Simplified implementation of callback logic for slightly better redability.

1. Avoiding use of too many if..else if..else constructs.
2. Returning/breaking on errors to make it easier to read.
3. Sticking to using LOG_LEVEL style tags everywhere.

Bug: 304826859
Test: m -j $(nproc)
Change-Id: Ie70bfd84f2d82c0ff98c2259814302d4ab354aad