// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * block.c
 */

/*
 * This file implements the low-level routines to read and decompress
 * datablocks and metadata blocks.
 */

#include <linux/blkdev.h>
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/buffer_head.h>
#include <linux/bio.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"
#include "decompressor.h"
#include "page_actor.h"

/*
 * Returns the amount of bytes copied to the page actor.
 */
static int copy_bio_to_actor(struct bio *bio,
                             struct squashfs_page_actor *actor,
                             int offset, int req_length)
{
        void *actor_addr = squashfs_first_page(actor);
        struct bvec_iter_all iter_all = {};
        struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
        int copied_bytes = 0;
        int actor_offset = 0;

        if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all)))
                return 0;

        while (copied_bytes < req_length) {
                int bytes_to_copy = min_t(int, bvec->bv_len - offset,
                                          PAGE_SIZE - actor_offset);

                bytes_to_copy = min_t(int, bytes_to_copy,
                                      req_length - copied_bytes);
                memcpy(actor_addr + actor_offset,
                       page_address(bvec->bv_page) + bvec->bv_offset + offset,
                       bytes_to_copy);

                actor_offset += bytes_to_copy;
                copied_bytes += bytes_to_copy;
                offset += bytes_to_copy;

                if (actor_offset >= PAGE_SIZE) {
                        actor_addr = squashfs_next_page(actor);
                        if (!actor_addr)
                                break;
                        actor_offset = 0;
                }
                if (offset >= bvec->bv_len) {
                        if (!bio_next_segment(bio, &iter_all))
                                break;
                        offset = 0;
                }
        }
        squashfs_finish_page(actor);
        return copied_bytes;
}

static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
                             struct bio **biop, int *block_offset)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        const u64 read_start = round_down(index, msblk->devblksize);
        const sector_t block = read_start >> msblk->devblksize_log2;
        const u64 read_end = round_up(index + length, msblk->devblksize);
        const sector_t block_end = read_end >> msblk->devblksize_log2;
        int offset = read_start - round_down(index, PAGE_SIZE);
        int total_len = (block_end - block) << msblk->devblksize_log2;
        const int page_count = DIV_ROUND_UP(total_len + offset, PAGE_SIZE);
        int error, i;
        struct bio *bio;

        if (page_count <= BIO_MAX_VECS)
                bio = bio_alloc(GFP_NOIO, page_count);
        else
                bio = bio_kmalloc(GFP_NOIO, page_count);

        if (!bio)
                return -ENOMEM;

        bio_set_dev(bio, sb->s_bdev);
        bio->bi_opf = READ;
        bio->bi_iter.bi_sector = block * (msblk->devblksize >> SECTOR_SHIFT);

        for (i = 0; i < page_count; ++i) {
                unsigned int len =
                        min_t(unsigned int, PAGE_SIZE - offset, total_len);
                struct page *page = alloc_page(GFP_NOIO);

                if (!page) {
                        error = -ENOMEM;
                        goto out_free_bio;
                }
                if (!bio_add_page(bio, page, len, offset)) {
                        error = -EIO;
                        goto out_free_bio;
                }
                offset = 0;
                total_len -= len;
        }

        error = submit_bio_wait(bio);
        if (error)
                goto out_free_bio;

        *biop = bio;
        *block_offset = index & ((1 << msblk->devblksize_log2) - 1);
        return 0;

out_free_bio:
        bio_free_pages(bio);
        bio_put(bio);
        return error;
}

/*
 * Read and decompress a metadata block or datablock.  Length is non-zero
 * if a datablock is being read (the size is stored elsewhere in the
 * filesystem), otherwise the length is obtained from the first two bytes of
 * the metadata block.  A bit in the length field indicates if the block
 * is stored uncompressed in the filesystem (usually because compression
 * generated a larger block - this does occasionally happen with compression
 * algorithms).
 */
int squashfs_read_data(struct super_block *sb, u64 index, int length,
                       u64 *next_index, struct squashfs_page_actor *output)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        struct bio *bio = NULL;
        int compressed;
        int res;
        int offset;

        if (length) {
                /*
                 * Datablock.
                 */
                compressed = SQUASHFS_COMPRESSED_BLOCK(length);
                length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
                TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
                        index, compressed ? "" : "un", length, output->length);
        } else {
                /*
                 * Metadata block.
                 */
                const u8 *data;
                struct bvec_iter_all iter_all = {};
                struct bio_vec *bvec = bvec_init_iter_all(&iter_all);

                if (index + 2 > msblk->bytes_used) {
                        res = -EIO;
                        goto out;
                }
                res = squashfs_bio_read(sb, index, 2, &bio, &offset);
                if (res)
                        goto out;

                if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
                        res = -EIO;
                        goto out_free_bio;
                }
                /* Extract the length of the metadata block */
                data = page_address(bvec->bv_page) + bvec->bv_offset;
                length = data[offset];
                if (offset < bvec->bv_len - 1) {
                        length |= data[offset + 1] << 8;
                } else {
                        if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
                                res = -EIO;
                                goto out_free_bio;
                        }
                        data = page_address(bvec->bv_page) + bvec->bv_offset;
                        length |= data[0] << 8;
                }
                bio_free_pages(bio);
                bio_put(bio);

                compressed = SQUASHFS_COMPRESSED(length);
                length = SQUASHFS_COMPRESSED_SIZE(length);
                index += 2;

                TRACE("Block @ 0x%llx, %scompressed size %d\n", index - 2,
                      compressed ? "" : "un", length);
        }
        if (length < 0 || length > output->length ||
                        (index + length) > msblk->bytes_used) {
                res = -EIO;
                goto out;
        }

        if (next_index)
                *next_index = index + length;

        res = squashfs_bio_read(sb, index, length, &bio, &offset);
        if (res)
                goto out;

        if (compressed) {
                if (!msblk->stream) {
                        res = -EIO;
                        goto out_free_bio;
                }
                res = squashfs_decompress(msblk, bio, offset, length, output);
        } else {
                res = copy_bio_to_actor(bio, output, offset, length);
        }

out_free_bio:
        bio_free_pages(bio);
        bio_put(bio);
out:
        if (res < 0) {
                ERROR("Failed to read block 0x%llx: %d\n", index, res);
                if (msblk->panic_on_errors)
                        panic("squashfs read failed");
        }

        return res;
}