// 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/pagemap.h>
#include <linux/string.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;
        struct bvec_iter_all iter_all = {};
        struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
        int copied_bytes = 0;
        int actor_offset = 0;

        squashfs_actor_nobuff(actor);
        actor_addr = squashfs_first_page(actor);

        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);
                if (!IS_ERR(actor_addr))
                        memcpy(actor_addr + actor_offset, bvec_virt(bvec) +
                                        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_cached(struct bio *fullbio,
                struct address_space *cache_mapping, u64 index, int length,
                u64 read_start, u64 read_end, int page_count)
{
        struct folio *head_to_cache = NULL, *tail_to_cache = NULL;
        struct block_device *bdev = fullbio->bi_bdev;
        int start_idx = 0, end_idx = 0;
        struct folio_iter fi;
        struct bio *bio = NULL;
        int idx = 0;
        int err = 0;
#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
        struct folio **cache_folios = kmalloc_objs(*cache_folios, page_count,
                                                   GFP_KERNEL | __GFP_ZERO);
#endif

        bio_for_each_folio_all(fi, fullbio) {
                struct folio *folio = fi.folio;

                if (folio->mapping == cache_mapping) {
                        idx++;
                        continue;
                }

                /*
                 * We only use this when the device block size is the same as
                 * the page size, so read_start and read_end cover full pages.
                 *
                 * Compare these to the original required index and length to
                 * only cache pages which were requested partially, since these
                 * are the ones which are likely to be needed when reading
                 * adjacent blocks.
                 */
                if (idx == 0 && index != read_start)
                        head_to_cache = folio;
                else if (idx == page_count - 1 && index + length != read_end)
                        tail_to_cache = folio;
#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
                /* Cache all pages in the BIO for repeated reads */
                else if (cache_folios)
                        cache_folios[idx] = folio;
#endif

                if (!bio || idx != end_idx) {
                        struct bio *new = bio_alloc_clone(bdev, fullbio,
                                                          GFP_NOIO, &fs_bio_set);

                        if (bio) {
                                bio_trim(bio, start_idx * PAGE_SECTORS,
                                         (end_idx - start_idx) * PAGE_SECTORS);
                                bio_chain(bio, new);
                                submit_bio(bio);
                        }

                        bio = new;
                        start_idx = idx;
                }

                idx++;
                end_idx = idx;
        }

        if (bio) {
                bio_trim(bio, start_idx * PAGE_SECTORS,
                         (end_idx - start_idx) * PAGE_SECTORS);
                err = submit_bio_wait(bio);
                bio_put(bio);
        }

        if (err)
                return err;

        if (head_to_cache) {
                int ret = filemap_add_folio(cache_mapping, head_to_cache,
                                                read_start >> PAGE_SHIFT,
                                                GFP_NOIO);

                if (!ret) {
                        folio_mark_uptodate(head_to_cache);
                        folio_unlock(head_to_cache);
                }

        }

        if (tail_to_cache) {
                int ret = filemap_add_folio(cache_mapping, tail_to_cache,
                                                (read_end >> PAGE_SHIFT) - 1,
                                                GFP_NOIO);

                if (!ret) {
                        folio_mark_uptodate(tail_to_cache);
                        folio_unlock(tail_to_cache);
                }
        }

#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL
        if (!cache_folios)
                goto out;

        for (idx = 0; idx < page_count; idx++) {
                if (!cache_folios[idx])
                        continue;
                int ret = filemap_add_folio(cache_mapping, cache_folios[idx],
                                                (read_start >> PAGE_SHIFT) + idx,
                                                GFP_NOIO);

                if (!ret) {
                        folio_mark_uptodate(cache_folios[idx]);
                        folio_unlock(cache_folios[idx]);
                }
        }
        kfree(cache_folios);
out:
#endif
        return 0;
}

static struct page *squashfs_get_cache_page(struct address_space *mapping,
                                            pgoff_t index)
{
        struct page *page;

        if (!mapping)
                return NULL;

        page = find_get_page(mapping, index);
        if (!page)
                return NULL;

        if (!PageUptodate(page)) {
                put_page(page);
                return NULL;
        }

        return page;
}

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;
        struct address_space *cache_mapping = msblk->cache_mapping;
        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;

        bio = bio_kmalloc(page_count, GFP_NOIO);
        if (!bio)
                return -ENOMEM;
        bio_init_inline(bio, sb->s_bdev, page_count, REQ_OP_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);
                pgoff_t index = (read_start >> PAGE_SHIFT) + i;
                struct page *page;

                page = squashfs_get_cache_page(cache_mapping, index);
                if (!page)
                        page = alloc_page(GFP_NOIO);

                if (!page) {
                        error = -ENOMEM;
                        goto out_free_bio;
                }

                /*
                 * Use the __ version to avoid merging since we need each page
                 * to be separate when we check for and avoid cached pages.
                 */
                __bio_add_page(bio, page, len, offset);
                offset = 0;
                total_len -= len;
        }

        if (cache_mapping)
                error = squashfs_bio_read_cached(bio, cache_mapping, index,
                                                 length, read_start, read_end,
                                                 page_count);
        else
                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_uninit(bio);
        kfree(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 = bvec_virt(bvec);
                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 = bvec_virt(bvec);
                        length |= data[0] << 8;
                }
                bio_free_pages(bio);
                bio_uninit(bio);
                kfree(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 = msblk->thread_ops->decompress(msblk, bio, offset, length, output);
        } else {
                res = copy_bio_to_actor(bio, output, offset, length);
        }

out_free_bio:
        bio_free_pages(bio);
        bio_uninit(bio);
        kfree(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;
}