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 "sys-queue.h"
  17 #include "qemu_socket.h"
  18
  19 typedef struct AioHandler AioHandler;
  20
  21 /* The list of registered AIO handlers */
  22 static LIST_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     int deleted;
  37     void *opaque;
  38     LIST_ENTRY(AioHandler) node;
  39 };
  40
  41 static AioHandler *find_aio_handler(int fd)
  42 {
  43     AioHandler *node;
  44
  45     LIST_FOREACH(node, &aio_handlers, node) {
  46         if (node->fd == fd)
  47             return node;
  48     }
  49
  50     return NULL;
  51 }
  52
  53 int qemu_aio_set_fd_handler(int fd,
  54                             IOHandler *io_read,
  55                             IOHandler *io_write,
  56                             AioFlushHandler *io_flush,
  57                             void *opaque)
  58 {
  59     AioHandler *node;
  60
  61     node = find_aio_handler(fd);
  62
  63     /* Are we deleting the fd handler? */
  64     if (!io_read && !io_write) {
  65         if (node) {
  66             /* If the lock is held, just mark the node as deleted */
  67             if (walking_handlers)
  68                 node->deleted = 1;
  69             else {
  70                 /* Otherwise, delete it for real.  We can't just mark it as
  71                  * deleted because deleted nodes are only cleaned up after
  72                  * releasing the walking_handlers lock.
  73                  */
  74                 LIST_REMOVE(node, node);
  75                 qemu_free(node);
  76             }
  77         }
  78     } else {
  79         if (node == NULL) {
  80             /* Alloc and insert if it's not already there */
  81             node = qemu_mallocz(sizeof(AioHandler));
  82             if (node == NULL)
  83                 return -ENOMEM;
  84             node->fd = fd;
  85             LIST_INSERT_HEAD(&aio_handlers, node, node);
  86         }
  87         /* Update handler with latest information */
  88         node->io_read = io_read;
  89         node->io_write = io_write;
  90         node->io_flush = io_flush;
  91         node->opaque = opaque;
  92     }
  93
  94     qemu_set_fd_handler2(fd, NULL, io_read, io_write, opaque);
  95
  96     return 0;
  97 }
  98
  99 void qemu_aio_flush(void)
 100 {
 101     AioHandler *node;
 102     int ret;
 103
 104     do {
 105         ret = 0;
 106
 107         LIST_FOREACH(node, &aio_handlers, node) {
 108             ret |= node->io_flush(node->opaque);
 109         }
 110
 111         qemu_aio_wait();
 112     } while (ret > 0);
 113 }
 114
 115 void qemu_aio_wait(void)
 116 {
 117     int ret;
 118
 119     if (qemu_bh_poll())
 120         return;
 121
 122     do {
 123         AioHandler *node;
 124         fd_set rdfds, wrfds;
 125         int max_fd = -1;
 126
 127         walking_handlers = 1;
 128
 129         FD_ZERO(&rdfds);
 130         FD_ZERO(&wrfds);
 131
 132         /* fill fd sets */
 133         LIST_FOREACH(node, &aio_handlers, node) {
 134             /* If there aren't pending AIO operations, don't invoke callbacks.
 135              * Otherwise, if there are no AIO requests, qemu_aio_wait() would
 136              * wait indefinitely.
 137              */
 138             if (node->io_flush && node->io_flush(node->opaque) == 0)
 139                 continue;
 140
 141             if (!node->deleted && node->io_read) {
 142                 FD_SET(node->fd, &rdfds);
 143                 max_fd = MAX(max_fd, node->fd + 1);
 144             }
 145             if (!node->deleted && node->io_write) {
 146                 FD_SET(node->fd, &wrfds);
 147                 max_fd = MAX(max_fd, node->fd + 1);
 148             }
 149         }
 150
 151         walking_handlers = 0;
 152
 153         /* No AIO operations?  Get us out of here */
 154         if (max_fd == -1)
 155             break;
 156
 157         /* wait until next event */
 158         ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);
 159         if (ret == -1 && errno == EINTR)
 160             continue;
 161
 162         /* if we have any readable fds, dispatch event */
 163         if (ret > 0) {
 164             walking_handlers = 1;
 165
 166             /* we have to walk very carefully in case
 167              * qemu_aio_set_fd_handler is called while we're walking */
 168             node = LIST_FIRST(&aio_handlers);
 169             while (node) {
 170                 AioHandler *tmp;
 171
 172                 if (!node->deleted &&
 173                     FD_ISSET(node->fd, &rdfds) &&
 174                     node->io_read) {
 175                     node->io_read(node->opaque);
 176                 }
 177                 if (!node->deleted &&
 178                     FD_ISSET(node->fd, &wrfds) &&
 179                     node->io_write) {
 180                     node->io_write(node->opaque);
 181                 }
 182
 183                 tmp = node;
 184                 node = LIST_NEXT(node, node);
 185
 186                 if (tmp->deleted) {
 187                     LIST_REMOVE(tmp, node);
 188                     qemu_free(tmp);
 189                 }
 190             }
 191
 192             walking_handlers = 0;
 193         }
 194     } while (ret == 0);
 195 }