# mod_hello


## building

```shell
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

```shell
$> 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:

```shell
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`.

```shell
$> 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`:

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

### cleanup

```shell
make clean
sudo rmmod mod_hello
```