1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright (c) 2016-present, Facebook, Inc.
4  * All rights reserved.
5  *
6  */
7 
8 #include <linux/bio.h>
9 #include <linux/bitmap.h>
10 #include <linux/err.h>
11 #include <linux/init.h>
12 #include <linux/kernel.h>
13 #include <linux/mm.h>
14 #include <linux/sched/mm.h>
15 #include <linux/pagemap.h>
16 #include <linux/refcount.h>
17 #include <linux/sched.h>
18 #include <linux/slab.h>
19 #include <linux/zstd.h>
20 #include "misc.h"
21 #include "compression.h"
22 #include "ctree.h"
23 
24 #define ZSTD_BTRFS_MAX_WINDOWLOG 17
25 #define ZSTD_BTRFS_MAX_INPUT (1 << ZSTD_BTRFS_MAX_WINDOWLOG)
26 #define ZSTD_BTRFS_DEFAULT_LEVEL 3
27 #define ZSTD_BTRFS_MAX_LEVEL 15
28 /* 307s to avoid pathologically clashing with transaction commit */
29 #define ZSTD_BTRFS_RECLAIM_JIFFIES (307 * HZ)
30 
zstd_get_btrfs_parameters(unsigned int level,size_t src_len)31 static zstd_parameters zstd_get_btrfs_parameters(unsigned int level,
32 						 size_t src_len)
33 {
34 	zstd_parameters params = zstd_get_params(level, src_len);
35 
36 	if (params.cParams.windowLog > ZSTD_BTRFS_MAX_WINDOWLOG)
37 		params.cParams.windowLog = ZSTD_BTRFS_MAX_WINDOWLOG;
38 	WARN_ON(src_len > ZSTD_BTRFS_MAX_INPUT);
39 	return params;
40 }
41 
42 struct workspace {
43 	void *mem;
44 	size_t size;
45 	char *buf;
46 	unsigned int level;
47 	unsigned int req_level;
48 	unsigned long last_used; /* jiffies */
49 	struct list_head list;
50 	struct list_head lru_list;
51 	zstd_in_buffer in_buf;
52 	zstd_out_buffer out_buf;
53 };
54 
55 /*
56  * Zstd Workspace Management
57  *
58  * Zstd workspaces have different memory requirements depending on the level.
59  * The zstd workspaces are managed by having individual lists for each level
60  * and a global lru.  Forward progress is maintained by protecting a max level
61  * workspace.
62  *
63  * Getting a workspace is done by using the bitmap to identify the levels that
64  * have available workspaces and scans up.  This lets us recycle higher level
65  * workspaces because of the monotonic memory guarantee.  A workspace's
66  * last_used is only updated if it is being used by the corresponding memory
67  * level.  Putting a workspace involves adding it back to the appropriate places
68  * and adding it back to the lru if necessary.
69  *
70  * A timer is used to reclaim workspaces if they have not been used for
71  * ZSTD_BTRFS_RECLAIM_JIFFIES.  This helps keep only active workspaces around.
72  * The upper bound is provided by the workqueue limit which is 2 (percpu limit).
73  */
74 
75 struct zstd_workspace_manager {
76 	const struct btrfs_compress_op *ops;
77 	spinlock_t lock;
78 	struct list_head lru_list;
79 	struct list_head idle_ws[ZSTD_BTRFS_MAX_LEVEL];
80 	unsigned long active_map;
81 	wait_queue_head_t wait;
82 	struct timer_list timer;
83 };
84 
85 static struct zstd_workspace_manager wsm;
86 
87 static size_t zstd_ws_mem_sizes[ZSTD_BTRFS_MAX_LEVEL];
88 
list_to_workspace(struct list_head * list)89 static inline struct workspace *list_to_workspace(struct list_head *list)
90 {
91 	return container_of(list, struct workspace, list);
92 }
93 
94 void zstd_free_workspace(struct list_head *ws);
95 struct list_head *zstd_alloc_workspace(unsigned int level);
96 
97 /**
98  * Timer callback to free unused workspaces.
99  *
100  * @t: timer
101  *
102  * This scans the lru_list and attempts to reclaim any workspace that hasn't
103  * been used for ZSTD_BTRFS_RECLAIM_JIFFIES.
104  *
105  * The context is softirq and does not need the _bh locking primitives.
