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test/nbd_server_v6.py
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271
test/nbd_server_v6.py
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#!/usr/bin/env python3
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"""
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NBD server v6 — chunk translation + backup GDT overlay.
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The primary GDT has invalid checksums (written through PERC which stored
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its own checksums). The backup GDT at block group 1 has valid checksums.
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We serve the backup GDT bytes at the primary GDT location so the kernel
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can validate and mount the filesystem.
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Reads the backup GDT once at startup and caches it.
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All other reads: pure chunk translation, no modification.
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Usage:
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python3 nbd_server_v6.py &
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nbd-client 127.0.0.1 10809 /dev/nbd0 -N ""
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mount -o ro,norecovery -t ext4 /dev/nbd0 /mnt/root
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"""
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import socket
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import struct
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import threading
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import sys
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DEV = '/dev/md0'
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CHUNK_BYTES = 128 * 512 # 64 KB
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LV_PHYS_START = 5120000 * 512 # byte 2,621,440,000
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VIRT_SIZE = 9365766144 * 512 # from superblock
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BSIZE = 4096
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GDT_ENTRY = 64
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BPG = 32768
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NUM_GROUPS = 35728
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# Primary GDT: virtual bytes 4096 to 4096+NUM_GROUPS*64
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PRIMARY_GDT_START = BSIZE
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PRIMARY_GDT_SIZE = NUM_GROUPS * GDT_ENTRY
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PRIMARY_GDT_END = PRIMARY_GDT_START + PRIMARY_GDT_SIZE
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# Backup GDT: at block group 1, block 1 = (BPG+1)*BSIZE
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BACKUP_GDT_START = (BPG + 1) * BSIZE
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# Cached backup GDT (loaded at startup)
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_backup_gdt = None
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# NBD protocol
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NBDMAGIC = 0x4e42444d41474943
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IHAVEOPT = 0x49484156454F5054
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REPLYMAGIC = 0x3e889045565a9
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NBD_OPT_EXPORT_NAME = 1
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NBD_OPT_ABORT = 2
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NBD_OPT_LIST = 3
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NBD_OPT_GO = 7
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NBD_REP_ACK = 1
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NBD_REP_SERVER = 2
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NBD_REP_INFO = 3
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NBD_REP_ERR_UNSUP = (1 << 31) | 1
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NBD_INFO_EXPORT = 0
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NBD_FLAG_HAS_FLAGS = 1 << 0
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NBD_FLAG_READ_ONLY = 1 << 1
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NBD_FLAG_SEND_FLUSH = 1 << 2
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NBD_REQUEST_MAGIC = 0x25609513
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NBD_REPLY_MAGIC = 0x67446698
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NBD_CMD_READ = 0
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NBD_CMD_DISC = 2
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NBD_CMD_FLUSH = 3
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TX_FLAGS = NBD_FLAG_HAS_FLAGS | NBD_FLAG_READ_ONLY | NBD_FLAG_SEND_FLUSH
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def raw_read(virt_offset, length):
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"""Pure chunk translation — no modifications."""
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result = bytearray(length)
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pos = virt_offset
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remaining = length
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with open(DEV, 'rb') as f:
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while remaining > 0:
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group = pos // (5 * CHUNK_BYTES)
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in_group = pos % (5 * CHUNK_BYTES)
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chunk_idx = in_group // CHUNK_BYTES
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intra = in_group % CHUNK_BYTES
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seg_len = min(CHUNK_BYTES - intra, remaining)
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dst_off = pos - virt_offset
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if chunk_idx != 4:
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phys = (LV_PHYS_START
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+ group * 4 * CHUNK_BYTES
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+ chunk_idx * CHUNK_BYTES
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+ intra)
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f.seek(phys)
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chunk = f.read(seg_len)
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result[dst_off:dst_off + len(chunk)] = chunk
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pos += seg_len
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remaining -= seg_len
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return bytes(result)
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def load_backup_gdt():
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"""Read and cache the backup GDT from group 1."""
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global _backup_gdt
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print(f'[gdt] loading backup GDT from virtual byte {BACKUP_GDT_START}...')
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_backup_gdt = raw_read(BACKUP_GDT_START, PRIMARY_GDT_SIZE)
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# Verify first few entries look sane
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ok = True
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for i in range(min(5, NUM_GROUPS)):
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e = _backup_gdt[i*GDT_ENTRY:(i+1)*GDT_ENTRY]
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bb = struct.unpack_from('<I', e, 0)[0]
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ib = struct.unpack_from('<I', e, 4)[0]
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it = struct.unpack_from('<I', e, 8)[0]
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cs = struct.unpack_from('<H', e, 30)[0]
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print(f'[gdt] group {i}: bb={bb} ib={ib} it={it} csum=0x{cs:04x}')
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if bb == 0 and ib == 0 and it == 0:
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ok = False
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if not ok:
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print('[gdt] WARNING: backup GDT looks empty, check parameters')
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else:
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print(f'[gdt] backup GDT loaded OK ({PRIMARY_GDT_SIZE//1024}KB)')
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return ok
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def read_virtual(virt_offset, length):
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"""
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Read with backup GDT overlay.
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Primary GDT region (virtual bytes 4096..4096+NUM_GROUPS*64) is
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served from the cached backup GDT instead of the primary location.
