| # | |
| # Copyright (C) 2012 Samsung Electronics | |
| # | |
| # Lukasz Majewski <l.majewski@samsung.com> | |
| # | |
| # | |
| # See file CREDITS for list of people who contributed to this | |
| # project. | |
| # | |
| # This program is free software; you can redistribute it and/or | |
| # modify it under the terms of the GNU General Public License as | |
| # published by the Free Software Foundation; either version 2 of | |
| # the License, or (at your option) any later version. | |
| # | |
| # This program is distributed in the hope that it will be useful, | |
| # but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| # GNU General Public License for more details. | |
| # | |
| # You should have received a copy of the GNU General Public License | |
| # along with this program; if not, write to the Free Software | |
| # Foundation, Inc., 59 Temple Place, Suite 330, Boston, | |
| # MA 02111-1307 USA | |
| 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| Secondary | |
| -------------------------------------------------- (bkp) | |
| LBA -33 |Entries 5 - 128 | GPT | |
| | | | |
| | | | |
| LBA -2 | | | |
| -------------------------------------------------- | |
| LBA -1 |Secondary 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/Secondary 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 Secondary 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 Secondary 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 | |
| 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. | |
| 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. | |
| 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. |