grub-dev: Finding your way around
3 Finding your way around
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Here is a brief map of the GRUB code base.
GRUB uses Autoconf and Automake, with most of the Automake input
generated by a Python script. The top-level build rules are in
'configure.ac', 'grub-core/Makefile.core.def', and 'Makefile.util.def'.
Each block in a '*.def' file represents a build target, and specifies
the source files used to build it on various platforms. The '*.def'
files are processed into Automake input by 'gentpl.py' (which you only
need to look at if you are extending the build system). If you are
adding a new module which follows an existing pattern, such as a new
command or a new filesystem implementation, it is usually easiest to
grep 'grub-core/Makefile.core.def' and 'Makefile.util.def' for an
existing example of that pattern to find out where it should be added.
In general, code that may be run at boot time is in a subdirectory of
'grub-core', while code that is only run from within a full operating
system is in a subdirectory of the top level.
Low-level boot code, such as the MBR implementation on PC BIOS
systems, is in the 'grub-core/boot/' directory.
The GRUB kernel is in 'grub-core/kern/'. This contains core
facilities such as the device, disk, and file frameworks, environment
variable handling, list processing, and so on. The kernel should
contain enough to get up to a rescue prompt. Header files for kernel
facilities, among others, are in 'include/'.
Terminal implementations are in 'grub-core/term/'.
Disk access code is spread across 'grub-core/disk/' (for accessing
the disk devices themselves), 'grub-core/partmap/' (for interpreting
partition table data), and 'grub-core/fs/' (for accessing filesystems).
Note that, with the odd specialised exception, GRUB only contains code
to _read_ from filesystems and tries to avoid containing any code to
_write_ to filesystems; this lets us confidently assure users that GRUB
cannot be responsible for filesystem corruption.
PCI and USB bus handling is in 'grub-core/bus/'.
Video handling code is in 'grub-core/video/'. The graphical menu
system uses this heavily, but is in a separate directory,
'grub-core/gfxmenu/'.
Most commands are implemented by files in 'grub-core/commands/', with
the following exceptions:
* A few core commands live in 'grub-core/kern/corecmd.c'.
* Commands related to normal mode live under 'grub-core/normal/'.
* Commands that load and boot kernels live under 'grub-core/loader/'.
* The 'loopback' command is really a disk device, and so lives in
'grub-core/disk/loopback.c'.
* The 'gettext' command lives under 'grub-core/gettext/'.
* The 'loadfont' and 'lsfonts' commands live under 'grub-core/font/'.
* The 'serial', 'terminfo', and 'background_image' commands live
under 'grub-core/term/'.
* The 'efiemu_*' commands live under 'grub-core/efiemu/'.
* OS-dependent code should be under 'grub-core/osdep/'
* Utility programs meant to be run from a full operating system
(except OS-dependent code mentioned previously) are in 'util/'.
There are a few other special-purpose exceptions; grep for them if
they matter to you.
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