// 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 "fs.h"
#include "btrfs_inode.h"
#include "compression.h"
#include "super.h"

#define ZSTD_BTRFS_MAX_WINDOWLOG 17
#define ZSTD_BTRFS_MAX_INPUT (1U << ZSTD_BTRFS_MAX_WINDOWLOG)
#define ZSTD_BTRFS_DEFAULT_LEVEL 3
#define ZSTD_BTRFS_MIN_LEVEL -15
#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(int level,
                                                 size_t src_len)
{
        zstd_parameters params = zstd_get_params(level, src_len);

        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;
        int level;
        int req_level;
        unsigned long last_used; /* jiffies */
        struct list_head list;
        struct list_head lru_list;
        zstd_in_buffer in_buf;
        zstd_out_buffer out_buf;
        zstd_parameters params;
};

/*
 * 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 {
        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 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 inline int clip_level(int level)
{
        return max(0, level - 1);
}

/*
 * Timer callback to free unused workspaces.
 *
 * @t: timer
 *
 * This scans the lru_list and attempts to reclaim any workspace that hasn't
 * been used for ZSTD_BTRFS_RECLAIM_JIFFIES.
 *
 * The context is softirq and does not need the _bh locking primitives.
 */
static void zstd_reclaim_timer_fn(struct timer_list *timer)
{
        struct zstd_workspace_manager *zwsm =
                container_of(timer, struct zstd_workspace_manager, timer);
        unsigned long reclaim_threshold = jiffies - ZSTD_BTRFS_RECLAIM_JIFFIES;
        struct list_head *pos, *next;

        spin_lock(&zwsm->lock);

        if (list_empty(&zwsm->lru_list)) {
                spin_unlock(&zwsm->lock);
                return;
        }

        list_for_each_prev_safe(pos, next, &zwsm->lru_list) {
                struct workspace *victim = container_of(pos, struct workspace,
                                                        lru_list);
                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(&zwsm->idle_ws[level]))
                        clear_bit(level, &zwsm->active_map);

        }

        if (!list_empty(&zwsm->lru_list))
                mod_timer(&zwsm->timer, jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);

        spin_unlock(&zwsm->lock);
}

/*
 * 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;
        int level;

        for (level = ZSTD_BTRFS_MIN_LEVEL; level <= ZSTD_BTRFS_MAX_LEVEL; level++) {
                if (level == 0)
                        continue;
                zstd_parameters params =
                        zstd_get_btrfs_parameters(level, ZSTD_BTRFS_MAX_INPUT);
                size_t level_size =
                        max_t(size_t,
                              zstd_cstream_workspace_bound(&params.cParams),
                              zstd_dstream_workspace_bound(ZSTD_BTRFS_MAX_INPUT));

                max_size = max_t(size_t, max_size, level_size);
                /* Use level 1 workspace size for all the fast mode negative levels. */
                zstd_ws_mem_sizes[clip_level(level)] = max_size;
        }
}

int zstd_alloc_workspace_manager(struct btrfs_fs_info *fs_info)
{
        struct zstd_workspace_manager *zwsm;
        struct list_head *ws;

        ASSERT(fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD] == NULL);
        zwsm = kzalloc_obj(*zwsm);
        if (!zwsm)
                return -ENOMEM;
        zstd_calc_ws_mem_sizes();
        spin_lock_init(&zwsm->lock);
        init_waitqueue_head(&zwsm->wait);
        timer_setup(&zwsm->timer, zstd_reclaim_timer_fn, 0);

