Re: [PATCH v4 6/7] block/copy-before-write: implement cbw-timeout option

[Vladimir Sementsov-Ogievskiy]

While debugging my "[PULL 00/10] Block jobs & NBD patches", I found that we 
have bdrv_dec_in_flight() and bdrv_inc_in_flight().

So, this should be fixed:

On 4/7/22 16:27, Vladimir Sementsov-Ogievskiy wrote:
> In some scenarios, when copy-before-write operations lasts too long
> time, it's better to cancel it.
>
> Most useful would be to use the new option together with
> on-cbw-error=break-snapshot: this way if cbw operation takes too long
> time we'll just cancel backup process but do not disturb the guest too
> much.

[..]

>   
> +static void block_copy_cb(void *opaque)
> +{
> +    BlockDriverState *bs = opaque;
> +
> +    bs->in_flight--;
> +    aio_wait_kick();

Just bdrv_dec_in_flight(bs), which includes aio_wait_kick().

> +}
> +
>   /*
>    * Do copy-before-write operation.
>    *
> @@ -111,7 +120,16 @@ static coroutine_fn int 
> cbw_do_copy_before_write(BlockDriverState *bs,
>       off = QEMU_ALIGN_DOWN(offset, cluster_size);
>       end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
>   
> -    ret = block_copy(s->bcs, off, end - off, true, 0, NULL, NULL);
> +    /*
> +     * Increase in_flight, so that in case of timed-out block-copy, the
> +     * remaining background block_copy() request (which can't be immediately
> +     * cancelled by timeout) is presented in bs->in_flight. This way we are
> +     * sure that on bs close() we'll previously wait for all timed-out but yet
> +     * running block_copy calls.
> +     */
> +    bs->in_flight++;

bdrv_inc_in_flight(bs)

> +    ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns,
> +                     block_copy_cb, bs);
>       if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
>           return ret;
>       }
> @@ -377,6 +395,7 @@ static BlockdevOptions *cbw_parse_options(QDict *options, 
> Error **errp)
>        */
>       qdict_extract_subqdict(options, NULL, "bitmap");
>       qdict_del(options, "on-cbw-error");
> +    qdict_del(options, "cbw-timeout");
>   

I'm going to resend "[PULL 00/10] Block jobs & NBD patches" with this fix and 
with fix in 03, if no objections.

--
Best regards,
Vladimir