1 /* 2 * QEMU aio implementation 3 * 4 * Copyright IBM, Corp. 2008 5 * 6 * Authors: 7 * Anthony Liguori <aliguori@us.ibm.com> 8 * 9 * This work is licensed under the terms of the GNU GPL, version 2. See 10 * the COPYING file in the top-level directory. 11 * 12 */ 13 14 #ifndef QEMU_AIO_H 15 #define QEMU_AIO_H 16 17 #include "qemu-common.h" 18 #include "qemu/queue.h" 19 #include "qemu/event_notifier.h" 20 #include "qemu/thread.h" 21 #include "qemu/timer.h" 22 23 typedef struct BlockAIOCB BlockAIOCB; 24 typedef void BlockCompletionFunc(void *opaque, int ret); 25 26 typedef struct AIOCBInfo { 27 void (*cancel_async)(BlockAIOCB *acb); 28 AioContext *(*get_aio_context)(BlockAIOCB *acb); 29 size_t aiocb_size; 30 } AIOCBInfo; 31 32 struct BlockAIOCB { 33 const AIOCBInfo *aiocb_info; 34 BlockDriverState *bs; 35 BlockCompletionFunc *cb; 36 void *opaque; 37 int refcnt; 38 }; 39 40 void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs, 41 BlockCompletionFunc *cb, void *opaque); 42 void qemu_aio_unref(void *p); 43 void qemu_aio_ref(void *p); 44 45 typedef struct AioHandler AioHandler; 46 typedef void QEMUBHFunc(void *opaque); 47 typedef bool AioPollFn(void *opaque); 48 typedef void IOHandler(void *opaque); 49 50 struct ThreadPool; 51 struct LinuxAioState; 52 53 struct AioContext { 54 GSource source; 55 56 /* Protects all fields from multi-threaded access */ 57 QemuRecMutex lock; 58 59 /* The list of registered AIO handlers */ 60 QLIST_HEAD(, AioHandler) aio_handlers; 61 62 /* This is a simple lock used to protect the aio_handlers list. 63 * Specifically, it's used to ensure that no callbacks are removed while 64 * we're walking and dispatching callbacks. 65 */ 66 int walking_handlers; 67 68 /* Used to avoid unnecessary event_notifier_set calls in aio_notify; 69 * accessed with atomic primitives. If this field is 0, everything 70 * (file descriptors, bottom halves, timers) will be re-evaluated 71 * before the next blocking poll(), thus the event_notifier_set call 72 * can be skipped. If it is non-zero, you may need to wake up a 73 * concurrent aio_poll or the glib main event loop, making 74 * event_notifier_set necessary. 75 * 76 * Bit 0 is reserved for GSource usage of the AioContext, and is 1 77 * between a call to aio_ctx_prepare and the next call to aio_ctx_check. 78 * Bits 1-31 simply count the number of active calls to aio_poll 79 * that are in the prepare or poll phase. 80 * 81 * The GSource and aio_poll must use a different mechanism because 82 * there is no certainty that a call to GSource's prepare callback 83 * (via g_main_context_prepare) is indeed followed by check and 84 * dispatch. It's not clear whether this would be a bug, but let's 85 * play safe and allow it---it will just cause extra calls to 86 * event_notifier_set until the next call to dispatch. 87 * 88 * Instead, the aio_poll calls include both the prepare and the 89 * dispatch phase, hence a simple counter is enough for them. 90 */ 91 uint32_t notify_me; 92 93 /* lock to protect between bh's adders and deleter */ 94 QemuMutex bh_lock; 95 96 /* Anchor of the list of Bottom Halves belonging to the context */ 97 struct QEMUBH *first_bh; 98 99 /* A simple lock used to protect the first_bh list, and ensure that 100 * no callbacks are removed while we're walking and dispatching callbacks. 101 */ 102 int walking_bh; 103 104 /* Used by aio_notify. 105 * 106 * "notified" is used to avoid expensive event_notifier_test_and_clear 107 * calls. When it is clear, the EventNotifier is clear, or one thread 108 * is going to clear "notified" before processing more events. False 109 * positives are possible, i.e. "notified" could be set even though the 110 * EventNotifier is clear. 111 * 112 * Note that event_notifier_set *cannot* be optimized the same way. For 113 * more information on the problem that would result, see "#ifdef BUG2" 114 * in the docs/aio_notify_accept.promela formal model. 115 */ 116 bool notified; 117 EventNotifier notifier; 118 119 /* Thread pool for performing work and receiving completion callbacks */ 120 struct ThreadPool *thread_pool; 121 122 #ifdef CONFIG_LINUX_AIO 123 /* State for native Linux AIO. Uses aio_context_acquire/release for 124 * locking. 