1 /* 2 * AioContext wait support 3 * 4 * Copyright (C) 2018 Red Hat, Inc. 5 * 6 * Permission is hereby granted, free of charge, to any person obtaining a copy 7 * of this software and associated documentation files (the "Software"), to deal 8 * in the Software without restriction, including without limitation the rights 9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 10 * copies of the Software, and to permit persons to whom the Software is 11 * furnished to do so, subject to the following conditions: 12 * 13 * The above copyright notice and this permission notice shall be included in 14 * all copies or substantial portions of the Software. 15 * 16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 22 * THE SOFTWARE. 23 */ 24 25 #ifndef QEMU_AIO_WAIT_H 26 #define QEMU_AIO_WAIT_H 27 28 #include "block/aio.h" 29 #include "qemu/main-loop.h" 30 31 /** 32 * AioWait: 33 * 34 * An object that facilitates synchronous waiting on a condition. A single 35 * global AioWait object (global_aio_wait) is used internally. 36 * 37 * The main loop can wait on an operation running in an IOThread as follows: 38 * 39 * AioContext *ctx = ...; 40 * MyWork work = { .done = false }; 41 * schedule_my_work_in_iothread(ctx, &work); 42 * AIO_WAIT_WHILE(ctx, !work.done); 43 * 44 * The IOThread must call aio_wait_kick() to notify the main loop when 45 * work.done changes: 46 * 47 * static void do_work(...) 48 * { 49 * ... 50 * work.done = true; 51 * aio_wait_kick(); 52 * } 53 */ 54 typedef struct { 55 /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */ 56 unsigned num_waiters; 57 } AioWait; 58 59 extern AioWait global_aio_wait; 60 61 /** 62 * AIO_WAIT_WHILE: 63 * @ctx: the aio context, or NULL if multiple aio contexts (for which the 64 * caller does not hold a lock) are involved in the polling condition. 65 * @cond: wait while this conditional expression is true 66 * 67 * Wait while a condition is true. Use this to implement synchronous 68 * operations that require event loop activity. 69 * 70 * The caller must be sure that something calls aio_wait_kick() when the value 71 * of @cond might have changed. 72 * 73 * The caller's thread must be the IOThread that owns @ctx or the main loop 74 * thread (with @ctx acquired exactly once). This function cannot be used to 75 * wait on conditions between two IOThreads since that could lead to deadlock, 76 * go via the main loop instead. 77 */ 78 #define AIO_WAIT_WHILE(ctx, cond) ({ \ 79 bool waited_ = false; \ 80 AioWait *wait_ = &global_aio_wait; \ 81 AioContext *ctx_ = (ctx); \ 82 /* Increment wait_->num_waiters before evaluating cond. */ \ 83 qatomic_inc(&wait_->num_waiters); \ 84 if (ctx_ && in_aio_context_home_thread(ctx_)) { \ 85 while ((cond)) { \ 86 aio_poll(ctx_, true); \ 87 waited_ = true; \ 88 } \ 89 } else { \ 90 assert(qemu_get_current_aio_context() == \ 91 qemu_get_aio_context()); \ 92 while ((cond)) { \ 93 if (ctx_) { \ 94 aio_context_release(ctx_); \ 95 } \ 96 aio_poll(qemu_get_aio_context(), true); \ 97 if (ctx_) { \ 98 aio_context_acquire(ctx_); \ 99 } \ 100 waited_ = true; \ 101 } \ 102 } \ 103 qatomic_dec(&wait_->num_waiters); \ 104 waited_; }) 105 106 /** 107 * aio_wait_kick: 108 * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During 109 * synchronous operations performed in an IOThread, the main thread lets the 110 * IOThread's event loop run, waiting for the operation to complete. A 111 * aio_wait_kick() call will wake up the main thread. 112 */ 113 void aio_wait_kick(void); 114 115 /** 116 * aio_wait_bh_oneshot: 117 * @ctx: the aio context 118 * @cb: the BH callback function 119 * @opaque: user data for the BH callback function 120 * 121 * Run a BH in @ctx and wait for it to complete. 122 * 123 * Must be called from the main loop thread with @ctx acquired exactly once. 124 * Note that main loop event processing may occur. 125 */ 126 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 127 128 /** 129 * in_aio_context_home_thread: 130 * @ctx: the aio context 131 * 132 * Return whether we are running in the thread that normally runs @ctx. Note 133 * that acquiring/releasing ctx does not affect the outcome, each AioContext 134 * still only has one home thread that is responsible for running it. 135 */ 136 static inline bool in_aio_context_home_thread(AioContext *ctx) 137 { 138 if (ctx == qemu_get_current_aio_context()) { 139 return true; 140 } 141 142 if (ctx == qemu_get_aio_context()) { 143 return qemu_mutex_iothread_locked(); 144 } else { 145 return false; 146 } 147 } 148 149 #endif /* QEMU_AIO_WAIT_H */ 150