106  */
zstd_reclaim_timer_fn(struct timer_list * timer)107 static void zstd_reclaim_timer_fn(struct timer_list *timer)
108 {
109 	unsigned long reclaim_threshold = jiffies - ZSTD_BTRFS_RECLAIM_JIFFIES;
110 	struct list_head *pos, *next;
111 
112 	spin_lock(&wsm.lock);
113 
114 	if (list_empty(&wsm.lru_list)) {
115 		spin_unlock(&wsm.lock);
116 		return;
117 	}
118 
119 	list_for_each_prev_safe(pos, next, &wsm.lru_list) {
120 		struct workspace *victim = container_of(pos, struct workspace,
121 							lru_list);
122 		unsigned int level;
123 
124 		if (time_after(victim->last_used, reclaim_threshold))
125 			break;
126 
127 		/* workspace is in use */
128 		if (victim->req_level)
129 			continue;
130 
131 		level = victim->level;
132 		list_del(&victim->lru_list);
133 		list_del(&victim->list);
134 		zstd_free_workspace(&victim->list);
135 
136 		if (list_empty(&wsm.idle_ws[level - 1]))
137 			clear_bit(level - 1, &wsm.active_map);
138 
139 	}
140 
141 	if (!list_empty(&wsm.lru_list))
142 		mod_timer(&wsm.timer, jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);
143 
144 	spin_unlock(&wsm.lock);
145 }
146 
147 /*
148  * zstd_calc_ws_mem_sizes - calculate monotonic memory bounds
149  *
150  * It is possible based on the level configurations that a higher level
151  * workspace uses less memory than a lower level workspace.  In order to reuse
152  * workspaces, this must be made a monotonic relationship.  This precomputes
153  * the required memory for each level and enforces the monotonicity between
154  * level and memory required.
155  */
zstd_calc_ws_mem_sizes(void)156 static void zstd_calc_ws_mem_sizes(void)
157 {
158 	size_t max_size = 0;
159 	unsigned int level;
160 
161 	for (level = 1; level <= ZSTD_BTRFS_MAX_LEVEL; level++) {
162 		zstd_parameters params =
163 			zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
164 		size_t level_size =
165 			max_t(size_t,
166 			      zstd_cstream_workspace_bound(&params.cParams),
167 			      zstd_dstream_workspace_bound(ZSTD_BTRFS_MAX_INPUT));
168 
169 		max_size = max_t(size_t, max_size, level_size);
170 		zstd_ws_mem_sizes[level - 1] = max_size;
171 	}
172 }
173 
zstd_init_workspace_manager(void)174 void zstd_init_workspace_manager(void)
175 {
176 	struct list_head *ws;
177 	int i;
178 
179 	zstd_calc_ws_mem_sizes();
180 
181 	wsm.ops = &btrfs_zstd_compress;
182 	spin_lock_init(&wsm.lock);
183 	init_waitqueue_head(&wsm.wait);
184 	timer_setup(&wsm.timer, zstd_reclaim_timer_fn, 0);
185 
186 	INIT_LIST_HEAD(&wsm.lru_list);
187 	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++)
188 		INIT_LIST_HEAD(&wsm.idle_ws[i]);
189 
190 	ws = zstd_alloc_workspace(ZSTD_BTRFS_MAX_LEVEL);
191 	if (IS_ERR(ws)) {
192 		pr_warn(
193 		"BTRFS: cannot preallocate zstd compression workspace\n");
194 	} else {
195 		set_bit(ZSTD_BTRFS_MAX_LEVEL - 1, &wsm.active_map);
196 		list_add(ws, &wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1]);
197 	}
198 }
199 
zstd_cleanup_workspace_manager(void)200 void zstd_cleanup_workspace_manager(void)
201 {
202 	struct workspace *workspace;
203 	int i;
204 
205 	spin_lock_bh(&wsm.lock);
206 	for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++) {
207 		while (!list_empty(&wsm.idle_ws[i])) {
208 			workspace = container_of(wsm.idle_ws[i].next,
209 						 struct workspace, list);
210 			list_del(&workspace->list);
211 			list_del(&workspace->lru_list);
212 			zstd_free_workspace(&workspace->list);
213 		}
214 	}
215 	spin_unlock_bh(&wsm.lock);
216 
217 	del_timer_sync(&wsm.timer);
218 }
219 
220 /*
221  * zstd_find_workspace - find workspace
222  * @level: compression level
223  *
224  * This iterates over the set bits in the active_map beginning at the requested
225  * compression level.  This lets us utilize already allocated workspaces before
226  * allocating a new one.  If the workspace is of a larger size, it is used, but
227  * the place in the lru_list and last_used times are not updated.  This is to
228  * offer the opportunity to reclaim the workspace in favor of allocating an
229  * appropriately sized one in the future.
