linux/fs/btrfs/lzo.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2008 Oracle.  All rights reserved.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/bio.h>
#include <linux/lzo.h>
#include <linux/refcount.h>
#include "messages.h"
#include "compression.h"
#include "ctree.h"
#include "super.h"
#include "btrfs_inode.h"

#define LZO_LEN …

/*
 * Btrfs LZO compression format
 *
 * Regular and inlined LZO compressed data extents consist of:
 *
 * 1.  Header
 *     Fixed size. LZO_LEN (4) bytes long, LE32.
 *     Records the total size (including the header) of compressed data.
 *
 * 2.  Segment(s)
 *     Variable size. Each segment includes one segment header, followed by data
 *     payload.
 *     One regular LZO compressed extent can have one or more segments.
 *     For inlined LZO compressed extent, only one segment is allowed.
 *     One segment represents at most one sector of uncompressed data.
 *
 * 2.1 Segment header
 *     Fixed size. LZO_LEN (4) bytes long, LE32.
 *     Records the total size of the segment (not including the header).
 *     Segment header never crosses sector boundary, thus it's possible to
 *     have at most 3 padding zeros at the end of the sector.
 *
 * 2.2 Data Payload
 *     Variable size. Size up limit should be lzo1x_worst_compress(sectorsize)
 *     which is 4419 for a 4KiB sectorsize.
 *
 * Example with 4K sectorsize:
 * Page 1:
 *          0     0x2   0x4   0x6   0x8   0xa   0xc   0xe     0x10
 * 0x0000   |  Header   | SegHdr 01 | Data payload 01 ...     |
 * ...
 * 0x0ff0   | SegHdr  N | Data payload  N     ...          |00|
 *                                                          ^^ padding zeros
 * Page 2:
 * 0x1000   | SegHdr N+1| Data payload N+1 ...                |
 */

#define WORKSPACE_BUF_LENGTH …
#define WORKSPACE_CBUF_LENGTH …

struct workspace { … };

static struct workspace_manager wsm;

void lzo_free_workspace(struct list_head *ws)
{ … }

struct list_head *lzo_alloc_workspace(unsigned int level)
{ … }

static inline void write_compress_length(char *buf, size_t len)
{ … }

static inline size_t read_compress_length(const char *buf)
{ … }

/*
 * Will do:
 *
 * - Write a segment header into the destination
 * - Copy the compressed buffer into the destination
 * - Make sure we have enough space in the last sector to fit a segment header
 *   If not, we will pad at most (LZO_LEN (4)) - 1 bytes of zeros.
 *
 * Will allocate new pages when needed.
 */
static int copy_compressed_data_to_page(char *compressed_data,
					size_t compressed_size,
					struct folio **out_folios,
					unsigned long max_nr_folio,
					u32 *cur_out,
					const u32 sectorsize)
{ … }

int lzo_compress_folios(struct list_head *ws, struct address_space *mapping,
			u64 start, struct folio **folios, unsigned long *out_folios,
			unsigned long *total_in, unsigned long *total_out)
{ … }

/*
 * Copy the compressed segment payload into @dest.
 *
 * For the payload there will be no padding, just need to do page switching.
 */
static void copy_compressed_segment(struct compressed_bio *cb,
				    char *dest, u32 len, u32 *cur_in)
{ … }

int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
{ … }

int lzo_decompress(struct list_head *ws, const u8 *data_in,
		struct page *dest_page, unsigned long dest_pgoff, size_t srclen,
		size_t destlen)
{ … }

const struct btrfs_compress_op btrfs_lzo_compress = …;