Initial remote commit

test/patch.py

@@ -0,0 +1,38 @@
+import struct
+
+with open('/tmp/fs_meta.img', 'r+b') as f:
+    # Patch primary superblock at byte 1024
+    f.seek(1024)
+    sb = bytearray(f.read(1024))
+    
+    ro_compat = struct.unpack_from('<I', sb, 100)[0]
+    incompat  = struct.unpack_from('<I', sb, 96)[0]
+    print(f'ro_compat before: 0x{ro_compat:08x}')
+    print(f'incompat  before: 0x{incompat:08x}')
+    
+    ro_compat &= ~0x400  # clear metadata_csum
+    ro_compat &= ~0x010  # clear gdt_csum
+    incompat  &= ~0x004  # clear has_journal
+    
+    struct.pack_into('<I', sb, 100, ro_compat)
+    struct.pack_into('<I', sb,  96, incompat)
+    struct.pack_into('<I', sb, 1020, 0)  # clear sb checksum
+    
+    f.seek(1024)
+    f.write(bytes(sb))
+    print(f'ro_compat after:  0x{ro_compat:08x}')
+    print(f'incompat  after:  0x{incompat:08x}')
+
+    # Also patch every GDT entry checksum to 0
+    # GDT starts at byte 4096, each entry is 64 bytes
+    # checksum is at offset 30 within each entry
+    NUM_GROUPS = 35728
+    f.seek(4096)
+    gdt = bytearray(f.read(NUM_GROUPS * 64))
+    for g in range(NUM_GROUPS):
+        struct.pack_into('<H', gdt, g*64+30, 0)
+    f.seek(4096)
+    f.write(bytes(gdt))
+    print(f'Zeroed checksums for {NUM_GROUPS} GDT entries')
+    
+print('Done')