fs/btrfs/zstd.c - linux-imx - Git at Google

 /*
  * Copyright (c) 2016-present, Facebook, Inc.
  * 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.
  */
 #include <linux/bio.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/refcount.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/zstd.h>
 #include "compression.h"

 #define ZSTD_BTRFS_MAX_WINDOWLOG 17
 #define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
 #define ZSTD_BTRFS_DEFAULT_LEVEL 3

 static ZSTD_parameters zstd_get_btrfs_parameters(size_t src_len)
 {
 	ZSTD_parameters params = ZSTD_getParams(ZSTD_BTRFS_DEFAULT_LEVEL,
 						src_len, 0);

 	if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
 		params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
 	WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
 	return params;
 }

 struct workspace {
 	void *mem;
 	size_t size;
 	char *buf;
 	struct list_head list;
 };

 static void zstd_free_workspace(struct list_head *ws)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);

 	kvfree(workspace->mem);
 	kfree(workspace->buf);
 	kfree(workspace);
 }

 static struct list_head *zstd_alloc_workspace(void)
 {
 	ZSTD_parameters params =
 			zstd_get_btrfs_parameters(ZSTD_BTRFS_MAX_INPUT);
 	struct workspace *workspace;

 	workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
 	if (!workspace)
 		return ERR_PTR(-ENOMEM);

 	workspace->size = max_t(size_t,
 			ZSTD_CStreamWorkspaceBound(params.cParams),
 			ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
 	workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
 	workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 	if (!workspace->mem || !workspace->buf)
 		goto fail;

 	INIT_LIST_HEAD(&workspace->list);

 	return &workspace->list;
 fail:
 	zstd_free_workspace(&workspace->list);
 	return ERR_PTR(-ENOMEM);
 }

 static int zstd_compress_pages(struct list_head *ws,
 		struct address_space *mapping,
 		u64 start,
 		struct page **pages,
 		unsigned long *out_pages,
 		unsigned long *total_in,
 		unsigned long *total_out)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
 	ZSTD_CStream *stream;
 	int ret = 0;
 	int nr_pages = 0;
 	struct page *in_page = NULL;  /* The current page to read */
 	struct page *out_page = NULL; /* The current page to write to */
 	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
 	ZSTD_outBuffer out_buf = { NULL, 0, 0 };
 	unsigned long tot_in = 0;
 	unsigned long tot_out = 0;
 	unsigned long len = *total_out;
 	const unsigned long nr_dest_pages = *out_pages;
 	unsigned long max_out = nr_dest_pages * PAGE_SIZE;
 	ZSTD_parameters params = zstd_get_btrfs_parameters(len);

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

 	/* Initialize the stream */
 	stream = ZSTD_initCStream(params, len, workspace->mem,
 			workspace->size);
 	if (!stream) {
 		pr_warn("BTRFS: ZSTD_initCStream failed\n");
 		ret = -EIO;
 		goto out;
 	}

 	/* map in the first page of input data */
 	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
 	in_buf.src = kmap(in_page);
 	in_buf.pos = 0;
 	in_buf.size = min_t(size_t, len, PAGE_SIZE);


 	/* Allocate and map in the output buffer */
 	out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 	if (out_page == NULL) {
 		ret = -ENOMEM;
 		goto out;
 	}
 	pages[nr_pages++] = out_page;
 	out_buf.dst = kmap(out_page);
 	out_buf.pos = 0;
 	out_buf.size = min_t(size_t, max_out, PAGE_SIZE);

 	while (1) {
 		size_t ret2;

 		ret2 = ZSTD_compressStream(stream, &out_buf, &in_buf);
 		if (ZSTD_isError(ret2)) {
 			pr_debug("BTRFS: ZSTD_compressStream returned %d\n",
 					ZSTD_getErrorCode(ret2));
 			ret = -EIO;
 			goto out;
 		}

