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