X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=doc%2FREADME.gpt;h=facd7afc3acdb70560096d3cdc417a68b734ae3f;hb=44f5c9ab459f5fafb72b39ec1e1bbedb7b164628;hp=81dfe584c5d16cd55e3db608051c544af3cd1011;hpb=3be2bdf5dc69b3142c1162a59bc67191c9077567;p=oweals%2Fu-boot.git diff --git a/doc/README.gpt b/doc/README.gpt index 81dfe584c5..facd7afc3a 100644 --- a/doc/README.gpt +++ b/doc/README.gpt @@ -1,11 +1,8 @@ +# SPDX-License-Identifier: GPL-2.0+ # # Copyright (C) 2012 Samsung Electronics # # Lukasz Majewski -# -# -# SPDX-License-Identifier: GPL-2.0+ - Glossary: ======== @@ -22,7 +19,6 @@ Introduction: This document describes the GPT partition table format and usage of the gpt command in u-boot. - UUID introduction: ==================== @@ -33,7 +29,8 @@ 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 +For instance, GUID of Basic data partition: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 +and GUID of Linux filesystem data: 0FC63DAF-8483-4772-8E79-3D69D8477DE4 Historically there are 5 methods to generate this number. The oldest one is combining machine's MAC address and timer (epoch) value. @@ -68,17 +65,16 @@ GPT brief explanation: |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 @@ -89,7 +85,7 @@ 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: +Primary/Backup GPT header: ---------------------------- Offset Size Description @@ -114,12 +110,11 @@ 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 @@ -129,16 +124,15 @@ 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 +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 [+] @@ -146,40 +140,157 @@ of the Primary. Attribute flags: Bit 0 - System partition + Bit 1 - Hide from EFI + Bit 2 - Legacy BIOS bootable + Bit 48-63 - Defined and used by the individual partition type + For Basic data 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=...; + "uuid_disk=...;name=u-boot,size=60MiB,uuid=...; name=kernel,size=60MiB,uuid=...;" or - "partitions=uuid_disk=${uuid_gpt_disk};name=${uboot_name}, + "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. + If field 'size' of the last partition is 0, the partition is extended + up to the end of the device. + + 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. The 'gpt guid' command reads the current value of the + uuid_disk from the GPT. + + The field 'bootable' is optional, it is used to mark the GPT partition + bootable (set attribute flags "Legacy BIOS bootable"). + "name=u-boot,size=60MiB;name=boot,size=60Mib,bootable;name=rootfs,size=0" + It can be used to locate bootable disks with command + "part list -bootable ", + please check out doc/README.distro for use. + 2. Define 'CONFIG_EFI_PARTITION' and 'CONFIG_CMD_GPT' -2. From u-boot prompt type: +3. From u-boot prompt type: gpt write mmc 0 $partitions +Checking (validating) GPT partitions in U-Boot: +=============================================== + +Procedure is the same as above. The only change is at point 3. + +At u-boot prompt one needs to write: + gpt verify mmc 0 [$partitions] + +where [$partitions] is an optional parameter. + +When it is not provided, only basic checks based on CRC32 calculation for GPT +header and PTEs are performed. +When provided, additionally partition data - name, size and starting +offset (last two in LBA) - are compared with data defined in '$partitions' +environment variable. + +After running this command, return code is set to 0 if no errors found in +on non-volatile medium stored GPT. + +Following line can be used to assess if GPT verification has succeed: + +U-BOOT> gpt verify mmc 0 $partitions +U-BOOT> if test $? = 0; then echo "GPT OK"; else echo "GPT ERR"; fi + +Renaming GPT partitions from U-Boot: +==================================== + +GPT partition names are a mechanism via which userspace and U-Boot can +communicate about software updates and boot failure. The 'gpt guid', +'gpt read', 'gpt rename' and 'gpt swap' commands facilitate +programmatic renaming of partitions from bootscripts by generating and +modifying the partitions layout string. Here is an illustration of +employing 'swap' to exchange 'primary' and 'backup' partition names: + +U-BOOT> gpt swap mmc 0 primary backup + +Afterwards, all partitions previously named 'primary' will be named +'backup', and vice-versa. Alternatively, single partitions may be +renamed. In this example, mmc0's first partition will be renamed +'primary': + +U-BOOT> gpt rename mmc 0 1 primary + +The GPT functionality may be tested with the 'sandbox' board by +creating a disk image as described under 'Block Device Emulation' in +doc/arch/index.rst: + +=>host bind 0 ./disk.raw +=> gpt read host 0 +[ . . . ] +=> gpt swap host 0 name othername +[ . . . ] + +Partition type GUID: +==================== + +For created partition, the used partition type GUID is +PARTITION_BASIC_DATA_GUID (EBD0A0A2-B9E5-4433-87C0-68B6B72699C7). + +If you define 'CONFIG_PARTITION_TYPE_GUID', a optionnal parameter 'type' +can specify a other partition type guid: + + "uuid_disk=...;name=u-boot,size=60MiB,uuid=...; + name=kernel,size=60MiB,uuid=..., + type=0FC63DAF-8483-4772-8E79-3D69D8477DE4;" + +Some strings can be also used at the place of known GUID : + "system" = PARTITION_SYSTEM_GUID + (C12A7328-F81F-11D2-BA4B-00A0C93EC93B) + "mbr" = LEGACY_MBR_PARTITION_GUID + (024DEE41-33E7-11D3-9D69-0008C781F39F) + "msft" = PARTITION_MSFT_RESERVED_GUID + (E3C9E316-0B5C-4DB8-817D-F92DF00215AE) + "data" = PARTITION_BASIC_DATA_GUID + (EBD0A0A2-B9E5-4433-87C0-68B6B72699C7) + "linux" = PARTITION_LINUX_FILE_SYSTEM_DATA_GUID + (0FC63DAF-8483-4772-8E79-3D69D8477DE4) + "raid" = PARTITION_LINUX_RAID_GUID + (A19D880F-05FC-4D3B-A006-743F0F84911E) + "swap" = PARTITION_LINUX_SWAP_GUID + (0657FD6D-A4AB-43C4-84E5-0933C84B4F4F) + "lvm" = PARTITION_LINUX_LVM_GUID + (E6D6D379-F507-44C2-A23C-238F2A3DF928) + + "uuid_disk=...;name=u-boot,size=60MiB,uuid=...; + name=kernel,size=60MiB,uuid=...,type=linux;" + +They are also used to display the type of partition in "part list" command. + 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.