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