compress.c

/* -*- linux-c -*- ------------------------------------------------------- *
 *   
 *   Copyright 2001 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 675 Mass Ave, Cambridge MA 02139,
 *   USA; either version 2 of the License, or (at your option) any later
 *   version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

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

#include <linux/module.h>
#include <linux/init.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_CACHE_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 struct semaphore zisofs_zlib_semaphore;

/*
 * 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->f_dentry->d_inode;
	struct address_space *mapping = inode->i_mapping;
	unsigned int maxpage, xpage, fpage, blockindex;
	unsigned long offset;
	unsigned long blockptr, blockendptr, cstart, cend, csize;
	struct buffer_head *bh, *ptrbh[2];
	unsigned long bufsize = ISOFS_BUFFER_SIZE(inode);
	unsigned int bufshift = ISOFS_BUFFER_BITS(inode);
	unsigned long bufmask  = bufsize - 1;
	int err = -EIO;
	int i;
	unsigned int header_size = ISOFS_I(inode)->i_format_parm[0];
	unsigned int zisofs_block_shift = ISOFS_I(inode)->i_format_parm[1];
	/* unsigned long zisofs_block_size = 1UL << zisofs_block_shift; */
	unsigned int zisofs_block_page_shift = zisofs_block_shift-PAGE_CACHE_SHIFT;
	unsigned long zisofs_block_pages = 1UL << zisofs_block_page_shift;
	unsigned long zisofs_block_page_mask = zisofs_block_pages-1;
	struct page *pages[zisofs_block_pages];
	unsigned long index = page->index;
	int indexblocks;

	/* We have already been given one page, this is the one
	   we must do. */
	xpage = index & zisofs_block_page_mask;
	pages[xpage] = page;
 
	/* The remaining pages need to be allocated and inserted */
	offset = index & ~zisofs_block_page_mask;
	blockindex = offset >> zisofs_block_page_shift;
	maxpage = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
	maxpage = min(zisofs_block_pages, maxpage-offset);

	for ( i = 0 ; i < maxpage ; i++, offset++ ) {
		if ( i != xpage ) {
			pages[i] = grab_cache_page_nowait(mapping, offset);
		}
		page = pages[i];
		if ( page ) {
			ClearPageError(page);
			kmap(page);
		}
	}

	/* This is the last page filled, plus one; used in case of abort. */
	fpage = 0;

	/* 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 + blockindex) << 2;
	blockendptr = blockptr + 4;

	indexblocks = ((blockptr^blockendptr) >> bufshift) ? 2 : 1;
	ptrbh[0] = ptrbh[1] = NULL;

	if ( isofs_get_blocks(inode, blockptr >> bufshift, ptrbh, indexblocks) != indexblocks ) {
		if ( ptrbh[0] ) brelse(ptrbh[0]);
		printk(KERN_DEBUG "zisofs: Null buffer on reading block table, inode = %lu, block = %lu\n",
		       inode->i_ino, blockptr >> bufshift);
		goto eio;
	}
	ll_rw_block(READ, indexblocks, ptrbh);

	bh = ptrbh[0];
	if ( !bh || (wait_on_buffer(bh), !buffer_uptodate(bh)) ) {
		printk(KERN_DEBUG "zisofs: Failed to read block table, inode = %lu, block = %lu\n",
		       inode->i_ino, blockptr >> bufshift);
		if ( ptrbh[1] )
			brelse(ptrbh[1]);
		goto eio;
	}
	cstart = le32_to_cpu(*(__le32 *)(bh->b_data + (blockptr & bufmask)));

	if ( indexblocks == 2 ) {
		/* We just crossed a block boundary.  Switch to the next block */
		brelse(bh);
		bh = ptrbh[1];
		if ( !bh || (wait_on_buffer(bh), !buffer_uptodate(bh)) ) {
			printk(KERN_DEBUG "zisofs: Failed to read block table, inode = %lu, block = %lu\n",
			       inode->i_ino, blockendptr >> bufshift);
			goto eio;
		}
	}
	cend = le32_to_cpu(*(__le32 *)(bh->b_data + (blockendptr & bufmask)));
	brelse(bh);

	if (cstart > cend)
		goto eio;
		
	csize = cend-cstart;

	if (csize > deflateBound(1UL << zisofs_block_shift))
		goto eio;

	/* Now page[] contains an array of pages, any of which can be NULL,
	   and the locks on which we hold.  We should now read the data and
	   release the pages.  If the pages are NULL the decompressed data
	   for that particular page should be discarded. */
	
	if ( csize == 0 ) {
		/* This data block is empty. */

		for ( fpage = 0 ; fpage < maxpage ; fpage++ ) {
			if ( (page = pages[fpage]) != NULL ) {
				memset(page_address(page), 0, PAGE_CACHE_SIZE);
				
				flush_dcache_page(page);
				SetPageUptodate(page);
				kunmap(page);
				unlock_page(page);
				if ( fpage == xpage )
					err = 0; /* The critical page */
				else
					page_cache_release(page);
			}
		}
	} else {
		/* This data block is compressed. */
		z_stream stream;
		int bail = 0, left_out = -1;
		int zerr;
		int needblocks = (csize + (cstart & bufmask) + bufmask) >> bufshift;
		int haveblocks;
		struct buffer_head *bhs[needblocks+1];
		struct buffer_head **bhptr;

