Add Meter Choice framework

[cgzones]

Add the possibility for meters to have selectable choices, so they can display more exact information the user is interested in.

As examples the following meters are added:

• Hostname: show the IP address based on the selected network interface
• DiskUsage: show the space utilization based on the selected mountpoint
• NetworkIO: show the IO usage based on the selected network interface
• LibSensorsFan: show the speed based on the selected libsensors provided sensor
• LibSensorsTemp: show the temperature based on the selected libsensors provided sensor

Data is only available on Linux for now.

[BenBE]

Not tested, but does this list all local IP addresses, or does it select one? Like: Waht happens on a multihomed system with e.g. LAN+wireless+VPN?

[cgzones]

Only the the first (whatever the kernel decides to be first) non-loopback link-local IP address is displayed.

Maybe in the future Meters can have runtime options, which can be set per enabled-meter (like display-mode). Than one can select which IP to display.

[BenBE]

$ ip a s
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    inet 10.116.112.196/24 brd 10.116.112.255 scope global dynamic noprefixroute eth0
    inet6 fe80::fedc:ba98:7654:3210/64 scope link noprefixroute 
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    inet 10.116.128.196/17 brd 10.116.255.255 scope global dynamic noprefixroute wlan0
    inet6 2a07:1:9:6:7:7:5:e/64 scope global temporary dynamic 
    inet6 2a07:1:9:6:e:0:a:f/64 scope global dynamic mngtmpaddr noprefixroute 
    inet6 fc00::4242:9:a:1:a/64 scope global temporary dynamic 
    inet6 fc00::4242:8:7:e:4/64 scope global dynamic mngtmpaddr noprefixroute 
    inet6 fe80::e:a:6:2/64 scope link noprefixroute 
4: br-lxc: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000
    inet 192.168.254.1/24 brd 192.168.254.255 scope global br-lxc
    inet6 fe80::c000:8000:4000:23/64 scope link 
5: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
7: lxcbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    inet 10.0.3.1/24 scope global lxcbr0

$ ip r s
default via 10.116.112.254 dev eth0 proto dhcp metric 100 
default via 10.116.128.6 dev wlan0 proto dhcp metric 600 
10.0.3.0/24 dev lxcbr0 proto kernel scope link src 10.0.3.1 linkdown 
10.116.112.0/24 dev eth0 proto kernel scope link src 10.116.112.196 metric 100 
10.116.128.0/17 dev wlan0 proto kernel scope link src 10.116.128.196 metric 600 
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown 
192.168.254.0/24 dev br-lxc proto kernel scope link src 192.168.254.1 

$ ip -6 r s
::1 dev lo proto kernel metric 256 pref medium
2a07:1:9:6::/64 dev wlan0 proto ra metric 600 pref medium
fc00:0:0:4242::/64 dev wlan0 proto ra metric 600 pref medium
fe80::/64 dev eth0 proto kernel metric 100 pref medium
fe80::/64 dev br-lxc proto kernel metric 256 pref medium
fe80::/64 dev wlan0 proto kernel metric 600 pref medium
default via fe80::cafe:beef:beef:1 dev wlan0 proto ra metric 600 pref medium

Expected behaviour: IPv4: 10.116.112.196 (Default with lowest metric) IPv6: 2a07:1:9:6:e:0:a:f (Routable global network address on default-routed interface)

While fc00::4242:8:7:e:4 would be correct too, it's an ULA, and thus not globally routable.

For the difference between dynamic mngtmpaddr noprefixroute and temporary dynamic see the docs ;-)

[ghost]

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[BenBE]

Please fix the compilation issues that the CI complains about …

[BenBE]

Testing the Disk Usage meter the UX is not the best. Especially as it does not filter /snap, /run and several other memory FS. Furthermore the UI hangs if the filesystem is not reachable (e.g. with CIFS).

For the Hostname meter I'd like to have a combined Host IPv4/IPv6 meter to reduce information duplication. Or just have a blank IP address meter.

[BenBE]

Wondering if choices should have a preferred sorting order (either enforced by the "choice provider" or by the "meter framework".