linux/fs/squashfs/block.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Squashfs - a compressed read only filesystem for Linux
   4 *
   5 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
   6 * Phillip Lougher <phillip@squashfs.org.uk>
   7 *
   8 * block.c
   9 */
  10
  11/*
  12 * This file implements the low-level routines to read and decompress
  13 * datablocks and metadata blocks.
  14 */
  15
  16#include <linux/blkdev.h>
  17#include <linux/fs.h>
  18#include <linux/vfs.h>
  19#include <linux/slab.h>
  20#include <linux/string.h>
  21#include <linux/buffer_head.h>
  22#include <linux/bio.h>
  23
  24#include "squashfs_fs.h"
  25#include "squashfs_fs_sb.h"
  26#include "squashfs.h"
  27#include "decompressor.h"
  28#include "page_actor.h"
  29
  30/*
  31 * Returns the amount of bytes copied to the page actor.
  32 */
  33static int copy_bio_to_actor(struct bio *bio,
  34                             struct squashfs_page_actor *actor,
  35                             int offset, int req_length)
  36{
  37        void *actor_addr = squashfs_first_page(actor);
  38        struct bvec_iter_all iter_all = {};
  39        struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
  40        int copied_bytes = 0;
  41        int actor_offset = 0;
  42
  43        if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all)))
  44                return 0;
  45
  46        while (copied_bytes < req_length) {
  47                int bytes_to_copy = min_t(int, bvec->bv_len - offset,
  48                                          PAGE_SIZE - actor_offset);
  49
  50                bytes_to_copy = min_t(int, bytes_to_copy,
  51                                      req_length - copied_bytes);
  52                memcpy(actor_addr + actor_offset,
  53                       page_address(bvec->bv_page) + bvec->bv_offset + offset,
  54                       bytes_to_copy);
  55
  56                actor_offset += bytes_to_copy;
  57                copied_bytes += bytes_to_copy;
  58                offset += bytes_to_copy;
  59
  60                if (actor_offset >= PAGE_SIZE) {
  61                        actor_addr = squashfs_next_page(actor);
  62                        if (!actor_addr)
  63                                break;
  64                        actor_offset = 0;
  65                }
  66                if (offset >= bvec->bv_len) {
  67                        if (!bio_next_segment(bio, &iter_all))
  68                                break;
  69                        offset = 0;
  70                }
  71        }
  72        squashfs_finish_page(actor);
  73        return copied_bytes;
  74}
  75
  76static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
  77                             struct bio **biop, int *block_offset)
  78{
  79        struct squashfs_sb_info *msblk = sb->s_fs_info;
  80        const u64 read_start = round_down(index, msblk->devblksize);
  81        const sector_t block = read_start >> msblk->devblksize_log2;
  82        const u64 read_end = round_up(index + length, msblk->devblksize);
  83        const sector_t block_end = read_end >> msblk->devblksize_log2;
  84        int offset = read_start - round_down(index, PAGE_SIZE);
  85        int total_len = (block_end - block) << msblk->devblksize_log2;
  86        const int page_count = DIV_ROUND_UP(total_len + offset, PAGE_SIZE);
  87        int error, i;
  88        struct bio *bio;
  89
  90        if (page_count <= BIO_MAX_VECS)
  91                bio = bio_alloc(GFP_NOIO, page_count);
  92        else
  93                bio = bio_kmalloc(GFP_NOIO, page_count);
  94
  95        if (!bio)
  96                return -ENOMEM;
  97
  98        bio_set_dev(bio, sb->s_bdev);
  99        bio->bi_opf = READ;
 100        bio->bi_iter.bi_sector = block * (msblk->devblksize >> SECTOR_SHIFT);
 101
 102        for (i = 0; i < page_count; ++i) {
 103                unsigned int len =
 104                        min_t(unsigned int, PAGE_SIZE - offset, total_len);
 105                struct page *page = alloc_page(GFP_NOIO);
 106
 107                if (!page) {
 108                        error = -ENOMEM;
 109                        goto out_free_bio;
 110                }
 111                if (!bio_add_page(bio, page, len, offset)) {
 112                        error = -EIO;
 113                        goto out_free_bio;
 114                }
 115                offset = 0;
 116                total_len -= len;
 117        }
 118
 119        error = submit_bio_wait(bio);
 120        if (error)
 121                goto out_free_bio;
 122
 123        *biop = bio;
 124        *block_offset = index & ((1 << msblk->devblksize_log2) - 1);
 125        return 0;
 126
 127out_free_bio:
 128        bio_free_pages(bio);
 129        bio_put(bio);
 130        return error;
 131}
 132
 133/*
 134 * Read and decompress a metadata block or datablock.  Length is non-zero
 135 * if a datablock is being read (the size is stored elsewhere in the
 136 * filesystem), otherwise the length is obtained from the first two bytes of
 137 * the metadata block.  A bit in the length field indicates if the block
 138 * is stored uncompressed in the filesystem (usually because compression
 139 * generated a larger block - this does occasionally happen with compression
 140 * algorithms).
