[ovs-dev] [PATCH 1/2] monitor: Fix bad caching of conditional monitor_cond requests.

[Andy Zhou]

On Wed, Aug 30, 2017 at 9:33 AM, Ben Pfaff <blp at ovn.org> wrote:
> The current implementation of ovsdb-server caches only non-conditional
> monitors, that is, monitors for every table row, not those that monitor
> only rows that match some condition.  To figure out which monitors are
> conditional, the code track the number of tables that have conditions that
> are uniformly true (cond->n_true_cnd) and compares that against the number
> of tables in the condition (shash_count(&cond->tables)).  If they are the
> same, then every table has (effectively) no condition, and so
> cond->conditional is set to false.
>
> However, the implementation was buggy.  The function that adds a new
> table condition, ovsdb_monitor_table_condition_create(), only updated
> cond->conditional if the table condition being added was true.  This is
> wrong; only adding a non-true condition can actually change
> cond->conditional.  This commit fixes the problem by always recalculating
> cond->conditional.
>
> The most visible side effect of cond->conditional being true when it
> should be false, as caused by this bug, was that conditional monitors were
> being mixed with unconditional monitors for the purpose of caching.  This
> meant that, if a client requested a conditional monitor that was the
> same as an unconditional one, except for the condition, then the client
> would receive the cached data previously sent for the unconditional one.
> This commit fixes the problem.
>
> Signed-off-by: Ben Pfaff <blp at ovn.org>

I think the first paragraph of the commit message can be useful as comments
in the code as well.

Acked-by: Andy Zhou <azhou at ovn.org>