// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- linux-c -*- ------------------------------------------------------- *
 *   
 *   Copyright 2001 H. Peter Anvin - All Rights Reserved
 *
 * ----------------------------------------------------------------------- */

/*
 * linux/fs/isofs/compress.c
 *
 * Transparent decompression of files on an iso9660 filesystem
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>

#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/zlib.h>

#include "isofs.h"
#include "zisofs.h"

/* This should probably be global. */
static char zisofs_sink_page[PAGE_SIZE];

/*
 * This contains the zlib memory allocation and the mutex for the
 * allocation; this avoids failures at block-decompression time.
 */
static void *zisofs_zlib_workspace;
static DEFINE_MUTEX(zisofs_zlib_lock);

/*
 * Read data of @inode from @block_start to @block_end and uncompress
 * to one zisofs block. Store the data in the @pages array with @pcount
 * entries. Start storing at offset @poffset of the first page.
 */
static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start,
                                      loff_t block_end, int pcount,
                                      struct page **pages, unsigned poffset,
                                      int *errp)
{
        unsigned int zisofs_block_shift = ISOFS_I(inode)->i_format_parm[1];
        unsigned int bufsize = ISOFS_BUFFER_SIZE(inode);
        unsigned int bufshift = ISOFS_BUFFER_BITS(inode);
        unsigned int bufmask = bufsize - 1;
        int i, block_size = block_end - block_start;
        z_stream stream = { .total_out = 0,
                            .avail_in = 0,
                            .avail_out = 0, };
        int zerr;
        int needblocks = (block_size + (block_start & bufmask) + bufmask)
                                >> bufshift;
        int haveblocks;
        blkcnt_t blocknum;
        struct buffer_head **bhs;
        int curbh, curpage;

        if (block_size > deflateBound(1UL << zisofs_block_shift)) {
                *errp = -EIO;
                return 0;
        }
        /* Empty block? */
        if (block_size == 0) {
                for ( i = 0 ; i < pcount ; i++ ) {
                        if (!pages[i])
                                continue;
                        memset(page_address(pages[i]), 0, PAGE_SIZE);
                        flush_dcache_page(pages[i]);
                        SetPageUptodate(pages[i]);
                }
                return ((loff_t)pcount) << PAGE_SHIFT;
        }

        /* Because zlib is not thread-safe, do all the I/O at the top. */
        blocknum = block_start >> bufshift;
        bhs = kcalloc(needblocks + 1, sizeof(*bhs), GFP_KERNEL);
        if (!bhs) {
                *errp = -ENOMEM;
                return 0;
        }
        haveblocks = isofs_get_blocks(inode, blocknum, bhs, needblocks);
        ll_rw_block(REQ_OP_READ, 0, haveblocks, bhs);

        curbh = 0;
        curpage = 0;
        /*
         * First block is special since it may be fractional.  We also wait for
         * it before grabbing the zlib mutex; odds are that the subsequent
         * blocks are going to come in in short order so we don't hold the zlib
         * mutex longer than necessary.
         */

        if (!bhs[0])
                goto b_eio;

        wait_on_buffer(bhs[0]);
        if (!buffer_uptodate(bhs[0])) {
                *errp = -EIO;
                goto b_eio;
        }

        stream.workspace = zisofs_zlib_workspace;
        mutex_lock(&zisofs_zlib_lock);
                
        zerr = zlib_inflateInit(&stream);
        if (zerr != Z_OK) {
                if (zerr == Z_MEM_ERROR)
                        *errp = -ENOMEM;
                else
                        *errp = -EIO;
                printk(KERN_DEBUG "zisofs: zisofs_inflateInit returned %d\n",
                               zerr);
                goto z_eio;
        }

