25.02.2019 18:19, Kevin Wolf wrote:
> bdrv_drain() must not leave connection_co scheduled, so bs->in_flight
> needs to be increased while the coroutine is waiting to be scheduled
> in the new AioContext after nbd_client_attach_aio_context().
Hi!
I have some questions, could you explain, please?
"bdrv_drain() must not leave connection_co scheduled" - it's because we want to
be
sure that connection_co yielded from nbd_read_eof, yes?
But it is guaranteed by aio_wait_bh_oneshot.. Why do we need additioinally
inc/dec
bs->in_flight ?
>
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> ---
> block/nbd-client.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/block/nbd-client.c b/block/nbd-client.c
> index 60f38f0320..bfbaf7ebe9 100644
> --- a/block/nbd-client.c
> +++ b/block/nbd-client.c
> @@ -977,14 +977,30 @@ void nbd_client_detach_aio_context(BlockDriverState *bs)
> qio_channel_detach_aio_context(QIO_CHANNEL(client->ioc));
> }
>
> +static void nbd_client_attach_aio_context_bh(void *opaque)
> +{
> + BlockDriverState *bs = opaque;
> + NBDClientSession *client = nbd_get_client_session(bs);
> +
> + /* The node is still drained, so we know the coroutine has yielded in
> + * nbd_read_eof(), the only place where bs->in_flight can reach 0, or it
> is
> + * entered for the first time. Both places are safe for entering the
> + * coroutine.*/
> + qemu_aio_coroutine_enter(bs->aio_context, client->connection_co);
> + bdrv_dec_in_flight(bs);
> +}
> +
> void nbd_client_attach_aio_context(BlockDriverState *bs,
> AioContext *new_context)
> {
> NBDClientSession *client = nbd_get_client_session(bs);
> qio_channel_attach_aio_context(QIO_CHANNEL(client->ioc), new_context);
>
> - /* FIXME Really need a bdrv_inc_in_flight() here */
> - aio_co_schedule(new_context, client->connection_co);
> + bdrv_inc_in_flight(bs);
> +
> + /* Need to wait here for the BH to run because the BH must run while the
> + * node is still drained. */
> + aio_wait_bh_oneshot(new_context, nbd_client_attach_aio_context_bh, bs);
> }
>
> void nbd_client_close(BlockDriverState *bs)
>
--
Best regards,
Vladimir
