// SPDX-License-Identifier: GPL-2.0

  /*
   * Copyright (c) 2016-present, Facebook, Inc.
   * All rights reserved.
   *

   */

  #include <linux/bio.h>

  #include <linux/bitmap.h>

  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>

  #include <linux/sched/mm.h>

  #include <linux/pagemap.h>
  #include <linux/refcount.h>
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/zstd.h>

  #include "misc.h"

  #include "compression.h"

  #include "ctree.h"

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

  #define ZSTD_BTRFS_MAX_LEVEL 15

  /* 307s to avoid pathologically clashing with transaction commit */
  #define ZSTD_BTRFS_RECLAIM_JIFFIES (307 * HZ)

  static ZSTD_parameters zstd_get_btrfs_parameters(unsigned int level,
  						 size_t src_len)

  {

  	ZSTD_parameters params = ZSTD_getParams(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;

  	unsigned int level;

  	unsigned int req_level;

  	unsigned long last_used; /* jiffies */

  	struct list_head list;

  	struct list_head lru_list;

  	ZSTD_inBuffer in_buf;
  	ZSTD_outBuffer out_buf;

  };

  /*
   * Zstd Workspace Management
   *
   * Zstd workspaces have different memory requirements depending on the level.
   * The zstd workspaces are managed by having individual lists for each level
   * and a global lru.  Forward progress is maintained by protecting a max level
   * workspace.
   *
   * Getting a workspace is done by using the bitmap to identify the levels that
   * have available workspaces and scans up.  This lets us recycle higher level
   * workspaces because of the monotonic memory guarantee.  A workspace's
   * last_used is only updated if it is being used by the corresponding memory
   * level.  Putting a workspace involves adding it back to the appropriate places
   * and adding it back to the lru if necessary.
   *
   * A timer is used to reclaim workspaces if they have not been used for
   * ZSTD_BTRFS_RECLAIM_JIFFIES.  This helps keep only active workspaces around.
   * The upper bound is provided by the workqueue limit which is 2 (percpu limit).
   */
  
  struct zstd_workspace_manager {
  	const struct btrfs_compress_op *ops;
  	spinlock_t lock;
  	struct list_head lru_list;
  	struct list_head idle_ws[ZSTD_BTRFS_MAX_LEVEL];
  	unsigned long active_map;
  	wait_queue_head_t wait;
  	struct timer_list timer;
  };
  
  static struct zstd_workspace_manager wsm;

  static size_t zstd_ws_mem_sizes[ZSTD_BTRFS_MAX_LEVEL];

  static inline struct workspace *list_to_workspace(struct list_head *list)
  {
  	return container_of(list, struct workspace, list);
  }

  static void zstd_free_workspace(struct list_head *ws);
  static struct list_head *zstd_alloc_workspace(unsigned int level);

  /*
   * zstd_reclaim_timer_fn - reclaim timer
   * @t: timer
   *
   * This scans the lru_list and attempts to reclaim any workspace that hasn't
   * been used for ZSTD_BTRFS_RECLAIM_JIFFIES.
   */
  static void zstd_reclaim_timer_fn(struct timer_list *timer)
  {
  	unsigned long reclaim_threshold = jiffies - ZSTD_BTRFS_RECLAIM_JIFFIES;
  	struct list_head *pos, *next;

  	spin_lock_bh(&wsm.lock);

  
  	if (list_empty(&wsm.lru_list)) {

  		spin_unlock_bh(&wsm.lock);

  		return;
  	}
  
  	list_for_each_prev_safe(pos, next, &wsm.lru_list) {
  		struct workspace *victim = container_of(pos, struct workspace,
  							lru_list);
  		unsigned int level;
  
  		if (time_after(victim->last_used, reclaim_threshold))
  			break;
  
  		/* workspace is in use */
  		if (victim->req_level)
  			continue;
  
  		level = victim->level;
  		list_del(&victim->lru_list);
  		list_del(&victim->list);

  		zstd_free_workspace(&victim->list);

  
  		if (list_empty(&wsm.idle_ws[level - 1]))
  			clear_bit(level - 1, &wsm.active_map);
  
  	}
  
  	if (!list_empty(&wsm.lru_list))
  		mod_timer(&wsm.timer, jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);

  	spin_unlock_bh(&wsm.lock);

