PM handler - deleting lowest ranked peer

RE: PM handler - deleting lowest ranked peer

kchuva — Fri, 14 May 2021 11:23:21 GMT

Hi Einar,

Thanks for answer. Both strategies looks working. I can implement any in my application.

Question 1: is implementation below working model?

// 1) find the lowest ranked peer
pm_peer_id_t peer_id_to_delete;
err_code = pm_peer_ranks_get(NULL, NULL, &peer_id_to_delete, NULL);
if (err_code == NRF_SUCCEESS)
{
    uint16_t handle = BLE_CONN_HANDLE_INVALID;
    err_code = pm_conn_handle_get(peer_id_to_delete, &handle);
    APP_ERROR_CHECK(err_code);
    
    if (handle != BLE_CONN_HANDLE_INVALID)
    {
	    // 2) the lowest ranked peer is currently connected => delete any nonconnected peer
	    peer_id_to_delete = pm_next_peer_id_get(PM_PEER_ID_INVALID);
	    while (peer_id_to_delete != PM_PEER_ID_INVALID)
	    {
		    err_code = pm_conn_handle_get(peer_id_to_delete, &handle);
		    APP_ERROR_CHECK(err_code);
		    if (handle == BLE_CONN_HANDLE_INVALID)
			    break;

		    peer_id_to_delete = pm_next_peer_id_get(peer_id_to_delete);
	    }
    }
    
    // 3) delete finded peer
    if (peer_id_to_delete != PM_PEER_ID_INVALID)
    {
	    err_code = pm_peer_delete(peer_id_to_delete);
	    APP_ERROR_CHECK(err_code);
    }
}

Question 2: will a solution of issue be offered in peer_manager_handler in new version SDK?

Konstantin

RE: PM handler - deleting lowest ranked peer

Einar Thorsrud — Fri, 14 May 2021 09:13:57 GMT

Hi Konstantin,

Yes, this is a possible issue. The probability of it happening is application dependent, and how to best handle this is also application dependent.

If you have a application where you blindly write to FDS without thought of it becoming full or not, then this could happen. I would suggest that you regularly check amount of free FDS space and amount that can be garbage collected. If there is almost no free space left and a lot to garbage collect, simply do garbage collection. If there is almost no free space and nothing to garbage collect, you need to either delete some data or stop writing new data. That way you will never end up in a situation where there is no room to update peer manger ranks.

If the above is not possible, then you should add a check to verify that you never delete the bond of a currently connected peer, as that is as you write not supported and can lead to undefined behavior. Doing this is always a good idea if there is any chance of getting into the situation where you could otherwise delete the bond of a currently connected peer.

Einar