        INIT_LIST_HEAD(&zwsm->lru_list);
        for (int i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++)
                INIT_LIST_HEAD(&zwsm->idle_ws[i]);
        fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD] = zwsm;

        ws = zstd_alloc_workspace(fs_info, ZSTD_BTRFS_MAX_LEVEL);
        if (IS_ERR(ws)) {
                btrfs_warn(NULL, "cannot preallocate zstd compression workspace");
        } else {
                set_bit(ZSTD_BTRFS_MAX_LEVEL - 1, &zwsm->active_map);
                list_add(ws, &zwsm->idle_ws[ZSTD_BTRFS_MAX_LEVEL - 1]);
        }
        return 0;
}

void zstd_free_workspace_manager(struct btrfs_fs_info *fs_info)
{
        struct zstd_workspace_manager *zwsm = fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD];
        struct workspace *workspace;

        if (!zwsm)
                return;
        fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD] = NULL;
        spin_lock_bh(&zwsm->lock);
        for (int i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++) {
                while (!list_empty(&zwsm->idle_ws[i])) {
                        workspace = container_of(zwsm->idle_ws[i].next,
                                                 struct workspace, list);
                        list_del(&workspace->list);
                        list_del(&workspace->lru_list);
                        zstd_free_workspace(&workspace->list);
                }
        }
        spin_unlock_bh(&zwsm->lock);
        timer_delete_sync(&zwsm->timer);
        kfree(zwsm);
}

/*
 * Find workspace for given level.
 *
 * @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(struct btrfs_fs_info *fs_info, int level)
{
        struct zstd_workspace_manager *zwsm = fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD];
        struct list_head *ws;
        struct workspace *workspace;
        int i = clip_level(level);

        ASSERT(zwsm);
        spin_lock_bh(&zwsm->lock);
        for_each_set_bit_from(i, &zwsm->active_map, ZSTD_BTRFS_MAX_LEVEL) {
                if (!list_empty(&zwsm->idle_ws[i])) {
                        ws = zwsm->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 (clip_level(level) == workspace->level)
                                list_del(&workspace->lru_list);
                        if (list_empty(&zwsm->idle_ws[i]))
                                clear_bit(i, &zwsm->active_map);
                        spin_unlock_bh(&zwsm->lock);
                        return ws;
                }
        }
        spin_unlock_bh(&zwsm->lock);

        return NULL;
}

/*
 * Zstd get_workspace for level.
 *
 * @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.
 */
struct list_head *zstd_get_workspace(struct btrfs_fs_info *fs_info, int level)
{
        struct zstd_workspace_manager *zwsm = fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD];
        struct list_head *ws;
        unsigned int nofs_flag;

        ASSERT(zwsm);

        /* level == 0 means we can use any workspace */
        if (!level)
                level = 1;

again:
        ws = zstd_find_workspace(fs_info, level);
        if (ws)
                return ws;

        nofs_flag = memalloc_nofs_save();
        ws = zstd_alloc_workspace(fs_info, level);
        memalloc_nofs_restore(nofs_flag);

        if (IS_ERR(ws)) {
                DEFINE_WAIT(wait);

                prepare_to_wait(&zwsm->wait, &wait, TASK_UNINTERRUPTIBLE);
                schedule();
                finish_wait(&zwsm->wait, &wait);

                goto again;
        }

        return ws;
}

/*
 * 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.
 */
void zstd_put_workspace(struct btrfs_fs_info *fs_info, struct list_head *ws)
{
        struct zstd_workspace_manager *zwsm = fs_info->compr_wsm[BTRFS_COMPRESS_ZSTD];
        struct workspace *workspace = list_to_workspace(ws);

        ASSERT(zwsm);
        spin_lock_bh(&zwsm->lock);

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

        set_bit(workspace->level, &zwsm->active_map);
        list_add(&workspace->list, &zwsm->idle_ws[workspace->level]);
        workspace->req_level = 0;

        spin_unlock_bh(&zwsm->lock);

        if (workspace->level == clip_level(ZSTD_BTRFS_MAX_LEVEL))
                cond_wake_up(&zwsm->wait);
}

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);
}

struct list_head *zstd_alloc_workspace(struct btrfs_fs_info *fs_info, int level)
{
        const u32 blocksize = fs_info->sectorsize;
        struct workspace *workspace;

        workspace = kzalloc_obj(*workspace);
        if (!workspace)
                return ERR_PTR(-ENOMEM);