230  */
zstd_find_workspace(unsigned int level)231 static struct list_head *zstd_find_workspace(unsigned int level)
232 {
233 	struct list_head *ws;
234 	struct workspace *workspace;
235 	int i = level - 1;
236 
237 	spin_lock_bh(&wsm.lock);
238 	for_each_set_bit_from(i, &wsm.active_map, ZSTD_BTRFS_MAX_LEVEL) {
239 		if (!list_empty(&wsm.idle_ws[i])) {
240 			ws = wsm.idle_ws[i].next;
241 			workspace = list_to_workspace(ws);
242 			list_del_init(ws);
243 			/* keep its place if it's a lower level using this */
244 			workspace->req_level = level;
245 			if (level == workspace->level)
246 				list_del(&workspace->lru_list);
247 			if (list_empty(&wsm.idle_ws[i]))
248 				clear_bit(i, &wsm.active_map);
249 			spin_unlock_bh(&wsm.lock);
250 			return ws;
251 		}
252 	}
253 	spin_unlock_bh(&wsm.lock);
254 
255 	return NULL;
256 }
257 
258 /*
259  * zstd_get_workspace - zstd's get_workspace
260  * @level: compression level
261  *
262  * If @level is 0, then any compression level can be used.  Therefore, we begin
263  * scanning from 1.  We first scan through possible workspaces and then after
264  * attempt to allocate a new workspace.  If we fail to allocate one due to
265  * memory pressure, go to sleep waiting for the max level workspace to free up.
266  */
zstd_get_workspace(unsigned int level)267 struct list_head *zstd_get_workspace(unsigned int level)
268 {
269 	struct list_head *ws;
270 	unsigned int nofs_flag;
271 
272 	/* level == 0 means we can use any workspace */
273 	if (!level)
274 		level = 1;
275 
276 again:
277 	ws = zstd_find_workspace(level);
278 	if (ws)
279 		return ws;
280 
281 	nofs_flag = memalloc_nofs_save();
282 	ws = zstd_alloc_workspace(level);
283 	memalloc_nofs_restore(nofs_flag);
284 
285 	if (IS_ERR(ws)) {
286 		DEFINE_WAIT(wait);
287 
288 		prepare_to_wait(&wsm.wait, &wait, TASK_UNINTERRUPTIBLE);
289 		schedule();
290 		finish_wait(&wsm.wait, &wait);
291 
292 		goto again;
293 	}
294 
295 	return ws;
296 }
297 
298 /*
299  * zstd_put_workspace - zstd put_workspace
300  * @ws: list_head for the workspace
301  *
302  * When putting back a workspace, we only need to update the LRU if we are of
303  * the requested compression level.  Here is where we continue to protect the
304  * max level workspace or update last_used accordingly.  If the reclaim timer
305  * isn't set, it is also set here.  Only the max level workspace tries and wakes
306  * up waiting workspaces.
307  */
zstd_put_workspace(struct list_head * ws)308 void zstd_put_workspace(struct list_head *ws)
309 {
310 	struct workspace *workspace = list_to_workspace(ws);
311 
312 	spin_lock_bh(&wsm.lock);
313 
314 	/* A node is only taken off the lru if we are the corresponding level */
315 	if (workspace->req_level == workspace->level) {
316 		/* Hide a max level workspace from reclaim */
317 		if (list_empty(&wsm.idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1])) {
318 			INIT_LIST_HEAD(&workspace->lru_list);
319 		} else {
320 			workspace->last_used = jiffies;
321 			list_add(&workspace->lru_list, &wsm.lru_list);
322 			if (!timer_pending(&wsm.timer))
323 				mod_timer(&wsm.timer,
324 					  jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);
325 		}
326 	}
327 
328 	set_bit(workspace->level - 1, &wsm.active_map);
329 	list_add(&workspace->list, &wsm.idle_ws[workspace->level - 1]);
330 	workspace->req_level = 0;
331 
332 	spin_unlock_bh(&wsm.lock);
333 
334 	if (workspace->level == ZSTD_BTRFS_MAX_LEVEL)
335 		cond_wake_up(&wsm.wait);
336 }
337 
zstd_free_workspace(struct list_head * ws)338 void zstd_free_workspace(struct list_head *ws)
339 {
340 	struct workspace *workspace = list_entry(ws, struct workspace, list);
