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 typedef struct AioHandler AioHandler;
  22
  23 /* The list of registered AIO handlers */
  24 static QLIST_HEAD(, AioHandler) aio_handlers;
  25
  26 /* This is a simple lock used to protect the aio_handlers list.  Specifically,
  27  * it's used to ensure that no callbacks are removed while we're walking and
  28  * dispatching callbacks.
  29  */
  30 static int walking_handlers;
  31
  32 struct AioHandler
  33 {
  34     int fd;
  35     IOHandler *io_read;
  36     IOHandler *io_write;
  37     AioFlushHandler *io_flush;
  38     int deleted;
  39     void *opaque;
  40     QLIST_ENTRY(AioHandler) node;
  41 };
  42
  43 static AioHandler *find_aio_handler(int fd)
  44 {
  45     AioHandler *node;
  46
  47     QLIST_FOREACH(node, &aio_handlers, node) {
  48         if (node->fd == fd)
  49             if (!node->deleted)
  50                 return node;
  51     }
  52
  53     return NULL;
  54 }
  55
  56 void qemu_aio_set_fd_handler(int fd,
  57                              IOHandler *io_read,
  58                              IOHandler *io_write,
  59                              AioFlushHandler *io_flush,
  60                              void *opaque)
  61 {
  62     AioHandler *node;
  63
  64     node = find_aio_handler(fd);
  65
  66     /* Are we deleting the fd handler? */
  67     if (!io_read && !io_write) {
  68         if (node) {
  69             /* If the lock is held, just mark the node as deleted */
  70             if (walking_handlers)
  71                 node->deleted = 1;
  72             else {
  73                 /* Otherwise, delete it for real.  We can't just mark it as
  74                  * deleted because deleted nodes are only cleaned up after
  75                  * releasing the walking_handlers lock.
  76                  */
  77                 QLIST_REMOVE(node, node);
  78                 g_free(node);
  79             }
  80         }
  81     } else {
  82         if (node == NULL) {
  83             /* Alloc and insert if it's not already there */
  84             node = g_malloc0(sizeof(AioHandler));
  85             node->fd = fd;
  86             QLIST_INSERT_HEAD(&aio_handlers, node, node);
  87         }
  88         /* Update handler with latest information */
  89         node->io_read = io_read;
  90         node->io_write = io_write;
  91         node->io_flush = io_flush;
  92         node->opaque = opaque;
  93     }
  94
  95     qemu_set_fd_handler2(fd, NULL, io_read, io_write, opaque);
  96 }
  97
  98 void qemu_aio_set_event_notifier(EventNotifier *notifier,
  99                                  EventNotifierHandler *io_read,
 100                                  AioFlushEventNotifierHandler *io_flush)
 101 {
 102     qemu_aio_set_fd_handler(event_notifier_get_fd(notifier),
 103                             (IOHandler *)io_read, NULL,
 104                             (AioFlushHandler *)io_flush, notifier);
 105 }
 106
 107 void qemu_aio_flush(void)
 108 {
 109     while (qemu_aio_wait());
 110 }
 111
 112 bool qemu_aio_wait(void)
 113 {
 114     AioHandler *node;
 115     fd_set rdfds, wrfds;
 116     int max_fd = -1;
 117     int ret;
 118     bool busy;
 119
 120     /*
 121      * If there are callbacks left that have been queued, we need to call then.
 122      * Do not call select in this case, because it is possible that the caller
 123      * does not need a complete flush (as is the case for qemu_aio_wait loops).
 124      */
 125     if (qemu_bh_poll()) {
 126         return true;
 127     }
 128
 129     walking_handlers++;
 130
 131     FD_ZERO(&rdfds);
 132     FD_ZERO(&wrfds);
 133
 134     /* fill fd sets */
 135     busy = false;
 136     QLIST_FOREACH(node, &aio_handlers, node) {
 137         /* If there aren't pending AIO operations, don't invoke callbacks.
 138          * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 139          * wait indefinitely.
 140          */
 141         if (node->io_flush) {
 142             if (node->io_flush(node->opaque) == 0) {
 143                 continue;
 144             }
 145             busy = true;
 146         }
 147         if (!node->deleted && node->io_read) {
 148             FD_SET(node->fd, &rdfds);
 149             max_fd = MAX(max_fd, node->fd + 1);
 150         }
 151         if (!node->deleted && node->io_write) {
 152             FD_SET(node->fd, &wrfds);
 153             max_fd = MAX(max_fd, node->fd + 1);
 154         }
 155     }
 156
 157     walking_handlers--;
 158
 159     /* No AIO operations?  Get us out of here */
 160     if (!busy) {
 161         return false;
 162     }
 163
 164     /* wait until next event */
 165     ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 166
 167     /* if we have any readable fds, dispatch event */
 168     if (ret > 0) {
 169         /* we have to walk very carefully in case
 170          * qemu_aio_set_fd_handler is called while we're walking */
 171         node = QLIST_FIRST(&aio_handlers);
 172         while (node) {
 173             AioHandler *tmp;
 174
 175             walking_handlers++;
 176
 177             if (!node->deleted &&
 178                 FD_ISSET(node->fd, &rdfds) &&
 179                 node->io_read) {
 180                 node->io_read(node->opaque);
 181             }
 182             if (!node->deleted &&
 183                 FD_ISSET(node->fd, &wrfds) &&
 184                 node->io_write) {
 185                 node->io_write(node->opaque);
 186             }
 187
 188             tmp = node;
 189             node = QLIST_NEXT(node, node);
 190
 191             walking_handlers--;
 192
 193             if (!walking_handlers && tmp->deleted) {
 194                 QLIST_REMOVE(tmp, node);
 195                 g_free(tmp);
 196             }
 197         }
 198     }
 199
 200     return true;
 201 }