| Gilad Arnold | 553b0ec | 2013-01-26 01:00:39 -0800 | [diff] [blame^] | 1 | # Copyright (c) 2013 The Chromium OS Authors. All rights reserved. |
| 2 | # Use of this source code is governed by a BSD-style license that can be |
| 3 | # found in the LICENSE file. |
| 4 | |
| 5 | """Tracing block data source through a Chrome OS update payload. |
| 6 | |
| 7 | This module is used internally by the main Payload class for tracing block |
| 8 | content through an update payload. This is a useful feature in debugging |
| 9 | payload applying functionality in this package. The interface for invoking the |
| 10 | tracer is as follows: |
| 11 | |
| 12 | tracer = PayloadBlockTracer(payload) |
| 13 | tracer.Run(...) |
| 14 | |
| 15 | """ |
| 16 | |
| 17 | import common |
| 18 | |
| 19 | |
| 20 | # |
| 21 | # Payload block tracing. |
| 22 | # |
| 23 | class PayloadBlockTracer(object): |
| 24 | """Tracing the origin of block data through update instructions. |
| 25 | |
| 26 | This is a short-lived object whose purpose is to isolate the logic used for |
| 27 | tracing the origin of destination partition blocks. |
| 28 | |
| 29 | """ |
| 30 | |
| 31 | def __init__(self, payload): |
| 32 | assert payload.is_init, 'uninitialized update payload' |
| 33 | self.payload = payload |
| 34 | |
| 35 | @staticmethod |
| 36 | def _TraceBlock(block, skip, trace_out_file, operations, base_name): |
| 37 | """Trace the origin of a given block through a sequence of operations. |
| 38 | |
| 39 | This method tries to map the given dest block to the corresponding source |
| 40 | block from which its content originates in the course of an update. It |
| 41 | further tries to trace transitive origins through MOVE operations. It is |
| 42 | rather efficient, doing the actual tracing by means of a single reverse |
| 43 | sweep through the operation sequence. It dumps a log of operations and |
| 44 | source blocks responsible for the data in the given dest block to the |
| 45 | provided output file. |
| 46 | |
| 47 | Args: |
| 48 | block: the block number to trace |
| 49 | skip: number of initial transitive origins to ignore |
| 50 | trace_out_file: a file object to dump the trace to |
| 51 | operations: the sequence of operations |
| 52 | base_name: name of the operation sequence |
| 53 | |
| 54 | """ |
| 55 | # Traverse operations backwards. |
| 56 | for op, op_name in common.OperationIter(operations, base_name, |
| 57 | reverse=True): |
| 58 | total_block_offset = 0 |
| 59 | found = False |
| 60 | |
| 61 | # Is the traced block mentioned in the dest extents? |
| 62 | for dst_ex, dst_ex_name in common.ExtentIter(op.dst_extents, |
| 63 | op_name + '.dst_extents'): |
| 64 | if (block >= dst_ex.start_block |
| 65 | and block < dst_ex.start_block + dst_ex.num_blocks): |
| 66 | if skip: |
| 67 | skip -= 1 |
| 68 | else: |
| 69 | total_block_offset += block - dst_ex.start_block |
| 70 | trace_out_file.write( |
| 71 | '%s: found %s (total block offset: %d)\n' % |
| 72 | (dst_ex_name, common.FormatExtent(dst_ex), total_block_offset)) |
| 73 | found = True |
| 74 | break |
| 75 | |
| 76 | total_block_offset += dst_ex.num_blocks |
| 77 | |
| 78 | if found: |
| 79 | # Don't trace further, unless it's a MOVE. |
| 80 | if op.type != common.OpType.MOVE: |
| 81 | break |
| 82 | |
| 83 | # For MOVE, find corresponding source block and keep tracing. |
| 84 | for src_ex, src_ex_name in common.ExtentIter(op.src_extents, |
| 85 | op_name + '.src_extents'): |
| 86 | if total_block_offset < src_ex.num_blocks: |
| 87 | block = src_ex.start_block + total_block_offset |
| 88 | trace_out_file.write( |
| 89 | '%s: mapped to %s (%d)\n' % |
| 90 | (src_ex_name, common.FormatExtent(src_ex), block)) |
| 91 | break |
| 92 | |
| 93 | total_block_offset -= src_ex.num_blocks |
| 94 | |
| 95 | def Run(self, block, skip, trace_out_file, is_kernel): |
| 96 | """Block tracer entry point, invoking the actual search. |
| 97 | |
| 98 | Args: |
| 99 | block: the block number whose origin to trace |
| 100 | skip: the number of first origin mappings to skip |
| 101 | trace_out_file: file object to dump the trace to |
| 102 | is_kernel: trace through kernel (True) or rootfs (False) operations |
| 103 | |
| 104 | """ |
| 105 | if is_kernel: |
| 106 | self._TraceBlock(block, skip, trace_out_file, |
| 107 | self.payload.manifest.kernel_install_operations, |
| 108 | 'kernel_install_operations') |
| 109 | else: |
| 110 | self._TraceBlock(block, skip, trace_out_file, |
| 111 | self.payload.manifest.install_operations, |
| 112 | 'install_operations') |