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Everything else is pure chunk translation.
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"""
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req_end = virt_offset + length
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# Fast path: no overlap with primary GDT
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if req_end <= PRIMARY_GDT_START or virt_offset >= PRIMARY_GDT_END:
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return raw_read(virt_offset, length)
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# Build result from possibly multiple segments
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data = bytearray(raw_read(virt_offset, length))
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# Overlay backup GDT where request overlaps primary GDT
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ol_start = max(virt_offset, PRIMARY_GDT_START)
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ol_end = min(req_end, PRIMARY_GDT_END)
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if ol_start < ol_end and _backup_gdt is not None:
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src_off = ol_start - PRIMARY_GDT_START
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dst_off = ol_start - virt_offset
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n = ol_end - ol_start
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data[dst_off:dst_off + n] = _backup_gdt[src_off:src_off + n]
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return bytes(data)
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def recv_all(conn, n):
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buf = b''
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while len(buf) < n:
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d = conn.recv(n - len(buf))
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if not d:
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raise ConnectionError('disconnected')
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buf += d
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return buf
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def send_reply(conn, opt, rtype, data=b''):
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conn.sendall(struct.pack('>Q', REPLYMAGIC))
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conn.sendall(struct.pack('>I', opt))
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conn.sendall(struct.pack('>I', rtype))
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conn.sendall(struct.pack('>I', len(data)))
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if data:
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conn.sendall(data)
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def handle_client(conn, addr):
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print(f'[nbd] {addr} connected')
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try:
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conn.sendall(struct.pack('>Q', NBDMAGIC))
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conn.sendall(struct.pack('>Q', IHAVEOPT))
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conn.sendall(struct.pack('>H', 0x0003))
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recv_all(conn, 4)
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while True:
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hdr = recv_all(conn, 16)
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_, opt, opt_len = struct.unpack('>QII', hdr)
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opt_data = recv_all(conn, opt_len) if opt_len else b''
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if opt == NBD_OPT_EXPORT_NAME:
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conn.sendall(struct.pack('>Q', VIRT_SIZE))
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conn.sendall(struct.pack('>H', TX_FLAGS))
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break
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elif opt == NBD_OPT_GO:
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info = struct.pack('>HQH', NBD_INFO_EXPORT, VIRT_SIZE, TX_FLAGS)
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send_reply(conn, opt, NBD_REP_INFO, info)
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send_reply(conn, opt, NBD_REP_ACK)
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break
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elif opt == NBD_OPT_LIST:
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send_reply(conn, opt, NBD_REP_SERVER,
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struct.pack('>I', 0))
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send_reply(conn, opt, NBD_REP_ACK)
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elif opt == NBD_OPT_ABORT:
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send_reply(conn, opt, NBD_REP_ACK)
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return
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else:
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send_reply(conn, opt, NBD_REP_ERR_UNSUP)
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print(f'[nbd] {addr} transmission ({VIRT_SIZE//1024//1024//1024}GB)')
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while True:
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hdr = recv_all(conn, 28)
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magic, flags, cmd, handle, offset, length = \
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struct.unpack('>IHHQQI', hdr)
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if magic != NBD_REQUEST_MAGIC:
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return
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if cmd == NBD_CMD_READ:
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try:
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payload = read_virtual(offset, length)
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except Exception as e:
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print(f'[nbd] read error @ {offset}+{length}: {e}')
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payload = b'\x00' * length
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conn.sendall(struct.pack('>IIQ', NBD_REPLY_MAGIC, 0, handle))
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conn.sendall(payload)
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elif cmd == NBD_CMD_FLUSH:
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conn.sendall(struct.pack('>IIQ', NBD_REPLY_MAGIC, 0, handle))
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elif cmd == NBD_CMD_DISC:
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return
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else:
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conn.sendall(struct.pack('>IIQ', NBD_REPLY_MAGIC, 1, handle))
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except (ConnectionError, BrokenPipeError, ConnectionResetError):
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pass
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except Exception as e:
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print(f'[nbd] {addr} error: {e}')
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import traceback; traceback.print_exc()
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finally:
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conn.close()
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def main():
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print('PERC H710 recovery NBD server v6')
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print(f' device : {DEV}')
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print(f' lv_start : byte {LV_PHYS_START}')
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print(f' virt_size : {VIRT_SIZE//1024//1024//1024} GB')
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print(f' primary GDT: virtual bytes {PRIMARY_GDT_START}-{PRIMARY_GDT_END}')
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print(f' backup GDT : virtual byte {BACKUP_GDT_START}')
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print()
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if not load_backup_gdt():
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print('ERROR: backup GDT load failed, check BACKUP_GDT_START')
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sys.exit(1)
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srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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srv.bind(('127.0.0.1', 10809))
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srv.listen(5)
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print()
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print('Listening on 127.0.0.1:10809')
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print(' nbd-client 127.0.0.1 10809 /dev/nbd0 -N ""')
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print(' mount -o ro,norecovery -t ext4 /dev/nbd0 /mnt/root')
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print()
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while True:
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conn, addr = srv.accept()
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threading.Thread(target=handle_client, args=(conn, addr),
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daemon=True).start()
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if __name__ == '__main__':
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main()
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