/*
 * Copyright (C) 2008 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 *
 * Based on jffs2 zlib code:
 * Copyright © 2001-2007 Red Hat, Inc.
 * Created by David Woodhouse <dwmw2@infradead.org>
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/zlib.h>
#include <linux/zutil.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/pagemap.h>
#include <linux/bio.h>
#include "compression.h"

/* Plan: call deflate() with avail_in == *sourcelen,
        avail_out = *dstlen - 12 and flush == Z_FINISH.
        If it doesn't manage to finish, call it again with
        avail_in == 0 and avail_out set to the remaining 12
        bytes for it to clean up.
   Q: Is 12 bytes sufficient?
*/
#define STREAM_END_SPACE 12

struct workspace {
        z_stream inf_strm;
        z_stream def_strm;
        char *buf;
        struct list_head list;
};

static LIST_HEAD(idle_workspace);
static DEFINE_SPINLOCK(workspace_lock);
static unsigned long num_workspace;
static atomic_t alloc_workspace = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(workspace_wait);

/*
 * this finds an available zlib workspace or allocates a new one
 * NULL or an ERR_PTR is returned if things go bad.
 */
static struct workspace *find_zlib_workspace(void)
{
        struct workspace *workspace;
        int ret;
        int cpus = num_online_cpus();

again:
        spin_lock(&workspace_lock);
        if (!list_empty(&idle_workspace)) {
                workspace = list_entry(idle_workspace.next, struct workspace,
                                       list);
                list_del(&workspace->list);
                num_workspace--;
                spin_unlock(&workspace_lock);
                return workspace;

        }
        spin_unlock(&workspace_lock);
        if (atomic_read(&alloc_workspace) > cpus) {
                DEFINE_WAIT(wait);
                prepare_to_wait(&workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
                if (atomic_read(&alloc_workspace) > cpus)
                        schedule();
                finish_wait(&workspace_wait, &wait);
                goto again;
        }
        atomic_inc(&alloc_workspace);
        workspace = kzalloc(sizeof(*workspace), GFP_NOFS);
        if (!workspace) {
                ret = -ENOMEM;
                goto fail;
        }

        workspace->def_strm.workspace = vmalloc(zlib_deflate_workspacesize());
        if (!workspace->def_strm.workspace) {
                ret = -ENOMEM;
                goto fail;
        }
        workspace->inf_strm.workspace = vmalloc(zlib_inflate_workspacesize());
        if (!workspace->inf_strm.workspace) {
                ret = -ENOMEM;
                goto fail_inflate;
        }
        workspace->buf = kmalloc(PAGE_CACHE_SIZE, GFP_NOFS);
        if (!workspace->buf) {
                ret = -ENOMEM;
                goto fail_kmalloc;
        }
        return workspace;

fail_kmalloc:
        vfree(workspace->inf_strm.workspace);
fail_inflate:
        vfree(workspace->def_strm.workspace);
fail:
        kfree(workspace);
        atomic_dec(&alloc_workspace);
        wake_up(&workspace_wait);
        return ERR_PTR(ret);
}

/*
 * put a workspace struct back on the list or free it if we have enough
 * idle ones sitting around
 */
static int free_workspace(struct workspace *workspace)
{
        spin_lock(&workspace_lock);
        if (num_workspace < num_online_cpus()) {
                list_add_tail(&workspace->list, &idle_workspace);
                num_workspace++;
                spin_unlock(&workspace_lock);
                if (waitqueue_active(&workspace_wait))
                        wake_up(&workspace_wait);
                return 0;
        }
        spin_unlock(&workspace_lock);
        vfree(workspace->def_strm.workspace);
        vfree(workspace->inf_strm.workspace);
        kfree(workspace->buf);
        kfree(workspace);

        atomic_dec(&alloc_workspace);
        if (waitqueue_active(&workspace_wait))
                wake_up(&workspace_wait);
        return 0;
}

/*
 * cleanup function for module exit
 */
static void free_workspaces(void)
{
        struct workspace *workspace;
        while (!list_empty(&idle_workspace)) {
                workspace = list_entry(idle_workspace.next, struct workspace,
                                       list);
                list_del(&workspace->list);
                vfree(workspace->def_strm.workspace);
                vfree(workspace->inf_strm.workspace);
                kfree(workspace->buf);
                kfree(workspace);
                atomic_dec(&alloc_workspace);
        }
}

