settings: settings_save_one() doesn't always seem to store data, even if it returns success

[jhedberg]

I have the following configuration:

• tests/bluetooth/shell
• BOARD=nrf52840_mdk

I was playing around with adding and removing identities, and noticed that deleting identities didn't work. On the settings level this maps to the keys bt/id and bt/irk. First one is multiples of seven bytes (sizeof(bt_addr_le_t)) and the second is multiples of 16 bytes (sizeof(IRK)).

What it looks like is that if the new value for key is bigger than the previous value then it gets stored and later recovered (through settings_load) just fine, however if the new value is smaller than the previous (e.g. the identity deletion case) then the new value is not stored. I also noticed that I could work around this by inserting an "empty" entry before the next one, e.g. calling settings_save_one(NULL, 0) before the actual value.

[jhedberg]

I've used this commit to help debug the issue with the tests/bluetooth/shell app:
jhedberg@4389131

With that, you should be able to see the issue by performing the following operations in the shell:

bt init
bt id-show
bt id-create
bt id-show
(power-cycle your board)
bt init
bt id-show
bt id-delete 1
bt id-show
(power-cycle your board)
bt init
bt id-show