Brief
=====

This component creates a GPT on a Block device. It supports the common
actions, as in adding, deleting and modifying entries in the GPT, while
considering alignment constraints. If needed it will round the length of
a partition down to meet those constraints. The component will not perform
layout checking, i.e., it does not care about overlapping partitions. Only
when apping a partition it will make sure that the partition will fit.

As a temporary limitation it does not handle Block devices with a logical
block size of 4096 or larger well.


Configuration
=============

The component is instructed to manage the GPT by specifying actions.
The actions are:

  * 'add' for adding a new partition. The used entry is set by
    the 'entry' attribute, while the 'start' attributes denotes the
    starting LBA of the partition. If the 'entry' attribute is missing,
    the component operates in append-mode and the next free entry will
    be used, while the component selects a proper start LBA and ignores
    the 'start' attribute. The mandatory 'label', 'size' and 'type'
    attributes must be used to set the corresponding property.

  * 'delete' for removing partitions by clearing the corresponding entry.
    The entry can by selected by using either the 'entry' or 'label'
    attribute.

  * 'modify' for changing properties of an existing entry. The
    entry can be selected by using either the 'entry' or 'label'
    attribute. The 'new_label', 'new_size' and 'new_type' attributes
    may be set to change the corresponding property.

The size-related attributes, 'size' and 'new_size', can take as value
a suffixed number (K, M, G) to interpret the value to the base of 2^10,
2^20 or 2^30. As special treatment it is also possible to use 'max' as
value. In this case the component will try to use all free space between
this partition and the next partition or, for that matter, the end of the
addressable space within the GPT.

The type-related attributes, 'type' and 'new_type', take a identifier,
which selects the proper GUID. Valid identifiers are:

  * 'EFI' for the EFI system partition type
  * 'BIOS' for a BIOS boot partition type (for GRUB to store its core.img)
  * 'BDP' for basic data partition type (Windows/DOS file systems)
  * 'Linux' for a Linux file system data type (Linux file systems)

The label-related attributes, 'label' and 'new_label', take a ASCII string,
i.e., [A-Za-z- *].

There are config node attributes, in addition to the actions, that instruct
the component to perform additional tasks.

To remove the GPT headers as well as the protective MBR the 'wipe'
attribute can be specified:

! <config wipe="yes"/>

In this case 'gpt_write' will only perform the wiping and than exit,
even if other attributes are set or actions specified.

To update the GPT information, in case the underlying Block device has
changed (for example a generated disk image is copied to a larger USB
stick), the 'update_geometry' attribute may be used to increase the
useable space of the GPT:

! <config update_geometry="yes"/>

When updating the geometry, setting the 'preserve_hybrid' attribute to 'yes'
will prevent the component from overriding a hybrid MBR with a proper
protective MBR.

Setting the 'initialize' attribute will instruct the component to clear
any existing GPT/PMBR.

! <config initialize="yes"/>

The alignment of partitions can by specified by setting the 'align'
attribute. It defaults to '4096' if not set.

These attributes can be freely mixed, considering the constraint of
using 'wipe'.

The following snippet shows a examplary configuration:

! <config initialize="yes" align="4K">
!  <actions>
!   <add entry="1" type="BIOS"  label="GRUB BIOS"  start="2048"  size="1M"/>
!   <add entry="2" type="EFI"   label="EFI System" start="4096"  size="16M"/>
!   <add entry="3" type="Linux" label="Genode"     start="36864" size="32G"/>
!   <add           type="BDP"   label="FAT32 Data" size="1G"/>
!
!   <delete entry="1"/>
!   <delete label="FAT32 Data"/>
!
!   <modify label="Genode" new_label="GENODE*" new_size="max"/>
!  </actions>