341 
342 	kvfree(workspace->mem);
343 	kfree(workspace->buf);
344 	kfree(workspace);
345 }
346 
zstd_alloc_workspace(unsigned int level)347 struct list_head *zstd_alloc_workspace(unsigned int level)
348 {
349 	struct workspace *workspace;
350 
351 	workspace = kzalloc(sizeof(*workspace), GFP_KERNEL);
352 	if (!workspace)
353 		return ERR_PTR(-ENOMEM);
354 
355 	workspace->size = zstd_ws_mem_sizes[level - 1];
356 	workspace->level = level;
357 	workspace->req_level = level;
358 	workspace->last_used = jiffies;
359 	workspace->mem = kvmalloc(workspace->size, GFP_KERNEL);
360 	workspace->buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
361 	if (!workspace->mem || !workspace->buf)
362 		goto fail;
363 
364 	INIT_LIST_HEAD(&workspace->list);
365 	INIT_LIST_HEAD(&workspace->lru_list);
366 
367 	return &workspace->list;
368 fail:
369 	zstd_free_workspace(&workspace->list);
370 	return ERR_PTR(-ENOMEM);
371 }
372 
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)373 int zstd_compress_pages(struct list_head *ws, struct address_space *mapping,
374 		u64 start, struct page **pages, unsigned long *out_pages,
375 		unsigned long *total_in, unsigned long *total_out)
376 {
377 	struct workspace *workspace = list_entry(ws, struct workspace, list);
378 	zstd_cstream *stream;
379 	int ret = 0;
380 	int nr_pages = 0;
381 	struct page *in_page = NULL;  /* The current page to read */
382 	struct page *out_page = NULL; /* The current page to write to */
383 	unsigned long tot_in = 0;
384 	unsigned long tot_out = 0;
385 	unsigned long len = *total_out;
386 	const unsigned long nr_dest_pages = *out_pages;
387 	unsigned long max_out = nr_dest_pages * PAGE_SIZE;
388 	zstd_parameters params = zstd_get_btrfs_parameters(workspace->req_level,
389 							   len);
390 
391 	*out_pages = 0;
392 	*total_out = 0;
393 	*total_in = 0;
394 
395 	/* Initialize the stream */
396 	stream = zstd_init_cstream(&params, len, workspace->mem,
397 			workspace->size);
398 	if (!stream) {
399 		pr_warn("BTRFS: zstd_init_cstream failed\n");
400 		ret = -EIO;
401 		goto out;
402 	}
403 
404 	/* map in the first page of input data */
405 	in_page = find_get_page(mapping, start >> PAGE_SHIFT);
406 	workspace->in_buf.src = kmap_local_page(in_page);
407 	workspace->in_buf.pos = 0;
408 	workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
409 
410 
411 	/* Allocate and map in the output buffer */
412 	out_page = alloc_page(GFP_NOFS);
413 	if (out_page == NULL) {
414 		ret = -ENOMEM;
415 		goto out;
416 	}
417 	pages[nr_pages++] = out_page;
418 	workspace->out_buf.dst = page_address(out_page);
419 	workspace->out_buf.pos = 0;
420 	workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
421 
422 	while (1) {
423 		size_t ret2;
424 
425 		ret2 = zstd_compress_stream(stream, &workspace->out_buf,
426 				&workspace->in_buf);
427 		if (zstd_is_error(ret2)) {
428 			pr_debug("BTRFS: zstd_compress_stream returned %d\n",
429 					zstd_get_error_code(ret2));
430 			ret = -EIO;
431 			goto out;
432 		}
433 
434 		/* Check to see if we are making it bigger */
435 		if (tot_in + workspace->in_buf.pos > 8192 &&
436 				tot_in + workspace->in_buf.pos <
437 				tot_out + workspace->out_buf.pos) {
438 			ret = -E2BIG;
439 			goto out;
440 		}
441 
442 		/* We've reached the end of our output range */
443 		if (workspace->out_buf.pos >= max_out) {
444 			tot_out += workspace->out_buf.pos;
445 			ret = -E2BIG;
446 			goto out;
447 		}
448 
449 		/* Check if we need more output space */
450 		if (workspace->out_buf.pos == workspace->out_buf.size) {
451 			tot_out += PAGE_SIZE;
452 			max_out -= PAGE_SIZE;
453 			if (nr_pages == nr_dest_pages) {
