--- /dev/null
+#
+# 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| Backup
+ -------------------------------------------------- GPT
+ LBA -33 |Entries 5 - 128 |
+ | |
+ | |
+ LBA -2 | |
+ --------------------------------------------------
+ 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
+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/Backup 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 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
+"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 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 (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.
Code Review / kvmfornfv.git / blobdiff