62 lines
1.6 KiB
Bash
62 lines
1.6 KiB
Bash
python3 -c "
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import struct, binascii
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# We need to recompute the GDT checksum for group 0
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# after modifying its flags
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#
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# ext4 GDT checksum = crc32c(uuid + group_num_le16 + gdt_entry_with_csum_zeroed)
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# The checksum seed is stored in the superblock at offset 408
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with open('/dev/nbd0','rb') as f:
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f.seek(1024)
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sb = f.read(1024)
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uuid = sb[104:120]
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csum_seed = struct.unpack_from('<I', sb, 408)[0]
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print(f'UUID: {uuid.hex()}')
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print(f'csum_seed: 0x{csum_seed:08x}')
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# Install crcmod for crc32c
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import subprocess
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subprocess.run(['pip','install','crcmod','--break-system-packages','-q'])
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import crcmod
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crc32c_fn = crcmod.predefined.mkCrcFun('crc-32c')
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data = bytearray(open('/tmp/merged_gdt.bin','rb').read())
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def compute_gdt_csum(g, entry):
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e = bytearray(entry)
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struct.pack_into('<H', e, 30, 0) # zero checksum field
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grp_le = struct.pack('<H', g)
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csum_data = uuid + grp_le + bytes(e)
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csum = crc32c_fn(csum_data, csum_seed)
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return csum & 0xFFFF
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# Recompute checksum for group 0 only
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g = 0
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entry = data[0:64]
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csum = compute_gdt_csum(g, entry)
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struct.pack_into('<H', data, 30, csum)
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print(f'Group 0 new checksum: 0x{csum:04x}')
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with open('/tmp/merged_gdt.bin','wb') as f:
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f.write(data)
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print('Saved')
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"
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# Restart and test
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pkill -f nbd_server
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nbd-client -d /dev/nbd0 2>/dev/null
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sleep 1
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python3 nbd_server_v9.py &
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sleep 2
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nbd-client 127.0.0.1 10809 /dev/nbd0 -N ""
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# Full e2fsck read-only check
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e2fsck -n /dev/nbd0 2>&1 | tee /tmp/e2fsck_full.log
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tail -5 /tmp/e2fsck_full.log
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# Try mounting
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mount -o ro,norecovery -t ext4 /dev/nbd0 /mnt/root
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ls /mnt/root
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