Network statistics unavailable for interfaces after switching network namespace on Linux

[rvql]

Describe the bug
I'm using sysinfo 0.26 on CentOS 7.

Sysinfo is reading /sys/class/net for interface list, but setting network namespace will not refresh sysfs, making it impossible for sysinfo to read statistics for interfaces in the new namespace.

To Reproduce

The code:

use sysinfo::{System, SystemExt, NetworksExt};

fn main() {
    let mut system = System::new();
    system.refresh_networks_list();
    system.networks().iter().for_each(|(s, _)| println!("{}", s));
}

Compile this code as netns and run it under CentOS 7:

[root@mars-1 ~]# ip netns add test
[root@mars-1 ~]# nsenter --net=/var/run/netns/test ip a
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: tunl0@NONE: <NOARP> mtu 1480 qdisc noop state DOWN group default qlen 1000
    link/ipip 0.0.0.0 brd 0.0.0.0
[root@mars-1 ~]# nsenter --net=/var/run/netns/test ./netns
cali90f3eb8a8da
calif27411bfc29
cali31894e8eb51
cali05f070dffe3
calia118c7520e3
lo
cali577f4fcaaf9
tunl0
... (more)

A possible fix is to use netlink to retrieve interface statistics.

[GuillaumeGomez]

Thanks for the bug report! I'll need to check how netlink works, might take some time.