  }

  /*
   * zstd_calc_ws_mem_sizes - calculate monotonic memory bounds
   *
   * It is possible based on the level configurations that a higher level
   * workspace uses less memory than a lower level workspace.  In order to reuse
   * workspaces, this must be made a monotonic relationship.  This precomputes
   * the required memory for each level and enforces the monotonicity between
   * level and memory required.
   */
  static void zstd_calc_ws_mem_sizes(void)
  {
  	size_t max_size = 0;
  	unsigned int level;
  
  	for (level = 1; level <= ZSTD_BTRFS_MAX_LEVEL; level++) {
  		ZSTD_parameters params =
  			zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
  		size_t level_size =
  			max_t(size_t,
  			      ZSTD_CStreamWorkspaceBound(params.cParams),
  			      ZSTD_DStreamWorkspaceBound(ZSTD_BTRFS_MAX_INPUT));
  
  		max_size = max_t(size_t, max_size, level_size);
  		zstd_ws_mem_sizes[level - 1] = max_size;
  	}
  }

  static void zstd_init_workspace_manager(void)
  {

  	struct list_head *ws;
  	int i;

  	zstd_calc_ws_mem_sizes();

  	wsm.ops = &btrfs_zstd_compress;
  	spin_lock_init(&wsm.lock);
  	init_waitqueue_head(&wsm.wait);
  	timer_setup(&wsm.timer, zstd_reclaim_timer_fn, 0);
  
  	INIT_LIST_HEAD(&wsm.lru_list);
  	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++)
  		INIT_LIST_HEAD(&wsm.idle_ws[i]);

  	ws = zstd_alloc_workspace(ZSTD_BTRFS_MAX_LEVEL);

  	if (IS_ERR(ws)) {
  		pr_warn(
  		"BTRFS: cannot preallocate zstd compression workspace
  ");
  	} else {
  		set_bit(ZSTD_BTRFS_MAX_LEVEL - 1, &wsm.active_map);
  		list_add(ws, &wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1]);
  	}

  }
  
  static void zstd_cleanup_workspace_manager(void)
  {

  	struct workspace *workspace;
  	int i;

  	spin_lock_bh(&wsm.lock);

  	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++) {
  		while (!list_empty(&wsm.idle_ws[i])) {
  			workspace = container_of(wsm.idle_ws[i].next,
  						 struct workspace, list);
  			list_del(&workspace->list);
  			list_del(&workspace->lru_list);

  			zstd_free_workspace(&workspace->list);

  		}
  	}

  	spin_unlock_bh(&wsm.lock);

  
  	del_timer_sync(&wsm.timer);

  }
  
  /*
   * zstd_find_workspace - find workspace
   * @level: compression level
   *
   * This iterates over the set bits in the active_map beginning at the requested
   * compression level.  This lets us utilize already allocated workspaces before
   * allocating a new one.  If the workspace is of a larger size, it is used, but
   * the place in the lru_list and last_used times are not updated.  This is to
   * offer the opportunity to reclaim the workspace in favor of allocating an
   * appropriately sized one in the future.
   */
  static struct list_head *zstd_find_workspace(unsigned int level)
  {
  	struct list_head *ws;
  	struct workspace *workspace;
  	int i = level - 1;

  	spin_lock_bh(&wsm.lock);

  	for_each_set_bit_from(i, &wsm.active_map, ZSTD_BTRFS_MAX_LEVEL) {
  		if (!list_empty(&wsm.idle_ws[i])) {
  			ws = wsm.idle_ws[i].next;
  			workspace = list_to_workspace(ws);
  			list_del_init(ws);
  			/* keep its place if it's a lower level using this */
  			workspace->req_level = level;
  			if (level == workspace->level)
  				list_del(&workspace->lru_list);
  			if (list_empty(&wsm.idle_ws[i]))
  				clear_bit(i, &wsm.active_map);

  			spin_unlock_bh(&wsm.lock);

  			return ws;
  		}
  	}

  	spin_unlock_bh(&wsm.lock);

  
  	return NULL;

  }

  /*
   * zstd_get_workspace - zstd's get_workspace
   * @level: compression level
   *
   * If @level is 0, then any compression level can be used.  Therefore, we begin
   * scanning from 1.  We first scan through possible workspaces and then after
   * attempt to allocate a new workspace.  If we fail to allocate one due to
   * memory pressure, go to sleep waiting for the max level workspace to free up.
   */

  static struct list_head *zstd_get_workspace(unsigned int level)

