/*
 * Copyright (C) 2008 Oracle.  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 v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 * Based on jffs2 zlib code:
 * Copyright © 2001-2007 Red Hat, Inc.
 * Created by David Woodhouse <dwmw2@infradead.org>
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/zlib.h>
#include <linux/zutil.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/bio.h>
#include "compression.h"

/* Plan: call deflate() with avail_in == *sourcelen,
	avail_out = *dstlen - 12 and flush == Z_FINISH.
	If it doesn't manage to finish,	call it again with
	avail_in == 0 and avail_out set to the remaining 12
	bytes for it to clean up.
   Q: Is 12 bytes sufficient?
*/
#define STREAM_END_SPACE 12

struct workspace {
	z_stream inf_strm;
	z_stream def_strm;
	char *buf;
	struct list_head list;
};

static LIST_HEAD(idle_workspace);
static DEFINE_SPINLOCK(workspace_lock);
static unsigned long num_workspace;
static atomic_t alloc_workspace = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(workspace_wait);

/*
 * this finds an available zlib workspace or allocates a new one
 * NULL or an ERR_PTR is returned if things go bad.
 */
static struct workspace *find_zlib_workspace(void)
{
	struct workspace *workspace;
	int ret;
	int cpus = num_online_cpus();

again:
	spin_lock(&workspace_lock);
	if (!list_empty(&idle_workspace)) {
		workspace = list_entry(idle_workspace.next, struct workspace,
				       list);
		list_del(&workspace->list);
		num_workspace--;
		spin_unlock(&workspace_lock);
		return workspace;

	}
	spin_unlock(&workspace_lock);
	if (atomic_read(&alloc_workspace) > cpus) {
		DEFINE_WAIT(wait);
		prepare_to_wait(&workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
		if (atomic_read(&alloc_workspace) > cpus)
			schedule();
		finish_wait(&workspace_wait, &wait);
		goto again;
	}
	atomic_inc(&alloc_workspace);
	workspace = kzalloc(sizeof(*workspace), GFP_NOFS);
	if (!workspace) {
		ret = -ENOMEM;
		goto fail;
	}

	workspace->def_strm.workspace = vmalloc(zlib_deflate_workspacesize());
	if (!workspace->def_strm.workspace) {
		ret = -ENOMEM;
		goto fail;
	}
	workspace->inf_strm.workspace = vmalloc(zlib_inflate_workspacesize());
	if (!workspace->inf_strm.workspace) {
		ret = -ENOMEM;
		goto fail_inflate;
	}
	workspace->buf = kmalloc(PAGE_CACHE_SIZE, GFP_NOFS);
	if (!workspace->buf) {
		ret = -ENOMEM;
		goto fail_kmalloc;
	}
	return workspace;

fail_kmalloc:
	vfree(workspace->inf_strm.workspace);
fail_inflate:
	vfree(workspace->def_strm.workspace);
fail:
	kfree(workspace);
	atomic_dec(&alloc_workspace);
	wake_up(&workspace_wait);
	return ERR_PTR(ret);
}

/*
 * put a workspace struct back on the list or free it if we have enough
 * idle ones sitting around
 */
static int free_workspace(struct workspace *workspace)
{
	spin_lock(&workspace_lock);
	if (num_workspace < num_online_cpus()) {
		list_add_tail(&workspace->list, &idle_workspace);
		num_workspace++;
		spin_unlock(&workspace_lock);
		if (waitqueue_active(&workspace_wait))
			wake_up(&workspace_wait);
		return 0;
	}
	spin_unlock(&workspace_lock);
	vfree(workspace->def_strm.workspace);
	vfree(workspace->inf_strm.workspace);
	kfree(workspace->buf);
	kfree(workspace);

	atomic_dec(&alloc_workspace);
	if (waitqueue_active(&workspace_wait))
		wake_up(&workspace_wait);
	return 0;
}

/*
 * cleanup function for module exit
 */
static void free_workspaces(void)
{
	struct workspace *workspace;
	while (!list_empty(&idle_workspace)) {
		workspace = list_entry(idle_workspace.next, struct workspace,
				       list);
		list_del(&workspace->list);
		vfree(workspace->def_strm.workspace);
		vfree(workspace->inf_strm.workspace);
		kfree(workspace->buf);
		kfree(workspace);
		atomic_dec(&alloc_workspace);
	}
}