        /* Use level 1 workspace size for all the fast mode negative levels. */
        workspace->size = zstd_ws_mem_sizes[clip_level(level)];
        workspace->level = clip_level(level);
        workspace->req_level = level;
        workspace->last_used = jiffies;
        workspace->mem = kvmalloc(workspace->size, GFP_KERNEL | __GFP_NOWARN);
        workspace->buf = kmalloc(blocksize, 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);
}

int zstd_compress_bio(struct list_head *ws, struct compressed_bio *cb)
{
        struct btrfs_inode *inode = cb->bbio.inode;
        struct btrfs_fs_info *fs_info = inode->root->fs_info;
        struct workspace *workspace = list_entry(ws, struct workspace, list);
        struct address_space *mapping = inode->vfs_inode.i_mapping;
        struct bio *bio = &cb->bbio.bio;
        zstd_cstream *stream;
        int ret = 0;
        /* The current folio to read. */
        struct folio *in_folio = NULL;
        /* The current folio to write to. */
        struct folio *out_folio = NULL;
        unsigned long tot_in = 0;
        unsigned long tot_out = 0;
        const u64 start = cb->start;
        const u32 len = cb->len;
        const u64 end = start + len;
        const u32 blocksize = fs_info->sectorsize;
        const u32 min_folio_size = btrfs_min_folio_size(fs_info);

        workspace->params = zstd_get_btrfs_parameters(workspace->req_level, len);

        /* Initialize the stream. */
        stream = zstd_init_cstream(&workspace->params, len, workspace->mem, workspace->size);
        if (unlikely(!stream)) {
                btrfs_err(fs_info,
        "zstd compression init level %d failed, root %llu inode %llu offset %llu",
                          workspace->req_level, btrfs_root_id(inode->root),
                          btrfs_ino(inode), start);
                ret = -EIO;
                goto out;
        }

        /* Map in the first page of input data. */
        ret = btrfs_compress_filemap_get_folio(mapping, start, &in_folio);
        if (ret < 0)
                goto out;
        workspace->in_buf.src = kmap_local_folio(in_folio, offset_in_folio(in_folio, start));
        workspace->in_buf.pos = 0;
        workspace->in_buf.size = btrfs_calc_input_length(in_folio, end, start);

        /* Allocate and map in the output buffer. */
        out_folio = btrfs_alloc_compr_folio(fs_info);
        if (out_folio == NULL) {
                ret = -ENOMEM;
                goto out;
        }
        workspace->out_buf.dst = folio_address(out_folio);
        workspace->out_buf.pos = 0;
        workspace->out_buf.size = min_folio_size;

        while (1) {
                size_t ret2;

                ret2 = zstd_compress_stream(stream, &workspace->out_buf, &workspace->in_buf);
                if (unlikely(zstd_is_error(ret2))) {
                        btrfs_warn(fs_info,
"zstd compression level %d failed, error %d root %llu inode %llu offset %llu",
                                   workspace->req_level, zstd_get_error_code(ret2),
                                   btrfs_root_id(inode->root), btrfs_ino(inode),
                                   start + tot_in);
                        ret = -EIO;
                        goto out;
                }

                /* Check to see if we are making it bigger. */
                if (tot_in + workspace->in_buf.pos > blocksize * 2 &&
                    tot_in + workspace->in_buf.pos < 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 += min_folio_size;
                        if (tot_out >= len) {
                                ret = -E2BIG;
                                goto out;
                        }
                        /* Queue the current foliot into the bio. */
                        if (!bio_add_folio(bio, out_folio, folio_size(out_folio), 0)) {
                                ret = -E2BIG;
                                goto out;
                        }

                        out_folio = btrfs_alloc_compr_folio(fs_info);
                        if (out_folio == NULL) {
                                ret = -ENOMEM;
                                goto out;
                        }
                        workspace->out_buf.dst = folio_address(out_folio);
                        workspace->out_buf.pos = 0;
                        workspace->out_buf.size = min_folio_size;
                }

