mod-webserver

Stub webserver in kernel, that always send you HTTP/1.1 200 OK response with body PONG Server listens to TCP port 2000 on all interfaces (currently this is hardcoded)

Building & using module

Linux version

Tested Linux kernel version is v6.4.11

Using make

# build for host system
make KSRC=/lib/modules/$(uname -r)/build

# load module
insmod mod-webserver.ko [host=127.0.0.1] [port=2000]

# unload module
rmmod mod-webserver.ko

# clean up
make KSRC=/lib/modules/$(uname -r)/build clean

Using DKMS

cd mod-webserver

# add module source to /usr/src tree
dkms add $(pwd)

# build & install module to /lib/modules/$(uname -r) tree
dkms install mod-webserver/1.0

# load module
modprobe -v mod-webserver

# unload module
rmmod mod-webserver

# remove it from DKMS tree
dkms remove mod-webserver/1.0 --all

Using module

After loading module creates path in /sys/kernel only. To start a webserver in current net ns, you need to write 1 in /sys/kernel/webserver/net/data/status path. To start a webserver in new/exitsting net ns, you should enter this ns, mount sysfs and write 1 in /sys/kernel/webserver/net/data/status. To disable webserver in current net ns, you need to write 0 in /sys/kernel/webserver/net/data/status path. Disabling webserver in one ns shouldn't somehow affect webservers in other net namespaces. Disabling webserver shouldn't affect sysfs and especially /sys/kernel/webserver created by module. By entering new net ns (unshare -t net sh) and mounting sysfs (mount -t sysfs sysfs /mnt) you can run multiple instances of webserver on a single host Don't forget to check if localhost is working in this net ns using ip a Otherwise you have to up this interface by following commands: ip addr add 127.0.0.1/8 dev lo && ip link set dev lo up Removing module leads to stopping webservers in all net ns. Removing module removes /sys/kernel/webserver - and this is the only way to remove it.

Developing module

Test cases

Test cases are keywords-like scenarios for testing webserver's functionality and also a kind of documentation (see tests as docs concept)

Essential

we can load module without kernel oops
we can remove module without kernel oops

Basic usage

we can load module without kernel oops
adding module leads to creation /sys/kernel/webserver
echo 1 > /sys/kernel/webserver... leads to enabling webserver (nc localhost 2000 return message)
echo 123 > /sys/kernel/webserver... (or any data except 1 or 0) returns error and doesn't affect webserver
echo 0 > /sys/kernel/webserver... leads to disabling webserver (nc localhost 2000 return nothing)
we can remove module without kernel oops

Multiple net NS usage

we can load module without kernel oops
adding module leads to creation /sys/kernel/webserver
echo 1 > /sys/kernel/webserver... leads to enabling webserver (nc localhost 2000 return message)
entering net ns (unshare -t net sh) leads to non-working webserver in this ns and doesn't generate kernel oops
mounting sysfs (mount -t sysfs sysfs /mnt) doesn't generate kernel oops
echo 1 > /mnt/sysfs/webserver... (mounted sysfs) leads to enabling webserver (nc localhost 2000 return message)
echo 0 > /mnt/sysfs/webserver... (mounted sysfs) leads to disabling webserver (nc localhost 2000 return nothing)
returning to old net ns (^D) leads to still working webserver (nc localhost 2000 return message)
we can remove module without kernel oops

Custom host/port

we can load module with custom params (host/port) without kernel oops
echo 1 > /sys/kernel/webserver... leads to enabling webserver (nc ... return message)
echo 0 > /sys/kernel/webserver... leads to disabling webserver (nc ... return nothing)
we can remove module with custom params without kernel oops

ansavin/mod-webserver