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                 qemu_free(node);
  79             }
  80         }
  81     } else {
  82         if (node == NULL) {
  83             /* Alloc and insert if it's not already there */
  84             node = qemu_mallocz(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             ret |= node->io_flush(node->opaque);
 117         }
 118     } while (qemu_bh_poll() || ret > 0);
 119 }
 120
 121 int qemu_aio_process_queue(void)
 122 {
 123     AioHandler *node;
 124     int ret = 0;
 125
 126     walking_handlers = 1;
 127
 128     QLIST_FOREACH(node, &aio_handlers, node) {
 129         if (node->io_process_queue) {
 130             if (node->io_process_queue(node->opaque)) {
 131                 ret = 1;
 132             }
 133         }
 134     }
 135
 136     walking_handlers = 0;
 137
 138     return ret;
 139 }
 140
 141 void qemu_aio_wait(void)
 142 {
 143     int ret;
 144
 145     if (qemu_bh_poll())
 146         return;
 147
 148     /*
 149      * If there are callbacks left that have been queued, we need to call then.
 150      * Return afterwards to avoid waiting needlessly in select().
 151      */
 152     if (qemu_aio_process_queue())
 153         return;
 154
 155     do {
 156         AioHandler *node;
 157         fd_set rdfds, wrfds;
 158         int max_fd = -1;
 159
 160         walking_handlers = 1;
 161
 162         FD_ZERO(&rdfds);
 163         FD_ZERO(&wrfds);
 164
 165         /* fill fd sets */
 166         QLIST_FOREACH(node, &aio_handlers, node) {
 167             /* If there aren't pending AIO operations, don't invoke callbacks.
 168              * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 169              * wait indefinitely.
 170              */
 171             if (node->io_flush && node->io_flush(node->opaque) == 0)
 172                 continue;
 173
 174             if (!node->deleted && node->io_read) {
 175                 FD_SET(node->fd, &rdfds);
 176                 max_fd = MAX(max_fd, node->fd + 1);
 177             }
 178             if (!node->deleted && node->io_write) {
 179                 FD_SET(node->fd, &wrfds);
 180                 max_fd = MAX(max_fd, node->fd + 1);
 181             }
 182         }
 183
 184         walking_handlers = 0;
 185
 186         /* No AIO operations?  Get us out of here */
 187         if (max_fd == -1)
 188             break;
 189
 190         /* wait until next event */
 191         ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 192         if (ret == -1 && errno == EINTR)
 193             continue;
 194
 195         /* if we have any readable fds, dispatch event */
 196         if (ret > 0) {
 197             walking_handlers = 1;
 198
 199             /* we have to walk very carefully in case
 200              * qemu_aio_set_fd_handler is called while we're walking */
 201             node = QLIST_FIRST(&aio_handlers);
 202             while (node) {
 203                 AioHandler *tmp;
 204
 205                 if (!node->deleted &&
 206                     FD_ISSET(node->fd, &rdfds) &&
 207                     node->io_read) {
 208                     node->io_read(node->opaque);
 209                 }
 210                 if (!node->deleted &&
 211                     FD_ISSET(node->fd, &wrfds) &&
 212                     node->io_write) {
 213                     node->io_write(node->opaque);
 214                 }
 215
 216                 tmp = node;
 217                 node = QLIST_NEXT(node, node);
 218
 219                 if (tmp->deleted) {
 220                     QLIST_REMOVE(tmp, node);
 221                     qemu_free(tmp);
 222                 }
 223             }
 224
 225             walking_handlers = 0;
 226         }
 227     } while (ret == 0);
 228 }