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/*
* AioContext wait support
*
* Copyright (C) 2018 Red Hat, Inc.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#ifndef QEMU_AIO_WAIT_H
#define QEMU_AIO_WAIT_H
#include "block/aio.h"
#include "qemu/main-loop.h"
/**
* AioWait:
*
* An object that facilitates synchronous waiting on a condition. A single
* global AioWait object (global_aio_wait) is used internally.
*
* The main loop can wait on an operation running in an IOThread as follows:
*
* AioContext *ctx = ...;
* MyWork work = { .done = false };
* schedule_my_work_in_iothread(ctx, &work);
* AIO_WAIT_WHILE(ctx, !work.done);
*
* The IOThread must call aio_wait_kick() to notify the main loop when
* work.done changes:
*
* static void do_work(...)
* {
* ...
* work.done = true;
* aio_wait_kick();
* }
*/
typedef struct {
/* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */
unsigned num_waiters;
} AioWait;
extern AioWait global_aio_wait;
/**
* AIO_WAIT_WHILE_INTERNAL:
* @ctx: the aio context, or NULL if multiple aio contexts (for which the
* caller does not hold a lock) are involved in the polling condition.
* @cond: wait while this conditional expression is true
* @unlock: whether to unlock and then lock again @ctx. This apples
* only when waiting for another AioContext from the main loop.
* Otherwise it's ignored.
*
* Wait while a condition is true. Use this to implement synchronous
* operations that require event loop activity.
*
* The caller must be sure that something calls aio_wait_kick() when the value
* of @cond might have changed.
*
* The caller's thread must be the IOThread that owns @ctx or the main loop
* thread (with @ctx acquired exactly once). This function cannot be used to
* wait on conditions between two IOThreads since that could lead to deadlock,
* go via the main loop instead.
*/
#define AIO_WAIT_WHILE_INTERNAL(ctx, cond, unlock) ({ \
bool waited_ = false; \
AioWait *wait_ = &global_aio_wait; \
AioContext *ctx_ = (ctx); \
/* Increment wait_->num_waiters before evaluating cond. */ \
qatomic_inc(&wait_->num_waiters); \
/* Paired with smp_mb in aio_wait_kick(). */ \
smp_mb__after_rmw(); \
if (ctx_ && in_aio_context_home_thread(ctx_)) { \
while ((cond)) { \
aio_poll(ctx_, true); \
waited_ = true; \
} \
} else { \
assert(qemu_get_current_aio_context() == \
qemu_get_aio_context()); \
while ((cond)) { \
if (unlock && ctx_) { \
aio_context_release(ctx_); \
} \
aio_poll(qemu_get_aio_context(), true); \
if (unlock && ctx_) { \
aio_context_acquire(ctx_); \
} \
waited_ = true; \
} \
} \
qatomic_dec(&wait_->num_waiters); \
waited_; })
#define AIO_WAIT_WHILE(ctx, cond) \
AIO_WAIT_WHILE_INTERNAL(ctx, cond, true)
#define AIO_WAIT_WHILE_UNLOCKED(ctx, cond) \
AIO_WAIT_WHILE_INTERNAL(ctx, cond, false)
/**
* aio_wait_kick:
* Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During
* synchronous operations performed in an IOThread, the main thread lets the
* IOThread's event loop run, waiting for the operation to complete. A
* aio_wait_kick() call will wake up the main thread.
*/
void aio_wait_kick(void);
/**
* aio_wait_bh_oneshot:
* @ctx: the aio context
* @cb: the BH callback function
* @opaque: user data for the BH callback function
*
* Run a BH in @ctx and wait for it to complete.
*
* Must be called from the main loop thread with @ctx acquired exactly once.
* Note that main loop event processing may occur.
*/
void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
/**
* in_aio_context_home_thread:
* @ctx: the aio context
*
* Return whether we are running in the thread that normally runs @ctx. Note
* that acquiring/releasing ctx does not affect the outcome, each AioContext
* still only has one home thread that is responsible for running it.
*/
static inline bool in_aio_context_home_thread(AioContext *ctx)
{
if (ctx == qemu_get_current_aio_context()) {
return true;
}
if (ctx == qemu_get_aio_context()) {
return qemu_mutex_iothread_locked();
} else {
return false;
}
}
#endif /* QEMU_AIO_WAIT_H */
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