/*
 * given an address space and start/len, compress the bytes.
 *
 * pages are allocated to hold the compressed result and stored
 * in 'pages'
 *
 * out_pages is used to return the number of pages allocated.  There
 * may be pages allocated even if we return an error
 *
 * total_in is used to return the number of bytes actually read.  It
 * may be smaller then len if we had to exit early because we
 * ran out of room in the pages array or because we cross the
 * max_out threshold.
 *
 * total_out is used to return the total number of compressed bytes
 *
 * max_out tells us the max number of bytes that we're allowed to
 * stuff into pages
 */
int btrfs_zlib_compress_pages(struct address_space *mapping,
                              u64 start, unsigned long len,
                              struct page **pages,
                              unsigned long nr_dest_pages,
                              unsigned long *out_pages,
                              unsigned long *total_in,
                              unsigned long *total_out,
                              unsigned long max_out)
{
        int ret;
        struct workspace *workspace;
        char *data_in;
        char *cpage_out;
        int nr_pages = 0;
        struct page *in_page = NULL;
        struct page *out_page = NULL;
        int out_written = 0;
        int in_read = 0;
        unsigned long bytes_left;

        *out_pages = 0;
        *total_out = 0;
        *total_in = 0;

        workspace = find_zlib_workspace();
        if (IS_ERR(workspace))
                return -1;

        if (Z_OK != zlib_deflateInit(&workspace->def_strm, 3)) {
                printk(KERN_WARNING "deflateInit failed\n");
                ret = -1;
                goto out;
        }

        workspace->def_strm.total_in = 0;
        workspace->def_strm.total_out = 0;

        in_page = find_get_page(mapping, start >> PAGE_CACHE_SHIFT);
        data_in = kmap(in_page);

        out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
        cpage_out = kmap(out_page);
        pages[0] = out_page;
        nr_pages = 1;

        workspace->def_strm.next_in = data_in;
        workspace->def_strm.next_out = cpage_out;
        workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
        workspace->def_strm.avail_in = min(len, PAGE_CACHE_SIZE);

        out_written = 0;
        in_read = 0;

        while (workspace->def_strm.total_in < len) {
                ret = zlib_deflate(&workspace->def_strm, Z_SYNC_FLUSH);
                if (ret != Z_OK) {
                        printk(KERN_DEBUG "btrfs deflate in loop returned %d\n",
                               ret);
                        zlib_deflateEnd(&workspace->def_strm);
                        ret = -1;
                        goto out;
                }

                /* we're making it bigger, give up */
                if (workspace->def_strm.total_in > 8192 &&
                    workspace->def_strm.total_in <
                    workspace->def_strm.total_out) {
                        ret = -1;
                        goto out;
                }
                /* we need another page for writing out.  Test this
                 * before the total_in so we will pull in a new page for
                 * the stream end if required
                 */
                if (workspace->def_strm.avail_out == 0) {
                        kunmap(out_page);
                        if (nr_pages == nr_dest_pages) {
                                out_page = NULL;
                                ret = -1;
                                goto out;
                        }
                        out_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
                        cpage_out = kmap(out_page);
                        pages[nr_pages] = out_page;
                        nr_pages++;
                        workspace->def_strm.avail_out = PAGE_CACHE_SIZE;
                        workspace->def_strm.next_out = cpage_out;
                }
                /* we're all done */
                if (workspace->def_strm.total_in >= len)
                        break;

                /* we've read in a full page, get a new one */
                if (workspace->def_strm.avail_in == 0) {
                        if (workspace->def_strm.total_out > max_out)
                                break;

                        bytes_left = len - workspace->def_strm.total_in;
                        kunmap(in_page);
                        page_cache_release(in_page);

                        start += PAGE_CACHE_SIZE;
                        in_page = find_get_page(mapping,
                                                start >> PAGE_CACHE_SHIFT);
                        data_in = kmap(in_page);
                        workspace->def_strm.avail_in = min(bytes_left,
                                                           PAGE_CACHE_SIZE);
                        workspace->def_strm.next_in = data_in;
                }
        }
        workspace->def_strm.avail_in = 0;
        ret = zlib_deflate(&workspace->def_strm, Z_FINISH);
        zlib_deflateEnd(&workspace->def_strm);

        if (ret != Z_STREAM_END) {
                ret = -1;
                goto out;
        }

        if (workspace->def_strm.total_out >= workspace->def_strm.total_in) {
                ret = -1;
                goto out;
        }

        ret = 0;
        *total_out = workspace->def_strm.total_out;
        *total_in = workspace->def_strm.total_in;
out:
        *out_pages = nr_pages;
        if (out_page)
                kunmap(out_page);

        if (in_page) {
                kunmap(in_page);
                page_cache_release(in_page);
        }
        free_workspace(workspace);
        return ret;
}

