qemu-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-common.h"
  18 #include "qemu-queue.h"
  19 #include "event_notifier.h"
  20
  21 typedef struct BlockDriverAIOCB BlockDriverAIOCB;
  22 typedef void BlockDriverCompletionFunc(void *opaque, int ret);
  23
  24 typedef struct AIOCBInfo {
  25     void (*cancel)(BlockDriverAIOCB *acb);
  26     size_t aiocb_size;
  27 } AIOCBInfo;
  28
  29 struct BlockDriverAIOCB {
  30     const AIOCBInfo *aiocb_info;
  31     BlockDriverState *bs;
  32     BlockDriverCompletionFunc *cb;
  33     void *opaque;
  34 };
  35
  36 void *qemu_aio_get(const AIOCBInfo *aiocb_info, BlockDriverState *bs,
  37                    BlockDriverCompletionFunc *cb, void *opaque);
  38 void qemu_aio_release(void *p);
  39
  40 typedef struct AioHandler AioHandler;
  41 typedef void QEMUBHFunc(void *opaque);
  42 typedef void IOHandler(void *opaque);
  43
  44 typedef struct AioContext {
  45     GSource source;
  46
  47     /* The list of registered AIO handlers */
  48     QLIST_HEAD(, AioHandler) aio_handlers;
  49
  50     /* This is a simple lock used to protect the aio_handlers list.
  51      * Specifically, it's used to ensure that no callbacks are removed while
  52      * we're walking and dispatching callbacks.
  53      */
  54     int walking_handlers;
  55
  56     /* Anchor of the list of Bottom Halves belonging to the context */
  57     struct QEMUBH *first_bh;
  58
  59     /* A simple lock used to protect the first_bh list, and ensure that
  60      * no callbacks are removed while we're walking and dispatching callbacks.
  61      */
  62     int walking_bh;
  63
  64     /* Used for aio_notify.  */
  65     EventNotifier notifier;
  66 } AioContext;
  67
  68 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
  69 typedef int (AioFlushEventNotifierHandler)(EventNotifier *e);
  70
  71 /**
  72  * aio_context_new: Allocate a new AioContext.
  73  *
  74  * AioContext provide a mini event-loop that can be waited on synchronously.
  75  * They also provide bottom halves, a service to execute a piece of code
  76  * as soon as possible.
  77  */
  78 AioContext *aio_context_new(void);
  79
  80 /**
  81  * aio_context_ref:
  82  * @ctx: The AioContext to operate on.
  83  *
  84  * Add a reference to an AioContext.
  85  */
  86 void aio_context_ref(AioContext *ctx);
  87
  88 /**
  89  * aio_context_unref:
  90  * @ctx: The AioContext to operate on.
  91  *
  92  * Drop a reference to an AioContext.
  93  */
  94 void aio_context_unref(AioContext *ctx);
  95
  96 /**
  97  * aio_bh_new: Allocate a new bottom half structure.
  98  *
  99  * Bottom halves are lightweight callbacks whose invocation is guaranteed
 100  * to be wait-free, thread-safe and signal-safe.  The #QEMUBH structure
 101  * is opaque and must be allocated prior to its use.
 102  */
 103 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque);
 104
 105 /**
 106  * aio_notify: Force processing of pending events.
 107  *
 108  * Similar to signaling a condition variable, aio_notify forces
 109  * aio_wait to exit, so that the next call will re-examine pending events.
 110  * The caller of aio_notify will usually call aio_wait again very soon,
 111  * or go through another iteration of the GLib main loop.  Hence, aio_notify
 112  * also has the side effect of recalculating the sets of file descriptors
 113  * that the main loop waits for.
 114  *
 115  * Calling aio_notify is rarely necessary, because for example scheduling
 116  * a bottom half calls it already.
 117  */
 118 void aio_notify(AioContext *ctx);
 119
 120 /**
 121  * aio_bh_poll: Poll bottom halves for an AioContext.
 122  *
 123  * These are internal functions used by the QEMU main loop.
 124  */
 125 int aio_bh_poll(AioContext *ctx);
 126
 127 /**
 128  * qemu_bh_schedule: Schedule a bottom half.
 129  *
 130  * Scheduling a bottom half interrupts the main loop and causes the
 131  * execution of the callback that was passed to qemu_bh_new.
 132  *
 133  * Bottom halves that are scheduled from a bottom half handler are instantly
 134  * invoked.  This can create an infinite loop if a bottom half handler
 135  * schedules itself.