 		/* Check to see if we are making it bigger */
 		if (tot_in + in_buf.pos > 8192 &&
 				tot_in + in_buf.pos <
 				tot_out + out_buf.pos) {
 			ret = -E2BIG;
 			goto out;
 		}

 		/* We've reached the end of our output range */
 		if (out_buf.pos >= max_out) {
 			tot_out += out_buf.pos;
 			ret = -E2BIG;
 			goto out;
 		}

 		/* Check if we need more output space */
 		if (out_buf.pos == out_buf.size) {
 			tot_out += PAGE_SIZE;
 			max_out -= PAGE_SIZE;
 			kunmap(out_page);
 			if (nr_pages == nr_dest_pages) {
 				out_page = NULL;
 				ret = -E2BIG;
 				goto out;
 			}
 			out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 			if (out_page == NULL) {
 				ret = -ENOMEM;
 				goto out;
 			}
 			pages[nr_pages++] = out_page;
 			out_buf.dst = kmap(out_page);
 			out_buf.pos = 0;
 			out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
 		}

 		/* We've reached the end of the input */
 		if (in_buf.pos >= len) {
 			tot_in += in_buf.pos;
 			break;
 		}

 		/* Check if we need more input */
 		if (in_buf.pos == in_buf.size) {
 			tot_in += PAGE_SIZE;
 			kunmap(in_page);
 			put_page(in_page);

 			start += PAGE_SIZE;
 			len -= PAGE_SIZE;
 			in_page = find_get_page(mapping, start >> PAGE_SHIFT);
 			in_buf.src = kmap(in_page);
 			in_buf.pos = 0;
 			in_buf.size = min_t(size_t, len, PAGE_SIZE);
 		}
 	}
 	while (1) {
 		size_t ret2;

 		ret2 = ZSTD_endStream(stream, &out_buf);
 		if (ZSTD_isError(ret2)) {
 			pr_debug("BTRFS: ZSTD_endStream returned %d\n",
 					ZSTD_getErrorCode(ret2));
 			ret = -EIO;
 			goto out;
 		}
 		if (ret2 == 0) {
 			tot_out += out_buf.pos;
 			break;
 		}
 		if (out_buf.pos >= max_out) {
 			tot_out += out_buf.pos;
 			ret = -E2BIG;
 			goto out;
 		}

 		tot_out += PAGE_SIZE;
 		max_out -= PAGE_SIZE;
 		kunmap(out_page);
 		if (nr_pages == nr_dest_pages) {
 			out_page = NULL;
 			ret = -E2BIG;
 			goto out;
 		}
 		out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 		if (out_page == NULL) {
 			ret = -ENOMEM;
 			goto out;
 		}
 		pages[nr_pages++] = out_page;
 		out_buf.dst = kmap(out_page);
 		out_buf.pos = 0;
 		out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
 	}

 	if (tot_out >= tot_in) {
 		ret = -E2BIG;
 		goto out;
 	}

 	ret = 0;
 	*total_in = tot_in;
 	*total_out = tot_out;
 out:
 	*out_pages = nr_pages;
 	/* Cleanup */
 	if (in_page) {
 		kunmap(in_page);
 		put_page(in_page);
 	}
 	if (out_page)
 		kunmap(out_page);
 	return ret;
 }

 static int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
 	struct page **pages_in = cb->compressed_pages;
 	u64 disk_start = cb->start;
 	struct bio *orig_bio = cb->orig_bio;
 	size_t srclen = cb->compressed_len;
 	ZSTD_DStream *stream;
 	int ret = 0;
 	unsigned long page_in_index = 0;
 	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_SIZE);
 	unsigned long buf_start;
 	unsigned long total_out = 0;
 	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
 	ZSTD_outBuffer out_buf = { NULL, 0, 0 };

 	stream = ZSTD_initDStream(
 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
 	if (!stream) {
 		pr_debug("BTRFS: ZSTD_initDStream failed\n");
 		ret = -EIO;
 		goto done;
 	}

 	in_buf.src = kmap(pages_in[page_in_index]);
 	in_buf.pos = 0;
 	in_buf.size = min_t(size_t, srclen, PAGE_SIZE);

 	out_buf.dst = workspace->buf;
 	out_buf.pos = 0;
 	out_buf.size = PAGE_SIZE;

 	while (1) {
 		size_t ret2;

