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      1 /*
      2  * QEMU aio implementation
      3  *
      4  * Copyright IBM, Corp. 2008
      5  *
      6  * Authors:
      7  *  Anthony Liguori   <aliguori (at) 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/block.h"
     16 #include "qemu/queue.h"
     17 #include "qemu/sockets.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 }
    231