        while (curpage < pcount && curbh < haveblocks &&
               zerr != Z_STREAM_END) {
                if (!stream.avail_out) {
                        if (pages[curpage]) {
                                stream.next_out = page_address(pages[curpage])
                                                + poffset;
                                stream.avail_out = PAGE_SIZE - poffset;
                                poffset = 0;
                        } else {
                                stream.next_out = (void *)&zisofs_sink_page;
                                stream.avail_out = PAGE_SIZE;
                        }
                }
                if (!stream.avail_in) {
                        wait_on_buffer(bhs[curbh]);
                        if (!buffer_uptodate(bhs[curbh])) {
                                *errp = -EIO;
                                break;
                        }
                        stream.next_in  = bhs[curbh]->b_data +
                                                (block_start & bufmask);
                        stream.avail_in = min_t(unsigned, bufsize -
                                                (block_start & bufmask),
                                                block_size);
                        block_size -= stream.avail_in;
                        block_start = 0;
                }

                while (stream.avail_out && stream.avail_in) {
                        zerr = zlib_inflate(&stream, Z_SYNC_FLUSH);
                        if (zerr == Z_BUF_ERROR && stream.avail_in == 0)
                                break;
                        if (zerr == Z_STREAM_END)
                                break;
                        if (zerr != Z_OK) {
                                /* EOF, error, or trying to read beyond end of input */
                                if (zerr == Z_MEM_ERROR)
                                        *errp = -ENOMEM;
                                else {
                                        printk(KERN_DEBUG
                                               "zisofs: zisofs_inflate returned"
                                               " %d, inode = %lu,"
                                               " page idx = %d, bh idx = %d,"
                                               " avail_in = %ld,"
                                               " avail_out = %ld\n",
                                               zerr, inode->i_ino, curpage,
                                               curbh, stream.avail_in,
                                               stream.avail_out);
                                        *errp = -EIO;
                                }
                                goto inflate_out;
                        }
                }

                if (!stream.avail_out) {
                        /* This page completed */
                        if (pages[curpage]) {
                                flush_dcache_page(pages[curpage]);
                                SetPageUptodate(pages[curpage]);
                        }
                        curpage++;
                }
                if (!stream.avail_in)
                        curbh++;
        }
inflate_out:
        zlib_inflateEnd(&stream);

z_eio:
        mutex_unlock(&zisofs_zlib_lock);

b_eio:
        for (i = 0; i < haveblocks; i++)
                brelse(bhs[i]);
        kfree(bhs);
        return stream.total_out;
}

/*
 * Uncompress data so that pages[full_page] is fully uptodate and possibly
 * fills in other pages if we have data for them.
 */
static int zisofs_fill_pages(struct inode *inode, int full_page, int pcount,
                             struct page **pages)
{
        loff_t start_off, end_off;
        loff_t block_start, block_end;
        unsigned int header_size = ISOFS_I(inode)->i_format_parm[0];
        unsigned int zisofs_block_shift = ISOFS_I(inode)->i_format_parm[1];
        unsigned int blockptr;
        loff_t poffset = 0;
        blkcnt_t cstart_block, cend_block;
        struct buffer_head *bh;
        unsigned int blkbits = ISOFS_BUFFER_BITS(inode);
        unsigned int blksize = 1 << blkbits;
        int err;
        loff_t ret;

        BUG_ON(!pages[full_page]);

        /*
         * We want to read at least 'full_page' page. Because we have to
         * uncompress the whole compression block anyway, fill the surrounding
         * pages with the data we have anyway...
         */
        start_off = page_offset(pages[full_page]);
        end_off = min_t(loff_t, start_off + PAGE_SIZE, inode->i_size);

        cstart_block = start_off >> zisofs_block_shift;
        cend_block = (end_off + (1 << zisofs_block_shift) - 1)
                        >> zisofs_block_shift;

        WARN_ON(start_off - (full_page << PAGE_SHIFT) !=
                ((cstart_block << zisofs_block_shift) & PAGE_MASK));

        /* Find the pointer to this specific chunk */
        /* Note: we're not using isonum_731() here because the data is known aligned */
        /* Note: header_size is in 32-bit words (4 bytes) */
        blockptr = (header_size + cstart_block) << 2;
        bh = isofs_bread(inode, blockptr >> blkbits);
        if (!bh)
                return -EIO;
        block_start = le32_to_cpu(*(__le32 *)
                                (bh->b_data + (blockptr & (blksize - 1))));

        while (cstart_block < cend_block && pcount > 0) {
                /* Load end of the compressed block in the file */
                blockptr += 4;
                /* Traversed to next block? */
                if (!(blockptr & (blksize - 1))) {
                        brelse(bh);