125 */ 126 struct LinuxAioState *linux_aio; 127 #endif 128 129 /* TimerLists for calling timers - one per clock type */ 130 QEMUTimerListGroup tlg; 131 132 int external_disable_cnt; 133 134 /* epoll(7) state used when built with CONFIG_EPOLL */ 135 int epollfd; 136 bool epoll_enabled; 137 bool epoll_available; 138 }; 139 140 /** 141 * aio_context_new: Allocate a new AioContext. 142 * 143 * AioContext provide a mini event-loop that can be waited on synchronously. 144 * They also provide bottom halves, a service to execute a piece of code 145 * as soon as possible. 146 */ 147 AioContext *aio_context_new(Error **errp); 148 149 /** 150 * aio_context_ref: 151 * @ctx: The AioContext to operate on. 152 * 153 * Add a reference to an AioContext. 154 */ 155 void aio_context_ref(AioContext *ctx); 156 157 /** 158 * aio_context_unref: 159 * @ctx: The AioContext to operate on. 160 * 161 * Drop a reference to an AioContext. 162 */ 163 void aio_context_unref(AioContext *ctx); 164 165 /* Take ownership of the AioContext. If the AioContext will be shared between 166 * threads, and a thread does not want to be interrupted, it will have to 167 * take ownership around calls to aio_poll(). Otherwise, aio_poll() 168 * automatically takes care of calling aio_context_acquire and 169 * aio_context_release. 170 * 171 * Access to timers and BHs from a thread that has not acquired AioContext 172 * is possible. Access to callbacks for now must be done while the AioContext 173 * is owned by the thread (FIXME). 174 */ 175 void aio_context_acquire(AioContext *ctx); 176 177 /* Relinquish ownership of the AioContext. */ 178 void aio_context_release(AioContext *ctx); 179 180 /** 181 * aio_bh_schedule_oneshot: Allocate a new bottom half structure that will run 182 * only once and as soon as possible. 183 */ 184 void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 185 186 /** 187 * aio_bh_new: Allocate a new bottom half structure. 188 * 189 * Bottom halves are lightweight callbacks whose invocation is guaranteed 190 * to be wait-free, thread-safe and signal-safe. The #QEMUBH structure 191 * is opaque and must be allocated prior to its use. 192 */ 193 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque); 194 195 /** 196 * aio_notify: Force processing of pending events. 197 * 198 * Similar to signaling a condition variable, aio_notify forces 199 * aio_poll to exit, so that the next call will re-examine pending events. 200 * The caller of aio_notify will usually call aio_poll again very soon, 201 * or go through another iteration of the GLib main loop. Hence, aio_notify 202 * also has the side effect of recalculating the sets of file descriptors 203 * that the main loop waits for. 204 * 205 * Calling aio_notify is rarely necessary, because for example scheduling 206 * a bottom half calls it already. 207 */ 208 void aio_notify(AioContext *ctx); 209 210 /** 211 * aio_notify_accept: Acknowledge receiving an aio_notify. 212 * 213 * aio_notify() uses an EventNotifier in order to wake up a sleeping 214 * aio_poll() or g_main_context_iteration(). Calls to aio_notify() are 215 * usually rare, but the AioContext has to clear the EventNotifier on 216 * every aio_poll() or g_main_context_iteration() in order to avoid 217 * busy waiting. This event_notifier_test_and_clear() cannot be done 218 * using the usual aio_context_set_event_notifier(), because it must 219 * be done before processing all events (file descriptors, bottom halves, 220 * timers). 221 * 222 * aio_notify_accept() is an optimized event_notifier_test_and_clear() 223 * that is specific to an AioContext's notifier; it is used internally 224 * to clear the EventNotifier only if aio_notify() had been called. 225 */ 226 void aio_notify_accept(AioContext *ctx); 227 228 /** 229 * aio_bh_call: Executes callback function of the specified BH. 230 */ 231 void aio_bh_call(QEMUBH *bh); 232 233 /** 234 * aio_bh_poll: Poll bottom halves for an AioContext. 