 136  *
 137  * @bh: The bottom half to be scheduled.
 138  */
 139 void qemu_bh_schedule(QEMUBH *bh);
 140
 141 /**
 142  * qemu_bh_cancel: Cancel execution of a bottom half.
 143  *
 144  * Canceling execution of a bottom half undoes the effect of calls to
 145  * qemu_bh_schedule without freeing its resources yet.  While cancellation
 146  * itself is also wait-free and thread-safe, it can of course race with the
 147  * loop that executes bottom halves unless you are holding the iothread
 148  * mutex.  This makes it mostly useless if you are not holding the mutex.
 149  *
 150  * @bh: The bottom half to be canceled.
 151  */
 152 void qemu_bh_cancel(QEMUBH *bh);
 153
 154 /**
 155  *qemu_bh_delete: Cancel execution of a bottom half and free its resources.
 156  *
 157  * Deleting a bottom half frees the memory that was allocated for it by
 158  * qemu_bh_new.  It also implies canceling the bottom half if it was
 159  * scheduled.
 160  *
 161  * @bh: The bottom half to be deleted.
 162  */
 163 void qemu_bh_delete(QEMUBH *bh);
 164
 165 /* Return whether there are any pending callbacks from the GSource
 166  * attached to the AioContext.
 167  *
 168  * This is used internally in the implementation of the GSource.
 169  */
 170 bool aio_pending(AioContext *ctx);
 171
 172 /* Progress in completing AIO work to occur.  This can issue new pending
 173  * aio as a result of executing I/O completion or bh callbacks.
 174  *
 175  * If there is no pending AIO operation or completion (bottom half),
 176  * return false.  If there are pending bottom halves, return true.
 177  *
 178  * If there are no pending bottom halves, but there are pending AIO
 179  * operations, it may not be possible to make any progress without
 180  * blocking.  If @blocking is true, this function will wait until one
 181  * or more AIO events have completed, to ensure something has moved
 182  * before returning.
 183  *
 184  * If @blocking is false, this function will also return false if the
 185  * function cannot make any progress without blocking.
 186  */
 187 bool aio_poll(AioContext *ctx, bool blocking);
 188
 189 #ifdef CONFIG_POSIX
 190 /* Returns 1 if there are still outstanding AIO requests; 0 otherwise */
 191 typedef int (AioFlushHandler)(void *opaque);
 192
 193 /* Register a file descriptor and associated callbacks.  Behaves very similarly
 194  * to qemu_set_fd_handler2.  Unlike qemu_set_fd_handler2, these callbacks will
 195  * be invoked when using qemu_aio_wait().
 196  *
 197  * Code that invokes AIO completion functions should rely on this function
 198  * instead of qemu_set_fd_handler[2].
 199  */
 200 void aio_set_fd_handler(AioContext *ctx,
 201                         int fd,
 202                         IOHandler *io_read,
 203                         IOHandler *io_write,
 204                         AioFlushHandler *io_flush,
 205                         void *opaque);
 206 #endif
 207
 208 /* Register an event notifier and associated callbacks.  Behaves very similarly
 209  * to event_notifier_set_handler.  Unlike event_notifier_set_handler, these callbacks
 210  * will be invoked when using qemu_aio_wait().
 211  *
 212  * Code that invokes AIO completion functions should rely on this function
 213  * instead of event_notifier_set_handler.
 214  */
 215 void aio_set_event_notifier(AioContext *ctx,
 216                             EventNotifier *notifier,
 217                             EventNotifierHandler *io_read,
 218                             AioFlushEventNotifierHandler *io_flush);
 219
 220 /* Return a GSource that lets the main loop poll the file descriptors attached
 221  * to this AioContext.
 222  */
 223 GSource *aio_get_g_source(AioContext *ctx);
 224
 225 /* Functions to operate on the main QEMU AioContext.  */
 226
 227 bool qemu_aio_wait(void);
 228 void qemu_aio_set_event_notifier(EventNotifier *notifier,
 229                                  EventNotifierHandler *io_read,
 230                                  AioFlushEventNotifierHandler *io_flush);
 231
 232 #ifdef CONFIG_POSIX
 233 void qemu_aio_set_fd_handler(int fd,
 234                              IOHandler *io_read,
 235                              IOHandler *io_write,
 236                              AioFlushHandler *io_flush,
 237                              void *opaque);
 238 #endif
 239
 240 #endif