/*
 * pages_in is an array of pages with compressed data.
 *
 * disk_start is the starting logical offset of this array in the file
 *
 * bvec is a bio_vec of pages from the file that we want to decompress into
 *
 * vcnt is the count of pages in the biovec
 *
 * srclen is the number of bytes in pages_in
 *
 * The basic idea is that we have a bio that was created by readpages.
 * The pages in the bio are for the uncompressed data, and they may not
 * be contiguous.  They all correspond to the range of bytes covered by
 * the compressed extent.
 */
int btrfs_zlib_decompress_biovec(struct page **pages_in,
                              u64 disk_start,
                              struct bio_vec *bvec,
                              int vcnt,
                              size_t srclen)
{
        int ret = 0;
        int wbits = MAX_WBITS;
        struct workspace *workspace;
        char *data_in;
        size_t total_out = 0;
        unsigned long page_bytes_left;
        unsigned long page_in_index = 0;
        unsigned long page_out_index = 0;
        struct page *page_out;
        unsigned long total_pages_in = (srclen + PAGE_CACHE_SIZE - 1) /
                                        PAGE_CACHE_SIZE;
        unsigned long buf_start;
        unsigned long buf_offset;
        unsigned long bytes;
        unsigned long working_bytes;
        unsigned long pg_offset;
        unsigned long start_byte;
        unsigned long current_buf_start;
        char *kaddr;

        workspace = find_zlib_workspace();
        if (IS_ERR(workspace))
                return -ENOMEM;

        data_in = kmap(pages_in[page_in_index]);
        workspace->inf_strm.next_in = data_in;
        workspace->inf_strm.avail_in = min_t(size_t, srclen, PAGE_CACHE_SIZE);
        workspace->inf_strm.total_in = 0;

        workspace->inf_strm.total_out = 0;
        workspace->inf_strm.next_out = workspace->buf;
        workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
        page_out = bvec[page_out_index].bv_page;
        page_bytes_left = PAGE_CACHE_SIZE;
        pg_offset = 0;

        /* If it's deflate, and it's got no preset dictionary, then
           we can tell zlib to skip the adler32 check. */
        if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
            ((data_in[0] & 0x0f) == Z_DEFLATED) &&
            !(((data_in[0]<<8) + data_in[1]) % 31)) {

                wbits = -((data_in[0] >> 4) + 8);
                workspace->inf_strm.next_in += 2;
                workspace->inf_strm.avail_in -= 2;
        }

        if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
                printk(KERN_WARNING "inflateInit failed\n");
                ret = -1;
                goto out;
        }
        while (workspace->inf_strm.total_in < srclen) {
                ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
                if (ret != Z_OK && ret != Z_STREAM_END)
                        break;
                /*
                 * buf start is the byte offset we're of the start of
                 * our workspace buffer
                 */
                buf_start = total_out;

                /* total_out is the last byte of the workspace buffer */
                total_out = workspace->inf_strm.total_out;

                working_bytes = total_out - buf_start;

                /*
                 * start byte is the first byte of the page we're currently
                 * copying into relative to the start of the compressed data.
                 */
                start_byte = page_offset(page_out) - disk_start;

                if (working_bytes == 0) {
                        /* we didn't make progress in this inflate
                         * call, we're done
                         */
                        if (ret != Z_STREAM_END)
                                ret = -1;
                        break;
                }

                /* we haven't yet hit data corresponding to this page */
                if (total_out <= start_byte)
                        goto next;

                /*
                 * the start of the data we care about is offset into
                 * the middle of our working buffer
                 */
                if (total_out > start_byte && buf_start < start_byte) {
                        buf_offset = start_byte - buf_start;
                        working_bytes -= buf_offset;
                } else {
                        buf_offset = 0;
                }
                current_buf_start = buf_start;

                /* copy bytes from the working buffer into the pages */
                while (working_bytes > 0) {
                        bytes = min(PAGE_CACHE_SIZE - pg_offset,
                                    PAGE_CACHE_SIZE - buf_offset);
                        bytes = min(bytes, working_bytes);
                        kaddr = kmap_atomic(page_out, KM_USER0);
                        memcpy(kaddr + pg_offset, workspace->buf + buf_offset,
                               bytes);
                        kunmap_atomic(kaddr, KM_USER0);
                        flush_dcache_page(page_out);

