include/block/aio.h

   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/typedefs.h"
  18 #include "qemu-common.h"
  19 #include "qemu/queue.h"
  20 #include "qemu/event_notifier.h"
  21 #include "qemu/thread.h"
  22 #include "qemu/rfifolock.h"
  23 #include "qemu/timer.h"
  24
  25 typedef struct BlockAIOCB BlockAIOCB;
  26 typedef void BlockCompletionFunc(void *opaque, int ret);
  27
  28 typedef struct AIOCBInfo {
  29     void (*cancel_async)(BlockAIOCB *acb);
  30     AioContext *(*get_aio_context)(BlockAIOCB *acb);
  31     size_t aiocb_size;
  32 } AIOCBInfo;
  33
  34 struct BlockAIOCB {
  35     const AIOCBInfo *aiocb_info;
  36     BlockDriverState *bs;
  37     BlockCompletionFunc *cb;
  38     void *opaque;
  39     int refcnt;
  40 };
  41
  42 void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
  43                    BlockCompletionFunc *cb, void *opaque);
  44 void qemu_aio_unref(void *p);
  45 void qemu_aio_ref(void *p);
  46
  47 typedef struct AioHandler AioHandler;
  48 typedef void QEMUBHFunc(void *opaque);
  49 typedef void IOHandler(void *opaque);
  50
  51 struct AioContext {
  52     GSource source;
  53
  54     /* Protects all fields from multi-threaded access */
  55     RFifoLock lock;
  56
  57     /* The list of registered AIO handlers */
  58     QLIST_HEAD(, AioHandler) aio_handlers;
  59
  60     /* This is a simple lock used to protect the aio_handlers list.
  61      * Specifically, it's used to ensure that no callbacks are removed while
  62      * we're walking and dispatching callbacks.
  63      */
  64     int walking_handlers;
  65
  66     /* Used to avoid unnecessary event_notifier_set calls in aio_notify.
  67      * Writes protected by lock or BQL, reads are lockless.
  68      */
  69     bool dispatching;
  70
  71     /* lock to protect between bh's adders and deleter */
  72     QemuMutex bh_lock;
  73
  74     /* Anchor of the list of Bottom Halves belonging to the context */
  75     struct QEMUBH *first_bh;
  76
  77     /* A simple lock used to protect the first_bh list, and ensure that
  78      * no callbacks are removed while we're walking and dispatching callbacks.
  79      */
  80     int walking_bh;
  81
  82     /* Used for aio_notify.  */
  83     EventNotifier notifier;
  84
  85     /* GPollFDs for aio_poll() */
  86     GArray *pollfds;
  87
  88     /* Thread pool for performing work and receiving completion callbacks */
  89     struct ThreadPool *thread_pool;
  90
  91     /* TimerLists for calling timers - one per clock type */
  92     QEMUTimerListGroup tlg;
  93 };
  94
  95 /* Used internally to synchronize aio_poll against qemu_bh_schedule.  */
  96 void aio_set_dispatching(AioContext *ctx, bool dispatching);
  97
  98 /**
  99  * aio_context_new: Allocate a new AioContext.
 100  *
 101  * AioContext provide a mini event-loop that can be waited on synchronously.
 102  * They also provide bottom halves, a service to execute a piece of code
 103  * as soon as possible.
 104  */
 105 AioContext *aio_context_new(Error **errp);
 106
 107 /**
 108  * aio_context_ref:
 109  * @ctx: The AioContext to operate on.
 110  *
 111  * Add a reference to an AioContext.
 112  */
 113 void aio_context_ref(AioContext *ctx);
 114
 115 /**
 116  * aio_context_unref:
 117  * @ctx: The AioContext to operate on.
 118  *
 119  * Drop a reference to an AioContext.
 120  */
 121 void aio_context_unref(AioContext *ctx);
 122
 123 /* Take ownership of the AioContext.  If the AioContext will be shared between
 124  * threads, a thread must have ownership when calling aio_poll().
