aio.c

   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  * Contributions after 2012-01-13 are licensed under the terms of the
  13  * GNU GPL, version 2 or (at your option) any later version.
  14  */
  15
  16 #include "qemu-common.h"
  17 #include "block.h"
  18 #include "qemu-queue.h"
  19 #include "qemu_socket.h"
  20
  21 struct AioHandler
  22 {
  23     int fd;
  24     IOHandler *io_read;
  25     IOHandler *io_write;
  26     AioFlushHandler *io_flush;
  27     int deleted;
  28     void *opaque;
  29     QLIST_ENTRY(AioHandler) node;
  30 };
  31
  32 static AioHandler *find_aio_handler(AioContext *ctx, int fd)
  33 {
  34     AioHandler *node;
  35
  36     QLIST_FOREACH(node, &ctx->aio_handlers, node) {
  37         if (node->fd == fd)
  38             if (!node->deleted)
  39                 return node;
  40     }
  41
  42     return NULL;
  43 }
  44
  45 void aio_set_fd_handler(AioContext *ctx,
  46                         int fd,
  47                         IOHandler *io_read,
  48                         IOHandler *io_write,
  49                         AioFlushHandler *io_flush,
  50                         void *opaque)
  51 {
  52     AioHandler *node;
  53
  54     node = find_aio_handler(ctx, fd);
  55
  56     /* Are we deleting the fd handler? */
  57     if (!io_read && !io_write) {
  58         if (node) {
  59             /* If the lock is held, just mark the node as deleted */
  60             if (ctx->walking_handlers)
  61                 node->deleted = 1;
  62             else {
  63                 /* Otherwise, delete it for real.  We can't just mark it as
  64                  * deleted because deleted nodes are only cleaned up after
  65                  * releasing the walking_handlers lock.
  66                  */
  67                 QLIST_REMOVE(node, node);
  68                 g_free(node);
  69             }
  70         }
  71     } else {
  72         if (node == NULL) {
  73             /* Alloc and insert if it's not already there */
  74             node = g_malloc0(sizeof(AioHandler));
  75             node->fd = fd;
  76             QLIST_INSERT_HEAD(&ctx->aio_handlers, node, node);
  77         }
  78         /* Update handler with latest information */
  79         node->io_read = io_read;
  80         node->io_write = io_write;
  81         node->io_flush = io_flush;
  82         node->opaque = opaque;
  83     }
  84 }
  85
  86 void aio_set_event_notifier(AioContext *ctx,
  87                             EventNotifier *notifier,
  88                             EventNotifierHandler *io_read,
  89                             AioFlushEventNotifierHandler *io_flush)
  90 {
  91     aio_set_fd_handler(ctx, event_notifier_get_fd(notifier),
  92                        (IOHandler *)io_read, NULL,
  93                        (AioFlushHandler *)io_flush, notifier);
  94 }
  95
  96 bool aio_wait(AioContext *ctx)
  97 {
  98     AioHandler *node;
  99     fd_set rdfds, wrfds;
 100     int max_fd = -1;
 101     int ret;
 102     bool busy;
 103
 104     /*
 105      * If there are callbacks left that have been queued, we need to call then.
 106      * Do not call select in this case, because it is possible that the caller
 107      * does not need a complete flush (as is the case for qemu_aio_wait loops).
 108      */
 109     if (aio_bh_poll(ctx)) {
 110         return true;
 111     }
 112
 113     ctx->walking_handlers++;
 114
 115     FD_ZERO(&rdfds);
 116     FD_ZERO(&wrfds);
 117
 118     /* fill fd sets */
 119     busy = false;
 120     QLIST_FOREACH(node, &ctx->aio_handlers, node) {
 121         /* If there aren't pending AIO operations, don't invoke callbacks.
 122          * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 123          * wait indefinitely.
 124          */
 125         if (node->io_flush) {
 126             if (node->io_flush(node->opaque) == 0) {
 127                 continue;
 128             }
 129             busy = true;
 130         }
 131         if (!node->deleted && node->io_read) {
 132             FD_SET(node->fd, &rdfds);
 133             max_fd = MAX(max_fd, node->fd + 1);
 134         }
 135         if (!node->deleted && node->io_write) {
 136             FD_SET(node->fd, &wrfds);
 137             max_fd = MAX(max_fd, node->fd + 1);
 138         }
 139     }
 140
 141     ctx->walking_handlers--;
 142
 143     /* No AIO operations?  Get us out of here */
 144     if (!busy) {
 145         return false;
 146     }
 147
 148     /* wait until next event */
 149     ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 150
 151     /* if we have any readable fds, dispatch event */
 152     if (ret > 0) {
 153         /* we have to walk very carefully in case
 154          * qemu_aio_set_fd_handler is called while we're walking */
 155         node = QLIST_FIRST(&ctx->aio_handlers);
 156         while (node) {
 157             AioHandler *tmp;
 158
 159             ctx->walking_handlers++;
 160
 161             if (!node->deleted &&
 162                 FD_ISSET(node->fd, &rdfds) &&
 163                 node->io_read) {
 164                 node->io_read(node->opaque);
 165             }
 166             if (!node->deleted &&
 167                 FD_ISSET(node->fd, &wrfds) &&
 168                 node->io_write) {
 169                 node->io_write(node->opaque);
 170             }
 171
 172             tmp = node;
 173             node = QLIST_NEXT(node, node);
 174
 175             ctx->walking_handlers--;
 176
 177             if (!ctx->walking_handlers && tmp->deleted) {
 178                 QLIST_REMOVE(tmp, node);
 179                 g_free(tmp);
 180             }
 181         }
 182     }
 183
 184     return true;
 185 }