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  */
  13
  14 #include "qemu-common.h"
  15 #include "block.h"
  16 #include "qemu-queue.h"
  17 #include "qemu_socket.h"
  18
  19 typedef struct AioHandler AioHandler;
  20
  21 /* The list of registered AIO handlers */
  22 static QLIST_HEAD(, AioHandler) aio_handlers;
  23
  24 /* This is a simple lock used to protect the aio_handlers list.  Specifically,
  25  * it's used to ensure that no callbacks are removed while we're walking and
  26  * dispatching callbacks.
  27  */
  28 static int walking_handlers;
  29
  30 struct AioHandler
  31 {
  32     int fd;
  33     IOHandler *io_read;
  34     IOHandler *io_write;
  35     AioFlushHandler *io_flush;
  36     AioProcessQueue *io_process_queue;
  37     int deleted;
  38     void *opaque;
  39     QLIST_ENTRY(AioHandler) node;
  40 };
  41
  42 static AioHandler *find_aio_handler(int fd)
  43 {
  44     AioHandler *node;
  45
  46     QLIST_FOREACH(node, &aio_handlers, node) {
  47         if (node->fd == fd)
  48             if (!node->deleted)
  49                 return node;
  50     }
  51
  52     return NULL;
  53 }
  54
  55 int qemu_aio_set_fd_handler(int fd,
  56                             IOHandler *io_read,
  57                             IOHandler *io_write,
  58                             AioFlushHandler *io_flush,
  59                             AioProcessQueue *io_process_queue,
  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->io_process_queue = io_process_queue;
  93         node->opaque = opaque;
  94     }
  95
  96     qemu_set_fd_handler2(fd, NULL, io_read, io_write, opaque);
  97
  98     return 0;
  99 }
 100
 101 void qemu_aio_flush(void)
 102 {
 103     AioHandler *node;
 104     int ret;
 105
 106     do {
 107         ret = 0;
 108
 109         /*
 110          * If there are pending emulated aio start them now so flush
 111          * will be able to return 1.
 112          */
 113         qemu_aio_wait();
 114
 115         QLIST_FOREACH(node, &aio_handlers, node) {
 116             if (node->io_flush) {
 117                 ret |= node->io_flush(node->opaque);
 118             }
 119         }
 120     } while (qemu_bh_poll() || ret > 0);
 121 }
 122
 123 int qemu_aio_process_queue(void)
 124 {
 125     AioHandler *node;
 126     int ret = 0;
 127
 128     walking_handlers = 1;
 129
 130     QLIST_FOREACH(node, &aio_handlers, node) {
 131         if (node->io_process_queue) {
 132             if (node->io_process_queue(node->opaque)) {
 133                 ret = 1;
 134             }
 135         }
 136     }
 137
 138     walking_handlers = 0;
 139
 140     return ret;
 141 }
 142
 143 void qemu_aio_wait(void)
 144 {
 145     int ret;
 146
 147     if (qemu_bh_poll())
 148         return;
 149
 150     /*
 151      * If there are callbacks left that have been queued, we need to call then.
 152      * Return afterwards to avoid waiting needlessly in select().
 153      */
 154     if (qemu_aio_process_queue())
 155         return;
 156
 157     do {
 158         AioHandler *node;
 159         fd_set rdfds, wrfds;
 160         int max_fd = -1;
 161
 162         walking_handlers = 1;
 163
 164         FD_ZERO(&rdfds);
 165         FD_ZERO(&wrfds);
 166
 167         /* fill fd sets */
 168         QLIST_FOREACH(node, &aio_handlers, node) {
 169             /* If there aren't pending AIO operations, don't invoke callbacks.
 170              * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 171              * wait indefinitely.
 172              */
 173             if (node->io_flush && node->io_flush(node->opaque) == 0)
 174                 continue;
 175
 176             if (!node->deleted && node->io_read) {
 177                 FD_SET(node->fd, &rdfds);
 178                 max_fd = MAX(max_fd, node->fd + 1);
 179             }
 180             if (!node->deleted && node->io_write) {
 181                 FD_SET(node->fd, &wrfds);
 182                 max_fd = MAX(max_fd, node->fd + 1);
 183             }
 184         }
 185
 186         walking_handlers = 0;
 187
 188         /* No AIO operations?  Get us out of here */
 189         if (max_fd == -1)
 190             break;
 191
 192         /* wait until next event */
 193         ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 194         if (ret == -1 && errno == EINTR)
 195             continue;
 196
 197         /* if we have any readable fds, dispatch event */
 198         if (ret > 0) {
 199             walking_handlers = 1;
 200
 201             /* we have to walk very carefully in case
 202              * qemu_aio_set_fd_handler is called while we're walking */
 203             node = QLIST_FIRST(&aio_handlers);
 204             while (node) {
 205                 AioHandler *tmp;
 206
 207                 if (!node->deleted &&
 208                     FD_ISSET(node->fd, &rdfds) &&
 209                     node->io_read) {
 210                     node->io_read(node->opaque);
 211                 }
 212                 if (!node->deleted &&
 213                     FD_ISSET(node->fd, &wrfds) &&
 214                     node->io_write) {
 215                     node->io_write(node->opaque);
 216                 }
 217
 218                 tmp = node;
 219                 node = QLIST_NEXT(node, node);
 220
 221                 if (tmp->deleted) {
 222                     QLIST_REMOVE(tmp, node);
 223                     g_free(tmp);
 224                 }
 225             }
 226
 227             walking_handlers = 0;
 228         }
 229     } while (ret == 0);
 230 }