summaryrefslogtreecommitdiff
path: root/include/sqfs/meta_writer.h
blob: 58968f58dd5ca7a5303e9b9a838a3cbfbc674c34 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
/* SPDX-License-Identifier: LGPL-3.0-or-later */
/*
 * meta_writer.h - This file is part of libsquashfs
 *
 * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
#ifndef SQFS_META_WRITER_H
#define SQFS_META_WRITER_H

#include "sqfs/predef.h"

/**
 * @file meta_writer.h
 *
 * @brief Contains declarations for the @ref sqfs_meta_writer_t.
 */

/**
 * @struct sqfs_meta_writer_t
 *
 * @implements sqfs_object_t
 *
 * @brief Abstracts generating of meta data blocks, either in memory or
 *        directly on disk.
 *
 * SquashFS stores meta data by dividing it into fixed size (8k) chunks
 * that are written to disk with a small header indicating the on-disk
 * size and whether it is compressed or not.
 *
 * Data written to meta data blocks doesn't have to be aligned, i.e.
 * SquashFS doesn't care if an object is written across two blocks.
 *
 * The main task of the meta data writer is to provide a simple append
 * function that transparently takes care of chopping data up into blocks,
 * compressing the blocks and pre-pending a header.
 *
 * This object is not copyable, i.e. @ref sqfs_copy will always return NULL.
 */

/**
 * @enum E_SQFS_META_WRITER_FLAGS
 *
 * @brief Possible flags for @ref sqfs_meta_writer_create.
 */
typedef enum {
	/**
	 * @brief If set, keep finished blocks in memory.
	 *
	 * To write them to disk, explicitly call
	 * @ref sqfs_meta_write_write_to_file.
	 */
	SQFS_META_WRITER_KEEP_IN_MEMORY = 0x01,

	SQFS_META_WRITER_ALL_FLAGS = 0x01,
} E_SQFS_META_WRITER_FLAGS;

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @brief Create a meta data writer.
 *
 * @memberof sqfs_meta_writer_t
 *
 * @note The meta writer internally keeps references to the pointers passed
 *       to this function, so don't destroy them before destroying the
 *       meta writer.
 *
 * @param file An output file to write the data to.
 * @param cmp A compressor to use.
 * @param flags A combination of @ref E_SQFS_META_WRITER_FLAGS.
 *
 * @return A pointer to a meta writer on success, NULL on allocation failure
 *         or if an unknown flag was set.
 */
SQFS_API sqfs_meta_writer_t *sqfs_meta_writer_create(sqfs_file_t *file,
						     sqfs_compressor_t *cmp,
						     sqfs_u32 flags);

/**
 * @brief Finish the current block, even if it isn't full yet.
 *
 * @memberof sqfs_meta_writer_t
 *
 * This function forces the meta writer to compress and store the block it
 * is currently writing to, even if it isn't full yet, and either write it
 * out to disk (or append it to the in memory chain if told to keep blocks
 * in memory).
 *
 * @param m A pointer to a meta data writer.
 *
 * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
 */
SQFS_API int sqfs_meta_writer_flush(sqfs_meta_writer_t *m);

/**
 * @brief Finish the current block, even if it isn't full yet.
 *
 * @memberof sqfs_meta_writer_t
 *
 * This function forces reads a speicifed number of bytes from a given data
 * block and appends it to the meta data block that the writer is currently
 * working on. If the block becomes full, it is compressed, written to disk
 * and a new block is started that the remaining data is written to.
 *
 * @param m A pointer to a meta data writer.
 * @param data A pointer to a chunk of data to append to the writer.
 * @param size The number of data bytes to append.
 *
 * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
 */
SQFS_API int sqfs_meta_writer_append(sqfs_meta_writer_t *m, const void *data,
				     size_t size);

/**
 * @brief Query the current block start position and offset within the block
 *
 * @memberof sqfs_meta_writer_t
 *
 * Get the byte offset relative to the first block that the current block will
 * start at once it is written to disk and get the byte offset within this
 * block that the next call to @ref sqfs_meta_writer_append will start writing
 * data at.
 *
 * @param m A pointer to a meta data writer.
 * @param block_start Returns the offset of the current block from the first.
 * @param offset Returns an offset into the current block where the next write
 *               starts.
 */
SQFS_API void sqfs_meta_writer_get_position(const sqfs_meta_writer_t *m,
					    sqfs_u64 *block_start,
					    sqfs_u32 *offset);

/**
 * @brief Reset all internal state, including the current block start position.
 *
 * @memberof sqfs_meta_writer_t
 *
 * This functions forces the meta data writer to forget everything that
 * happened since it was created, so it can be recycled.
 *
 * The data written is not lost, unless it was kept in memory and never written
 * out to disk.
 */
SQFS_API void sqfs_meta_writer_reset(sqfs_meta_writer_t *m);

/**
 * @brief Write all blocks collected in memory to disk
 *
 * @memberof sqfs_meta_writer_t
 *
 * If the meta writer was created with the flag set to store blocks in
 * memory instead of writing them to disk, calling this function forces
 * the meta writer to write out all blocks it collected so far.
 *
 * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
 */
SQFS_API int sqfs_meta_write_write_to_file(sqfs_meta_writer_t *m);

/**
 * @brief A convenience function for encoding and writing an inode
 *
 * @memberof sqfs_meta_writer_t
 *
 * The SquashFS inode table is essentially a series of meta data blocks
 * containing variable sized inodes. This function takes a generic inode
 * structure, encodes it and writes the result to a meta data writer
 * using @ref sqfs_meta_writer_append internally.
 *
 * @param iw A pointer to a meta data writer.
 * @param n A pointer to an inode.
 *
 * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
 */
SQFS_API int sqfs_meta_writer_write_inode(sqfs_meta_writer_t *iw,
					  const sqfs_inode_generic_t *n);

#ifdef __cplusplus
}
#endif

#endif /* SQFS_META_WRITER_H */