 		ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
 		if (ZSTD_isError(ret2)) {
 			pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
 					ZSTD_getErrorCode(ret2));
 			ret = -EIO;
 			goto done;
 		}
 		buf_start = total_out;
 		total_out += out_buf.pos;
 		out_buf.pos = 0;

 		ret = btrfs_decompress_buf2page(out_buf.dst, buf_start,
 				total_out, disk_start, orig_bio);
 		if (ret == 0)
 			break;

 		if (in_buf.pos >= srclen)
 			break;

 		/* Check if we've hit the end of a frame */
 		if (ret2 == 0)
 			break;

 		if (in_buf.pos == in_buf.size) {
 			kunmap(pages_in[page_in_index++]);
 			if (page_in_index >= total_pages_in) {
 				in_buf.src = NULL;
 				ret = -EIO;
 				goto done;
 			}
 			srclen -= PAGE_SIZE;
 			in_buf.src = kmap(pages_in[page_in_index]);
 			in_buf.pos = 0;
 			in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
 		}
 	}
 	ret = 0;
 	zero_fill_bio(orig_bio);
 done:
 	if (in_buf.src)
 		kunmap(pages_in[page_in_index]);
 	return ret;
 }

 static int zstd_decompress(struct list_head *ws, unsigned char *data_in,
 		struct page *dest_page,
 		unsigned long start_byte,
 		size_t srclen, size_t destlen)
 {
 	struct workspace *workspace = list_entry(ws, struct workspace, list);
 	ZSTD_DStream *stream;
 	int ret = 0;
 	size_t ret2;
 	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
 	ZSTD_outBuffer out_buf = { NULL, 0, 0 };
 	unsigned long total_out = 0;
 	unsigned long pg_offset = 0;
 	char *kaddr;

 	stream = ZSTD_initDStream(
 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
 	if (!stream) {
 		pr_warn("BTRFS: ZSTD_initDStream failed\n");
 		ret = -EIO;
 		goto finish;
 	}

 	destlen = min_t(size_t, destlen, PAGE_SIZE);

 	in_buf.src = data_in;
 	in_buf.pos = 0;
 	in_buf.size = srclen;

 	out_buf.dst = workspace->buf;
 	out_buf.pos = 0;
 	out_buf.size = PAGE_SIZE;

 	ret2 = 1;
 	while (pg_offset < destlen && in_buf.pos < in_buf.size) {
 		unsigned long buf_start;
 		unsigned long buf_offset;
 		unsigned long bytes;

 		/* Check if the frame is over and we still need more input */
 		if (ret2 == 0) {
 			pr_debug("BTRFS: ZSTD_decompressStream ended early\n");
 			ret = -EIO;
 			goto finish;
 		}
 		ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
 		if (ZSTD_isError(ret2)) {
 			pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
 					ZSTD_getErrorCode(ret2));
 			ret = -EIO;
 			goto finish;
 		}

 		buf_start = total_out;
 		total_out += out_buf.pos;
 		out_buf.pos = 0;

 		if (total_out <= start_byte)
 			continue;

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

 		bytes = min_t(unsigned long, destlen - pg_offset,
 				out_buf.size - buf_offset);

 		kaddr = kmap_atomic(dest_page);
 		memcpy(kaddr + pg_offset, out_buf.dst + buf_offset, bytes);
 		kunmap_atomic(kaddr);

 		pg_offset += bytes;
 	}
 	ret = 0;
 finish:
 	if (pg_offset < destlen) {
 		kaddr = kmap_atomic(dest_page);
 		memset(kaddr + pg_offset, 0, destlen - pg_offset);
 		kunmap_atomic(kaddr);
 	}
 	return ret;
 }

