Menurut artikel Wikipedia ini , Alamat Blok Logis kedua dari Tabel Partisi GUID (LBA 1) adalah header GPT utama. Itu kemudian menyatakan di bagian tentang header bahwa 8 byte pertama dari header adalah untuk 'Tanda Tangan'.

Apa tanda tangan header GPT ini dan apa relevansinya dengan fungsi / operasi tabel / perangkat penyimpanan GPT?

Saya telah mencari-cari di web, tetapi menemukan sangat sedikit informasi untuk apa tanda tangan header ini.

Edit:

Saya mengajukan pertanyaan-pertanyaan lanjutan dalam komentar untuk jawaban Deltik , yang sangat membantu mereka diperluas untuk menjawab:

• Jika tanda tangan kosong, apakah tabel GPT tidak akan dikenali?
• Saat ini saya sedang memeriksa Chrome OS GPT, di mana tanda tangan tampaknya telah diatur ke 'IGNOREME'. Apa dampaknya?
• Apakah ada tanda tangan GPT lain yang valid tersedia? (terlepas dari 'BAGIAN EFI' default)

Tanda tangan EFI PART( 0x45 0x46 0x49 0x20 0x50 0x41 0x52 0x54) hanya mengatakan "Ini adalah Tabel Partisi GUID". Begitulah cara perangkat lunak tahu bahwa perangkat blok diformat dalam tata letak GPT.

Anda dapat melihatnya dari cuplikan hexdump ini:

*
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  |................|
*

Tanda tangan tidak unik untuk GPT. File juga memiliki tanda tangan yang dapat digunakan perangkat lunak untuk mengidentifikasi apa file tersebut. Ini adalah mekanisme operasi fileperintah. ( Contoh darifile )

Jawaban untuk Pertanyaan Tindak Lanjut

Jadi, jika tanda tangan ini kosong, maka tabel partisi GPT tidak akan dikenali?

Setidaknya, gdisktidak akan lagi mengenalinya. Lihat demo ini:

1. Buat file (bertindak sebagai perangkat blok) untuk demo:

   root@demo [/tmp]# truncate -s 1M gpt-demo
   

2. Format file dengan 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.
   

3. Periksa data biner dari tabel partisi:

   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
   

4. Periksa bagaimana gdiskmembaca tabel partisi:

   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
   

5. Ubah tanda tangan GPT:

   root@demo [/tmp]# sed -i 's/EFI PART/IGNOREME/g' gpt-demo
   

6. Verifikasi bahwa tanda tangan nuked:

   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
   

7. Perhatikan bahwa Tabel Partisi GUID (GPT) tidak lagi dikenali oleh 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
   

Saat ini saya sedang memeriksa Chrome OS GPT, di mana tanda tangan tampaknya telah diatur ke 'IGNOREME'. Apakah Anda tahu efek apa yang akan terjadi?

Sejauh yang saya tahu dari demo di atas, jika tanda tangannya berbeda dari EFI PART, GPT tidak dikenali.

The IGNOREME"tanda tangan" adalah tanda tangan khusus yang dibuat oleh Chromium. Ini adalah dokumentasi yang saya temukan untukIGNOREME :

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 <[email protected]>
Reviewed-on: https://chromium-review.googlesource.com/340072
Reviewed-by: Nam Nguyen <[email protected]>

Apakah Anda memeriksa GPT sekunder di akhir perangkat disk / blok?

Apakah ada tanda tangan GPT lain yang valid tersedia?

Tidak, tidak ada tanda tangan selain EFI PARTkarena itu adalah satu-satunya tanda tangan dalam Spesifikasi UEFI (lihat halaman 123). ( Salinan arsip UEFI Spesifikasi Versi 2.7 (Errata A) )