projects / people / ms / u-boot.git / blame
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1 | # |
| 2 | # Copyright (C) 2012 Samsung Electronics | |
| 3 | # | |
| 4 | # Lukasz Majewski <l.majewski@samsung.com> | |
| 5 | # | |
| 6 | # | |
| 1a459660 | 7 | # SPDX-License-Identifier: GPL-2.0+ |
| 36f2e8e0 | 8 | |
| 36f2e8e0 ŁM |
9 | Glossary: |
| 10 | ======== | |
| 11 | - UUID -(Universally Unique Identifier) | |
| 12 | - GUID - (Globally Unique ID) | |
| 13 | - EFI - (Extensible Firmware Interface) | |
| 14 | - UEFI - (Unified EFI) - EFI evolution | |
| 15 | - GPT (GUID Partition Table) - it is the EFI standard part | |
| 16 | - partitions - lists of available partitions (defined at u-boot): | |
| 17 | ./include/configs/{target}.h | |
| 18 | ||
| 19 | Introduction: | |
| 20 | ============= | |
| 21 | This document describes the GPT partition table format and usage of | |
| 22 | the gpt command in u-boot. | |
| 23 | ||
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24 | UUID introduction: |
| 25 | ==================== | |
| 26 | ||
| 27 | GPT for marking disks/partitions is using the UUID. It is supposed to be a | |
| 28 | globally unique value. A UUID is a 16-byte (128-bit) number. The number of | |
| 29 | theoretically possible UUIDs is therefore about 3 x 10^38. | |
| 30 | More often UUID is displayed as 32 hexadecimal digits, in 5 groups, | |
| 31 | separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters | |
| 32 | (32 digits and 4 hyphens) | |
| 33 | ||
| 34 | For instance, GUID of Linux data partition: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 | |
| 35 | ||
| 36 | Historically there are 5 methods to generate this number. The oldest one is | |
| 37 | combining machine's MAC address and timer (epoch) value. | |
| 38 | ||
| 39 | Successive versions are using MD5 hash, random numbers and SHA-1 hash. All major | |
| 40 | OSes and programming languages are providing libraries to compute UUID (e.g. | |
| 41 | uuid command line tool). | |
| 42 | ||
| 43 | GPT brief explanation: | |
| 44 | ====================== | |
| 45 | ||
| 46 | Layout: | |
| 47 | ------- | |
| 48 | ||
| 49 | -------------------------------------------------- | |
| 50 | LBA 0 |Protective MBR | | |
| 51 | ---------------------------------------------------------- | |
| 52 | LBA 1 |Primary GPT Header | Primary | |
| 53 | -------------------------------------------------- GPT | |
| 54 | LBA 2 |Entry 1|Entry 2| Entry 3| Entry 4| | |
| 55 | -------------------------------------------------- | |
| 56 | LBA 3 |Entries 5 - 128 | | |
| 57 | | | | |
| 58 | | | | |
| 59 | ---------------------------------------------------------- | |
| 60 | LBA 34 |Partition 1 | | |
| 61 | | | | |
| 62 | ----------------------------------- | |
| 63 | |Partition 2 | | |
| 64 | | | | |
| 65 | ----------------------------------- | |
| 66 | |Partition n | | |
| 67 | | | | |
| 68 | ---------------------------------------------------------- | |
| 69 | LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Secondary | |
| 70 | -------------------------------------------------- (bkp) | |
| 71 | LBA -33 |Entries 5 - 128 | GPT | |
| 72 | | | | |
| 73 | | | | |
| 74 | LBA -2 | | | |
| 75 | -------------------------------------------------- | |
| 76 | LBA -1 |Secondary GPT Header | | |
| 77 | ---------------------------------------------------------- | |
| 78 | ||
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79 | For a legacy reasons, GPT's LBA 0 sector has a MBR structure. It is called |
| 80 | "protective MBR". | |
| 81 | Its first partition entry ID has 0xEE value, and disk software, which is not | |
| 82 | handling the GPT sees it as a storage device without free space. | |
| 83 | ||
| 84 | It is possible to define 128 linearly placed partition entries. | |
| 85 | ||
| 86 | "LBA -1" means the last addressable block (in the mmc subsystem: | |
| 87 | "dev_desc->lba - 1") | |
| 88 | ||
| 89 | Primary/Secondary GPT header: | |
| 90 | ---------------------------- | |
| 91 | Offset Size Description | |