/*
 * given an address space and start/len, compress the bytes.
 *
 * pages are allocated to hold the compressed result and stored
 * in 'pages'
 *
 * out_pages is used to return the number of pages allocated.  There
 * may be pages allocated even if we return an error
 *
 * total_in is used to return the number of bytes actually read.  It
 * may be smaller then len if we had to exit early because we
 * ran out of room in the pages array or because we cross the
 * max_out threshold.
 *
 * total_out is used to return the total number of compressed bytes
 *
 * max_out tells us the max number of bytes that we're allowed to
 * stuff into pages
 */
int btrfs_zlib_compress_pages(struct address_space *mapping,
			      u64 start, unsigned long len,
			      struct page **pages,
			      unsigned long nr_dest_pages,
			      unsigned long *out_pages,
			      unsigned long *total_in,
			      unsigned long *total_out,
			      unsigned long max_out)
{
	int ret;
	struct workspace *workspace;
	char *data_in;
	char *cpage_out;
	int nr_pages = 0;
	struct page *in_page = NULL;
	struct page *out_page = NULL;
	unsigned long bytes_left;

	*out_pages = 0;
	*total_out = 0;
	*total_in = 0;

	workspace = find_zlib_workspace();
	if (IS_ERR(workspace))
		return -1;

	if (Z_OK != zlib_deflateInit(&workspace->def_strm, 3)) {
		printk(KERN_WARNING "deflateInit failed\n");
		ret = -1;
		goto out;
	}

	workspace->def_strm.total_in = 0;
	workspace->def_strm.total_out = 0;

	in_page = find_get_page(mapping, start >> PAGE_CACHE_SHIFT);
	data_in = kmap(in_page);

	out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
	cpage_out = kmap(out_page);
	pages[0] = out_page;
	nr_pages = 1;

	workspace->def_strm.next_in = data_in;
	workspace->def_strm.next_out = cpage_out;
	workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
	workspace->def_strm.avail_in = min(len, PAGE_CACHE_SIZE);

	while (workspace->def_strm.total_in < len) {
		ret = zlib_deflate(&workspace->def_strm, Z_SYNC_FLUSH);
		if (ret != Z_OK) {
			printk(KERN_DEBUG "btrfs deflate in loop returned %d\n",
			       ret);
			zlib_deflateEnd(&workspace->def_strm);
			ret = -1;
			goto out;
		}

		/* we're making it bigger, give up */
		if (workspace->def_strm.total_in > 8192 &&
		    workspace->def_strm.total_in <
		    workspace->def_strm.total_out) {
			ret = -1;
			goto out;
		}
		/* we need another page for writing out.  Test this
		 * before the total_in so we will pull in a new page for
		 * the stream end if required
		 */
		if (workspace->def_strm.avail_out == 0) {
			kunmap(out_page);
			if (nr_pages == nr_dest_pages) {
				out_page = NULL;
				ret = -1;
				goto out;
			}
			out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
			cpage_out = kmap(out_page);
			pages[nr_pages] = out_page;
			nr_pages++;
			workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
			workspace->def_strm.next_out = cpage_out;
		}
		/* we're all done */
		if (workspace->def_strm.total_in >= len)
			break;

		/* we've read in a full page, get a new one */
		if (workspace->def_strm.avail_in == 0) {
			if (workspace->def_strm.total_out > max_out)
				break;

			bytes_left = len - workspace->def_strm.total_in;
			kunmap(in_page);
			page_cache_release(in_page);

			start += PAGE_CACHE_SIZE;
			in_page = find_get_page(mapping,
						start >> PAGE_CACHE_SHIFT);
			data_in = kmap(in_page);
			workspace->def_strm.avail_in = min(bytes_left,
							   PAGE_CACHE_SIZE);
			workspace->def_strm.next_in = data_in;
		}
	}
	workspace->def_strm.avail_in = 0;
	ret = zlib_deflate(&workspace->def_strm, Z_FINISH);
	zlib_deflateEnd(&workspace->def_strm);

	if (ret != Z_STREAM_END) {
		ret = -1;
		goto out;
	}

	if (workspace->def_strm.total_out >= workspace->def_strm.total_in) {
		ret = -1;
		goto out;
	}

	ret = 0;
	*total_out = workspace->def_strm.total_out;
	*total_in = workspace->def_strm.total_in;
out:
	*out_pages = nr_pages;
	if (out_page)
		kunmap(out_page);

	if (in_page) {
		kunmap(in_page);
		page_cache_release(in_page);
	}
	free_workspace(workspace);
	return ret;
}

