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![Patrick Delaunay](/assets/img/avatar_default.png)
The optional parameter bootable is added in gpt command to set the partition attribute flag "Legacy BIOS bootable" This flag is used in extlinux and so in with distro to select the boot partition where is located the configuration file (please check out doc/README.distro for details). With this parameter, U-Boot can be used to create the boot partition needed for device using distro. example of use: setenv partitions "name=u-boot,size=60MiB;name=boot,size=60Mib,bootable;\ name=rootfs,size=0" > gpt write mmc 0 $partitions > part list mmc 0 Partition Map for MMC device 0 -- Partition Type: EFI Part Start LBA End LBA Name Attributes Type GUID Partition GUID 1 0x00000022 0x0001e021 "u-boot" attrs: 0x0000000000000000 type: ebd0a0a2-b9e5-4433-87c0-68b6b72699c7 guid: cceb0b18-39cb-d547-9db7-03b405fa77d4 2 0x0001e022 0x0003c021 "boot" attrs: 0x0000000000000004 type: ebd0a0a2-b9e5-4433-87c0-68b6b72699c7 guid: d4981a2b-0478-544e-9607-7fd3c651068d 3 0x0003c022 0x003a9fde "rootfs" attrs: 0x0000000000000000 type: ebd0a0a2-b9e5-4433-87c0-68b6b72699c7 guid: 6d6c9a36-e919-264d-a9ee-bd00379686c7 > part list mmc 0 -bootable devplist > printenv devplist devplist=2 Then the distro scripts will search extlinux in partition 2 and not in the first partition. Signed-off-by: Patrick Delaunay <patrick.delaunay73@gmail.com>
270 lines
10 KiB
Plaintext
270 lines
10 KiB
Plaintext
#
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# Copyright (C) 2012 Samsung Electronics
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#
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# Lukasz Majewski <l.majewski@samsung.com>
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#
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#
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# SPDX-License-Identifier: GPL-2.0+
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Glossary:
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========
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- UUID -(Universally Unique Identifier)
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- GUID - (Globally Unique ID)
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- EFI - (Extensible Firmware Interface)
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- UEFI - (Unified EFI) - EFI evolution
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- GPT (GUID Partition Table) - it is the EFI standard part
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- partitions - lists of available partitions (defined at u-boot):
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./include/configs/{target}.h
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Introduction:
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=============
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This document describes the GPT partition table format and usage of
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the gpt command in u-boot.
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UUID introduction:
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====================
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GPT for marking disks/partitions is using the UUID. It is supposed to be a
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globally unique value. A UUID is a 16-byte (128-bit) number. The number of
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theoretically possible UUIDs is therefore about 3 x 10^38.
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More often UUID is displayed as 32 hexadecimal digits, in 5 groups,
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separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters
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(32 digits and 4 hyphens)
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For instance, GUID of Basic data partition: EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
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and GUID of Linux filesystem data: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
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Historically there are 5 methods to generate this number. The oldest one is
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combining machine's MAC address and timer (epoch) value.
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Successive versions are using MD5 hash, random numbers and SHA-1 hash. All major
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OSes and programming languages are providing libraries to compute UUID (e.g.
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uuid command line tool).
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GPT brief explanation:
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======================
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Layout:
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-------
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--------------------------------------------------
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LBA 0 |Protective MBR |
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----------------------------------------------------------
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LBA 1 |Primary GPT Header | Primary
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-------------------------------------------------- GPT
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LBA 2 |Entry 1|Entry 2| Entry 3| Entry 4|
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--------------------------------------------------
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LBA 3 |Entries 5 - 128 |
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----------------------------------------------------------
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LBA 34 |Partition 1 |
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-----------------------------------
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|Partition 2 |
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-----------------------------------
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|Partition n |
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----------------------------------------------------------
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LBA -34 |Entry 1|Entry 2| Entry 3| Entry 4| Backup
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-------------------------------------------------- GPT
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LBA -33 |Entries 5 - 128 |
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LBA -2 | |
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--------------------------------------------------
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LBA -1 |Backup GPT Header |
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----------------------------------------------------------
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For a legacy reasons, GPT's LBA 0 sector has a MBR structure. It is called
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"protective MBR".