 125  *
 126  * Note that multiple threads calling aio_poll() means timers, BHs, and
 127  * callbacks may be invoked from a different thread than they were registered
 128  * from.  Therefore, code must use AioContext acquire/release or use
 129  * fine-grained synchronization to protect shared state if other threads will
 130  * be accessing it simultaneously.
 131  */
 132 void aio_context_acquire(AioContext *ctx);
 133
 134 /* Relinquish ownership of the AioContext. */
 135 void aio_context_release(AioContext *ctx);
 136
 137 /**
 138  * aio_bh_new: Allocate a new bottom half structure.
 139  *
 140  * Bottom halves are lightweight callbacks whose invocation is guaranteed
 141  * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
 142  * is opaque and must be allocated prior to its use.
 143  */
 144 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
 145
 146 /**
 147  * aio_notify: Force processing of pending events.
 148  *
 149  * Similar to signaling a condition variable, aio_notify forces
 150  * aio_wait to exit, so that the next call will re-examine pending events.
 151  * The caller of aio_notify will usually call aio_wait again very soon,
 152  * or go through another iteration of the GLib main loop.  Hence, aio_notify
 153  * also has the side effect of recalculating the sets of file descriptors
 154  * that the main loop waits for.
 155  *
 156  * Calling aio_notify is rarely necessary, because for example scheduling
 157  * a bottom half calls it already.
 158  */
 159 void aio_notify(AioContext *ctx);
 160
 161 /**
 162  * aio_bh_poll: Poll bottom halves for an AioContext.
 163  *
 164  * These are internal functions used by the QEMU main loop.
 165  * And notice that multiple occurrences of aio_bh_poll cannot
 166  * be called concurrently
 167  */
 168 int aio_bh_poll(AioContext *ctx);
 169
 170 /**
 171  * qemu_bh_schedule: Schedule a bottom half.
 172  *
 173  * Scheduling a bottom half interrupts the main loop and causes the
 174  * execution of the callback that was passed to qemu_bh_new.
 175  *
 176  * Bottom halves that are scheduled from a bottom half handler are instantly
 177  * invoked.  This can create an infinite loop if a bottom half handler
 178  * schedules itself.
 179  *
 180  * @bh: The bottom half to be scheduled.
 181  */
 182 void qemu_bh_schedule(QEMUBH *bh);
 183
 184 /**
 185  * qemu_bh_cancel: Cancel execution of a bottom half.
 186  *
 187  * Canceling execution of a bottom half undoes the effect of calls to
 188  * qemu_bh_schedule without freeing its resources yet.  While cancellation
 189  * itself is also wait-free and thread-safe, it can of course race with the
 190  * loop that executes bottom halves unless you are holding the iothread
 191  * mutex.  This makes it mostly useless if you are not holding the mutex.
 192  *
 193  * @bh: The bottom half to be canceled.
 194  */
 195 void qemu_bh_cancel(QEMUBH *bh);
 196
 197 /**
 198  *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
 199  *
 200  * Deleting a bottom half frees the memory that was allocated for it by
 201  * qemu_bh_new.  It also implies canceling the bottom half if it was
 202  * scheduled.
 203  * This func is async. The bottom half will do the delete action at the finial
 204  * end.
 205  *
 206  * @bh: The bottom half to be deleted.
 207  */
 208 void qemu_bh_delete(QEMUBH *bh);
 209
 210 /* Return whether there are any pending callbacks from the GSource
 211  * attached to the AioContext, before g_poll is invoked.
 212  *
 213  * This is used internally in the implementation of the GSource.
 214  */
 215 bool aio_prepare(AioContext *ctx);
 216
 217 /* Return whether there are any pending callbacks from the GSource
 218  * attached to the AioContext, after g_poll is invoked.
 219  *
 220  * This is used internally in the implementation of the GSource.
 221  */
 222 bool aio_pending(AioContext *ctx);
 223
 224 /* Dispatch any pending callbacks from the GSource attached to the AioContext.
 225  *
 226  * This is used internally in the implementation of the GSource.
