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drgn/contrib/btrfs_tree.py
Boris Burkov c0694d6ce2 Add btrfs helpers to contrib 
btrfs_tree.py is a pile of helpers Omar gave me once that I have
cherished ever since. It mostly deals with walking and parsing btrees.

btrfs_tree_mod_log.py is a script I wrote to do a tree mod log search
and rewind while debugging a btrfs issue.

Signed-off-by: Boris Burkov <boris@bur.io>
2023-06-09 09:38:26 -07:00

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# Copyright (c) Meta Platforms, Inc. and affiliates.
# SPDX-License-Identifier: LGPL-2.1-or-later
import enum
import struct
from typing import NamedTuple, Sequence
import uuid
import drgn
from drgn import NULL, cast, offsetof
from drgn.helpers.linux.mm import page_to_virt
from drgn.helpers.linux.radixtree import radix_tree_lookup
"""Helpers for introspecting btrfs btree structures"""
page_address = page_to_virt
_crc32c_table = [0] * 256
for i in range(256):
fwd = i
for j in range(8, 0, -1):
if fwd & 1:
fwd = (fwd >> 1) ^ 0x82f63b78
else:
fwd >>= 1
_crc32c_table[i] = fwd & 0xffffffff
def crc32c(b: bytes, crc: int = 0) -> int:
for c in b:
crc = (crc >> 8) ^ _crc32c_table[(crc ^ c) & 0xff]
return crc
def btrfs_name_hash(name: bytes) -> int:
return crc32c(name, 0xfffffffe)
_btrfs_disk_key_fmt = "<QBQ"
_btrfs_disk_key_struct = struct.Struct(_btrfs_disk_key_fmt)
_btrfs_item_struct = struct.Struct(_btrfs_disk_key_fmt + "II")
_btrfs_header_struct = struct.Struct("<32s16sQQ16sQQIB")
_btrfs_key_ptr_struct = struct.Struct(_btrfs_disk_key_fmt + "QQ")
class BtrfsDiskKey(NamedTuple):
objectid: int
type: int
offset: int
@staticmethod
def from_bytes(b, offset=0):
return BtrfsDiskKey(*_btrfs_disk_key_struct.unpack_from(b, offset))
@staticmethod
def sizeof():
return _btrfs_disk_key_struct.size
class BtrfsKeyPtr(NamedTuple):
key: BtrfsDiskKey
blockptr: int
generation: int
@staticmethod
def from_bytes(b, offset=0):
t = _btrfs_key_ptr_struct.unpack_from(b, offset)
return BtrfsKeyPtr(BtrfsDiskKey(*t[:3]), *t[3:])
@staticmethod
def sizeof():
return _btrfs_key_ptr_struct.size
class BtrfsHeader(NamedTuple):
csum: bytes
fsid: bytes
bytenr: int
flags: int
chunk_tree_uuid: bytes
generation: int
owner: int
nritems: int
level: int
@staticmethod
def from_bytes(b, offset=0):
return BtrfsHeader(*_btrfs_header_struct.unpack_from(b, offset))
@staticmethod
def sizeof():
return _btrfs_header_struct.size
class BtrfsNode(NamedTuple):
header: BtrfsHeader
ptrs: Sequence[BtrfsKeyPtr]
class BtrfsType(enum.IntEnum):
UNTYPED = 0
# Generated with
# sed -rn 's/^#\s*define\s+BTRFS_([0-9A-Za-z_]+)_KEY\s+([0-9]+)/ \1 = \2/p' include/uapi/linux/btrfs_tree.h
INODE_ITEM = 1
INODE_REF = 12
INODE_EXTREF = 13
XATTR_ITEM = 24
ORPHAN_ITEM = 48
DIR_LOG_ITEM = 60
DIR_LOG_INDEX = 72
DIR_ITEM = 84
DIR_INDEX = 96
EXTENT_DATA = 108
EXTENT_CSUM = 128
ROOT_ITEM = 132
ROOT_BACKREF = 144
ROOT_REF = 156
EXTENT_ITEM = 168
METADATA_ITEM = 169
TREE_BLOCK_REF = 176
EXTENT_DATA_REF = 178
EXTENT_REF_V0 = 180
SHARED_BLOCK_REF = 182
SHARED_DATA_REF = 184
BLOCK_GROUP_ITEM = 192
FREE_SPACE_INFO = 198
FREE_SPACE_EXTENT = 199
FREE_SPACE_BITMAP = 200
DEV_EXTENT = 204
DEV_ITEM = 216
CHUNK_ITEM = 228
QGROUP_STATUS = 240
QGROUP_INFO = 242
QGROUP_LIMIT = 244
QGROUP_RELATION = 246
BALANCE_ITEM = 248
TEMPORARY_ITEM = 248
DEV_STATS = 249
PERSISTENT_ITEM = 249
DEV_REPLACE = 250
STRING_ITEM = 253
_btrfs_types = {
BtrfsType.INODE_ITEM: "struct btrfs_inode_item",
BtrfsType.INODE_REF: "struct btrfs_inode_ref",
