tree ff6217d29de9caf9892e7c471f858618bac61d7d
parent 8e8152c5cebfe278086fced75cbc64ecb4b5046b
author Lei YU <yulei.sh@bytedance.com> 1638866440 +0800
committer Vernon Mauery <vernon.mauery@linux.intel.com> 1641948031 +0000

sensor-cache: Invalidate cache when sensor disappears

When a sensor disappears from DBus, invalidate the cache.
Ideally it could be done by adding a match for interfacesRemoved
signal.
However, interfacesRemoved signal is not emitted if a service is
terminated or crashed, so we have to use nameOwnerChanged signal
as well. The `nameOwnerChanged` signal does not provide DBus object's
information, so the code needs to record the relationship between sensor
ids and the services, so that when the event occurs, it knows which
sensors should be invalidated.

Tested: Manually stop virtual-sensor, and verify the related sensors are
        shown as `na` in ipmitool sensor list:

            total_power      | na         |            | na    | na        | na        | na        | na        | na        | na

        Restart virtual-sensor, and verify the related sensors have
        valid readings:

            total_power      | 510.000    | Watts      | ok    | na        | na        | na        | na        | na        | na

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: If145a1cd163477c3aca3fd17f3dbde96263f6b75