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     AioProcessQueue *io_process_queue;
  39     int deleted;
  40     void *opaque;
  41     QLIST_ENTRY(AioHandler) node;
  42 };
  43
  44 static AioHandler *find_aio_handler(int fd)
  45 {
  46     AioHandler *node;
  47
  48     QLIST_FOREACH(node, &aio_handlers, node) {
  49         if (node->fd == fd)
  50             if (!node->deleted)
  51                 return node;
  52     }
  53
  54     return NULL;
  55 }
  56
  57 int qemu_aio_set_fd_handler(int fd,
  58                             IOHandler *io_read,
  59                             IOHandler *io_write,
  60                             AioFlushHandler *io_flush,
  61                             AioProcessQueue *io_process_queue,
  62                             void *opaque)
  63 {
  64     AioHandler *node;
  65
  66     node = find_aio_handler(fd);
  67
  68     /* Are we deleting the fd handler? */
  69     if (!io_read && !io_write) {
  70         if (node) {
  71             /* If the lock is held, just mark the node as deleted */
  72             if (walking_handlers)
  73                 node->deleted = 1;
  74             else {
  75                 /* Otherwise, delete it for real.  We can't just mark it as
  76                  * deleted because deleted nodes are only cleaned up after
  77                  * releasing the walking_handlers lock.
  78                  */
  79                 QLIST_REMOVE(node, node);
  80                 g_free(node);
  81             }
  82         }
  83     } else {
  84         if (node == NULL) {
  85             /* Alloc and insert if it's not already there */
  86             node = g_malloc0(sizeof(AioHandler));
  87             node->fd = fd;
  88             QLIST_INSERT_HEAD(&aio_handlers, node, node);
  89         }
  90         /* Update handler with latest information */
  91         node->io_read = io_read;
  92         node->io_write = io_write;
  93         node->io_flush = io_flush;
  94         node->io_process_queue = io_process_queue;
  95         node->opaque = opaque;
  96     }
  97
  98     qemu_set_fd_handler2(fd, NULL, io_read, io_write, opaque);
  99
 100     return 0;
 101 }
 102
 103 void qemu_aio_flush(void)
 104 {
 105     AioHandler *node;
 106     int ret;
 107
 108     do {
 109         ret = 0;
 110
 111         /*
 112          * If there are pending emulated aio start them now so flush
 113          * will be able to return 1.
 114          */
 115         qemu_aio_wait();
 116
 117         QLIST_FOREACH(node, &aio_handlers, node) {
 118             if (node->io_flush) {
 119                 ret |= node->io_flush(node->opaque);
 120             }
 121         }
 122     } while (qemu_bh_poll() || ret > 0);
 123 }
 124
 125 int qemu_aio_process_queue(void)
 126 {
 127     AioHandler *node;
 128     int ret = 0;
 129
 130     walking_handlers = 1;
 131
 132     QLIST_FOREACH(node, &aio_handlers, node) {
 133         if (node->io_process_queue) {
 134             if (node->io_process_queue(node->opaque)) {
 135                 ret = 1;
 136             }
 137         }
 138     }
 139
 140     walking_handlers = 0;
 141
 142     return ret;
 143 }
 144
 145 void qemu_aio_wait(void)
 146 {
 147     int ret;
 148
 149     if (qemu_bh_poll())
 150         return;
 151
 152     /*
 153      * If there are callbacks left that have been queued, we need to call then.
 154      * Return afterwards to avoid waiting needlessly in select().
 155      */
 156     if (qemu_aio_process_queue())
 157         return;
 158
 159     do {
 160         AioHandler *node;
 161         fd_set rdfds, wrfds;
 162         int max_fd = -1;
 163
 164         walking_handlers = 1;
 165
 166         FD_ZERO(&rdfds);
 167         FD_ZERO(&wrfds);
 168
 169         /* fill fd sets */
 170         QLIST_FOREACH(node, &aio_handlers, node) {
 171             /* If there aren't pending AIO operations, don't invoke callbacks.
 172              * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 173              * wait indefinitely.
 174              */
 175             if (node->io_flush && node->io_flush(node->opaque) == 0)
 176                 continue;
 177
 178             if (!node->deleted && node->io_read) {
 179                 FD_SET(node->fd, &rdfds);
 180                 max_fd = MAX(max_fd, node->fd + 1);
 181             }
 182             if (!node->deleted && node->io_write) {
 183                 FD_SET(node->fd, &wrfds);
 184                 max_fd = MAX(max_fd, node->fd + 1);
 185             }
 186         }
 187
 188         walking_handlers = 0;
 189
 190         /* No AIO operations?  Get us out of here */
 191         if (max_fd == -1)
 192             break;
 193
 194         /* wait until next event */
 195         ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 196         if (ret == -1 && errno == EINTR)
 197             continue;
 198
 199         /* if we have any readable fds, dispatch event */
 200         if (ret > 0) {
 201             walking_handlers = 1;
 202
 203             /* we have to walk very carefully in case
 204              * qemu_aio_set_fd_handler is called while we're walking */
 205             node = QLIST_FIRST(&aio_handlers);
 206             while (node) {
 207                 AioHandler *tmp;
 208
 209                 if (!node->deleted &&
 210                     FD_ISSET(node->fd, &rdfds) &&
 211                     node->io_read) {
 212                     node->io_read(node->opaque);
 213                 }
 214                 if (!node->deleted &&
 215                     FD_ISSET(node->fd, &wrfds) &&
 216                     node->io_write) {
 217                     node->io_write(node->opaque);
 218                 }
 219
 220                 tmp = node;
 221                 node = QLIST_NEXT(node, node);
 222
 223                 if (tmp->deleted) {
 224                     QLIST_REMOVE(tmp, node);
 225                     g_free(tmp);
 226                 }
 227             }
 228
 229             walking_handlers = 0;
 230         }
 231     } while (ret == 0);
 232 }