Crate atags

This is based on https://www.simtec.co.uk/products/SWLINUX/files/booting_article.html#appendix_tag_reference. Please open a pull request for missing tags.

To get started with this crate, create a Atags struct with a given memory position. The iter() method will return an iterator that returns Atag entries.

use atags::{Atag, Atags};

let mut buffer = [
    // Core tag
    0x00, 0x00, 0x00, 0x05, // size
    0x54, 0x41, 0x00, 0x01, // tag
    0x00, 0x00, 0x00, 0x01, //  flags
    0x00, 0x00, 0x10, 0x00, //  page_size
    0x12, 0x34, 0x56, 0x78, //  root_device_number

    // Empty tag
    0x0, 0x0, 0x0, 0x0, // size
    0x0, 0x0, 0x0, 0x0, // tag
];
let ptr = core::ptr::NonNull::new(buffer.as_mut_ptr()).unwrap();
let tags = unsafe { Atags::new(ptr.cast()) };

for tag in tags.iter() {
    // first tag is a core tag
    match tag {
        Atag::Core(core) => {
            assert_eq!(core.flags, 1);
            assert_eq!(core.page_size, 0x1000);
            assert_eq!(core.root_device_number, 0x12345678);
        },
        // Do something with the other tags
        // In this example we only get 1 core tag and nothing else
        _ => panic!("Unknown tag {:?}", tag),
    }
}

Features

nightly

Will enable the nightly strict_provenance feature in this crate.

• Core docs
• Tracking issue

Structs

AtagCore

This tag must be used to start the list, it contains the basic information any bootloader must pass.

AtagHeader

A raw headera. Used for debugging.

AtagInitRd2

Location of a compressed ramdisk image, usually combined with an AtagRamDisk. Can be used as an initial root file system with the addition of a command line parameter of ‘root=/dev/ram’. This tag supersedes the original ATAG_INITRD which used virtual addressing, this was a mistake and produced issues on some systems. All new bootloaders should use this tag in preference.

AtagIter

Iterator returned from Atags. Yields Atag entries.

AtagMemory

Describes an area of physical memory the kernel is to use.

AtagRamDisk

Describes how the (initial) ramdisk will be configured by the kernel, specifically this allows for the bootloader to ensure the ramdisk will be large enough to take the decompressed initial ramdisk image the bootloader is passing using AtagInitRd2

AtagRevision

Tag for the board revision

AtagSerial

Tag with 64 bit serial number of the board

AtagVideoLfb

Tag describing parameters for a framebuffer type display

AtagVideoText

Tag used to describe VGA text type displays.

Atags

Handler that points to a memory location that holds the tag definitions.

Enums

Atag

Determines which tag is in the given memory region.