 227  */
 228 bool aio_dispatch(AioContext *ctx);
 229
 230 /* Progress in completing AIO work to occur.  This can issue new pending
 231  * aio as a result of executing I/O completion or bh callbacks.
 232  *
 233  * Return whether any progress was made by executing AIO or bottom half
 234  * handlers.  If @blocking == true, this should always be true except
 235  * if someone called aio_notify.
 236  *
 237  * If there are no pending bottom halves, but there are pending AIO
 238  * operations, it may not be possible to make any progress without
 239  * blocking.  If @blocking is true, this function will wait until one
 240  * or more AIO events have completed, to ensure something has moved
 241  * before returning.
 242  */
 243 bool aio_poll(AioContext *ctx, bool blocking);
 244
 245 /* Register a file descriptor and associated callbacks.  Behaves very similarly
 246  * to qemu_set_fd_handler2.  Unlike qemu_set_fd_handler2, these callbacks will
 247  * be invoked when using aio_poll().
 248  *
 249  * Code that invokes AIO completion functions should rely on this function
 250  * instead of qemu_set_fd_handler[2].
 251  */
 252 void aio_set_fd_handler(AioContext *ctx,
 253                         int fd,
 254                         IOHandler *io_read,
 255                         IOHandler *io_write,
 256                         void *opaque);
 257
 258 /* Register an event notifier and associated callbacks.  Behaves very similarly
 259  * to event_notifier_set_handler.  Unlike event_notifier_set_handler, these callbacks
 260  * will be invoked when using aio_poll().
 261  *
 262  * Code that invokes AIO completion functions should rely on this function
 263  * instead of event_notifier_set_handler.
 264  */
 265 void aio_set_event_notifier(AioContext *ctx,
 266                             EventNotifier *notifier,
 267                             EventNotifierHandler *io_read);
 268
 269 /* Return a GSource that lets the main loop poll the file descriptors attached
 270  * to this AioContext.
 271  */
 272 GSource *aio_get_g_source(AioContext *ctx);
 273
 274 /* Return the ThreadPool bound to this AioContext */
 275 struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
 276
 277 /**
 278  * aio_timer_new:
 279  * @ctx: the aio context
 280  * @type: the clock type
 281  * @scale: the scale
 282  * @cb: the callback to call on timer expiry
 283  * @opaque: the opaque pointer to pass to the callback
 284  *
 285  * Allocate a new timer attached to the context @ctx.
 286  * The function is responsible for memory allocation.
 287  *
 288  * The preferred interface is aio_timer_init. Use that
 289  * unless you really need dynamic memory allocation.
 290  *
 291  * Returns: a pointer to the new timer
 292  */
 293 static inline QEMUTimer *aio_timer_new(AioContext *ctx, QEMUClockType type,
 294                                        int scale,
 295                                        QEMUTimerCB *cb, void *opaque)
 296 {
 297     return timer_new_tl(ctx->tlg.tl[type], scale, cb, opaque);
 298 }
 299
 300 /**
 301  * aio_timer_init:
 302  * @ctx: the aio context
 303  * @ts: the timer
 304  * @type: the clock type
 305  * @scale: the scale
 306  * @cb: the callback to call on timer expiry
 307  * @opaque: the opaque pointer to pass to the callback
 308  *
 309  * Initialise a new timer attached to the context @ctx.
 310  * The caller is responsible for memory allocation.
 311  */
 312 static inline void aio_timer_init(AioContext *ctx,
 313                                   QEMUTimer *ts, QEMUClockType type,
 314                                   int scale,
 315                                   QEMUTimerCB *cb, void *opaque)
 316 {
 317     timer_init(ts, ctx->tlg.tl[type], scale, cb, opaque);
 318 }
 319
 320 /**
 321  * aio_compute_timeout:
 322  * @ctx: the aio context
 323  *
 324  * Compute the timeout that a blocking aio_poll should use.
 325  */
 326 int64_t aio_compute_timeout(AioContext *ctx);
 327
 328 #endif