mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-19 11:18:28 +00:00
39206382de
Changes: - randomly generate partition uuid if any is undefined and CONFIG_RAND_UUID is defined - print debug info about set/unset/generated uuid - update doc/README.gpt Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com> Acked-by: Lukasz Majewski <l.majewski@samsung.com> Cc: Piotr Wilczek <p.wilczek@samsung.com> Cc: Tom Rini <trini@ti.com> Cc: Stephen Warren <swarren@nvidia.com> Cc: Lukasz Majewski <l.majewski@samsung.com>
190 lines
7 KiB
Text
190 lines
7 KiB
Text
#
|
|
# Copyright (C) 2012 Samsung Electronics
|
|
#
|
|
# Lukasz Majewski <l.majewski@samsung.com>
|
|
#
|
|
#
|
|
# SPDX-License-Identifier: GPL-2.0+
|
|
|
|
Glossary:
|
|
========
|
|
- UUID -(Universally Unique Identifier)
|
|
- GUID - (Globally Unique ID)
|
|
- EFI - (Extensible Firmware Interface)
|
|
- UEFI - (Unified EFI) - EFI evolution
|
|
- GPT (GUID Partition Table) - it is the EFI standard part
|
|
- partitions - lists of available partitions (defined at u-boot):
|
|
./include/configs/{target}.h
|
|
|
|
Introduction:
|
|
=============
|
|
This document describes the GPT partition table format and usage of
|
|
the gpt command in u-boot.
|
|
|
|
UUID introduction:
|
|
====================
|
|
|
|
GPT for marking disks/partitions is using the UUID. It is supposed to be a
|
|
globally unique value. A UUID is a 16-byte (128-bit) number. The number of
|
|
theoretically possible UUIDs is therefore about 3 x 10^38.
|
|
More often UUID is displayed as 32 hexadecimal digits, in 5 groups,
|
|
separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters
|
|
(32 digits and 4 hyphens)
|
|
|
|
For instance, GUID of Linux data partition: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
|
|
|
|
Historically there are 5 methods to generate this number. The oldest one is
|
|
combining machine's MAC address and timer (epoch) value.
|
|
|
|
Successive versions are using MD5 hash, random numbers and SHA-1 hash. All major
|
|
OSes and programming languages are providing libraries to compute UUID (e.g.
|
|
uuid command line tool).
|
|
|
|
GPT brief explanation:
|
|
======================
|
|
|
|
Layout:
|
|
-------
|
|
|
|
--------------------------------------------------
|
|
LBA 0 |Protective MBR |
|
|
----------------------------------------------------------
|
|
LBA 1 |Primary GPT Header | Primary
|
|
-------------------------------------------------- GPT
|
|
LBA 2 |Entry 1|Entry 2| Entry 3| Entry 4|
|
|
--------------------------------------------------
|
|
LBA 3 |Entries 5 - 128 |
|
|
| |
|
|
| |
|
|
----------------------------------------------------------
|
|
LBA 34 |Partition 1 |
|
|
| |
|
|
-----------------------------------
|
|
|Partition 2 |
|
|
| |
|
|
-----------------------------------
|
|
|Partition n |
|
|
| |
|
|
----------------------------------------------------------
|
|
LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Secondary
|
|
-------------------------------------------------- (bkp)
|
|
LBA -33 |Entries 5 - 128 | GPT
|
|
| |
|
|
| |
|
|
LBA -2 | |
|
|
--------------------------------------------------
|
|
LBA -1 |Secondary GPT Header |
|
|
----------------------------------------------------------
|
|
|
|
For a legacy reasons, GPT's LBA 0 sector has a MBR structure. It is called
|
|
"protective MBR".
|
|
Its first partition entry ID has 0xEE value, and disk software, which is not
|
|
handling the GPT sees it as a storage device without free space.
|
|
|
|
It is possible to define 128 linearly placed partition entries.