		/* Because zlib is not thread-safe, do all the I/O at the top. */

		blockptr = cstart >> bufshift;
		memset(bhs, 0, (needblocks+1)*sizeof(struct buffer_head *));
		haveblocks = isofs_get_blocks(inode, blockptr, bhs, needblocks);
		ll_rw_block(READ, haveblocks, bhs);

		bhptr = &bhs[0];
		bh = *bhptr++;

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

		if ( !bh || (wait_on_buffer(bh), !buffer_uptodate(bh)) ) {
			printk(KERN_DEBUG "zisofs: Hit null buffer, fpage = %d, xpage = %d, csize = %ld\n",
			       fpage, xpage, csize);
			goto b_eio;
		}
		stream.next_in  = bh->b_data + (cstart & bufmask);
		stream.avail_in = min(bufsize-(cstart & bufmask), csize);
		csize -= stream.avail_in;

		stream.workspace = zisofs_zlib_workspace;
		down(&zisofs_zlib_semaphore);
		
		zerr = zlib_inflateInit(&stream);
		if ( zerr != Z_OK ) {
			if ( err && zerr == Z_MEM_ERROR )
				err = -ENOMEM;
			printk(KERN_DEBUG "zisofs: zisofs_inflateInit returned %d\n",
			       zerr);
			goto z_eio;
		}

		while ( !bail && fpage < maxpage ) {
			page = pages[fpage];
			if ( page )
				stream.next_out = page_address(page);
			else
				stream.next_out = (void *)&zisofs_sink_page;
			stream.avail_out = PAGE_CACHE_SIZE;

			while ( stream.avail_out ) {
				int ao, ai;
				if ( stream.avail_in == 0 && left_out ) {
					if ( !csize ) {
						printk(KERN_WARNING "zisofs: ZF read beyond end of input\n");
						bail = 1;
						break;
					} else {
						bh = *bhptr++;
						if ( !bh ||
						     (wait_on_buffer(bh), !buffer_uptodate(bh)) ) {
							/* Reached an EIO */
 							printk(KERN_DEBUG "zisofs: Hit null buffer, fpage = %d, xpage = %d, csize = %ld\n",
							       fpage, xpage, csize);
							       
							bail = 1;
							break;
						}
						stream.next_in = bh->b_data;
						stream.avail_in = min(csize,bufsize);
						csize -= stream.avail_in;
					}
				}
				ao = stream.avail_out;  ai = stream.avail_in;
				zerr = zlib_inflate(&stream, Z_SYNC_FLUSH);
				left_out = stream.avail_out;
				if ( zerr == Z_BUF_ERROR && stream.avail_in == 0 )
					continue;
				if ( zerr != Z_OK ) {
					/* EOF, error, or trying to read beyond end of input */
					if ( err && zerr == Z_MEM_ERROR )
						err = -ENOMEM;
					if ( zerr != Z_STREAM_END )
						printk(KERN_DEBUG "zisofs: zisofs_inflate returned %d, inode = %lu, index = %lu, fpage = %d, xpage = %d, avail_in = %d, avail_out = %d, ai = %d, ao = %d\n",
						       zerr, inode->i_ino, index,
						       fpage, xpage,
						       stream.avail_in, stream.avail_out,
						       ai, ao);
					bail = 1;
					break;
				}
			}

			if ( stream.avail_out && zerr == Z_STREAM_END ) {
				/* Fractional page written before EOF.  This may
				   be the last page in the file. */
				memset(stream.next_out, 0, stream.avail_out);
				stream.avail_out = 0;
			}

			if ( !stream.avail_out ) {
				/* This page completed */
				if ( page ) {
					flush_dcache_page(page);
					SetPageUptodate(page);
					kunmap(page);
					unlock_page(page);
					if ( fpage == xpage )
						err = 0; /* The critical page */
					else
						page_cache_release(page);
				}
				fpage++;
			}
		}
		zlib_inflateEnd(&stream);

	z_eio:
		up(&zisofs_zlib_semaphore);

	b_eio:
		for ( i = 0 ; i < haveblocks ; i++ ) {
			if ( bhs[i] )
				brelse(bhs[i]);
		}
	}

eio:

	/* Release any residual pages, do not SetPageUptodate */
	while ( fpage < maxpage ) {
		page = pages[fpage];
		if ( page ) {
			flush_dcache_page(page);
			if ( fpage == xpage )
				SetPageError(page);
			kunmap(page);
			unlock_page(page);
			if ( fpage != xpage )
				page_cache_release(page);
		}
		fpage++;
	}			

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

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

static int initialized;

int __init zisofs_init(void)
{
	if ( initialized ) {
		printk("zisofs_init: called more than once\n");
		return 0;
	}

	zisofs_zlib_workspace = vmalloc(zlib_inflate_workspacesize());
	if ( !zisofs_zlib_workspace )
		return -ENOMEM;
	init_MUTEX(&zisofs_zlib_semaphore);

	initialized = 1;
	return 0;
}

void zisofs_cleanup(void)
{
	if ( !initialized ) {
		printk("zisofs_cleanup: called without initialization\n");
		return;
	}

	vfree(zisofs_zlib_workspace);
	initialized = 0;
}