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// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Update file format: A delta update file contains all the deltas needed
// to update a system from one specific version to another specific
// version. The update format is represented by this struct pseudocode:
// struct delta_update_file {
// char magic[4] = "CrAU";
// uint64 file_format_version = 1;
// uint64 manifest_size; // Size of protobuf DeltaArchiveManifest
// // The Bzip2 compressed DeltaArchiveManifest
// char manifest[];
// // Data blobs for files, no specific format. The specific offset
// // and length of each data blob is recorded in the DeltaArchiveManifest.
// struct {
// char data[];
// } blobs[];
// // These two are not signed:
// uint64 signatures_message_size;
// char signatures_message[];
// };
// The DeltaArchiveManifest protobuf is an ordered list of InstallOperation
// objects. These objects are stored in a linear array in the
// DeltaArchiveManifest. Each operation is applied in order by the client.
// The DeltaArchiveManifest also contains the initial and final
// checksums for the device.
// The client will perform each InstallOperation in order, beginning even
// before the entire delta file is downloaded (but after at least the
// protobuf is downloaded). The types of operations are explained:
// - REPLACE: Replace the dst_extents on the drive with the attached data,
// zero padding out to block size.
// - REPLACE_BZ: bzip2-uncompress the attached data and write it into
// dst_extents on the drive, zero padding to block size.
// - MOVE: Copy the data in src_extents to dst_extents. Extents may overlap,
// so it may be desirable to read all src_extents data into memory before
// writing it out.
// - BSDIFF: Read src_length bytes from src_extents into memory, perform
// bspatch with attached data, write new data to dst_extents, zero padding
// to block size.
package chromeos_update_engine;
// Data is packed into blocks on disk, always starting from the beginning
// of the block. If a file's data is too large for one block, it overflows
// into another block, which may or may not be the following block on the
// physical partition. An ordered list of extents is another
// representation of an ordered list of blocks. For example, a file stored
// in blocks 9, 10, 11, 2, 18, 12 (in that order) would be stored in
// extents { {9, 3}, {2, 1}, {18, 1}, {12, 1} } (in that order).
// In general, files are stored sequentially on disk, so it's more efficient
// to use extents to encode the block lists (this is effectively
// run-length encoding).
// A sentinel value (kuint64max) as the start block denotes a sparse-hole
// in a file whose block-length is specified by num_blocks.
// Signatures: Updates may be signed by the OS vendor. The client verifies
// an update's signature by hashing the entire download. The section of the
// download the contains the signature is at the end of the file, so when
// signing a file, only the part up to the signature part is signed.
// Then, the client looks inside the download's Signatures message for a
// Signature message that it knows how to handle. Generally, a client will
// only know how to handle one type of signature, but an update may contain
// many signatures to support many different types of client. Then client
// selects a Signature message and uses that, along with a known public key,
// to verify the download. The public key is expected to be part of the
// client.
message Extent {
optional uint64 start_block = 1;
optional uint64 num_blocks = 2;
message Signatures {
message Signature {
optional uint32 version = 1;
optional bytes data = 2;
repeated Signature signatures = 1;
message PartitionInfo {
optional uint64 size = 1;
optional bytes hash = 2;
message DeltaArchiveManifest {
message InstallOperation {
enum Type {
REPLACE = 0; // Replace destination extents w/ attached data
REPLACE_BZ = 1; // Replace destination extents w/ attached bzipped data
MOVE = 2; // Move source extents to destination extents
BSDIFF = 3; // The data is a bsdiff binary diff
required Type type = 1;
// The offset into the delta file (after the protobuf)
// where the data (if any) is stored
optional uint32 data_offset = 2;
// The length of the data in the delta file
optional uint32 data_length = 3;
// Ordered list of extents that are read from (if any) and written to.
repeated Extent src_extents = 4;
// Byte length of src, not necessarily block aligned. It's only used for
// BSDIFF, because we need to pass that external program the number
// of bytes to read from the blocks we pass it.
optional uint64 src_length = 5;
repeated Extent dst_extents = 6;
// byte length of dst, not necessarily block aligned. It's only used for
// BSDIFF, because we need to fill in the rest of the last block
// that bsdiff writes with '\0' bytes.
optional uint64 dst_length = 7;
repeated InstallOperation install_operations = 1;
repeated InstallOperation kernel_install_operations = 2;
// (At time of writing) usually 4096
optional uint32 block_size = 3 [default = 4096];
// If signatures are present, the offset into the blobs, generally
// tacked onto the end of the file, and the length. We use an offset
// rather than a bool to allow for more flexibility in future file formats.
// If either is absent, it means signatures aren't supported in this
// file.
optional uint64 signatures_offset = 4;
optional uint64 signatures_size = 5;
// Partition data that can be used to validate the update.
optional PartitionInfo old_kernel_info = 6;
optional PartitionInfo new_kernel_info = 7;
optional PartitionInfo old_rootfs_info = 8;
optional PartitionInfo new_rootfs_info = 9;