|
|
|
|
"LBA -1" means the last addressable block (in the mmc subsystem:
|
|
"dev_desc->lba - 1")
|
|
|
|
Primary/Secondary GPT header:
|
|
----------------------------
|
|
Offset Size Description
|
|
|
|
0 8 B Signature ("EFI PART", 45 46 49 20 50 41 52 54)
|
|
8 4 B Revision (For version 1.0, the value is 00 00 01 00)
|
|
12 4 B Header size (in bytes, usually 5C 00 00 00 meaning 92 bytes)
|
|
16 4 B CRC32 of header (0 to header size), with this field zeroed
|
|
during calculation
|
|
20 4 B Reserved (ZERO);
|
|
24 8 B Current LBA (location of this header copy)
|
|
32 8 B Backup LBA (location of the other header copy)
|
|
40 8 B First usable LBA for partitions (primary partition table last
|
|
LBA + 1)
|
|
48 8 B Last usable LBA (secondary partition table first LBA - 1)
|
|
56 16 B Disk GUID (also referred as UUID on UNIXes)
|
|
72 8 B Partition entries starting LBA (always 2 in primary copy)
|
|
80 4 B Number of partition entries
|
|
84 4 B Size of a partition entry (usually 128)
|
|
88 4 B CRC32 of partition array
|
|
92 * Reserved; must be ZERO (420 bytes for a 512-byte LBA)
|
|
|
|
TOTAL: 512 B
|
|
|
|
|
|
IMPORTANT:
|
|
|
|
GPT headers and partition entries are protected by CRC32 (the POSIX CRC32).
|
|
|
|
Primary GPT header and Secondary GPT header have swapped values of "Current LBA"
|
|
and "Backup LBA" and therefore different CRC32 check-sum.
|
|
|
|
CRC32 for GPT headers (field "CRC of header") are calculated up till
|
|
"Header size" (92), NOT 512 bytes.
|
|
|
|
CRC32 for partition entries (field "CRC32 of partition array") is calculated for
|
|
the whole array entry ( Number_of_partition_entries *
|
|
sizeof(partition_entry_size (usually 128)))
|
|
|
|
Observe, how Secondary GPT is placed in the memory. It is NOT a mirror reflect
|
|
of the Primary.
|
|
|
|
Partition Entry Format:
|
|
----------------------
|
|
Offset Size Description
|
|
|
|
0 16 B Partition type GUID (Big Endian)
|
|
16 16 B Unique partition GUID in (Big Endian)
|
|
32 8 B First LBA (Little Endian)
|
|
40 8 B Last LBA (inclusive)
|
|
48 8 B Attribute flags [+]
|
|
56 72 B Partition name (text)
|
|
|
|
Attribute flags:
|
|
Bit 0 - System partition
|
|
Bit 60 - Read-only
|
|
Bit 62 - Hidden
|
|
Bit 63 - Not mount
|
|
|
|
Creating GPT partitions in U-Boot:
|
|
==============
|
|
|
|
To restore GUID partition table one needs to:
|
|
1. Define partition layout in the environment.
|
|
Format of partitions layout:
|
|
"partitions=uuid_disk=...;name=u-boot,size=60MiB,uuid=...;
|
|
name=kernel,size=60MiB,uuid=...;"
|
|
or
|
|
"partitions=uuid_disk=${uuid_gpt_disk};name=${uboot_name},
|
|
size=${uboot_size},uuid=${uboot_uuid};"
|
|
|
|
Fields 'name', 'size' and 'uuid' are mandatory for every partition.
|
|
The field 'start' is optional.
|
|
|
|
option: CONFIG_RANDOM_UUID
|
|
If any partition "UUID" no exists then it is randomly generated.
|
|
|
|
2. Define 'CONFIG_EFI_PARTITION' and 'CONFIG_CMD_GPT'
|
|
|
|
2. From u-boot prompt type:
|
|
gpt write mmc 0 $partitions
|
|
|
|
Useful info:
|
|
============
|
|
|
|
Two programs, namely: 'gdisk' and 'parted' are recommended to work with GPT
|
|
recovery. Both are able to handle GUID partitions.
|
|
Please, pay attention at -l switch for parted.
|
|
|
|
"uuid" program is recommended to generate UUID string. Moreover it can decode
|
|
(-d switch) passed in UUID string. It can be used to generate partitions UUID
|
|
passed to u-boot environment variables.
|
|
If optional CONFIG_RANDOM_UUID is defined then for any partition which environment
|
|
uuid is unset, uuid is randomly generated and stored in correspond environment
|
|
variable.
|
|
|
|
note:
|
|
Each string block of UUID generated by program "uuid" is in big endian and it is
|
|
also stored in big endian in disk GPT.
|
|
Partitions layout can be printed by typing "mmc part". Note that each partition
|
|
GUID has different byte order than UUID generated before, this is because first
|
|
three blocks of GUID string are in Little Endian.
|