safe to call as long as @ref is between init and exit.

423

_read_unlock() - marks the end of an RCU read-side critical section.* In most situations, rcu_read_unlock() is immune from deadlock.* However, in kernels built with CONFIG_RCU_BOOST, rcu_read_unlock()

425

If success Then Return 0

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If flags & BLK_MQ_REQ_NOWAIT Then Return -EBUSY

438

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wait_event - sleep until a condition gets true*@wq_head: the waitqueue to wait on*@condition: a C expression for the event to wait for* The process is put to sleep (TASK_UNINTERRUPTIBLE) until the*@condition evaluates to true(mq_freeze_wq, (!mq_freeze_depth && (pm || (blk_pm_request_resume(q), !blk_queue_pm_only(q)))) || blk_queue_dying(q))

445

If blk_queue_dying(q) Then Return -ENODEV

**Caller**
Name	Describe
generic_make_request	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
direct_make_request	direct_make_request - hand a buffer directly to its device driver for I/O@bio: The bio describing the location in memory and on the device. This function behaves like generic_make_request(), but does not protect* against recursion
blk_mq_alloc_request
blk_mq_alloc_request_hctx
bdev_write_page	dev_write_page() - Start writing a page to a block device@bdev: The device to write the page to@sector: The offset on the device to write the page to (need not be aligned)@page: The page to write@wbc: The writeback_control for the write

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