1. The mirror technology instantiates its own BLK, sets 0/BLK_PERM_ALL for it
on exit and then, via subsequent call to bdrv_child_refresh_perms(), calls
bdrv_child_try_set_perm(). We don't have the extra BLK for our filter in stream
and do call the same function directly.
2. The function remove_filter() can't be used in the stream job on exit because
we should remove the filter and change a backing file in the same critical
'drain' section.
3. Due to the specifics above, I suggest that we make insert/remove filter as
an interface when there gets another user of it.
Andrey
________________________________
From: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
Sent: Tuesday, April 21, 2020 3:58 PM
To: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>; qemu-bl...@nongnu.org
<qemu-bl...@nongnu.org>
Cc: qemu-devel@nongnu.org <qemu-devel@nongnu.org>; kw...@redhat.com
<kw...@redhat.com>; mre...@redhat.com <mre...@redhat.com>; js...@redhat.com
<js...@redhat.com>; arm...@redhat.com <arm...@redhat.com>; dgilb...@redhat.com
<dgilb...@redhat.com>; ebl...@redhat.com <ebl...@redhat.com>; Denis Lunev
<d...@virtuozzo.com>
Subject: Re: [PATCH 7/7] block: apply COR-filter to block-stream jobs
20.04.2020 21:36, Andrey Shinkevich wrote:
> The patch completes the series with the COR-filter insertion to any
> block-stream operation. It also makes changes to the iotests 030, 141
> and 245.
>
> Signed-off-by: Andrey Shinkevich <andrey.shinkev...@virtuozzo.com>
> ---
> block/stream.c | 151
> +++++++++++++++++++++++++++++++++++++++------
> tests/qemu-iotests/030 | 6 +-
> tests/qemu-iotests/141.out | 2 +-
> tests/qemu-iotests/245 | 5 +-
> 4 files changed, 141 insertions(+), 23 deletions(-)
>
> diff --git a/block/stream.c b/block/stream.c
> index fab7923..af14ba8 100644
> --- a/block/stream.c
> +++ b/block/stream.c
[..]
> +static int stream_exit(Job *job, bool abort)
> +{
> + StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
> + BlockJob *bjob = &s->common;
> + BlockDriverState *target_bs = s->target_bs;
> + int ret = 0;
> +
> + if (s->chain_frozen) {
> + bdrv_unfreeze_chain(s->target_bs, s->bottom_cow_node);
> + s->chain_frozen = false;
> + }
> +
> + /* Retain the BDS until we complete the graph change. */
> + bdrv_ref(target_bs);
> + /* Hold a guest back from writing while permissions are being reset. */
> + bdrv_drained_begin(target_bs);
> + /* Drop permissions before the graph change. */
> + bdrv_child_try_set_perm(bdrv_filtered_rw_child(s->cor_filter_bs),
> + 0, BLK_PERM_ALL, &error_abort);
Hmm. I don't remember what's wrong with it, but something is. Neither mirror
nor backup do this now,
instead they use some flag, that permissions are not needed anymore and call
bdrv_child_refresh_perms()
Also, strange that you have insert_filter function, but don't use it here.
Also, could we keep add/remove filter api in block/copy-on-read.c, like it is
done for backup-top ?
--
Best regards,
Vladimir