  {

  	struct list_head *ws;
  	unsigned int nofs_flag;

  	/* level == 0 means we can use any workspace */
  	if (!level)
  		level = 1;
  
  again:
  	ws = zstd_find_workspace(level);
  	if (ws)
  		return ws;
  
  	nofs_flag = memalloc_nofs_save();

  	ws = zstd_alloc_workspace(level);

  	memalloc_nofs_restore(nofs_flag);
  
  	if (IS_ERR(ws)) {
  		DEFINE_WAIT(wait);
  
  		prepare_to_wait(&wsm.wait, &wait, TASK_UNINTERRUPTIBLE);
  		schedule();
  		finish_wait(&wsm.wait, &wait);
  
  		goto again;
  	}

  
  	return ws;

  }

  /*
   * zstd_put_workspace - zstd put_workspace
   * @ws: list_head for the workspace
   *
   * When putting back a workspace, we only need to update the LRU if we are of
   * the requested compression level.  Here is where we continue to protect the
   * max level workspace or update last_used accordingly.  If the reclaim timer
   * isn't set, it is also set here.  Only the max level workspace tries and wakes
   * up waiting workspaces.
   */

  static void zstd_put_workspace(struct list_head *ws)
  {

  	struct workspace *workspace = list_to_workspace(ws);

  	spin_lock_bh(&wsm.lock);

  
  	/* A node is only taken off the lru if we are the corresponding level */
  	if (workspace->req_level == workspace->level) {
  		/* Hide a max level workspace from reclaim */
  		if (list_empty(&wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1])) {
  			INIT_LIST_HEAD(&workspace->lru_list);
  		} else {
  			workspace->last_used = jiffies;
  			list_add(&workspace->lru_list, &wsm.lru_list);
  			if (!timer_pending(&wsm.timer))
  				mod_timer(&wsm.timer,
  					  jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);
  		}
  	}
  
  	set_bit(workspace->level - 1, &wsm.active_map);
  	list_add(&workspace->list, &wsm.idle_ws[workspace->level - 1]);
  	workspace->req_level = 0;

  	spin_unlock_bh(&wsm.lock);

  
  	if (workspace->level == ZSTD_BTRFS_MAX_LEVEL)
  		cond_wake_up(&wsm.wait);

  }

  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(unsigned int level)

  {

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

  	workspace->size = zstd_ws_mem_sizes[level - 1];

  	workspace->level = level;
  	workspace->req_level = level;
  	workspace->last_used = jiffies;

  	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);

  	INIT_LIST_HEAD(&workspace->lru_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 */

  	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(workspace->req_level,
  							   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
  ");
  		ret = -EIO;
  		goto out;
  	}
  
  	/* map in the first page of input data */
  	in_page = find_get_page(mapping, start >> PAGE_SHIFT);

  	workspace->in_buf.src = kmap(in_page);
  	workspace->in_buf.pos = 0;
  	workspace->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;

  	workspace->out_buf.dst = kmap(out_page);
  	workspace->out_buf.pos = 0;
  	workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);

  
  	while (1) {
  		size_t ret2;

  		ret2 = ZSTD_compressStream(stream, &workspace->out_buf,
  				&workspace->in_buf);

  		if (ZSTD_isError(ret2)) {
  			pr_debug("BTRFS: ZSTD_compressStream returned %d
  ",
  					ZSTD_getErrorCode(ret2));
  			ret = -EIO;
  			goto out;
  		}
  
  		/* Check to see if we are making it bigger */

  		if (tot_in + workspace->in_buf.pos > 8192 &&
  				tot_in + workspace->in_buf.pos <
  				tot_out + workspace->out_buf.pos) {

  			ret = -E2BIG;
  			goto out;
  		}
  
  		/* We've reached the end of our output range */

  		if (workspace->out_buf.pos >= max_out) {
  			tot_out += workspace->out_buf.pos;

  			ret = -E2BIG;
  			goto out;
  		}
  
  		/* Check if we need more output space */

  		if (workspace->out_buf.pos == workspace->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;

  			workspace->out_buf.dst = kmap(out_page);
  			workspace->out_buf.pos = 0;
  			workspace->out_buf.size = min_t(size_t, max_out,
  							PAGE_SIZE);