235 * 236 * These are internal functions used by the QEMU main loop. 237 * And notice that multiple occurrences of aio_bh_poll cannot 238 * be called concurrently 239 */ 240 int aio_bh_poll(AioContext *ctx); 241 242 /** 243 * qemu_bh_schedule: Schedule a bottom half. 244 * 245 * Scheduling a bottom half interrupts the main loop and causes the 246 * execution of the callback that was passed to qemu_bh_new. 247 * 248 * Bottom halves that are scheduled from a bottom half handler are instantly 249 * invoked. This can create an infinite loop if a bottom half handler 250 * schedules itself. 251 * 252 * @bh: The bottom half to be scheduled. 253 */ 254 void qemu_bh_schedule(QEMUBH *bh); 255 256 /** 257 * qemu_bh_cancel: Cancel execution of a bottom half. 258 * 259 * Canceling execution of a bottom half undoes the effect of calls to 260 * qemu_bh_schedule without freeing its resources yet. While cancellation 261 * itself is also wait-free and thread-safe, it can of course race with the 262 * loop that executes bottom halves unless you are holding the iothread 263 * mutex. This makes it mostly useless if you are not holding the mutex. 264 * 265 * @bh: The bottom half to be canceled. 266 */ 267 void qemu_bh_cancel(QEMUBH *bh); 268 269 /** 270 *qemu_bh_delete: Cancel execution of a bottom half and free its resources. 271 * 272 * Deleting a bottom half frees the memory that was allocated for it by 273 * qemu_bh_new. It also implies canceling the bottom half if it was 274 * scheduled. 275 * This func is async. The bottom half will do the delete action at the finial 276 * end. 277 * 278 * @bh: The bottom half to be deleted. 279 */ 280 void qemu_bh_delete(QEMUBH *bh); 281 282 /* Return whether there are any pending callbacks from the GSource 283 * attached to the AioContext, before g_poll is invoked. 284 * 285 * This is used internally in the implementation of the GSource. 286 */ 287 bool aio_prepare(AioContext *ctx); 288 289 /* Return whether there are any pending callbacks from the GSource 290 * attached to the AioContext, after g_poll is invoked. 291 * 292 * This is used internally in the implementation of the GSource. 293 */ 294 bool aio_pending(AioContext *ctx); 295 296 /* Dispatch any pending callbacks from the GSource attached to the AioContext. 297 * 298 * This is used internally in the implementation of the GSource. 299 * 300 * @dispatch_fds: true to process fds, false to skip them 301 * (can be used as an optimization by callers that know there 302 * are no fds ready) 303 */ 304 bool aio_dispatch(AioContext *ctx, bool dispatch_fds); 305 306 /* Progress in completing AIO work to occur. This can issue new pending 307 * aio as a result of executing I/O completion or bh callbacks. 308 * 309 * Return whether any progress was made by executing AIO or bottom half 310 * handlers. If @blocking == true, this should always be true except 311 * if someone called aio_notify. 312 * 313 * If there are no pending bottom halves, but there are pending AIO 314 * operations, it may not be possible to make any progress without 315 * blocking. If @blocking is true, this function will wait until one 316 * or more AIO events have completed, to ensure something has moved 317 * before returning. 318 */ 319 bool aio_poll(AioContext *ctx, bool blocking); 320 321 /* Register a file descriptor and associated callbacks. Behaves very similarly 322 * to qemu_set_fd_handler. Unlike qemu_set_fd_handler, these callbacks will 323 * be invoked when using aio_poll(). 324 * 325 * Code that invokes AIO completion functions should rely on this function 326 * instead of qemu_set_fd_handler[2]. 327 */ 328 void aio_set_fd_handler(AioContext *ctx, 329 int fd, 330 bool is_external, 331 IOHandler *io_read, 332 IOHandler *io_write, 333 AioPollFn *io_poll, 334 void *opaque); 335 336 /* Register an event notifier and associated callbacks. Behaves very similarly 337 * to event_notifier_set_handler. Unlike event_notifier_set_handler, these callbacks 338 * will be invoked when using aio_poll(). 339 * 340 * Code that invokes AIO completion functions should rely on this function 341 * instead of event_notifier_set_handler. 