collectd has always been able to grab interface traffic statistics from Linux. But what if we want to collect data about individual WiFi clients that connect to it? How much bandwidth is each of the clients using?
That information is already being recorded by the wireless driver; all we need to do is to query it. Turns out you can do that with the
wl utility. This is Broadcom’s proprietary tool to control and query the wireless interfaces.
To do this, first use
wl to get associated stations:
wl -i eth2 assoclist
Given a particular MAC address that is associated to the AP, query its info using
# wl -i eth2 sta_info d4:a3:00:aa:bb:cc STA d4:a3:00:aa:bb:cc: aid:2 rateset [ 6 9 12 18 24 36 48 54 ] idle 0 seconds in network 16 seconds state: AUTHENTICATED ASSOCIATED AUTHORIZED flags 0x11e03b: BRCM WME N_CAP VHT_CAP AMPDU AMSDU HT caps 0x6f: LDPC 40MHz SGI20 SGI40 VHT caps 0x43: LDPC SGI80 SU-BFE tx data pkts: 663916 tx data bytes: 68730715 tx ucast pkts: 155 tx ucast bytes: 42699 tx mcast/bcast pkts: 663761 tx mcast/bcast bytes: 68688016 tx failures: 0 rx data pkts: 234 rx data bytes: 73557 rx ucast pkts: 192 rx ucast bytes: 62971 rx mcast/bcast pkts: 42 rx mcast/bcast bytes: 10586 rate of last tx pkt: 866667 kbps rate of last rx pkt: 780000 kbps rx decrypt succeeds: 195 rx decrypt failures: 1 tx data pkts retried: 19 tx data pkts retry exhausted: 0 per antenna rssi of last rx data frame: -61 -56 -59 0 per antenna average rssi of rx data frames: -61 -56 -57 0 per antenna noise floor: -104 -98 -98 0
The “easy way” is probably to write a shell script, invoked via the Exec plugin that calls
wl multiple times (once per interface, and once for each WiFi client) and uses
awk to get the information we need. This won’t be performant, of course.
wl itself does have quite a fair bit of overhead. It does some verification of the provided interface name. It checks for the Broadcom driver magic to ensure that the interface is a Broadcom device. It then needs to convert the MAC address from the argument string to binary, and vice-versa. Sure, that’s not really much “these days”, but we can definitely do better.
Instead, let’s short-circuit the process and write a plugin that directly collects the data, without going through
wl. This way, we avoid creating several new processes for every query.