Archipelago » qemu

/*

 * QEMU aio implementation

 *

 * Copyright IBM, Corp. 2008

 *

 * Authors:

 *  Anthony Liguori   <aliguori@us.ibm.com>

 *

 * This work is licensed under the terms of the GNU GPL, version 2.  See

 * the COPYING file in the top-level directory.

 *

 */

#include "qemu-common.h"

#include "block.h"

#include "sys-queue.h"

#include "qemu_socket.h"

typedef struct AioHandler AioHandler;

/* The list of registered AIO handlers */

static LIST_HEAD(, AioHandler) aio_handlers;

/* This is a simple lock used to protect the aio_handlers list.  Specifically,

 * it's used to ensure that no callbacks are removed while we're walking and

 * dispatching callbacks.

 */

static int walking_handlers;

struct AioHandler

{

    int fd;

    IOHandler *io_read;

    IOHandler *io_write;

    AioFlushHandler *io_flush;

    int deleted;

    void *opaque;

    LIST_ENTRY(AioHandler) node;

};

static AioHandler *find_aio_handler(int fd)

{

    AioHandler *node;

    LIST_FOREACH(node, &aio_handlers, node) {

        if (node->fd == fd)

            return node;

    }

    return NULL;

}

int qemu_aio_set_fd_handler(int fd,

                            IOHandler *io_read,

                            IOHandler *io_write,

                            AioFlushHandler *io_flush,

                            void *opaque)

{

    AioHandler *node;

    node = find_aio_handler(fd);

    /* Are we deleting the fd handler? */

    if (!io_read && !io_write) {

        if (node) {

            /* If the lock is held, just mark the node as deleted */

            if (walking_handlers)

                node->deleted = 1;

            else {

                /* Otherwise, delete it for real.  We can't just mark it as

                 * deleted because deleted nodes are only cleaned up after

                 * releasing the walking_handlers lock.

                 */

                LIST_REMOVE(node, node);

                qemu_free(node);

            }

        }

    } else {

        if (node == NULL) {

            /* Alloc and insert if it's not already there */

            node = qemu_mallocz(sizeof(AioHandler));

            if (node == NULL)

                return -ENOMEM;

            node->fd = fd;

            LIST_INSERT_HEAD(&aio_handlers, node, node);

        }

        /* Update handler with latest information */

        node->io_read = io_read;

        node->io_write = io_write;

        node->io_flush = io_flush;

        node->opaque = opaque;

    }

    qemu_set_fd_handler2(fd, NULL, io_read, io_write, opaque);

    return 0;

}

void qemu_aio_flush(void)

{

    AioHandler *node;

    int ret;

    do {

        ret = 0;

        LIST_FOREACH(node, &aio_handlers, node) {

            ret |= node->io_flush(node->opaque);

        }

        qemu_aio_wait();

    } while (ret > 0);

}

void qemu_aio_wait(void)

{

    int ret;

    if (qemu_bh_poll())

        return;

    do {

        AioHandler *node;

        fd_set rdfds, wrfds;

        int max_fd = -1;

        walking_handlers = 1;

        FD_ZERO(&rdfds);

        FD_ZERO(&wrfds);

        /* fill fd sets */

        LIST_FOREACH(node, &aio_handlers, node) {

            /* If there aren't pending AIO operations, don't invoke callbacks.

             * Otherwise, if there are no AIO requests, qemu_aio_wait() would

             * wait indefinitely.

             */

            if (node->io_flush && node->io_flush(node->opaque) == 0)

                continue;

            if (!node->deleted && node->io_read) {

                FD_SET(node->fd, &rdfds);

                max_fd = MAX(max_fd, node->fd + 1);

            }

            if (!node->deleted && node->io_write) {

                FD_SET(node->fd, &wrfds);

                max_fd = MAX(max_fd, node->fd + 1);

            }

        }

        walking_handlers = 0;

        /* No AIO operations?  Get us out of here */

        if (max_fd == -1)

            break;

        /* wait until next event */

        ret = select(max_fd, &rdfds, &wrfds, NULL, NULL);

        if (ret == -1 && errno == EINTR)

            continue;

        /* if we have any readable fds, dispatch event */

        if (ret > 0) {

            walking_handlers = 1;

            /* we have to walk very carefully in case

             * qemu_aio_set_fd_handler is called while we're walking */

            node = LIST_FIRST(&aio_handlers);

            while (node) {

                AioHandler *tmp;

                if (!node->deleted &&

                    FD_ISSET(node->fd, &rdfds) &&

                    node->io_read) {

                    node->io_read(node->opaque);

                }

                if (!node->deleted &&

                    FD_ISSET(node->fd, &wrfds) &&

                    node->io_write) {

                    node->io_write(node->opaque);

                }

                tmp = node;

                node = LIST_NEXT(node, node);

                if (tmp->deleted) {

                    LIST_REMOVE(tmp, node);

                    qemu_free(tmp);

                }

            }

            walking_handlers = 0;

        }

    } while (ret == 0);

}