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_INTERNAL: 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 * @unlock: whether to unlock and then lock again @ctx. This applies 67 * only when waiting for another AioContext from the main loop. 68 * Otherwise it's ignored. 69 * 70 * Wait while a condition is true. Use this to implement synchronous 71 * operations that require event loop activity. 72 * 73 * The caller must be sure that something calls aio_wait_kick() when the value 74 * of @cond might have changed. 75 * 76 * The caller's thread must be the IOThread that owns @ctx or the main loop 77 * thread (with @ctx acquired exactly once). This function cannot be used to 78 * wait on conditions between two IOThreads since that could lead to deadlock, 79 * go via the main loop instead. 80 */ 81 #define AIO_WAIT_WHILE_INTERNAL(ctx, cond, unlock) ({ \ 82 bool waited_ = false; \ 83 AioWait *wait_ = &global_aio_wait; \ 84 AioContext *ctx_ = (ctx); \ 85 /* Increment wait_->num_waiters before evaluating cond. */ \ 86 qatomic_inc(&wait_->num_waiters); \ 87 /* Paired with smp_mb in aio_wait_kick(). */ \ 88 smp_mb__after_rmw(); \ 89 if (ctx_ && in_aio_context_home_thread(ctx_)) { \ 90 while ((cond)) { \ 91 aio_poll(ctx_, true); \ 92 waited_ = true; \ 93 } \ 94 } else { \ 95 assert(qemu_get_current_aio_context() == \ 96 qemu_get_aio_context()); \ 97 while ((cond)) { \ 98 if (unlock && ctx_) { \ 99 aio_context_release(ctx_); \ 100 } \ 101 aio_poll(qemu_get_aio_context(), true); \ 102 if (unlock && ctx_) { \ 103 aio_context_acquire(ctx_); \ 104 } \ 105 waited_ = true; \ 106 } \ 107 } \ 108 qatomic_dec(&wait_->num_waiters); \ 109 waited_; }) 110 111 #define AIO_WAIT_WHILE(ctx, cond) \ 112 AIO_WAIT_WHILE_INTERNAL(ctx, cond, true) 113 114 #define AIO_WAIT_WHILE_UNLOCKED(ctx, cond) \ 115 AIO_WAIT_WHILE_INTERNAL(ctx, cond, false) 116 117 /** 118 * aio_wait_kick: 119 * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During 120 * synchronous operations performed in an IOThread, the main thread lets the 121 * IOThread's event loop run, waiting for the operation to complete. A 122 * aio_wait_kick() call will wake up the main thread. 123 */ 124 void aio_wait_kick(void); 125 126 /** 127 * aio_wait_bh_oneshot: 128 * @ctx: the aio context 129 * @cb: the BH callback function 130 * @opaque: user data for the BH callback function 131 * 132 * Run a BH in @ctx and wait for it to complete. 133 * 134 * Must be called from the main loop thread with @ctx acquired exactly once. 135 * Note that main loop event processing may occur. 136 */ 137 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 138 139 /** 140 * in_aio_context_home_thread: 141 * @ctx: the aio context 142 * 143 * Return whether we are running in the thread that normally runs @ctx. Note 144 * that acquiring/releasing ctx does not affect the outcome, each AioContext 145 * still only has one home thread that is responsible for running it. 146 */ 147 static inline bool in_aio_context_home_thread(AioContext *ctx) 148 { 149 if (ctx == qemu_get_current_aio_context()) { 150 return true; 151 } 152 153 if (ctx == qemu_get_aio_context()) { 154 return qemu_mutex_iothread_locked(); 155 } else { 156 return false; 157 } 158 } 159 160 #endif /* QEMU_AIO_WAIT_H */ 161