ramdisk

An experimental/teaching project to create a linux block driver kernel module for a ramdisk - reimplementing brd.

This is a kernel module that implements an in-memory blockstore, as a device /dev/ramdisk. The device is 100Mb in size.

The project is based on Oleg Kutkov's article from 2020 - Linux block device driver.

The Linux block device API varies over different versions of the kernel, please see the following table for the branch which is compatible given your distro:

Linux Distribution	Version	Linux Kernel	Branch
Ubuntu	22.04 LTS	5.15.0-91-generic	linux-5.15.x
Ubuntu	22.04 LTS	6.2.0-39-generic	linux-6.2.x
Alpine	3.19.0	6.6.7-0-lts	linux-6.2.x
Raspberry Pi OS	Debian GNU/Linux 11	6.1.21-v8+	linux-6.1.x
Fedora	39	6.5.6-300.fc39.x86_64	linux-6.2.x

These branches have been tested only with the specific distros and kernels. If your distro isn't listed, use the branch closest to your Linux kernel version - you can get the linux kernel version of your distro with the following:

uname -r

It is my hope this might be useful as a starting point if you're writing your own block devices.

Status

ramdisk has been tested working in Jan 2024 on the platforms and kernels above, and can be considered BETA.

Build tools, linux headers, kernel module tools

Please follow the build instructions for your distro.

Example Usage

These commands should show the device at /dev/ramdisk, format the ramdisk for ext4, create a mount directoy /rdtest and then mount the ramdisk at that mountpoint. The last lsblk will show the ramdisk mounted at that path.

make load
lsblk -l
mkfs.ext4 /dev/ramdisk
mkdir /rdtest
mount /dev/ramdisk /rdtest
lsblk -f

Benchmark

You can measure the peformance of the ramdisk with dd. This assumes you mounted it at /rdtest as above:

dd if=/dev/zero of=/rdtest/testfile bs=1M count=50 oflag=direct

License

ramdisk is licensed under the GNU General Public License v3. Please see LICENSE.