Initial remote commit

misc_tools/verify_mapping.py

@@ -0,0 +1,59 @@
+CHUNK    = 128*512
+LV_START = 5120000*512
+BSIZE    = 4096
+
+# Root dir data block = 9262
+# We read this successfully, so our translation works for it
+# Let's verify: block 9262 as filesystem block (offset from LV start)
+# vs block 9262 as PERC virtual block
+
+fs_virt_byte   = 9262 * BSIZE          # filesystem block offset from LV start
+perc_virt_byte = 9262 * BSIZE          # same number, different interpretation
+
+# As filesystem block (what our NBD server does):
+# The NBD server presents a virtual address space where block N = byte N*4096
+# And applies the 4/5 chunk translation to convert to physical
+fs_group     = fs_virt_byte // (5*CHUNK)
+fs_in_group  = fs_virt_byte % (5*CHUNK)
+fs_chunk_idx = fs_in_group // CHUNK
+fs_intra     = fs_in_group % CHUNK
+
+print(f'Block 9262 as filesystem virtual (via NBD translation):')
+print(f'  virt_byte={fs_virt_byte}')
+print(f'  chunk_group={fs_group} chunk_idx={fs_chunk_idx} intra={fs_intra}')
+if fs_chunk_idx != 4:
+    phys = LV_START + fs_group*4*CHUNK + fs_chunk_idx*CHUNK + fs_intra
+    print(f'  physical={phys}')
+    with open('/dev/md0','rb') as f:
+        f.seek(phys)
+        data = f.read(64)
+    print(f'  first 32: {data[:32].hex()}')
+
+# We know from istat that block 9262 contains the root directory
+# and we verified it has valid directory entries
+# So the block numbers ARE filesystem-level, and our translation IS correct
+
+# Now: why does block 5251104 (var dir data) fall in a metadata chunk?
+# 5251104 * 4096 = 21508521984
+# group = 21508521984 // (5*65536) = 65638
+# in_group = 21508521984 % (5*65536) = 262144 = 4*65536
+# chunk_idx = 4 -> METADATA
+
+# This means the /var directory data genuinely falls in a PERC metadata slot
+# The PERC would have stored its OWN metadata there
+# and the filesystem data for block 5251104 would need to be
+# at a DIFFERENT physical location
+
+# Unless... the ext4 filesystem uses block numbers differently
+# In ext4 with flex_bg, block numbers might be relative to something else
+
+# Let's check: what block does istat say for /var?
+# We need to run istat on inode 1310721
+import subprocess
+r = subprocess.run(['istat', '/dev/nbd0', '1310721'],
+                  capture_output=True, text=True)
+print()
+print('istat output for /var (inode 1310721):')
+print(r.stdout)
+print(r.stderr[:200] if r.stderr else '')
+