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// Copyright (C) 2020 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#pragma once
namespace android {
namespace snapshot {
#define DM_USER_REQ_MAP_READ 0
#define DM_USER_REQ_MAP_WRITE 1
#define DM_USER_RESP_SUCCESS 0
#define DM_USER_RESP_ERROR 1
#define DM_USER_RESP_UNSUPPORTED 2
// Kernel COW header fields
static constexpr uint32_t SNAP_MAGIC = 0x70416e53;
static constexpr uint32_t SNAPSHOT_DISK_VERSION = 1;
static constexpr uint32_t NUM_SNAPSHOT_HDR_CHUNKS = 1;
static constexpr uint32_t SNAPSHOT_VALID = 1;
/*
* The basic unit of block I/O is a sector. It is used in a number of contexts
* in Linux (blk, bio, genhd). The size of one sector is 512 = 2**9
* bytes. Variables of type sector_t represent an offset or size that is a
* multiple of 512 bytes. Hence these two constants.
*/
static constexpr uint32_t SECTOR_SHIFT = 9;
typedef __u64 sector_t;
typedef sector_t chunk_t;
static constexpr uint32_t CHUNK_SIZE = 8;
static constexpr uint32_t CHUNK_SHIFT = (__builtin_ffs(CHUNK_SIZE) - 1);
#define DIV_ROUND_UP(n, d) (((n) + (d)-1) / (d))
// This structure represents the kernel COW header.
// All the below fields should be in Little Endian format.
struct disk_header {
uint32_t magic;
/*
* Is this snapshot valid. There is no way of recovering
* an invalid snapshot.
*/
uint32_t valid;
/*
* Simple, incrementing version. no backward
* compatibility.
*/
uint32_t version;
/* In sectors */
uint32_t chunk_size;
} __packed;
// A disk exception is a mapping of old_chunk to new_chunk
// old_chunk is the chunk ID of a dm-snapshot device.
// new_chunk is the chunk ID of the COW device.
struct disk_exception {
uint64_t old_chunk;
uint64_t new_chunk;
} __packed;
// Control structures to communicate with dm-user
// It comprises of header and a payload
struct dm_user_header {
__u64 seq;
__u64 type;
__u64 flags;
__u64 sector;
__u64 len;
} __attribute__((packed));
struct dm_user_payload {
__u8 buf[];
};
// Message comprising both header and payload
struct dm_user_message {
struct dm_user_header header;
struct dm_user_payload payload;
};
} // namespace snapshot
} // namespace android
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