/*
 * pages_in is an array of pages with compressed data.
 *
 * disk_start is the starting logical offset of this array in the file
 *
 * bvec is a bio_vec of pages from the file that we want to decompress into
 *
 * vcnt is the count of pages in the biovec
 *
 * srclen is the number of bytes in pages_in
 *
 * The basic idea is that we have a bio that was created by readpages.
 * The pages in the bio are for the uncompressed data, and they may not
 * be contiguous.  They all correspond to the range of bytes covered by
 * the compressed extent.
 */
int btrfs_zlib_decompress_biovec(struct page **pages_in,
			      u64 disk_start,
			      struct bio_vec *bvec,
			      int vcnt,
			      size_t srclen)
{
	int ret = 0;
	int wbits = MAX_WBITS;
	struct workspace *workspace;
	char *data_in;
	size_t total_out = 0;
	unsigned long page_bytes_left;
	unsigned long page_in_index = 0;
	unsigned long page_out_index = 0;
	struct page *page_out;
	unsigned long total_pages_in = (srclen + PAGE_CACHE_SIZE - 1) /
					PAGE_CACHE_SIZE;
	unsigned long buf_start;
	unsigned long buf_offset;
	unsigned long bytes;
	unsigned long working_bytes;
	unsigned long pg_offset;
	unsigned long start_byte;
	unsigned long current_buf_start;
	char *kaddr;

	workspace = find_zlib_workspace();
	if (IS_ERR(workspace))
		return -ENOMEM;

	data_in = kmap(pages_in[page_in_index]);
	workspace->inf_strm.next_in = data_in;
	workspace->inf_strm.avail_in = min_t(size_t, srclen, PAGE_CACHE_SIZE);
	workspace->inf_strm.total_in = 0;

	workspace->inf_strm.total_out = 0;
	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	page_out = bvec[page_out_index].bv_page;
	page_bytes_left = PAGE_CACHE_SIZE;
	pg_offset = 0;

	/* If it's deflate, and it's got no preset dictionary, then
	   we can tell zlib to skip the adler32 check. */
	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
	    ((data_in[0] & 0x0f) == Z_DEFLATED) &&
	    !(((data_in[0]<<8) + data_in[1]) % 31)) {

		wbits = -((data_in[0] >> 4) + 8);
		workspace->inf_strm.next_in += 2;
		workspace->inf_strm.avail_in -= 2;
	}

	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
		printk(KERN_WARNING "inflateInit failed\n");
		ret = -1;
		goto out;
	}
	while (workspace->inf_strm.total_in < srclen) {
		ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
		if (ret != Z_OK && ret != Z_STREAM_END)
			break;
		/*
		 * buf start is the byte offset we're of the start of
		 * our workspace buffer
		 */
		buf_start = total_out;

		/* total_out is the last byte of the workspace buffer */
		total_out = workspace->inf_strm.total_out;

		working_bytes = total_out - buf_start;

		/*
		 * start byte is the first byte of the page we're currently
		 * copying into relative to the start of the compressed data.
		 */
		start_byte = page_offset(page_out) - disk_start;

		if (working_bytes == 0) {
			/* we didn't make progress in this inflate
			 * call, we're done
			 */
			if (ret != Z_STREAM_END)
				ret = -1;
			break;
		}

		/* we haven't yet hit data corresponding to this page */
		if (total_out <= start_byte)
			goto next;

		/*
		 * the start of the data we care about is offset into
		 * the middle of our working buffer
		 */
		if (total_out > start_byte && buf_start < start_byte) {
			buf_offset = start_byte - buf_start;
			working_bytes -= buf_offset;
		} else {
			buf_offset = 0;
		}
		current_buf_start = buf_start;

		/* copy bytes from the working buffer into the pages */
		while (working_bytes > 0) {
			bytes = min(PAGE_CACHE_SIZE - pg_offset,
				    PAGE_CACHE_SIZE - buf_offset);
			bytes = min(bytes, working_bytes);
			kaddr = kmap_atomic(page_out, KM_USER0);
			memcpy(kaddr + pg_offset, workspace->buf + buf_offset,
			       bytes);
			kunmap_atomic(kaddr, KM_USER0);
			flush_dcache_page(page_out);

			pg_offset += bytes;
			page_bytes_left -= bytes;
			buf_offset += bytes;
			working_bytes -= bytes;
			current_buf_start += bytes;

			/* check if we need to pick another page */
			if (page_bytes_left == 0) {
				page_out_index++;
				if (page_out_index >= vcnt) {
					ret = 0;
					goto done;
				}

				page_out = bvec[page_out_index].bv_page;
				pg_offset = 0;
				page_bytes_left = PAGE_CACHE_SIZE;
				start_byte = page_offset(page_out) - disk_start;