                /* We've reached the end of the input. */
                if (tot_in + 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) {
                        u64 cur;

                        tot_in += workspace->in_buf.size;
                        cur = start + tot_in;

                        kunmap_local(workspace->in_buf.src);
                        workspace->in_buf.src = NULL;
                        folio_put(in_folio);

                        ret = btrfs_compress_filemap_get_folio(mapping, cur, &in_folio);
                        if (ret < 0)
                                goto out;
                        workspace->in_buf.src = kmap_local_folio(in_folio,
                                                         offset_in_folio(in_folio, cur));
                        workspace->in_buf.pos = 0;
                        workspace->in_buf.size = btrfs_calc_input_length(in_folio, end, cur);
                }
        }

        while (1) {
                size_t ret2;

                ret2 = zstd_end_stream(stream, &workspace->out_buf);
                if (unlikely(zstd_is_error(ret2))) {
                        btrfs_err(fs_info,
"zstd compression end level %d failed, error %d root %llu inode %llu offset %llu",
                                  workspace->req_level, zstd_get_error_code(ret2),
                                  btrfs_root_id(inode->root), btrfs_ino(inode),
                                  start + tot_in);
                        ret = -EIO;
                        goto out;
                }
                /* Queue the remaining part of the output folio into bio. */
                if (ret2 == 0) {
                        tot_out += workspace->out_buf.pos;
                        if (tot_out >= len) {
                                ret = -E2BIG;
                                goto out;
                        }
                        if (!bio_add_folio(bio, out_folio, workspace->out_buf.pos, 0)) {
                                ret = -E2BIG;
                                goto out;
                        }
                        out_folio = NULL;
                        break;
                }
                tot_out += min_folio_size;
                if (tot_out >= len) {
                        ret = -E2BIG;
                        goto out;
                }
                if (!bio_add_folio(bio, out_folio, folio_size(out_folio), 0)) {
                        ret = -E2BIG;
                        goto out;
                }
                out_folio = btrfs_alloc_compr_folio(fs_info);
                if (out_folio == NULL) {
                        ret = -ENOMEM;
                        goto out;
                }
                workspace->out_buf.dst = folio_address(out_folio);
                workspace->out_buf.pos = 0;
                workspace->out_buf.size = min_folio_size;
        }

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

        ret = 0;
        ASSERT(tot_out == bio->bi_iter.bi_size);
out:
        if (out_folio)
                btrfs_free_compr_folio(out_folio);
        if (workspace->in_buf.src) {
                kunmap_local(workspace->in_buf.src);
                folio_put(in_folio);
        }
        return ret;
}

int zstd_decompress_bio(struct list_head *ws, struct compressed_bio *cb)
{
        struct btrfs_fs_info *fs_info = cb_to_fs_info(cb);
        struct workspace *workspace = list_entry(ws, struct workspace, list);
        struct folio_iter fi;
        size_t srclen = cb->compressed_len;
        zstd_dstream *stream;
        int ret = 0;
        const u32 blocksize = fs_info->sectorsize;
        const unsigned int min_folio_size = btrfs_min_folio_size(fs_info);
        unsigned long folio_in_index = 0;
        unsigned long total_folios_in = DIV_ROUND_UP(srclen, min_folio_size);
        unsigned long buf_start;
        unsigned long total_out = 0;

        bio_first_folio(&fi, &cb->bbio.bio, 0);
        if (unlikely(!fi.folio))
                return -EINVAL;
        ASSERT(folio_size(fi.folio) == min_folio_size);

        stream = zstd_init_dstream(
                        ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
        if (unlikely(!stream)) {
                struct btrfs_inode *inode = cb->bbio.inode;

                btrfs_err(inode->root->fs_info,
                "zstd decompression init failed, root %llu inode %llu offset %llu",
                          btrfs_root_id(inode->root), btrfs_ino(inode), cb->start);
                ret = -EIO;
                goto done;
        }

        workspace->in_buf.src = kmap_local_folio(fi.folio, 0);
        workspace->in_buf.pos = 0;
        workspace->in_buf.size = min_t(size_t, srclen, min_folio_size);

