text: #include <linux/kernel.h>
  #include <linux/slab.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 <linux/zstd.h>
  #include "compression.h"
  
  #define ZSTD_BTRFS_MAX_WINDOWLOG 17
  #define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
  
  static ZSTD_parameters zstd_get_btrfs_parameters(size_t src_len)
  {
  	ZSTD_parameters params = ZSTD_getParams(3, 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);
  
  	vfree(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_NOFS);
  	if (!workspace)
  		return ERR_PTR(-ENOMEM);
  
  	workspace->size = max_t(size_t,
  			ZSTD_CStreamWorkspaceBound(params.cParams),
  			ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
  	workspace->mem = vmalloc(workspace->size);
  	workspace->buf = kmalloc(PAGE_SIZE, GFP_NOFS);
  	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_createCStream(params, len, workspace->mem,
  			workspace->size);
  	if (!stream) {
  		pr_warn("BTRFS: ZSTD_createStream 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 page **pages_in,
  		u64 disk_start,
  		struct bio *orig_bio,
  		size_t srclen)
  {
  	struct workspace *workspace = list_entry(ws, struct workspace, list);
  	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_createDStream(
  			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
  	if (!stream) {
  		pr_debug("BTRFS: ZSTD_createDStream 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_createDStream(
  			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
  	if (!stream) {
  		pr_warn("BTRFS: ZSTD_createDStream 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,
  };
  