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Its first partition entry ID has 0xEE value, and disk software, which is not
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handling the GPT sees it as a storage device without free space.
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It is possible to define 128 linearly placed partition entries.
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"LBA -1" means the last addressable block (in the mmc subsystem:
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"dev_desc->lba - 1")
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Primary/Backup GPT header:
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----------------------------
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Offset Size Description
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0 8 B Signature ("EFI PART", 45 46 49 20 50 41 52 54)
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8 4 B Revision (For version 1.0, the value is 00 00 01 00)
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12 4 B Header size (in bytes, usually 5C 00 00 00 meaning 92 bytes)
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16 4 B CRC32 of header (0 to header size), with this field zeroed
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during calculation
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20 4 B Reserved (ZERO);
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24 8 B Current LBA (location of this header copy)
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32 8 B Backup LBA (location of the other header copy)
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40 8 B First usable LBA for partitions (primary partition table last
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LBA + 1)
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48 8 B Last usable LBA (secondary partition table first LBA - 1)
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56 16 B Disk GUID (also referred as UUID on UNIXes)
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72 8 B Partition entries starting LBA (always 2 in primary copy)
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80 4 B Number of partition entries
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84 4 B Size of a partition entry (usually 128)
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88 4 B CRC32 of partition array
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92 * Reserved; must be ZERO (420 bytes for a 512-byte LBA)
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TOTAL: 512 B
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IMPORTANT:
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GPT headers and partition entries are protected by CRC32 (the POSIX CRC32).
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Primary GPT header and Backup GPT header have swapped values of "Current LBA"
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and "Backup LBA" and therefore different CRC32 check-sum.
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CRC32 for GPT headers (field "CRC of header") are calculated up till
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"Header size" (92), NOT 512 bytes.
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CRC32 for partition entries (field "CRC32 of partition array") is calculated for
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the whole array entry ( Number_of_partition_entries *
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sizeof(partition_entry_size (usually 128)))
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Observe, how Backup GPT is placed in the memory. It is NOT a mirror reflect
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of the Primary.
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Partition Entry Format:
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----------------------
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Offset Size Description
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0 16 B Partition type GUID (Big Endian)
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16 16 B Unique partition GUID in (Big Endian)
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32 8 B First LBA (Little Endian)
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40 8 B Last LBA (inclusive)
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48 8 B Attribute flags [+]
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56 72 B Partition name (text)
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Attribute flags:
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Bit 0 - System partition
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Bit 1 - Hide from EFI
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Bit 2 - Legacy BIOS bootable
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Bit 48-63 - Defined and used by the individual partition type
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For Basic data partition :
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Bit 60 - Read-only
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Bit 62 - Hidden
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Bit 63 - Not mount
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Creating GPT partitions in U-Boot:
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==============
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To restore GUID partition table one needs to:
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1. Define partition layout in the environment.
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Format of partitions layout:
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"partitions=uuid_disk=...;name=u-boot,size=60MiB,uuid=...;
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name=kernel,size=60MiB,uuid=...;"
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or
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"partitions=uuid_disk=${uuid_gpt_disk};name=${uboot_name},
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size=${uboot_size},uuid=${uboot_uuid};"
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The fields 'name' and 'size' are mandatory for every partition.
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The field 'start' is optional.
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If field 'size' of the last partition is 0, the partiton is extended
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up to the end of the device.
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The fields 'uuid' and 'uuid_disk' are optional if CONFIG_RANDOM_UUID is
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enabled. A random uuid will be used if omitted or they point to an empty/
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non-existent environment variable. The environment variable will be set to
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the generated UUID.
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The field 'bootable' is optional, it is used to mark the GPT partition
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bootable (set attribute flags "Legacy BIOS bootable").
