Re: [Qemu-devel] [PATCH] block: Fix bdrv_drain in coroutine

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/04/2016 11:46, Fam Zheng wrote:
> +
> +static void bdrv_co_drain_bh_cb(void *opaque)
> +{
> +    BdrvCoDrainData *data = opaque;
> +    Coroutine *co = data->co;
> +
> +    bdrv_drain(data->bs);
> +    data->done = true;
> +    qemu_coroutine_enter(co, NULL);
> +}
> +
> +static void coroutine_fn bdrv_co_drain(BlockDriverState *bs)
> +{
> +    QEMUBH *bh;
> +    BdrvCoDrainData data;
> +
> +    assert(qemu_in_coroutine());
> +    data = (BdrvCoDrainData) {
> +        .co = qemu_coroutine_self(),
> +        .bs = bs,
> +        .done = false,
> +    };
> +    bh = aio_bh_new(bdrv_get_aio_context(bs), bdrv_co_drain_bh_cb, &data),
> +    qemu_bh_schedule(bh);
> +
> +    do {
> +        qemu_coroutine_yield();
> +    } while (!data.done);

The loop and "done" is not necessary.  Also,

> +    qemu_bh_delete(bh);

this can be moved to bdrv_co_drain_bh_cb before bdrv_drain, so that the
bottom half doesn't slow down the event loop until bdrv_drain completes.

Paolo

> +}