Manual Pages  — IEEE8021_AMRR

ieee80211_amrr requires per-vap state and per-node state for each station it is to select rates for. The API's are designed for drivers to pre-allocate state in the driver-private extension areas of each vap and node. For example the ral(4) driver defines a vap as:

struct rt2560_vap {
        struct ieee80211vap     ral_vap;
        struct ieee80211_beacon_offsets ral_bo;
        struct ieee80211_amrr   amrr;

        int      (*ral_newstate)(struct ieee80211vap *,
                      enum ieee80211_state, int);
};

The amrr structure member holds the per-vap state for ieee80211_amrr and ral(4) initializes it in the vap create method with:

ieee80211_amrr_init(&rvp->amrr, vap,
    IEEE80211_AMRR_MIN_SUCCESS_THRESHOLD,
    IEEE80211_AMRR_MAX_SUCCESS_THRESHOLD,
    500 /* ms */);

The node is defined as:

struct rt2560_node {
        struct ieee80211_node   ni;
        struct ieee80211_amrr_node amrr;
};

with initialization done in the driver's iv_newassoc method:

static void
rt2560_newassoc(struct ieee80211_node *ni, int isnew)
{
        struct ieee80211vap *vap = ni->ni_vap;

        ieee80211_amrr_node_init(&RT2560_VAP(vap)->amrr,
            &RT2560_NODE(ni)->amrr, ni);
}

Once ieee80211_amrr state is setup, transmit rates are requested by calling ieee80211_amrr_choose() in the transmit path; e.g.:

tp = &vap->iv_txparms[ieee80211_chan2mode(ni->ni_chan)];
if (IEEE80211_IS_MULTICAST(wh->i_addr1)) {
        rate = tp->mcastrate;
} else if (m0->m_flags & M_EAPOL) {
        rate = tp->mgmtrate;
} else if (tp->ucastrate != IEEE80211_FIXED_RATE_NONE) {
        rate = tp->ucastrate;
} else {
        (void) ieee80211_amrr_choose(ni, &RT2560_NODE(ni)->amrr);
        rate = ni->ni_txrate;
}

Note a rate is chosen only for unicast data frames when a fixed transmit rate is not configured; the other cases are handled with the net80211 transmit parameters. Note also that ieee80211_amrr_choose() writes the chosen rate in ni_txrate; this eliminates copying the value as it is exported to user applications so they can display the current transmit rate in status.

The remaining work a driver must do is feed status back to ieee80211_amrr when a frame transmit completes using ieee80211_amrr_tx_complete(). Drivers that poll a device to retrieve statistics can use ieee80211_amrr_tx_update() (instead or in addition).