// 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\n");
        } 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\n");
                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\n",
                                        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\n",
                                        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\n");
                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\n",
                                        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\n");
                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\n");
                        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\n",
                                        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,
};