mod_hello

building

make all

This produces ./helloctl/helloctl binary for talking to the mod_hello over ioctl through /dev/helloctl, as well as ./mod_hello.ko kernel module itself.

Testing

Host

$> make build
$> sudo insmod ./mod_hello.ko
$> sudo dmesg | tail
[ 1679.566426] [mod_hello] pid: 8418, comm: insmod
[ 1679.566427] [mod_hello] module loaded.
[ 1679.566428] [mod_hello] looking up 'files'
[ 1679.574011] [mod_hello] files 0xffffffff87e57e40
[ 1679.574013] [mod_hello] files (0xffffffff87e57e40): usage
[ 1679.579120] [mod_hello] fib of 0 and 1 (up to 10000000): 8644293272739028509 (in only 5 jiffies)
$> sudo ./helloctl/helloctl
$> sudo dmesg | tail -1
[ 1734.248270] [mod_hello] received command: 1

Container

Assuming we've already insmod the module above:

sudo docker run -it --rm -v $(pwd)/helloctl/helloctl:/usr/bin/helloctl:ro --device /dev/helloctl fedora /usr/bin/helloctl

Now dmesg | tail will reflect the command ran successfully, but at the sake of running an non-isolated container.

runc

Determining major/minor for setting permissions requires inserting the module, then collecting the major/minor device, and putting that to a runc config.json.

$> stat -c "%t %T" /dev/helloctl
a 39
$> echo "$((16#$(stat -c "%t" /dev/helloctl )))"
10
$> echo "$((16#$(stat -c "%T" /dev/helloctl )))"
57

Now in the config.json, under linux.resources.devices, that array, it needs the following with the major/minor integers from your /dev/helloctl:

        {
          "allow": true,
          "type": "c",
          "major": 10,
          "minor": 57,
          "access": "rwm"
        },

cleanup

make clean
sudo rmmod mod_hello