Re: [PATCH v6 1/4] block/replication.c: Ignore requests after failover

[Max Reitz]

On 05.10.19 15:05, Lukas Straub wrote:
> After failover the Secondary side of replication shouldn't change state, 
> because
> it now functions as our primary disk.
> 
> In replication_start, replication_do_checkpoint, replication_stop, ignore
> the request if current state is BLOCK_REPLICATION_DONE (sucessful failover) or
> BLOCK_REPLICATION_FAILOVER (failover in progres i.e. currently merging active
> and hidden images into the base image).
> 
> Signed-off-by: Lukas Straub <address@hidden>
> Reviewed-by: Zhang Chen <address@hidden>
> ---
>  block/replication.c | 38 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 35 insertions(+), 3 deletions(-)

Disclaimer: I don’t know anything about the replication block driver.

> diff --git a/block/replication.c b/block/replication.c
> index 3d4dedddfc..97cc65c0cf 100644
> --- a/block/replication.c
> +++ b/block/replication.c

[...]

> @@ -529,8 +540,7 @@ static void replication_start(ReplicationState *rs, 
> ReplicationMode mode,
>                     "Block device is in use by internal backup job");
> 
>          top_bs = bdrv_lookup_bs(s->top_id, s->top_id, NULL);
> -        if (!top_bs || !bdrv_is_root_node(top_bs) ||
> -            !check_top_bs(top_bs, bs)) {
> +        if (!top_bs || !check_top_bs(top_bs, bs)) {

It appears to me that top_bs is only used to install op blockers.  It
seems reasonable to require a root node to be able to do so (because op
blockers are really only checked on a root node).
(And the commit message doesn’t tell why we’d want to drop the
is_root_node check here.)

Now OTOH I don’t know whether the replication driver needs an op blocker
at all or whether the permission system suffices...

I suppose the rest of this patch is not really about the block layer, so
I can’t really comment on it.  (It looks OK to me from a generic and
naïve standpoint, though.)

>              error_setg(errp, "No top_bs or it is invalid");
>              reopen_backing_file(bs, false, NULL);
>              aio_context_release(aio_context);

[...]

> @@ -593,7 +614,7 @@ static void replication_get_error(ReplicationState *rs, 
> Error **errp)
>      aio_context_acquire(aio_context);
>      s = bs->opaque;
> 
> -    if (s->stage != BLOCK_REPLICATION_RUNNING) {
> +    if (s->stage == BLOCK_REPLICATION_NONE) {

Just one question out of curiosity, though: Is this a bug fix?

Max

>          error_setg(errp, "Block replication is not running");
>          aio_context_release(aio_context);
>          return;

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