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"name=u-boot,size=60MiB;name=boot,size=60Mib,bootable;name=rootfs,size=0"
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It can be used to locate bootable disks with command
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"part list <interface> <dev> -bootable <varname>",
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please check out doc/README.distro for use.
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2. Define 'CONFIG_EFI_PARTITION' and 'CONFIG_CMD_GPT'
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3. From u-boot prompt type:
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gpt write mmc 0 $partitions
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Checking (validating) GPT partitions in U-Boot:
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===============================================
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Procedure is the same as above. The only change is at point 3.
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At u-boot prompt one needs to write:
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gpt verify mmc 0 [$partitions]
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where [$partitions] is an optional parameter.
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When it is not provided, only basic checks based on CRC32 calculation for GPT
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header and PTEs are performed.
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When provided, additionally partition data - name, size and starting
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offset (last two in LBA) - are compared with data defined in '$partitions'
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environment variable.
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After running this command, return code is set to 0 if no errors found in
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on non-volatile medium stored GPT.
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Following line can be used to assess if GPT verification has succeed:
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U-BOOT> gpt verify mmc 0 $partitions
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U-BOOT> if test $? = 0; then echo "GPT OK"; else echo "GPT ERR"; fi
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Partition type GUID:
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====================
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For created partition, the used partition type GUID is
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PARTITION_BASIC_DATA_GUID (EBD0A0A2-B9E5-4433-87C0-68B6B72699C7).
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If you define 'CONFIG_PARTITION_TYPE_GUID', a optionnal parameter 'type'
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can specify a other partition type guid:
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"partitions=uuid_disk=...;name=u-boot,size=60MiB,uuid=...;
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name=kernel,size=60MiB,uuid=...,
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type=0FC63DAF-8483-4772-8E79-3D69D8477DE4;"
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Some strings can be also used at the place of known GUID :
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"system" = PARTITION_SYSTEM_GUID
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(C12A7328-F81F-11D2-BA4B-00A0C93EC93B)
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"mbr" = LEGACY_MBR_PARTITION_GUID
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(024DEE41-33E7-11D3-9D69-0008C781F39F)
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"msft" = PARTITION_MSFT_RESERVED_GUID
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(E3C9E316-0B5C-4DB8-817D-F92DF00215AE)
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"data" = PARTITION_BASIC_DATA_GUID
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(EBD0A0A2-B9E5-4433-87C0-68B6B72699C7)
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"linux" = PARTITION_LINUX_FILE_SYSTEM_DATA_GUID
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(0FC63DAF-8483-4772-8E79-3D69D8477DE4)
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"raid" = PARTITION_LINUX_RAID_GUID
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(A19D880F-05FC-4D3B-A006-743F0F84911E)
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"swap" = PARTITION_LINUX_SWAP_GUID
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(0657FD6D-A4AB-43C4-84E5-0933C84B4F4F)
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"lvm" = PARTITION_LINUX_LVM_GUID
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(E6D6D379-F507-44C2-A23C-238F2A3DF928)
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"partitions=uuid_disk=...;name=u-boot,size=60MiB,uuid=...;
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name=kernel,size=60MiB,uuid=...,type=linux;"
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They are also used to display the type of partition in "part list" command.
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Useful info:
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============
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Two programs, namely: 'gdisk' and 'parted' are recommended to work with GPT
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recovery. Both are able to handle GUID partitions.
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Please, pay attention at -l switch for parted.
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"uuid" program is recommended to generate UUID string. Moreover it can decode
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(-d switch) passed in UUID string. It can be used to generate partitions UUID
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passed to u-boot environment variables.
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If optional CONFIG_RANDOM_UUID is defined then for any partition which environment
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uuid is unset, uuid is randomly generated and stored in correspond environment
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variable.
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note:
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Each string block of UUID generated by program "uuid" is in big endian and it is
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also stored in big endian in disk GPT.
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Partitions layout can be printed by typing "mmc part". Note that each partition
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GUID has different byte order than UUID generated before, this is because first
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three blocks of GUID string are in Little Endian.
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