Library and tools to create and parse initial ramdisk snapshots.

Description

Initial ramdisks (initrd) provide the capability to load a RAM disk by the boot loader. This RAM disk can then be mounted as the root file system and programs can be run from it. Afterwards, a new root file system can be mounted from a different device. The previous root (from initrd) is then moved to a directory and can be subsequently unmounted.

initrd snapshots are mainly designed to allow system startup to occur in two phases, where the kernel comes up with a minimum set of compiled-in drivers, and where additional modules are loaded from initrd.

This project contains different components, namely :

• A C++11 library initially developped to provide the Microcosm Kernel with the ability to load its root filesystem, though it is not dependant on any of microcosm's software components.
• A set of POSIX tools built on top the library to create and browse initrd images.

Library usage

Creating an image in memory

In order to create an initrd image you can use the image builder that is bundled with the library before writing it to a file :

auto image = initrd::builder_t()
  .addFile({ file: file_1, size: size_of_file_1 })
  .addFile({ file: file_2, size: size_of_file_2 })
  .addFiles(list_of_files)
  .build()

Writing the image to disk

Once the image has been constructed in memory, you can write the image raw data to disk by calling the .data() accessor on the initrd::image_t class :

std::ofstream file("initrd.img", std::ofstream::out);
file.write(image.data(), image.size());

Reading an image from disk

The operation here involves loading an image from the disk, and passing it to initrd::reader_t :

try {
  auto file = read_file("./initrd.img");
  initrd::reader_t reader(file.data(), file.size());
  std::cout << reader.image() << std::endl;
} catch (std::exception& e) {
  std::cout << e.what() << std::endl;
}