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

        while (1) {
                size_t ret2;

                ret2 = zstd_decompress_stream(stream, &workspace->out_buf,
                                &workspace->in_buf);
                if (unlikely(zstd_is_error(ret2))) {
                        struct btrfs_inode *inode = cb->bbio.inode;

                        btrfs_err(inode->root->fs_info,
                "zstd decompression failed, error %d root %llu inode %llu offset %llu",
                                  zstd_get_error_code(ret2), btrfs_root_id(inode->root),
                                  btrfs_ino(inode), cb->start);
                        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,
                                total_out - buf_start, cb, buf_start);
                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_local(workspace->in_buf.src);
                        folio_in_index++;
                        if (unlikely(folio_in_index >= total_folios_in)) {
                                workspace->in_buf.src = NULL;
                                ret = -EIO;
                                goto done;
                        }
                        srclen -= min_folio_size;
                        bio_next_folio(&fi, &cb->bbio.bio);
                        ASSERT(fi.folio);
                        workspace->in_buf.src = kmap_local_folio(fi.folio, 0);
                        workspace->in_buf.pos = 0;
                        workspace->in_buf.size = min_t(size_t, srclen, min_folio_size);
                }
        }
        ret = 0;
done:
        if (workspace->in_buf.src)
                kunmap_local(workspace->in_buf.src);
        return ret;
}

int zstd_decompress(struct list_head *ws, const u8 *data_in,
                struct folio *dest_folio, unsigned long dest_pgoff, size_t srclen,
                size_t destlen)
{
        struct workspace *workspace = list_entry(ws, struct workspace, list);
        struct btrfs_fs_info *fs_info = btrfs_sb(folio_inode(dest_folio)->i_sb);
        const u32 sectorsize = fs_info->sectorsize;
        zstd_dstream *stream;
        int ret = 0;
        unsigned long to_copy = 0;

        stream = zstd_init_dstream(
                        ZSTD_BTRFS_MAX_INPUT, workspace->mem, workspace->size);
        if (unlikely(!stream)) {
                struct btrfs_inode *inode = folio_to_inode(dest_folio);

                btrfs_err(inode->root->fs_info,
                "zstd decompression init failed, root %llu inode %llu offset %llu",
                          btrfs_root_id(inode->root), btrfs_ino(inode),
                          folio_pos(dest_folio));
                ret = -EIO;
                goto finish;
        }

        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 = sectorsize;

        /*
         * Since both input and output buffers should not exceed one sector,
         * one call should end the decompression.
         */
        ret = zstd_decompress_stream(stream, &workspace->out_buf, &workspace->in_buf);
        if (unlikely(zstd_is_error(ret))) {
                struct btrfs_inode *inode = folio_to_inode(dest_folio);

                btrfs_err(inode->root->fs_info,
                "zstd decompression failed, error %d root %llu inode %llu offset %llu",
                          zstd_get_error_code(ret), btrfs_root_id(inode->root),
                          btrfs_ino(inode), folio_pos(dest_folio));
                goto finish;
        }
        to_copy = workspace->out_buf.pos;
        memcpy_to_folio(dest_folio, dest_pgoff, workspace->out_buf.dst, to_copy);
finish:
        /* Error or early end. */
        if (unlikely(to_copy < destlen)) {
                ret = -EIO;
                folio_zero_range(dest_folio, dest_pgoff + to_copy, destlen - to_copy);
        }
        return ret;
}

const struct btrfs_compress_levels btrfs_zstd_compress = {
        .min_level      = ZSTD_BTRFS_MIN_LEVEL,
        .max_level      = ZSTD_BTRFS_MAX_LEVEL,
        .default_level  = ZSTD_BTRFS_DEFAULT_LEVEL,
};