| 92 | ||
| 93 | 0 8 B Signature ("EFI PART", 45 46 49 20 50 41 52 54) | |
| 94 | 8 4 B Revision (For version 1.0, the value is 00 00 01 00) | |
| 95 | 12 4 B Header size (in bytes, usually 5C 00 00 00 meaning 92 bytes) | |
| 96 | 16 4 B CRC32 of header (0 to header size), with this field zeroed | |
| 97 | during calculation | |
| 98 | 20 4 B Reserved (ZERO); | |
| 99 | 24 8 B Current LBA (location of this header copy) | |
| 100 | 32 8 B Backup LBA (location of the other header copy) | |
| 101 | 40 8 B First usable LBA for partitions (primary partition table last | |
| 102 | LBA + 1) | |
| 103 | 48 8 B Last usable LBA (secondary partition table first LBA - 1) | |
| 104 | 56 16 B Disk GUID (also referred as UUID on UNIXes) | |
| 105 | 72 8 B Partition entries starting LBA (always 2 in primary copy) | |
| 106 | 80 4 B Number of partition entries | |
| 107 | 84 4 B Size of a partition entry (usually 128) | |
| 108 | 88 4 B CRC32 of partition array | |
| 109 | 92 * Reserved; must be ZERO (420 bytes for a 512-byte LBA) | |
| 110 | ||
| 111 | TOTAL: 512 B | |
| 112 | ||
| 113 | ||
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114 | IMPORTANT: |
| 115 | ||
| 116 | GPT headers and partition entries are protected by CRC32 (the POSIX CRC32). | |
| 117 | ||
| 118 | Primary GPT header and Secondary GPT header have swapped values of "Current LBA" | |
| 119 | and "Backup LBA" and therefore different CRC32 check-sum. | |
| 120 | ||
| 121 | CRC32 for GPT headers (field "CRC of header") are calculated up till | |
| 122 | "Header size" (92), NOT 512 bytes. | |
| 123 | ||
| 124 | CRC32 for partition entries (field "CRC32 of partition array") is calculated for | |
| 125 | the whole array entry ( Number_of_partition_entries * | |
| 126 | sizeof(partition_entry_size (usually 128))) | |
| 127 | ||
| 128 | Observe, how Secondary GPT is placed in the memory. It is NOT a mirror reflect | |
| 129 | of the Primary. | |
| 130 | ||
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131 | Partition Entry Format: |
| 132 | ---------------------- | |
| 133 | Offset Size Description | |
| 134 | ||
| 135 | 0 16 B Partition type GUID | |
| 136 | 16 16 B Unique partition GUID | |
| 137 | 32 8 B First LBA (Little Endian) | |
| 138 | 40 8 B Last LBA (inclusive) | |
| 139 | 48 8 B Attribute flags [+] | |
| 140 | 56 72 B Partition name (text) | |
| 141 | ||
| 142 | Attribute flags: | |
| 143 | Bit 0 - System partition | |
| 144 | Bit 60 - Read-only | |
| 145 | Bit 62 - Hidden | |
| 146 | Bit 63 - Not mount | |
| 147 | ||
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148 | Creating GPT partitions in U-Boot: |
| 149 | ============== | |
| 150 | ||
| 151 | To restore GUID partition table one needs to: | |
| 152 | 1. Define partition layout in the environment. | |
| 153 | Format of partitions layout: | |
| 154 | "partitions=uuid_disk=...;name=u-boot,size=60MiB,uuid=...; | |
| 155 | name=kernel,size=60MiB,uuid=...;" | |
| 156 | or | |
| 157 | "partitions=uuid_disk=${uuid_gpt_disk};name=${uboot_name}, | |
| 158 | size=${uboot_size},uuid=${uboot_uuid};" | |
| 159 | ||
| 160 | Fields 'name', 'size' and 'uuid' are mandatory for every partition. | |
| 161 | The field 'start' is optional. | |
| 162 | ||
| 163 | 2. Define 'CONFIG_EFI_PARTITION' and 'CONFIG_CMD_GPT' | |
| 164 | ||
| 165 | 2. From u-boot prompt type: | |
| 166 | gpt write mmc 0 $partitions | |
| 167 | ||
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168 | Useful info: |
| 169 | ============ | |
| 170 | ||
| 171 | Two programs, namely: 'fdisk' and 'parted' are recommended to work with GPT | |
| 172 | recovery. Parted is able to handle GUID partitions. Unfortunately the 'fdisk' | |
| 173 | hasn't got such ability. | |
| 174 | Please, pay attention at -l switch for parted. | |
| 175 | ||
| 176 | "uuid" program is recommended to generate UUID string. Moreover it can decode | |
| 177 | (-d switch) passed in UUID string. It can be used to generate partitions UUID | |
| 178 | passed to u-boot environment variables. |