                        bh = isofs_bread(inode, blockptr >> blkbits);
                        if (!bh)
                                return -EIO;
                }
                block_end = le32_to_cpu(*(__le32 *)
                                (bh->b_data + (blockptr & (blksize - 1))));
                if (block_start > block_end) {
                        brelse(bh);
                        return -EIO;
                }
                err = 0;
                ret = zisofs_uncompress_block(inode, block_start, block_end,
                                              pcount, pages, poffset, &err);
                poffset += ret;
                pages += poffset >> PAGE_SHIFT;
                pcount -= poffset >> PAGE_SHIFT;
                full_page -= poffset >> PAGE_SHIFT;
                poffset &= ~PAGE_MASK;

                if (err) {
                        brelse(bh);
                        /*
                         * Did we finish reading the page we really wanted
                         * to read?
                         */
                        if (full_page < 0)
                                return 0;
                        return err;
                }

                block_start = block_end;
                cstart_block++;
        }

        if (poffset && *pages) {
                memset(page_address(*pages) + poffset, 0,
                       PAGE_SIZE - poffset);
                flush_dcache_page(*pages);
                SetPageUptodate(*pages);
        }
        return 0;
}

/*
 * When decompressing, we typically obtain more than one page
 * per reference.  We inject the additional pages into the page
 * cache as a form of readahead.
 */
static int zisofs_readpage(struct file *file, struct page *page)
{
        struct inode *inode = file_inode(file);
        struct address_space *mapping = inode->i_mapping;
        int err;
        int i, pcount, full_page;
        unsigned int zisofs_block_shift = ISOFS_I(inode)->i_format_parm[1];
        unsigned int zisofs_pages_per_cblock =
                PAGE_SHIFT <= zisofs_block_shift ?
                (1 << (zisofs_block_shift - PAGE_SHIFT)) : 0;
        struct page **pages;
        pgoff_t index = page->index, end_index;

        end_index = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
        /*
         * If this page is wholly outside i_size we just return zero;
         * do_generic_file_read() will handle this for us
         */
        if (index >= end_index) {
                SetPageUptodate(page);
                unlock_page(page);
                return 0;
        }

        if (PAGE_SHIFT <= zisofs_block_shift) {
                /* We have already been given one page, this is the one
                   we must do. */
                full_page = index & (zisofs_pages_per_cblock - 1);
                pcount = min_t(int, zisofs_pages_per_cblock,
                        end_index - (index & ~(zisofs_pages_per_cblock - 1)));
                index -= full_page;
        } else {
                full_page = 0;
                pcount = 1;
        }
        pages = kcalloc(max_t(unsigned int, zisofs_pages_per_cblock, 1),
                                        sizeof(*pages), GFP_KERNEL);
        if (!pages) {
                unlock_page(page);
                return -ENOMEM;
        }
        pages[full_page] = page;

        for (i = 0; i < pcount; i++, index++) {
                if (i != full_page)
                        pages[i] = grab_cache_page_nowait(mapping, index);
                if (pages[i]) {
                        ClearPageError(pages[i]);
                        kmap(pages[i]);
                }
        }

        err = zisofs_fill_pages(inode, full_page, pcount, pages);

        /* Release any residual pages, do not SetPageUptodate */
        for (i = 0; i < pcount; i++) {
                if (pages[i]) {
                        flush_dcache_page(pages[i]);
                        if (i == full_page && err)
                                SetPageError(pages[i]);
                        kunmap(pages[i]);
                        unlock_page(pages[i]);
                        if (i != full_page)
                                put_page(pages[i]);
                }
        }                       

        /* At this point, err contains 0 or -EIO depending on the "critical" page */
        kfree(pages);
        return err;
}

const struct address_space_operations zisofs_aops = {
        .readpage = zisofs_readpage,
        /* No bmap operation supported */
};

int __init zisofs_init(void)
{
        zisofs_zlib_workspace = vmalloc(zlib_inflate_workspacesize());
        if ( !zisofs_zlib_workspace )
                return -ENOMEM;

        return 0;
}

void zisofs_cleanup(void)
{
        vfree(zisofs_zlib_workspace);
}