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 30 /** 31 * AioWait: 32 * 33 * An object that facilitates synchronous waiting on a condition. A single 34 * global AioWait object (global_aio_wait) is used internally. 35 * 36 * The main loop can wait on an operation running in an IOThread as follows: 37 * 38 * AioContext *ctx = ...; 39 * MyWork work = { .done = false }; 40 * schedule_my_work_in_iothread(ctx, &work); 41 * AIO_WAIT_WHILE(ctx, !work.done); 42 * 43 * The IOThread must call aio_wait_kick() to notify the main loop when 44 * work.done changes: 45 * 46 * static void do_work(...) 47 * { 48 * ... 49 * work.done = true; 50 * aio_wait_kick(); 51 * } 52 */ 53 typedef struct { 54 /* Number of waiting AIO_WAIT_WHILE() callers. Accessed with atomic ops. */ 55 unsigned num_waiters; 56 } AioWait; 57 58 extern AioWait global_aio_wait; 59 60 /** 61 * AIO_WAIT_WHILE: 62 * @ctx: the aio context, or NULL if multiple aio contexts (for which the 63 * caller does not hold a lock) are involved in the polling condition. 64 * @cond: wait while this conditional expression is true 65 * 66 * Wait while a condition is true. Use this to implement synchronous 67 * operations that require event loop activity. 68 * 69 * The caller must be sure that something calls aio_wait_kick() when the value 70 * of @cond might have changed. 71 * 72 * The caller's thread must be the IOThread that owns @ctx or the main loop 73 * thread (with @ctx acquired exactly once). This function cannot be used to 74 * wait on conditions between two IOThreads since that could lead to deadlock, 75 * go via the main loop instead. 76 */ 77 #define AIO_WAIT_WHILE(ctx, cond) ({ \ 78 bool waited_ = false; \ 79 AioWait *wait_ = &global_aio_wait; \ 80 AioContext *ctx_ = (ctx); \ 81 /* Increment wait_->num_waiters before evaluating cond. */ \ 82 atomic_inc(&wait_->num_waiters); \ 83 if (ctx_ && in_aio_context_home_thread(ctx_)) { \ 84 while ((cond)) { \ 85 aio_poll(ctx_, true); \ 86 waited_ = true; \ 87 } \ 88 } else { \ 89 assert(qemu_get_current_aio_context() == \ 90 qemu_get_aio_context()); \ 91 while ((cond)) { \ 92 if (ctx_) { \ 93 aio_context_release(ctx_); \ 94 } \ 95 aio_poll(qemu_get_aio_context(), true); \ 96 if (ctx_) { \ 97 aio_context_acquire(ctx_); \ 98 } \ 99 waited_ = true; \ 100 } \ 101 } \ 102 atomic_dec(&wait_->num_waiters); \ 103 waited_; }) 104 105 /** 106 * aio_wait_kick: 107 * Wake up the main thread if it is waiting on AIO_WAIT_WHILE(). During 108 * synchronous operations performed in an IOThread, the main thread lets the 109 * IOThread's event loop run, waiting for the operation to complete. A 110 * aio_wait_kick() call will wake up the main thread. 111 */ 112 void aio_wait_kick(void); 113 114 /** 115 * aio_wait_bh_oneshot: 116 * @ctx: the aio context 117 * @cb: the BH callback function 118 * @opaque: user data for the BH callback function 119 * 120 * Run a BH in @ctx and wait for it to complete. 121 * 122 * Must be called from the main loop thread with @ctx acquired exactly once. 123 * Note that main loop event processing may occur. 124 */ 125 void aio_wait_bh_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 126 127 #endif /* QEMU_AIO_WAIT_H */ 128