# BtrfsType.INODE_EXTREF
BtrfsType.XATTR_ITEM: "struct btrfs_dir_item",
# BtrfsType.ORPHAN_ITEM
# BtrfsType.DIR_LOG_ITEM
# BtrfsType.DIR_LOG_INDEX
BtrfsType.DIR_ITEM: "struct btrfs_dir_item",
BtrfsType.DIR_INDEX: "struct btrfs_dir_item",
# BtrfsType.EXTENT_DATA
# BtrfsType.EXTENT_CSUM
# BtrfsType.ROOT_ITEM
# BtrfsType.ROOT_BACKREF
# BtrfsType.ROOT_REF
# BtrfsType.EXTENT_ITEM
# BtrfsType.METADATA_ITEM
# BtrfsType.TREE_BLOCK_REF
# BtrfsType.EXTENT_DATA_REF
# BtrfsType.EXTENT_REF_V0
# BtrfsType.SHARED_BLOCK_REF
# BtrfsType.SHARED_DATA_REF
# BtrfsType.BLOCK_GROUP_ITEM
# BtrfsType.FREE_SPACE_INFO
# BtrfsType.FREE_SPACE_EXTENT
# BtrfsType.FREE_SPACE_BITMAP
# BtrfsType.DEV_EXTENT
# BtrfsType.DEV_ITEM
# BtrfsType.CHUNK_ITEM
# BtrfsType.QGROUP_STATUS
# BtrfsType.QGROUP_INFO
# BtrfsType.QGROUP_LIMIT
# BtrfsType.QGROUP_RELATION
# BtrfsType.BALANCE_ITEM
# BtrfsType.TEMPORARY_ITEM
# BtrfsType.DEV_STATS
# BtrfsType.PERSISTENT_ITEM
# BtrfsType.DEV_REPLACE
# BtrfsType.STRING_ITEM
}
_btrfs_types_with_name = {
"struct btrfs_inode_ref",
"struct btrfs_dir_item",
}
class BtrfsKey(NamedTuple):
objectid: int
type: BtrfsType
offset: int
class BtrfsItem(NamedTuple):
key: BtrfsKey
offset: int
size: int
def offset_in_page(p):
return (p & ~p.prog_["PAGE_MASK"]).value_()
# TODO: these can probably hardcode more offsets and sizes since that's part of
# the on-disk format
_btrfs_leaf_items_offset = 101 # offsetof(struct btrfs_leaf, items)
_btrfs_item_size = 25 # sizeof(struct btrfs_item)
_btrfs_node_ptrs_offset = 101 # offsetof(struct btrfs_node, ptrs)
_btrfs_key_ptr_size = 33 # sizeof(prog.type("struct btrfs_key_ptr"))
def btrfs_header_level(eb):
return eb.prog_.read_u8(
page_address(eb.pages[0])
+ offset_in_page(eb.start)
+ offsetof(eb.prog_.type("struct btrfs_header"), "level")
)
def btrfs_header_nritems(eb):
return int.from_bytes(
eb.prog_.read(
page_address(eb.pages[0])
+ offset_in_page(eb.start)
+ offsetof(eb.prog_.type("struct btrfs_header"), "nritems"),
4,
),
"little",
)
def btrfs_node_blockptr(eb, nr):
prog = eb.prog_
return int.from_bytes(
prog.read(
page_address(eb.pages[0])
+ offset_in_page(eb.start)
+ _btrfs_node_ptrs_offset
+ _btrfs_key_ptr_size * nr
+ offsetof(prog.type("struct btrfs_key_ptr"), "blockptr"),
8,
),
"little",
)
def read_extent_buffer(eb, start, len):
prog = eb.prog_
PAGE_SIZE = prog["PAGE_SIZE"].value_()
i = (start >> prog["PAGE_SHIFT"]).value_()
offset = offset_in_page(eb.start + start)
ret = []
while len > 0:
cur = min(len, PAGE_SIZE - offset)
ret.append(prog.read(page_address(eb.pages[i]) + offset, cur))
len -= cur
offset = 0
i += 1
return b"".join(ret)
def _btrfs_bin_search(eb, p, item_size, key: BtrfsKey):
low = 0
high = btrfs_header_nritems(eb)
while low < high:
mid = (low + high) // 2
offset = p + mid * item_size
disk_objectid, disk_type, disk_offset = _btrfs_disk_key_struct.unpack(read_extent_buffer(eb, offset, 17))
disk_key = BtrfsKey(disk_objectid, BtrfsType(disk_type), disk_offset)
if disk_key < key:
low = mid + 1
elif disk_key > key:
high = mid
else:
return 0, mid
return 1, low
def _get_block_for_search(fs_info, eb, level, slot):
blocknr = btrfs_node_blockptr(eb, slot)
tmp = cast(
eb.type_,
radix_tree_lookup(fs_info.buffer_radix.address_of_(),
blocknr >> fs_info.sectorsize_bits)
)
if not tmp:
raise Exception(f"extent_buffer {blocknr} is not cached")
if tmp.refs.counter == 0:
raise Exception(f"extent_buffer {blocknr} is dead")
if not tmp.bflags & (1 << fs_info.prog_["EXTENT_BUFFER_UPTODATE"]):
raise Exception(f"extent_buffer {blocknr} is not up to date")
