# 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

Running ioctl's inside containers is a little tricky.
Assuming we've already `insmod` the module above:

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

You'll get a failure `Could not open /dev/helloctl`

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

Now `dmesg | tail` will reflect the command ran successfully.

### cleanup

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