342 */ 343 void aio_set_event_notifier(AioContext *ctx, 344 EventNotifier *notifier, 345 bool is_external, 346 EventNotifierHandler *io_read, 347 AioPollFn *io_poll); 348 349 /* Return a GSource that lets the main loop poll the file descriptors attached 350 * to this AioContext. 351 */ 352 GSource *aio_get_g_source(AioContext *ctx); 353 354 /* Return the ThreadPool bound to this AioContext */ 355 struct ThreadPool *aio_get_thread_pool(AioContext *ctx); 356 357 /* Return the LinuxAioState bound to this AioContext */ 358 struct LinuxAioState *aio_get_linux_aio(AioContext *ctx); 359 360 /** 361 * aio_timer_new: 362 * @ctx: the aio context 363 * @type: the clock type 364 * @scale: the scale 365 * @cb: the callback to call on timer expiry 366 * @opaque: the opaque pointer to pass to the callback 367 * 368 * Allocate a new timer attached to the context @ctx. 369 * The function is responsible for memory allocation. 370 * 371 * The preferred interface is aio_timer_init. Use that 372 * unless you really need dynamic memory allocation. 373 * 374 * Returns: a pointer to the new timer 375 */ 376 static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type, 377 int scale, 378 QEMUTimerCB *cb, void *opaque) 379 { 380 return timer_new_tl(ctx->tlg.tl[type], scale, cb, opaque); 381 } 382 383 /** 384 * aio_timer_init: 385 * @ctx: the aio context 386 * @ts: the timer 387 * @type: the clock type 388 * @scale: the scale 389 * @cb: the callback to call on timer expiry 390 * @opaque: the opaque pointer to pass to the callback 391 * 392 * Initialise a new timer attached to the context @ctx. 393 * The caller is responsible for memory allocation. 394 */ 395 static inline void aio_timer_init(AioContext *ctx, 396 QEMUTimer *ts, QEMUClockType type, 397 int scale, 398 QEMUTimerCB *cb, void *opaque) 399 { 400 timer_init_tl(ts, ctx->tlg.tl[type], scale, cb, opaque); 401 } 402 403 /** 404 * aio_compute_timeout: 405 * @ctx: the aio context 406 * 407 * Compute the timeout that a blocking aio_poll should use. 408 */ 409 int64_t aio_compute_timeout(AioContext *ctx); 410 411 /** 412 * aio_disable_external: 413 * @ctx: the aio context 414 * 415 * Disable the further processing of external clients. 416 */ 417 static inline void aio_disable_external(AioContext *ctx) 418 { 419 atomic_inc(&ctx->external_disable_cnt); 420 } 421 422 /** 423 * aio_enable_external: 424 * @ctx: the aio context 425 * 426 * Enable the processing of external clients. 427 */ 428 static inline void aio_enable_external(AioContext *ctx) 429 { 430 assert(ctx->external_disable_cnt > 0); 431 atomic_dec(&ctx->external_disable_cnt); 432 } 433 434 /** 435 * aio_external_disabled: 436 * @ctx: the aio context 437 * 438 * Return true if the external clients are disabled. 439 */ 440 static inline bool aio_external_disabled(AioContext *ctx) 441 { 442 return atomic_read(&ctx->external_disable_cnt); 443 } 444 445 /** 446 * aio_node_check: 447 * @ctx: the aio context 448 * @is_external: Whether or not the checked node is an external event source. 449 * 450 * Check if the node's is_external flag is okay to be polled by the ctx at this 451 * moment. True means green light. 452 */ 453 static inline bool aio_node_check(AioContext *ctx, bool is_external) 454 { 455 return !is_external || !atomic_read(&ctx->external_disable_cnt); 456 } 457 458 /** 459 * Return the AioContext whose event loop runs in the current thread. 460 * 461 * If called from an IOThread this will be the IOThread's AioContext. If 462 * called from another thread it will be the main loop AioContext. 463 */ 464 AioContext *qemu_get_current_aio_context(void); 465 466 /** 467 * @ctx: the aio context 468 * 469 * Return whether we are running in the I/O thread that manages @ctx. 470 */ 471 static inline bool aio_context_in_iothread(AioContext *ctx) 472 { 473 return ctx == qemu_get_current_aio_context(); 474 } 475 476 /** 477 * aio_context_setup: 478 * @ctx: the aio context 479 * 480 * Initialize the aio context. 481 */ 482 void aio_context_setup(AioContext *ctx); 483 484 #endif 485