#
# SPDX-License-Identifier: GPL-2.0+
-
Glossary:
========
- UUID -(Universally Unique Identifier)
This document describes the GPT partition table format and usage of
the gpt command in u-boot.
-
UUID introduction:
====================
|Partition n |
| |
----------------------------------------------------------
- LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Secondary
- -------------------------------------------------- (bkp)
- LBA -33 |Entries 5 - 128 | GPT
+ LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Backup
+ -------------------------------------------------- GPT
+ LBA -33 |Entries 5 - 128 |
| |
| |
LBA -2 | |
--------------------------------------------------
- LBA -1 |Secondary GPT Header |
+ LBA -1 |Backup 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
"LBA -1" means the last addressable block (in the mmc subsystem:
"dev_desc->lba - 1")
-Primary/Secondary GPT header:
+Primary/Backup GPT header:
----------------------------
Offset Size Description
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"
+Primary GPT header and Backup 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
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
+Observe, how Backup 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
- 16 16 B Unique partition GUID
+ 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 [+]
Bit 62 - Hidden
Bit 63 - Not mount
-
Creating GPT partitions in U-Boot:
==============
"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 fields 'name' and 'size' are mandatory for every partition.
The field 'start' is optional.
+ The fields 'uuid' and 'uuid_disk' are optional if CONFIG_RANDOM_UUID is
+ enabled. A random uuid will be used if omitted or they point to an empty/
+ non-existent environment variable. The environment variable will be set to
+ the generated UUID.
+
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: 'fdisk' and 'parted' are recommended to work with GPT
-recovery. Parted is able to handle GUID partitions. Unfortunately the 'fdisk'
-hasn't got such ability.
+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.
projects / karo-tx-uboot.git / blobdiff