 const struct btrfs_compress_op btrfs_zstd_compress = {
 	.alloc_workspace = zstd_alloc_workspace,
 	.free_workspace = zstd_free_workspace,
 	.compress_pages = zstd_compress_pages,
 	.decompress_bio = zstd_decompress_bio,
 	.decompress = zstd_decompress,
 };
	/*
	* Copyright (c) 2016-present, Facebook, Inc.
	* 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.
	*/
	#include <linux/bio.h>
	#include <linux/err.h>
	#include <linux/init.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/pagemap.h>
	#include <linux/refcount.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/zstd.h>
	#include "compression.h"

	#define ZSTD_BTRFS_MAX_WINDOWLOG 17
	#define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
	#define ZSTD_BTRFS_DEFAULT_LEVEL 3

	static ZSTD_parameters zstd_get_btrfs_parameters(size_t src_len)
	{
	ZSTD_parameters params = ZSTD_getParams(ZSTD_BTRFS_DEFAULT_LEVEL,
	src_len, 0);

	if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
	params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
	WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
	return params;
	}

	struct workspace {
	void *mem;
	size_t size;
	char *buf;
	struct list_head list;
	};

	static void zstd_free_workspace(struct list_head *ws)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);

	kvfree(workspace->mem);
	kfree(workspace->buf);
	kfree(workspace);
	}

	static struct list_head *zstd_alloc_workspace(void)
	{
	ZSTD_parameters params =
	zstd_get_btrfs_parameters(ZSTD_BTRFS_MAX_INPUT);
	struct workspace *workspace;

	workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
	if (!workspace)
	return ERR_PTR(-ENOMEM);

	workspace->size = max_t(size_t,
	ZSTD_CStreamWorkspaceBound(params.cParams),
	ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
	workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
	workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!workspace->mem \|\| !workspace->buf)
	goto fail;

	INIT_LIST_HEAD(&workspace->list);

	return &workspace->list;
	fail:
	zstd_free_workspace(&workspace->list);
	return ERR_PTR(-ENOMEM);
	}

	static int zstd_compress_pages(struct list_head *ws,
	struct address_space *mapping,
	u64 start,
	struct page **pages,
	unsigned long *out_pages,
	unsigned long *total_in,
	unsigned long *total_out)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);
	ZSTD_CStream *stream;
	int ret = 0;
	int nr_pages = 0;
	struct page in_page = NULL; / The current page to read */
	struct page out_page = NULL; / The current page to write to */
	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
	ZSTD_outBuffer out_buf = { NULL, 0, 0 };
	unsigned long tot_in = 0;
	unsigned long tot_out = 0;
	unsigned long len = *total_out;
	const unsigned long nr_dest_pages = *out_pages;
	unsigned long max_out = nr_dest_pages * PAGE_SIZE;
	ZSTD_parameters params = zstd_get_btrfs_parameters(len);

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

	/* Initialize the stream */
	stream = ZSTD_initCStream(params, len, workspace->mem,
	workspace->size);
	if (!stream) {
	pr_warn("BTRFS: ZSTD_initCStream failed\n");
	ret = -EIO;
	goto out;
	}

	/* map in the first page of input data */
	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
	in_buf.src = kmap(in_page);
	in_buf.pos = 0;
	in_buf.size = min_t(size_t, len, PAGE_SIZE);


	/* Allocate and map in the output buffer */
	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	pages[nr_pages++] = out_page;
	out_buf.dst = kmap(out_page);
	out_buf.pos = 0;
	out_buf.size = min_t(size_t, max_out, PAGE_SIZE);

	while (1) {
	size_t ret2;

	ret2 = ZSTD_compressStream(stream, &out_buf, &in_buf);
	if (ZSTD_isError(ret2)) {
	pr_debug("BTRFS: ZSTD_compressStream returned %d\n",
	ZSTD_getErrorCode(ret2));
	ret = -EIO;
	goto out;
	}

