Query regarding controlling phosphor-networkd Dbus "InteraceAdded" and "InterfaceRemoved" signals

[Pankaj.Patil at vertiv.com]

Query regarding phosphor-networkd:

With the openbmc version 2.18, I have written a custom software module that registers a callback to monitor the Dbus interface signals: "InterfacesAdded" and "InterfacesRemoved" from the phosphor-networkd.
I tried switching my ethernet interface eth0 on AST2600 SoC from DHCP to Static IP.

I could assign static IP successfully to eth0 interface and DHCP IP resource is released. But, I have several observations:

  1.  I see "InterfaceAdded" Dbus signal emitted first from the phosphor-network for DHCP->Static transition. I believe it represents a creation of a dbus static IP object, interface, and properties.
  2.  Followed with it, "InterfaceRemoved" signal is emitted from the phosphor-network that deletes existing DHCP IP object.
  3.  In the signal callback handlers, I have a custom implementation that consists of a mutex lock for my database that is acquired when the "InterfaceRemoved" signal is received and same lock is released when "InterfaceAdded" signal is received. Additionally, I did several database updates based on the signal received.

Now, I see an issue where this database lock is always acquired after DHCP->Static transition. Additionally, some of the database properties are corrupted. After root cause analysis for both the issues, i concluded that it is due to the order of the signals mentioned in point 1 and 2. Consistently, I see a similar order of the signals from phosphor-network i.e. "InterfacAdded" first followed by "InterfaceRemoved"

I want to understand if there is a mechanism to control this order of the "InterfaceAdded" and "InterfaceRemoved" signals from phosphor-network to achieve consistent behavior align to my expectations. My expectation in this case is "IntefaceRemoved" shall always be emitted first and then "InterfaceAdded".

Thanks,
Pankaj Patil
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