 141 */
 142int squashfs_read_data(struct super_block *sb, u64 index, int length,
 143                       u64 *next_index, struct squashfs_page_actor *output)
 144{
 145        struct squashfs_sb_info *msblk = sb->s_fs_info;
 146        struct bio *bio = NULL;
 147        int compressed;
 148        int res;
 149        int offset;
 150
 151        if (length) {
 152                /*
 153                 * Datablock.
 154                 */
 155                compressed = SQUASHFS_COMPRESSED_BLOCK(length);
 156                length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
 157                TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
 158                        index, compressed ? "" : "un", length, output->length);
 159        } else {
 160                /*
 161                 * Metadata block.
 162                 */
 163                const u8 *data;
 164                struct bvec_iter_all iter_all = {};
 165                struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
 166
 167                if (index + 2 > msblk->bytes_used) {
 168                        res = -EIO;
 169                        goto out;
 170                }
 171                res = squashfs_bio_read(sb, index, 2, &bio, &offset);
 172                if (res)
 173                        goto out;
 174
 175                if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
 176                        res = -EIO;
 177                        goto out_free_bio;
 178                }
 179                /* Extract the length of the metadata block */
 180                data = page_address(bvec->bv_page) + bvec->bv_offset;
 181                length = data[offset];
 182                if (offset < bvec->bv_len - 1) {
 183                        length |= data[offset + 1] << 8;
 184                } else {
 185                        if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
 186                                res = -EIO;
 187                                goto out_free_bio;
 188                        }
 189                        data = page_address(bvec->bv_page) + bvec->bv_offset;
 190                        length |= data[0] << 8;
 191                }
 192                bio_free_pages(bio);
 193                bio_put(bio);
 194
 195                compressed = SQUASHFS_COMPRESSED(length);
 196                length = SQUASHFS_COMPRESSED_SIZE(length);
 197                index += 2;
 198
 199                TRACE("Block @ 0x%llx, %scompressed size %d\n", index - 2,
 200                      compressed ? "" : "un", length);
 201        }
 202        if (length < 0 || length > output->length ||
 203                        (index + length) > msblk->bytes_used) {
 204                res = -EIO;
 205                goto out;
 206        }
 207
 208        if (next_index)
 209                *next_index = index + length;
 210
 211        res = squashfs_bio_read(sb, index, length, &bio, &offset);
 212        if (res)
 213                goto out;
 214
 215        if (compressed) {
 216                if (!msblk->stream) {
 217                        res = -EIO;
 218                        goto out_free_bio;
 219                }
 220                res = squashfs_decompress(msblk, bio, offset, length, output);
 221        } else {
 222                res = copy_bio_to_actor(bio, output, offset, length);
 223        }
 224
 225out_free_bio:
 226        bio_free_pages(bio);
 227        bio_put(bio);
 228out:
 229        if (res < 0)
 230                ERROR("Failed to read block 0x%llx: %d\n", index, res);
 231
 232        return res;
 233}
 234