La firma EFI PART
( 0x45 0x46 0x49 0x20 0x50 0x41 0x52 0x54
) simplemente dice "Esta es una tabla de particiones GUID". Así es como el software sabe que el dispositivo de bloque está formateado en el diseño GPT.
Puedes verlo desde este fragmento de un hexdump:
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00 |EFI PART....\...|
00000210 ea b5 99 a4 00 00 00 00 01 00 00 00 00 00 00 00 |................|
00000220 af 12 9e 3b 00 00 00 00 22 00 00 00 00 00 00 00 |...;....".......|
00000230 8e 12 9e 3b 00 00 00 00 7f 8c d6 05 c8 e8 01 4a |...;...........J|
00000240 b8 74 6b 37 30 7c bf 15 02 00 00 00 00 00 00 00 |.tk70|..........|
00000250 80 00 00 00 80 00 00 00 10 d3 0e 29 00 00 00 00 |...........)....|
00000260 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
Las firmas no son exclusivas de GPT. Los archivos también tienen firmas que el software puede usar para identificar cuáles son los archivos. Este es el mecanismo de operación del file
comando. ( Ejemplos defile
)
Respuestas a las preguntas de seguimiento
Entonces, si esta firma estaba en blanco, ¿no se reconocería la tabla de particiones GPT?
Al menos, gdisk
ya no lo reconocería. Mira esta demostración:
Cree un archivo (que actúe como un dispositivo de bloque) para la demostración:
root@demo [/tmp]# truncate -s 1M gpt-demo
Formatee el archivo con GPT:
root@demo [/tmp]# sgdisk --clear gpt-demo
Creating new GPT entries.
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.
Verifique los datos binarios de la tabla de particiones:
root@demo [/tmp]# hexdump -C gpt-demo
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001c0 02 00 ee 20 20 00 01 00 00 00 ff 07 00 00 00 00 |... ...........|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00 |EFI PART....\...|
00000210 13 14 6d 6a 00 00 00 00 01 00 00 00 00 00 00 00 |..mj............|
00000220 ff 07 00 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
00000230 de 07 00 00 00 00 00 00 be 2c cb 6e 58 d4 e3 46 |.........,.nX..F|
00000240 84 84 3c 83 52 59 5b 58 02 00 00 00 00 00 00 00 |..<.RY[X........|
00000250 80 00 00 00 80 00 00 00 86 d2 54 ab 00 00 00 00 |..........T.....|
00000260 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000ffe00 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00 |EFI PART....\...|
000ffe10 18 3a 1f d9 00 00 00 00 ff 07 00 00 00 00 00 00 |.:..............|
000ffe20 01 00 00 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
000ffe30 de 07 00 00 00 00 00 00 be 2c cb 6e 58 d4 e3 46 |.........,.nX..F|
000ffe40 84 84 3c 83 52 59 5b 58 df 07 00 00 00 00 00 00 |..<.RY[X........|
000ffe50 80 00 00 00 80 00 00 00 86 d2 54 ab 00 00 00 00 |..........T.....|
000ffe60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00100000
Examina cómo se gdisk
lee la tabla de particiones:
root@demo [/tmp]# gdisk gpt-demo
GPT fdisk (gdisk) version 1.0.3
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
Command (? for help): q
Cambiar la firma GPT:
root@demo [/tmp]# sed -i 's/EFI PART/IGNOREME/g' gpt-demo
Verifique que la firma fue insertada:
root@demo [/tmp]# hexdump -C gpt-demo
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001c0 02 00 ee 20 20 00 01 00 00 00 ff 07 00 00 00 00 |... ...........|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 aa |..............U.|
00000200 49 47 4e 4f 52 45 4d 45 00 00 01 00 5c 00 00 00 |IGNOREME....\...|
00000210 13 14 6d 6a 00 00 00 00 01 00 00 00 00 00 00 00 |..mj............|
00000220 ff 07 00 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
00000230 de 07 00 00 00 00 00 00 be 2c cb 6e 58 d4 e3 46 |.........,.nX..F|
00000240 84 84 3c 83 52 59 5b 58 02 00 00 00 00 00 00 00 |..<.RY[X........|
00000250 80 00 00 00 80 00 00 00 86 d2 54 ab 00 00 00 00 |..........T.....|
00000260 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000ffe00 49 47 4e 4f 52 45 4d 45 00 00 01 00 5c 00 00 00 |IGNOREME....\...|
000ffe10 18 3a 1f d9 00 00 00 00 ff 07 00 00 00 00 00 00 |.:..............|
000ffe20 01 00 00 00 00 00 00 00 22 00 00 00 00 00 00 00 |........".......|
000ffe30 de 07 00 00 00 00 00 00 be 2c cb 6e 58 d4 e3 46 |.........,.nX..F|
000ffe40 84 84 3c 83 52 59 5b 58 df 07 00 00 00 00 00 00 |..<.RY[X........|
000ffe50 80 00 00 00 80 00 00 00 86 d2 54 ab 00 00 00 00 |..........T.....|
000ffe60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00100000
Observe que la tabla de particiones GUID (GPT) ya no es reconocida por gdisk
:
root@demo [/tmp]# gdisk gpt-demo
GPT fdisk (gdisk) version 1.0.3
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: not present
Creating new GPT entries.
Command (? for help): q
Actualmente estoy inspeccionando un GPT de Chrome OS, donde la firma parece haberse configurado en 'IGNOREME'. ¿Sabes qué efecto tendría eso?
Por lo que puedo ver en la demostración anterior, si la firma es diferente EFI PART
, GPT no se reconoce.
La IGNOREME
"firma" es una firma especial creada por Chromium. Esta es la documentación que encontré paraIGNOREME
:
cgptlib: Add support for IGNOREME GPT signature
This patch makes cgpt aware of a special "IGNOREME" GPT header signature
string that may appear in either the primary or the secondary GPT and
cause cgpt (and other cgptlib clients) to completely ignore that GPT. It
will continue to function correctly for all other purposes (using the
data from the non-ignored GPT), but never write any data back to the
ignored GPT.
BRANCH=None
BUG=chrome-os-partner:52595
TEST=unit tests
Change-Id: I7e53542385ae9d8d24dc25b75e91f4ff4917f66f
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/340072
Reviewed-by: Nam Nguyen <namnguyen@google.com>
¿Verificó el GPT secundario al final del dispositivo de disco / bloque?
¿Hay otras firmas GPT válidas disponibles?
No, no hay firmas más que EFI PART
porque esa es la única firma en la Especificación UEFI (consulte la página 123). ( Copia de archivo de la especificación UEFI Versión 2.7 (Errata A) )