	/* Check to see if we are making it bigger */
	if (tot_in + in_buf.pos > 8192 &&
	tot_in + in_buf.pos <
	tot_out + out_buf.pos) {
	ret = -E2BIG;
	goto out;
	}

	/* We've reached the end of our output range */
	if (out_buf.pos >= max_out) {
	tot_out += out_buf.pos;
	ret = -E2BIG;
	goto out;
	}

	/* Check if we need more output space */
	if (out_buf.pos == out_buf.size) {
	tot_out += PAGE_SIZE;
	max_out -= PAGE_SIZE;
	kunmap(out_page);
	if (nr_pages == nr_dest_pages) {
	out_page = NULL;
	ret = -E2BIG;
	goto out;
	}
	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	pages[nr_pages++] = out_page;
	out_buf.dst = kmap(out_page);
	out_buf.pos = 0;
	out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
	}

	/* We've reached the end of the input */
	if (in_buf.pos >= len) {
	tot_in += in_buf.pos;
	break;
	}

	/* Check if we need more input */
	if (in_buf.pos == in_buf.size) {
	tot_in += PAGE_SIZE;
	kunmap(in_page);
	put_page(in_page);

	start += PAGE_SIZE;
	len -= PAGE_SIZE;
	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
	in_buf.src = kmap(in_page);
	in_buf.pos = 0;
	in_buf.size = min_t(size_t, len, PAGE_SIZE);
	}
	}
	while (1) {
	size_t ret2;

	ret2 = ZSTD_endStream(stream, &out_buf);
	if (ZSTD_isError(ret2)) {
	pr_debug("BTRFS: ZSTD_endStream returned %d\n",
	ZSTD_getErrorCode(ret2));
	ret = -EIO;
	goto out;
	}
	if (ret2 == 0) {
	tot_out += out_buf.pos;
	break;
	}
	if (out_buf.pos >= max_out) {
	tot_out += out_buf.pos;
	ret = -E2BIG;
	goto out;
	}

	tot_out += PAGE_SIZE;
	max_out -= PAGE_SIZE;
	kunmap(out_page);
	if (nr_pages == nr_dest_pages) {
	out_page = NULL;
	ret = -E2BIG;
	goto out;
	}
	out_page = alloc_page(GFP_NOFS \| __GFP_HIGHMEM);
	if (out_page == NULL) {
	ret = -ENOMEM;
	goto out;
	}
	pages[nr_pages++] = out_page;
	out_buf.dst = kmap(out_page);
	out_buf.pos = 0;
	out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
	}

	if (tot_out >= tot_in) {
	ret = -E2BIG;
	goto out;
	}

	ret = 0;
	*total_in = tot_in;
	*total_out = tot_out;
	out:
	*out_pages = nr_pages;
	/* Cleanup */
	if (in_page) {
	kunmap(in_page);
	put_page(in_page);
	}
	if (out_page)
	kunmap(out_page);
	return ret;
	}

	static int zstd_decompress_bio(struct list_head ws, struct compressed_bio cb)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);
	struct page **pages_in = cb->compressed_pages;
	u64 disk_start = cb->start;
	struct bio *orig_bio = cb->orig_bio;
	size_t srclen = cb->compressed_len;
	ZSTD_DStream *stream;
	int ret = 0;
	unsigned long page_in_index = 0;
	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_SIZE);
	unsigned long buf_start;
	unsigned long total_out = 0;
	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
	ZSTD_outBuffer out_buf = { NULL, 0, 0 };

	stream = ZSTD_initDStream(
	ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
	if (!stream) {
	pr_debug("BTRFS: ZSTD_initDStream failed\n");
	ret = -EIO;
	goto done;
	}

	in_buf.src = kmap(pages_in[page_in_index]);
	in_buf.pos = 0;
	in_buf.size = min_t(size_t, srclen, PAGE_SIZE);

	out_buf.dst = workspace->buf;
	out_buf.pos = 0;
	out_buf.size = PAGE_SIZE;

	while (1) {
	size_t ret2;

	ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
	if (ZSTD_isError(ret2)) {
	pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
	ZSTD_getErrorCode(ret2));
	ret = -EIO;
	goto done;
	}
	buf_start = total_out;
	total_out += out_buf.pos;
	out_buf.pos = 0;

	ret = btrfs_decompress_buf2page(out_buf.dst, buf_start,
	total_out, disk_start, orig_bio);
	if (ret == 0)
	break;

	if (in_buf.pos >= srclen)
	break;

	/* Check if we've hit the end of a frame */
	if (ret2 == 0)
	break;

	if (in_buf.pos == in_buf.size) {
	kunmap(pages_in[page_in_index++]);
	if (page_in_index >= total_pages_in) {
	in_buf.src = NULL;
	ret = -EIO;
	goto done;
	}
	srclen -= PAGE_SIZE;
	in_buf.src = kmap(pages_in[page_in_index]);
	in_buf.pos = 0;
	in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
	}
	}
	ret = 0;
	zero_fill_bio(orig_bio);
	done:
	if (in_buf.src)
	kunmap(pages_in[page_in_index]);
	return ret;
	}

	static int zstd_decompress(struct list_head ws, unsigned char data_in,
	struct page *dest_page,
	unsigned long start_byte,
	size_t srclen, size_t destlen)
	{
	struct workspace *workspace = list_entry(ws, struct workspace, list);
	ZSTD_DStream *stream;
	int ret = 0;
	size_t ret2;
	ZSTD_inBuffer in_buf = { NULL, 0, 0 };
	ZSTD_outBuffer out_buf = { NULL, 0, 0 };
	unsigned long total_out = 0;
	unsigned long pg_offset = 0;
	char *kaddr;

	stream = ZSTD_initDStream(
	ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
	if (!stream) {
	pr_warn("BTRFS: ZSTD_initDStream failed\n");
	ret = -EIO;
	goto finish;
	}

	destlen = min_t(size_t, destlen, PAGE_SIZE);

	in_buf.src = data_in;
	in_buf.pos = 0;
	in_buf.size = srclen;

	out_buf.dst = workspace->buf;
	out_buf.pos = 0;
	out_buf.size = PAGE_SIZE;

	ret2 = 1;
	while (pg_offset < destlen && in_buf.pos < in_buf.size) {
	unsigned long buf_start;
	unsigned long buf_offset;
	unsigned long bytes;

	/* Check if the frame is over and we still need more input */
	if (ret2 == 0) {
	pr_debug("BTRFS: ZSTD_decompressStream ended early\n");
	ret = -EIO;
	goto finish;
	}
	ret2 = ZSTD_decompressStream(stream, &out_buf, &in_buf);
	if (ZSTD_isError(ret2)) {
	pr_debug("BTRFS: ZSTD_decompressStream returned %d\n",
	ZSTD_getErrorCode(ret2));
	ret = -EIO;
	goto finish;
	}

	buf_start = total_out;
	total_out += out_buf.pos;
	out_buf.pos = 0;

	if (total_out <= start_byte)
	continue;

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

	bytes = min_t(unsigned long, destlen - pg_offset,
	out_buf.size - buf_offset);

	kaddr = kmap_atomic(dest_page);
	memcpy(kaddr + pg_offset, out_buf.dst + buf_offset, bytes);
	kunmap_atomic(kaddr);

	pg_offset += bytes;
	}
	ret = 0;
	finish:
	if (pg_offset < destlen) {
	kaddr = kmap_atomic(dest_page);
	memset(kaddr + pg_offset, 0, destlen - pg_offset);
	kunmap_atomic(kaddr);
	}
	return ret;
	}

	const struct btrfs_compress_op btrfs_zstd_compress = {
	.alloc_workspace = zstd_alloc_workspace,
	.free_workspace = zstd_free_workspace,
	.compress_pages = zstd_compress_pages,
	.decompress_bio = zstd_decompress_bio,
	.decompress = zstd_decompress,
	};