Initial remote commit

misc_tools/inspect_chunk.py

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+CHUNK    = 128*512
+LV_START = 5120000*512
+BSIZE    = 4096
+
+# Block 5251104 falls in:
+# virt_byte = 5251104 * 4096 = 21508521984
+# group=65638, chunk_idx=4, intra=0
+
+# The physical location of this metadata chunk:
+group = 65638
+phys_meta = LV_START + group*5*CHUNK + 4*CHUNK
+print(f'Metadata chunk physical byte: {phys_meta}')
+
+# Read the full 64KB metadata chunk
+with open('/dev/md0','rb') as f:
+    f.seek(phys_meta)
+    meta = f.read(CHUNK)
+
+nonzero = sum(1 for b in meta if b != 0)
+print(f'Nonzero bytes: {nonzero}/{CHUNK}')
+print()
+
+# Earlier we found that metadata chunks store 512 bytes per sector
+# of the 4 adjacent data chunks = 128 sectors * 4 chunks = 512 entries
+# But what if SOME of those 512-byte slots contain filesystem data
+# instead of PERC metadata?
+
+# The /var dir block should be 4096 bytes
+# Could it be stored in 8 consecutive 512-byte slots?
+# Let's look for directory signatures in the metadata chunk
+
+import struct
+
+# Search for directory entry signature: valid inode + rec_len + name_len
+print('Searching for directory entries in metadata chunk...')
+for off in range(0, CHUNK-8, 4):
+    ino     = struct.unpack_from('<I', meta, off)[0]
+    rec_len = struct.unpack_from('<H', meta, off+4)[0]
+    name_len= meta[off+6]
+    ftype   = meta[off+7]
+    if (10 < ino < 500_000_000 and
+        8 <= rec_len <= 256 and
+        0 < name_len <= rec_len-8 and
+        ftype in (1,2,7) and
+        rec_len % 4 == 0):
+        name = meta[off+8:off+8+name_len].decode('utf-8',errors='replace')
+        if name.isprintable() and len(name) == name_len:
+            print(f'  offset {off}: inode={ino} rec_len={rec_len} '
+                  f'name={name!r} ftype={ftype}')
+
+# Also check: does the metadata chunk contain the filesystem data
+# at a fixed offset? e.g. first 4096 bytes = filesystem data block?
+print()
+print('First 4096 bytes as directory:')
+off = 0
+while off < 4096-8:
+    ino     = struct.unpack_from('<I', meta, off)[0]
+    rec_len = struct.unpack_from('<H', meta, off+4)[0]
+    name_len= meta[off+6]
+    ftype   = meta[off+7]
+    if rec_len < 8: break
+    if ino > 0 and name_len > 0:
+        name = meta[off+8:off+8+name_len].decode('utf-8',errors='replace')
+        tname = {1:'file',2:'dir',7:'link'}.get(ftype,'?')
+        print(f'  {tname} inode={ino} {name!r}')
+    off += rec_len