Am 12.04.2012 14:00, schrieb Paolo Bonzini:
> The definition of when qemu_aio_flush should loop is much simpler
> than it looks. It just has to call qemu_aio_wait until it makes
> no progress and all flush callbacks return false. qemu_aio_wait
> is the logical place to tell the caller about this.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> aio.c | 44 ++++++++++++++++++--------------------------
> qemu-aio.h | 6 ++++--
> 2 files changed, 22 insertions(+), 28 deletions(-)
>
> diff --git a/aio.c b/aio.c
> index f19b3c6..5fcc0c6 100644
> --- a/aio.c
> +++ b/aio.c
> @@ -99,41 +99,26 @@ int qemu_aio_set_fd_handler(int fd,
>
> void qemu_aio_flush(void)
> {
> - AioHandler *node;
> - int ret;
> -
> - do {
> - ret = 0;
> -
> - /*
> - * If there are pending emulated aio start them now so flush
> - * will be able to return 1.
> - */
> - qemu_aio_wait();
> -
> - QLIST_FOREACH(node, &aio_handlers, node) {
> - if (node->io_flush) {
> - ret |= node->io_flush(node->opaque);
> - }
> - }
> - } while (qemu_bh_poll() || ret > 0);
> + while (qemu_aio_wait());
> }
>
> -void qemu_aio_wait(void)
> +bool qemu_aio_wait(void)
> {
> int ret;
>
> /*
> * If there are callbacks left that have been queued, we need to call
> then.
> - * Return afterwards to avoid waiting needlessly in select().
> + * Do not call select in this case, because it is possible that the
> caller
> + * does not need a complete flush (as is the case for qemu_aio_wait
> loops).
> */
> if (qemu_bh_poll()) {
> - return;
> + return true;
> }
>
> do {
> AioHandler *node;
> fd_set rdfds, wrfds;
> + bool busy;
> int max_fd = -1;
>
> walking_handlers = 1;
> @@ -142,14 +127,18 @@ void qemu_aio_wait(void)
> FD_ZERO(&wrfds);
>
> /* fill fd sets */
> + busy = false;
> QLIST_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->io_flush) {
> + if (node->io_flush(node->opaque) == 0) {
> + continue;
> + }
> + busy = true;
> + }
> if (!node->deleted && node->io_read) {
> FD_SET(node->fd, &rdfds);
> max_fd = MAX(max_fd, node->fd + 1);
> @@ -163,8 +152,9 @@ void qemu_aio_wait(void)
> walking_handlers = 0;
>
> /* No AIO operations? Get us out of here */
> - if (max_fd == -1)
> - break;
> + if (!busy) {
> + return false;
> + }
This can change the behaviour for aio_handlers that don't have a flush
callback. Previously we would run into the select, now we don't.
Hm, okay, such handlers don't exist. Maybe we should assert() it
somewhere, but I guess then it's not a problem with this patch.
Kevin