				/*
				 * make sure our new page is covered by this
				 * working buffer
				 */
				if (total_out <= start_byte)
					goto next;

				/* the next page in the biovec might not
				 * be adjacent to the last page, but it
				 * might still be found inside this working
				 * buffer.  bump our offset pointer
				 */
				if (total_out > start_byte &&
				    current_buf_start < start_byte) {
					buf_offset = start_byte - buf_start;
					working_bytes = total_out - start_byte;
					current_buf_start = buf_start +
						buf_offset;
				}
			}
		}
next:
		workspace->inf_strm.next_out = workspace->buf;
		workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;

		if (workspace->inf_strm.avail_in == 0) {
			unsigned long tmp;
			kunmap(pages_in[page_in_index]);
			page_in_index++;
			if (page_in_index >= total_pages_in) {
				data_in = NULL;
				break;
			}
			data_in = kmap(pages_in[page_in_index]);
			workspace->inf_strm.next_in = data_in;
			tmp = srclen - workspace->inf_strm.total_in;
			workspace->inf_strm.avail_in = min(tmp,
							   PAGE_CACHE_SIZE);
		}
	}
	if (ret != Z_STREAM_END)
		ret = -1;
	else
		ret = 0;
done:
	zlib_inflateEnd(&workspace->inf_strm);
	if (data_in)
		kunmap(pages_in[page_in_index]);
out:
	free_workspace(workspace);
	return ret;
}

/*
 * a less complex decompression routine.  Our compressed data fits in a
 * single page, and we want to read a single page out of it.
 * start_byte tells us the offset into the compressed data we're interested in
 */
int btrfs_zlib_decompress(unsigned char *data_in,
			  struct page *dest_page,
			  unsigned long start_byte,
			  size_t srclen, size_t destlen)
{
	int ret = 0;
	int wbits = MAX_WBITS;
	struct workspace *workspace;
	unsigned long bytes_left = destlen;
	unsigned long total_out = 0;
	char *kaddr;

	if (destlen > PAGE_CACHE_SIZE)
		return -ENOMEM;

	workspace = find_zlib_workspace();
	if (IS_ERR(workspace))
		return -ENOMEM;

	workspace->inf_strm.next_in = data_in;
	workspace->inf_strm.avail_in = srclen;
	workspace->inf_strm.total_in = 0;

	workspace->inf_strm.next_out = workspace->buf;
	workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	workspace->inf_strm.total_out = 0;
	/* If it's deflate, and it's got no preset dictionary, then
	   we can tell zlib to skip the adler32 check. */
	if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
	    ((data_in[0] & 0x0f) == Z_DEFLATED) &&
	    !(((data_in[0]<<8) + data_in[1]) % 31)) {

		wbits = -((data_in[0] >> 4) + 8);
		workspace->inf_strm.next_in += 2;
		workspace->inf_strm.avail_in -= 2;
	}

	if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
		printk(KERN_WARNING "inflateInit failed\n");
		ret = -1;
		goto out;
	}

	while (bytes_left > 0) {
		unsigned long buf_start;
		unsigned long buf_offset;
		unsigned long bytes;
		unsigned long pg_offset = 0;

		ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
		if (ret != Z_OK && ret != Z_STREAM_END)
			break;

		buf_start = total_out;
		total_out = workspace->inf_strm.total_out;

		if (total_out == buf_start) {
			ret = -1;
			break;
		}

		if (total_out <= start_byte)
			goto next;

		if (total_out > start_byte && buf_start < start_byte)
			buf_offset = start_byte - buf_start;
		else
			buf_offset = 0;

		bytes = min(PAGE_CACHE_SIZE - pg_offset,
			    PAGE_CACHE_SIZE - buf_offset);
		bytes = min(bytes, bytes_left);

		kaddr = kmap_atomic(dest_page, KM_USER0);
		memcpy(kaddr + pg_offset, workspace->buf + buf_offset, bytes);
		kunmap_atomic(kaddr, KM_USER0);

		pg_offset += bytes;
		bytes_left -= bytes;
next:
		workspace->inf_strm.next_out = workspace->buf;
		workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
	}

	if (ret != Z_STREAM_END && bytes_left != 0)
		ret = -1;
	else
		ret = 0;

	zlib_inflateEnd(&workspace->inf_strm);
out:
	free_workspace(workspace);
	return ret;
}

void btrfs_zlib_exit(void)
{
    free_workspaces();
}