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Expose data for custom boot image creation #535

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4ac2ce8
extract fat-partition creation into separate pub fn
Wasabi375 Jan 22, 2026
76a4cd7
mark bootloader images as pub
Wasabi375 Jan 22, 2026
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78 changes: 54 additions & 24 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -42,15 +42,20 @@ const RAMDISK_FILE_NAME: &str = "ramdisk";
const CONFIG_FILE_NAME: &str = "boot.json";

#[cfg(feature = "uefi")]
const UEFI_BOOTLOADER: &[u8] = include_bytes!(env!("UEFI_BOOTLOADER_PATH"));
/// The byte data of the UEFI bootloader
pub const UEFI_BOOTLOADER: &[u8] = include_bytes!(env!("UEFI_BOOTLOADER_PATH"));
#[cfg(feature = "bios")]
const BIOS_BOOT_SECTOR: &[u8] = include_bytes!(env!("BIOS_BOOT_SECTOR_PATH"));
/// The byte data of the BIOS boot sector
pub const BIOS_BOOT_SECTOR: &[u8] = include_bytes!(env!("BIOS_BOOT_SECTOR_PATH"));
#[cfg(feature = "bios")]
const BIOS_STAGE_2: &[u8] = include_bytes!(env!("BIOS_STAGE_2_PATH"));
/// The byte data of the second stage of the BIOS bootloader
pub const BIOS_STAGE_2: &[u8] = include_bytes!(env!("BIOS_STAGE_2_PATH"));
#[cfg(feature = "bios")]
const BIOS_STAGE_3: &[u8] = include_bytes!(env!("BIOS_STAGE_3_PATH"));
/// The byte data of the third stage of the BIOS bootloader
pub const BIOS_STAGE_3: &[u8] = include_bytes!(env!("BIOS_STAGE_3_PATH"));
#[cfg(feature = "bios")]
const BIOS_STAGE_4: &[u8] = include_bytes!(env!("BIOS_STAGE_4_PATH"));
/// The byte data of the fourth stage of the BIOS bootloader
pub const BIOS_STAGE_4: &[u8] = include_bytes!(env!("BIOS_STAGE_4_PATH"));
Comment on lines +48 to +58
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@Freax13 Freax13 Feb 1, 2026

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Are there use-cases where it's useful to have access to the raw stages?

I'm a bit worried about forward-compatibility here: If we ever decide to change number of stages or decide to change what each stage does, this will cause problems for users that directly use these constants.

I don't have this concern for the UEFI bootloader because it's just a single binary and I'm guessing that that's less likely to change.


/// Allows creating disk images for a specified set of files.
///
Expand Down Expand Up @@ -109,16 +114,11 @@ impl DiskImageBuilder {
#[cfg(feature = "bios")]
/// Create an MBR disk image for booting on BIOS systems.
pub fn create_bios_image(&self, image_path: &Path) -> anyhow::Result<()> {
const BIOS_STAGE_3_NAME: &str = "boot-stage-3";
const BIOS_STAGE_4_NAME: &str = "boot-stage-4";
let stage_3 = FileDataSource::Bytes(BIOS_STAGE_3);
let stage_4 = FileDataSource::Bytes(BIOS_STAGE_4);
let mut internal_files = BTreeMap::new();
internal_files.insert(BIOS_STAGE_3_NAME, stage_3);
internal_files.insert(BIOS_STAGE_4_NAME, stage_4);
let fat_partition = self
.create_fat_filesystem_image(internal_files)
let fat_partition = NamedTempFile::new().context("failed to create temp file")?;

self.create_bios_fat_partition(fat_partition.path())
.context("failed to create FAT partition")?;

mbr::create_mbr_disk(
BIOS_BOOT_SECTOR,
BIOS_STAGE_2,
Expand All @@ -133,16 +133,33 @@ impl DiskImageBuilder {
Ok(())
}

#[cfg(feature = "bios")]
/// create a bootable fat-partition for a BIOS system.
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@Freax13 Freax13 Feb 1, 2026

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Suggested change
/// create a bootable fat-partition for a BIOS system.
/// Create a bootable fat-partition for a BIOS system.

