Initial remote commit

misc_tools/test2.py

@@ -0,0 +1,55 @@
+# Inode 2 is at virtual byte 4382976 via NBD
+# Group 0 inode table should be at block = 4382976 // 4096 = 1069 or 1070?
+virt = 4382976
+BSIZE = 4096
+block = virt // BSIZE
+offset_in_block = virt % BSIZE
+inode_idx = offset_in_block // 256
+
+print(f'Inode 2 virtual byte: {virt}')
+print(f'Block: {block}')
+print(f'Offset in block: {offset_in_block}')
+print(f'Inode index in block: {inode_idx}')
+
+# istat said direct block = 9262 for root dir data
+# That means the root directory data is at block 9262
+# Let's read that directly via NBD
+import struct
+
+BSIZE = 4096
+with open('/dev/nbd0','rb') as f:
+    f.seek(9262 * BSIZE)
+    data = f.read(BSIZE)
+
+print()
+print('Root directory data block (block 9262):')
+off = 0
+while off < BSIZE - 8:
+    ino     = struct.unpack_from('<I', data, off)[0]
+    rec_len = struct.unpack_from('<H', data, off+4)[0]
+    name_len= data[off+6]
+    ftype   = data[off+7]
+    if rec_len < 8: break
+    if ino > 0 and name_len > 0:
+        name = data[off+8:off+8+name_len].decode('utf-8',errors='replace')
+        tname = {1:'file',2:'dir',7:'link'}.get(ftype,'?')
+        print(f'  {tname:4s} inode={ino:10d} {name!r}')
+    off += rec_len
+
+# Now check: our formula says group 0 inode table is at block 1070
+# But inode 2 is at virtual byte 4382976 = block 1069.something?
+print()
+print(f'Our formula block: 1070')
+print(f'Actual block from NBD: {virt//BSIZE} (byte {virt})')
+print(f'Difference: {1070 - virt//BSIZE}')
+
+# The key question: is our GDT formula wrong?
+# GDT says inode table at block 1070 for group 0
+# But inode 2 (second inode) is at:
+# block 1070, offset 256 bytes (one inode size)
+# = byte 1070*4096 + 256 = 4382976 + 256... wait
+print()
+print(f'1070 * 4096 = {1070*4096}')
+print(f'1070 * 4096 + 256 = {1070*4096+256}')
+print(f'Actual inode 2 virt byte from NBD: {virt}')
+print(f'Match: {1070*4096+256 == virt}')