Re: [Qemu-block] [PATCH v6 11/12] qed: Implement .bdrv_drain

[Kevin Wolf]

Am 22.10.2015 um 08:32 hat Fam Zheng geschrieben:
> The "need_check_timer" is used to clear the "NEED_CHECK" flag in the
> image header after a grace period once metadata update has finished. In
> compliance to the bdrv_drain semantics we should make sure it remains
> deleted once .bdrv_drain is called.
> 
> We cannot reuse qed_need_check_timer_cb because it calls bdrv_aio_flush
> with a completion callback that starts more I/O, bdrv_drain cannot cope
> with this.

For the record: I discussed this with Fam on IRC and we came to the
conclusion that we should instead fix bdrv_drain() to correctly drain
in-flight flushes.

In order to achieve this, Fam will send a series that adds a
BdrvTrackedRequest to all remaining asynchronous operations. So far we
have identified flush, discard and aio_ioctl. At the same time he will
send a rebased version of this series that goes back to asynchronous
flushing in bdrv_qed_drain().

> Also the assertions in qed_need_check_timer_cb and
> qed_unplug_allocating_write_reqs are not guaranteed in the case of
> bdrv_qed_drain.
> 
> Signed-off-by: Fam Zheng <address@hidden>

Kevin