  		}
  
  		/* We've reached the end of the input */

  		if (workspace->in_buf.pos >= len) {
  			tot_in += workspace->in_buf.pos;

  			break;
  		}
  
  		/* Check if we need more input */

  		if (workspace->in_buf.pos == workspace->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);

  			workspace->in_buf.src = kmap(in_page);
  			workspace->in_buf.pos = 0;
  			workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);

  		}
  	}
  	while (1) {
  		size_t ret2;

  		ret2 = ZSTD_endStream(stream, &workspace->out_buf);

  		if (ZSTD_isError(ret2)) {
  			pr_debug("BTRFS: ZSTD_endStream returned %d
  ",
  					ZSTD_getErrorCode(ret2));
  			ret = -EIO;
  			goto out;
  		}
  		if (ret2 == 0) {

  			tot_out += workspace->out_buf.pos;

  			break;
  		}

  		if (workspace->out_buf.pos >= max_out) {
  			tot_out += workspace->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;

  		workspace->out_buf.dst = kmap(out_page);
  		workspace->out_buf.pos = 0;
  		workspace->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;

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

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

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

  
  	while (1) {
  		size_t ret2;

  		ret2 = ZSTD_decompressStream(stream, &workspace->out_buf,
  				&workspace->in_buf);

  		if (ZSTD_isError(ret2)) {
  			pr_debug("BTRFS: ZSTD_decompressStream returned %d
  ",
  					ZSTD_getErrorCode(ret2));
  			ret = -EIO;
  			goto done;
  		}
  		buf_start = total_out;

  		total_out += workspace->out_buf.pos;
  		workspace->out_buf.pos = 0;

  		ret = btrfs_decompress_buf2page(workspace->out_buf.dst,
  				buf_start, total_out, disk_start, orig_bio);

  		if (ret == 0)
  			break;

  		if (workspace->in_buf.pos >= srclen)

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

  		if (workspace->in_buf.pos == workspace->in_buf.size) {

  			kunmap(pages_in[page_in_index++]);
  			if (page_in_index >= total_pages_in) {

  				workspace->in_buf.src = NULL;

  				ret = -EIO;
  				goto done;
  			}
  			srclen -= PAGE_SIZE;

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

  		}
  	}
  	ret = 0;
  	zero_fill_bio(orig_bio);
  done:

  	if (workspace->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;

  	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
  ");
  		ret = -EIO;
  		goto finish;
  	}
  
  	destlen = min_t(size_t, destlen, PAGE_SIZE);

  	workspace->in_buf.src = data_in;
  	workspace->in_buf.pos = 0;
  	workspace->in_buf.size = srclen;

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

  
  	ret2 = 1;

  	while (pg_offset < destlen
  	       && workspace->in_buf.pos < workspace->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
  ");
  			ret = -EIO;
  			goto finish;
  		}

  		ret2 = ZSTD_decompressStream(stream, &workspace->out_buf,
  				&workspace->in_buf);

  		if (ZSTD_isError(ret2)) {
  			pr_debug("BTRFS: ZSTD_decompressStream returned %d
  ",
  					ZSTD_getErrorCode(ret2));
  			ret = -EIO;
  			goto finish;
  		}
  
  		buf_start = total_out;

  		total_out += workspace->out_buf.pos;
  		workspace->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,

  				workspace->out_buf.size - buf_offset);

  
  		kaddr = kmap_atomic(dest_page);

  		memcpy(kaddr + pg_offset, workspace->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 = {

  	.init_workspace_manager = zstd_init_workspace_manager,
  	.cleanup_workspace_manager = zstd_cleanup_workspace_manager,
  	.get_workspace = zstd_get_workspace,
  	.put_workspace = zstd_put_workspace,

  	.alloc_workspace = zstd_alloc_workspace,
  	.free_workspace = zstd_free_workspace,
  	.compress_pages = zstd_compress_pages,
  	.decompress_bio = zstd_decompress_bio,
  	.decompress = zstd_decompress,

  	.max_level	= ZSTD_BTRFS_MAX_LEVEL,
  	.default_level	= ZSTD_BTRFS_DEFAULT_LEVEL,

  };