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