# TODO: check transid, level?
return tmp
def btrfs_search_slot(root, key: BtrfsKey, *, search_commit_root: bool = False):
prog = root.prog_
fs_info = root.fs_info.read_()
nodes = []
slots = []
prev_cmp = -1
if search_commit_root:
b = root.commit_root.read_()
else:
b = root.node.read_()
try:
while True:
nodes.append(b)
level = btrfs_header_level(b)
if prev_cmp == 0:
slot = 0
ret = 0
else:
if level == 0:
ret, slot = _btrfs_bin_search(b, _btrfs_leaf_items_offset, _btrfs_item_size, key)
else:
ret, slot = _btrfs_bin_search(b, _btrfs_node_ptrs_offset, _btrfs_key_ptr_size, key)
prev_cmp = ret
if level == 0:
slots.append(slot)
break
if ret and slot > 0:
slot -= 1
slots.append(slot)
b = _get_block_for_search(fs_info, b, level, slot)
except Exception as e:
print(e)
ret = -1
nodes.reverse()
slots.reverse()
return ret, nodes, slots
def btrfs_leaf_items(eb):
if btrfs_header_level(eb) != 0:
raise ValueError("buffer is not leaf")
nritems = btrfs_header_nritems(eb)
buf = read_extent_buffer(eb, _btrfs_leaf_items_offset, nritems * _btrfs_item_size)
items = []
for i in range(nritems):
raw_item = _btrfs_item_struct.unpack_from(buf, i * _btrfs_item_size)
items.append(
BtrfsItem(BtrfsKey(raw_item[0], raw_item[1], raw_item[2]), raw_item[3], raw_item[4])
)
return items
def _parse_item_from_buf(buf, type, offset):
while type.kind == drgn.TypeKind.TYPEDEF:
type = type.type
if type.kind == drgn.TypeKind.INT:
return int.from_bytes(buf[offset:offset + type.size], "little")
elif type.kind == drgn.TypeKind.STRUCT:
return {
member.name: _parse_item_from_buf(buf, member.type, offset + member.offset)
for member in type.members
}
elif type.kind == drgn.TypeKind.ARRAY:
element_type = type.type
element_size = sizeof(element_type)
return [
_parse_item_from_buf(buf, element_type, offset + i * element_size)
for i in range(type.length)
]
else:
assert False, type.kind
def btrfs_read_item(eb, slot):
if btrfs_header_level(eb) != 0:
raise ValueError("buffer is not leaf")
if slot >= btrfs_header_nritems(eb):
raise IndexError("slot is out of bounds")
item_buf = read_extent_buffer(eb, _btrfs_leaf_items_offset + slot * _btrfs_item_size, _btrfs_item_size)
objectid, type, offset, data_offset, data_size = _btrfs_item_struct.unpack(item_buf)
key = BtrfsKey(objectid, BtrfsType(type), offset)
data_buf = read_extent_buffer(eb, _btrfs_leaf_items_offset + data_offset, data_size)
try:
type_name = _btrfs_types[key.type]
except KeyError:
return key, data_buf
item_type = prog.type(type_name)
data = _parse_item_from_buf(data_buf, item_type, 0)
pos = sizeof(item_type)
if type_name in _btrfs_types_with_name:
data["name"] = data_buf[pos:pos + data["name_len"]]
pos += data["name_len"]
if type_name == "struct btrfs_dir_item":
data["data"] = data_buf[pos:pos + data["data_len"]]
pos += data["data_len"]
return key, data
def parse_extent_buffer(eb):
header = BtrfsHeader.from_bytes(read_extent_buffer(eb, 0, BtrfsHeader.sizeof()))
if header.level == 0:
assert False
else:
ptrs_buf = read_extent_buffer(eb, BtrfsHeader.sizeof(), header.nritems * BtrfsKeyPtr.sizeof())
return BtrfsNode(
header,
[
BtrfsKeyPtr.from_bytes(ptrs_buf, i * BtrfsKeyPtr.sizeof())
for i in range(header.nritems)
]
)
def print_extent_buffer(eb):
node = parse_extent_buffer(eb)
print(f"node {node.header.bytenr} level {node.header.level} items {node.header.nritems} generation {node.header.generation} owner {node.header.owner}")
print(f"node {node.header.bytenr} flags {node.header.flags:#x}")
print(f"fs uuid {uuid.UUID(bytes=node.header.fsid)}")
print(f"chunk uuid {uuid.UUID(bytes=node.header.chunk_tree_uuid)}")
for i, ptr in enumerate(node.ptrs):
print(f"\tptr {i} key ({ptr.key.objectid}, {ptr.key.type}, {ptr.key.offset}) block {ptr.blockptr} gen {ptr.generation}")
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