454 				ret = -E2BIG;
455 				goto out;
456 			}
457 			out_page = alloc_page(GFP_NOFS);
458 			if (out_page == NULL) {
459 				ret = -ENOMEM;
460 				goto out;
461 			}
462 			pages[nr_pages++] = out_page;
463 			workspace->out_buf.dst = page_address(out_page);
464 			workspace->out_buf.pos = 0;
465 			workspace->out_buf.size = min_t(size_t, max_out,
466 							PAGE_SIZE);
467 		}
468 
469 		/* We've reached the end of the input */
470 		if (workspace->in_buf.pos >= len) {
471 			tot_in += workspace->in_buf.pos;
472 			break;
473 		}
474 
475 		/* Check if we need more input */
476 		if (workspace->in_buf.pos == workspace->in_buf.size) {
477 			tot_in += PAGE_SIZE;
478 			kunmap_local(workspace->in_buf.src);
479 			put_page(in_page);
480 			start += PAGE_SIZE;
481 			len -= PAGE_SIZE;
482 			in_page = find_get_page(mapping, start >> PAGE_SHIFT);
483 			workspace->in_buf.src = kmap_local_page(in_page);
484 			workspace->in_buf.pos = 0;
485 			workspace->in_buf.size = min_t(size_t, len, PAGE_SIZE);
486 		}
487 	}
488 	while (1) {
489 		size_t ret2;
490 
491 		ret2 = zstd_end_stream(stream, &workspace->out_buf);
492 		if (zstd_is_error(ret2)) {
493 			pr_debug("BTRFS: zstd_end_stream returned %d\n",
494 					zstd_get_error_code(ret2));
495 			ret = -EIO;
496 			goto out;
497 		}
498 		if (ret2 == 0) {
499 			tot_out += workspace->out_buf.pos;
500 			break;
501 		}
502 		if (workspace->out_buf.pos >= max_out) {
503 			tot_out += workspace->out_buf.pos;
504 			ret = -E2BIG;
505 			goto out;
506 		}
507 
508 		tot_out += PAGE_SIZE;
509 		max_out -= PAGE_SIZE;
510 		if (nr_pages == nr_dest_pages) {
511 			ret = -E2BIG;
512 			goto out;
513 		}
514 		out_page = alloc_page(GFP_NOFS);
515 		if (out_page == NULL) {
516 			ret = -ENOMEM;
517 			goto out;
518 		}
519 		pages[nr_pages++] = out_page;
520 		workspace->out_buf.dst = page_address(out_page);
521 		workspace->out_buf.pos = 0;
522 		workspace->out_buf.size = min_t(size_t, max_out, PAGE_SIZE);
523 	}
524 
525 	if (tot_out >= tot_in) {
526 		ret = -E2BIG;
527 		goto out;
528 	}
529 
530 	ret = 0;
531 	*total_in = tot_in;
532 	*total_out = tot_out;
533 out:
534 	*out_pages = nr_pages;
535 	if (workspace->in_buf.src) {
536 		kunmap_local(workspace->in_buf.src);
537 		put_page(in_page);
538 	}
539 	return ret;
540 }
541 
zstd_decompress_bio(struct list_head * ws,struct compressed_bio * cb)542 int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
543 {
544 	struct workspace *workspace = list_entry(ws, struct workspace, list);
545 	struct page **pages_in = cb->compressed_pages;
546 	size_t srclen = cb->compressed_len;
547 	zstd_dstream *stream;
548 	int ret = 0;
549 	unsigned long page_in_index = 0;
550 	unsigned long total_pages_in = DIV_ROUND_UP(srclen, PAGE_SIZE);
551 	unsigned long buf_start;
552 	unsigned long total_out = 0;
553 
554 	stream = zstd_init_dstream(
555 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
556 	if (!stream) {
557 		pr_debug("BTRFS: zstd_init_dstream failed\n");
558 		ret = -EIO;
559 		goto done;
560 	}
561 
562 	workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
563 	workspace->in_buf.pos = 0;
564 	workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
565 
566 	workspace->out_buf.dst = workspace->buf;
567 	workspace->out_buf.pos = 0;
568 	workspace->out_buf.size = PAGE_SIZE;
569 
570 	while (1) {
571 		size_t ret2;
572 
573 		ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
574 				&workspace->in_buf);
575 		if (zstd_is_error(ret2)) {
576 			pr_debug("BTRFS: zstd_decompress_stream returned %d\n",
577 					zstd_get_error_code(ret2));
578 			ret = -EIO;
579 			goto done;
580 		}
581 		buf_start = total_out;
