# mkgpt: create GPT disk images from partition images

A simple tool for creating disk images with a GPT header and including the
contents of provided partition images.

## How to build

Just say `make` followed by `sudo make install` and you'll most likely be happy.
If you want a compact, statically-linked executable instead, install the `musl`
toolchain of your choice (even the `musl-gcc` wrapper works) and say
`make static` (or `CC=whatever make static`) followed by `sudo make install`
instead.

## How to use

### Program options

- `-o <output_file>`
  specify output filename
- `--sector-size <size>`
  size of a sector (defaults to 512)
- `--minimum-image-size <size>`
  minimum size of the image in sectors (defaults to 2048)
- `--disk-guid <guid>`
  GUID of the entire disk (see GUID format below, defaults to random)
- `--part <file> <options>`
  begin a partition entry containing the specified image as its data and
  options as below

### Partition options

- `--name <name>`
  set the name of the entry in the GPT
- `--type <type>`
  set the type of the entry, either a GUID, numeric MBR-style partition ID, or
  one of the known partition types
- `--uuid <guid>`
  specify the UUID of the partition in the GPT (defaults to a random UUID)

### Known partition types

- EFI system partition: `system`
- BIOS boot partition: `bios`
- FAT types: `fat12`, `fat16`, `fat16b`, `fat32`, `fat16x`, `fat32x`, `fat16+`,
  `fat32+`
- NTFS types: `ntfs`
- Linux types: `linux`, `swap`

### GUID format

GUIDs/UUIDs should be in the canonical representation as per
https://en.wikipedia.org/wiki/Universally_unique_identifier#Format
without any surrounding braces.
An example is:
`123E4567-E89B-12D3-A456-426655440000`
Optionally, the string `random` can be used to generate a random GUID.

## Why fork?

- the original build process seemed bloated for a tool this simple
- no way to create swap partitions (borked GUID parsing)
- some overly specific code (Linux, Windoze) without a strong need for it
- some strange code (static info in oversized, dynamically populated array?)
- some rather broken code (required calls in asserts, misaligned pointers, memory leaks)

## References

Not enough people seem to know about these things, so here you go:

- https://www.drdobbs.com/the-new-c-x-macros/184401387
- https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-1/
- https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-2/
- https://www.embedded.com/reduce-c-language-coding-errors-with-x-macros-part-3/
- http://www.catb.org/esr/structure-packing/
- https://nullprogram.com/blog/2016/11/22/

Here's some background on the whole GPT mess:

- https://en.wikipedia.org/wiki/GUID_Partition_Table
- https://en.wikipedia.org/wiki/BIOS_boot_partition
  (I misunderstood this at first, read if you come from MBR)
- Apple's [Secrets of the GPT](https://developer.apple.com/library/archive/technotes/tn2166/_index.html)
  has some useful background (once you ignore the Apple-rific stuff)
- https://thestarman.pcministry.com/asm/mbr/GPT.htm
  (points out disagreements between Windoze protective MBRs and the UEFI
  specification)

Want to scare yourself?

- https://uefi.org/sites/default/files/resources/UEFI_Spec_2_8_final.pdf
  (enjoy 2,500 pages of dread)

Similar tool with JSON input?

- https://gitlab.com/bztsrc/bootboot/tree/master/mkbootimg