///
/// Note that for the partition to work as a boot-partition [BIOS_BOOT_SECTOR] and [BIOS_STAGE_2]
/// have to be properly loaded into the MBR disk image.
pub fn create_bios_fat_partition(&self, partition_path: &Path) -> anyhow::Result<()> {
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@Freax13 Freax13 Feb 1, 2026 •
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How is this intended to be used without calling create_bios_image? Do we expect users to figure out themselves how to build the MBR?

const BIOS_STAGE_3_NAME: &str = "boot-stage-3";
const BIOS_STAGE_4_NAME: &str = "boot-stage-4";
let stage_3 = FileDataSource::Bytes(BIOS_STAGE_3);
let stage_4 = FileDataSource::Bytes(BIOS_STAGE_4);
let mut internal_files = BTreeMap::new();
internal_files.insert(BIOS_STAGE_3_NAME, stage_3);
internal_files.insert(BIOS_STAGE_4_NAME, stage_4);

self.create_fat_filesystem_image(internal_files, partition_path)
.context("failed to create FAT partition")?;

Ok(())
}

#[cfg(feature = "uefi")]
/// Create a GPT disk image for booting on UEFI systems.
pub fn create_uefi_image(&self, image_path: &Path) -> anyhow::Result<()> {
const UEFI_BOOT_FILENAME: &str = "efi/boot/bootx64.efi";

let mut internal_files = BTreeMap::new();
internal_files.insert(UEFI_BOOT_FILENAME, FileDataSource::Bytes(UEFI_BOOTLOADER));
let fat_partition = self
.create_fat_filesystem_image(internal_files)
let fat_partition = NamedTempFile::new().context("failed to create temp file")?;
self.create_uefi_fat_partition(fat_partition.path())
.context("failed to create FAT partition")?;

gpt::create_gpt_disk(fat_partition.path(), image_path)
.context("failed to create UEFI GPT disk image")?;
fat_partition
Expand All @@ -152,6 +169,19 @@ impl DiskImageBuilder {
Ok(())
}

#[cfg(feature = "uefi")]
/// create a bootable fat-partition for a UEFI system.
pub fn create_uefi_fat_partition(&self, partition_path: &Path) -> anyhow::Result<()> {
const UEFI_BOOT_FILENAME: &str = "efi/boot/bootx64.efi";

let mut internal_files = BTreeMap::new();
internal_files.insert(UEFI_BOOT_FILENAME, FileDataSource::Bytes(UEFI_BOOTLOADER));
self.create_fat_filesystem_image(internal_files, partition_path)
.context("failed to create FAT partition")?;

Ok(())
}

#[cfg(feature = "uefi")]
/// Create a folder containing the needed files for UEFI TFTP/PXE booting.
pub fn create_uefi_tftp_folder(&self, tftp_path: &Path) -> anyhow::Result<()> {
Expand Down Expand Up @@ -198,7 +228,8 @@ impl DiskImageBuilder {
fn create_fat_filesystem_image(
&self,
internal_files: BTreeMap<&str, FileDataSource>,
) -> anyhow::Result<NamedTempFile> {
partition_path: &Path,
) -> anyhow::Result<()> {
let mut local_map: BTreeMap<&str, _> = BTreeMap::new();

for (name, source) in &self.files {
Expand All @@ -214,10 +245,9 @@ impl DiskImageBuilder {
}
}

let out_file = NamedTempFile::new().context("failed to create temp file")?;
fat::create_fat_filesystem(local_map, out_file.path())
fat::create_fat_filesystem(local_map, partition_path)
.context("failed to create FAT filesystem")?;

Ok(out_file)
Ok(())
}
}
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