582 		total_out += workspace->out_buf.pos;
583 		workspace->out_buf.pos = 0;
584 
585 		ret = btrfs_decompress_buf2page(workspace->out_buf.dst,
586 				total_out - buf_start, cb, buf_start);
587 		if (ret == 0)
588 			break;
589 
590 		if (workspace->in_buf.pos >= srclen)
591 			break;
592 
593 		/* Check if we've hit the end of a frame */
594 		if (ret2 == 0)
595 			break;
596 
597 		if (workspace->in_buf.pos == workspace->in_buf.size) {
598 			kunmap_local(workspace->in_buf.src);
599 			page_in_index++;
600 			if (page_in_index >= total_pages_in) {
601 				workspace->in_buf.src = NULL;
602 				ret = -EIO;
603 				goto done;
604 			}
605 			srclen -= PAGE_SIZE;
606 			workspace->in_buf.src = kmap_local_page(pages_in[page_in_index]);
607 			workspace->in_buf.pos = 0;
608 			workspace->in_buf.size = min_t(size_t, srclen, PAGE_SIZE);
609 		}
610 	}
611 	ret = 0;
612 	zero_fill_bio(cb->orig_bio);
613 done:
614 	if (workspace->in_buf.src)
615 		kunmap_local(workspace->in_buf.src);
616 	return ret;
617 }
618 
zstd_decompress(struct list_head * ws,unsigned char * data_in,struct page * dest_page,unsigned long start_byte,size_t srclen,size_t destlen)619 int zstd_decompress(struct list_head *ws, unsigned char *data_in,
620 		struct page *dest_page, unsigned long start_byte, size_t srclen,
621 		size_t destlen)
622 {
623 	struct workspace *workspace = list_entry(ws, struct workspace, list);
624 	zstd_dstream *stream;
625 	int ret = 0;
626 	size_t ret2;
627 	unsigned long total_out = 0;
628 	unsigned long pg_offset = 0;
629 
630 	stream = zstd_init_dstream(
631 			ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
632 	if (!stream) {
633 		pr_warn("BTRFS: zstd_init_dstream failed\n");
634 		ret = -EIO;
635 		goto finish;
636 	}
637 
638 	destlen = min_t(size_t, destlen, PAGE_SIZE);
639 
640 	workspace->in_buf.src = data_in;
641 	workspace->in_buf.pos = 0;
642 	workspace->in_buf.size = srclen;
643 
644 	workspace->out_buf.dst = workspace->buf;
645 	workspace->out_buf.pos = 0;
646 	workspace->out_buf.size = PAGE_SIZE;
647 
648 	ret2 = 1;
649 	while (pg_offset < destlen
650 	       && workspace->in_buf.pos < workspace->in_buf.size) {
651 		unsigned long buf_start;
652 		unsigned long buf_offset;
653 		unsigned long bytes;
654 
655 		/* Check if the frame is over and we still need more input */
656 		if (ret2 == 0) {
657 			pr_debug("BTRFS: zstd_decompress_stream ended early\n");
658 			ret = -EIO;
659 			goto finish;
660 		}
661 		ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
662 				&workspace->in_buf);
663 		if (zstd_is_error(ret2)) {
664 			pr_debug("BTRFS: zstd_decompress_stream returned %d\n",
665 					zstd_get_error_code(ret2));
666 			ret = -EIO;
667 			goto finish;
668 		}
669 
670 		buf_start = total_out;
671 		total_out += workspace->out_buf.pos;
672 		workspace->out_buf.pos = 0;
673 
674 		if (total_out <= start_byte)
675 			continue;
676 
677 		if (total_out > start_byte && buf_start < start_byte)
678 			buf_offset = start_byte - buf_start;
679 		else
680 			buf_offset = 0;
681 
682 		bytes = min_t(unsigned long, destlen - pg_offset,
683 				workspace->out_buf.size - buf_offset);
684 
685 		memcpy_to_page(dest_page, pg_offset,
686 			       workspace->out_buf.dst + buf_offset, bytes);
687 
688 		pg_offset += bytes;
689 	}
690 	ret = 0;
691 finish:
692 	if (pg_offset < destlen) {
693 		memzero_page(dest_page, pg_offset, destlen - pg_offset);
694 	}
695 	return ret;
696 }
697 
698 const struct btrfs_compress_op btrfs_zstd_compress = {
699 	/* ZSTD uses own workspace manager */
700 	.workspace_manager = NULL,
701 	.max_level	= ZSTD_BTRFS_MAX_LEVEL,
702 	.default_level	= ZSTD_BTRFS_DEFAULT_LEVEL,
703 };
704