                        pg_offset += bytes;
                        page_bytes_left -= bytes;
                        buf_offset += bytes;
                        working_bytes -= bytes;
                        current_buf_start += bytes;

                        /* check if we need to pick another page */
                        if (page_bytes_left == 0) {
                                page_out_index++;
                                if (page_out_index >= vcnt) {
                                        ret = 0;
                                        goto done;
                                }

                                page_out = bvec[page_out_index].bv_page;
                                pg_offset = 0;
                                page_bytes_left = PAGE_CACHE_SIZE;
                                start_byte = page_offset(page_out) - disk_start;

                                /*
                                 * make sure our new page is covered by this
                                 * working buffer
                                 */
                                if (total_out <= start_byte)
                                        goto next;

                                /* the next page in the biovec might not
                                 * be adjacent to the last page, but it
                                 * might still be found inside this working
                                 * buffer.  bump our offset pointer
                                 */
                                if (total_out > start_byte &&
                                    current_buf_start < start_byte) {
                                        buf_offset = start_byte - buf_start;
                                        working_bytes = total_out - start_byte;
                                        current_buf_start = buf_start +
                                                buf_offset;
                                }
                        }
                }
next:
                workspace->inf_strm.next_out = workspace->buf;
                workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;

                if (workspace->inf_strm.avail_in == 0) {
                        unsigned long tmp;
                        kunmap(pages_in[page_in_index]);
                        page_in_index++;
                        if (page_in_index >= total_pages_in) {
                                data_in = NULL;
                                break;
                        }
                        data_in = kmap(pages_in[page_in_index]);
                        workspace->inf_strm.next_in = data_in;
                        tmp = srclen - workspace->inf_strm.total_in;
                        workspace->inf_strm.avail_in = min(tmp,
                                                           PAGE_CACHE_SIZE);
                }
        }
        if (ret != Z_STREAM_END)
                ret = -1;
        else
                ret = 0;
done:
        zlib_inflateEnd(&workspace->inf_strm);
        if (data_in)
                kunmap(pages_in[page_in_index]);
out:
        free_workspace(workspace);
        return ret;
}

/*
 * a less complex decompression routine.  Our compressed data fits in a
 * single page, and we want to read a single page out of it.
 * start_byte tells us the offset into the compressed data we're interested in
 */
int btrfs_zlib_decompress(unsigned char *data_in,
                          struct page *dest_page,
                          unsigned long start_byte,
                          size_t srclen, size_t destlen)
{
        int ret = 0;
        int wbits = MAX_WBITS;
        struct workspace *workspace;
        unsigned long bytes_left = destlen;
        unsigned long total_out = 0;
        char *kaddr;

        if (destlen > PAGE_CACHE_SIZE)
                return -ENOMEM;

        workspace = find_zlib_workspace();
        if (IS_ERR(workspace))
                return -ENOMEM;

        workspace->inf_strm.next_in = data_in;
        workspace->inf_strm.avail_in = srclen;
        workspace->inf_strm.total_in = 0;

        workspace->inf_strm.next_out = workspace->buf;
        workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
        workspace->inf_strm.total_out = 0;
        /* If it's deflate, and it's got no preset dictionary, then
           we can tell zlib to skip the adler32 check. */
        if (srclen > 2 && !(data_in[1] & PRESET_DICT) &&
            ((data_in[0] & 0x0f) == Z_DEFLATED) &&
            !(((data_in[0]<<8) + data_in[1]) % 31)) {

                wbits = -((data_in[0] >> 4) + 8);
                workspace->inf_strm.next_in += 2;
                workspace->inf_strm.avail_in -= 2;
        }

        if (Z_OK != zlib_inflateInit2(&workspace->inf_strm, wbits)) {
                printk(KERN_WARNING "inflateInit failed\n");
                ret = -1;
                goto out;
        }

        while (bytes_left > 0) {
                unsigned long buf_start;
                unsigned long buf_offset;
                unsigned long bytes;
                unsigned long pg_offset = 0;

                ret = zlib_inflate(&workspace->inf_strm, Z_NO_FLUSH);
                if (ret != Z_OK && ret != Z_STREAM_END)
                        break;

                buf_start = total_out;
                total_out = workspace->inf_strm.total_out;

                if (total_out == buf_start) {
                        ret = -1;
                        break;
                }

                if (total_out <= start_byte)
                        goto next;

                if (total_out > start_byte && buf_start < start_byte)
                        buf_offset = start_byte - buf_start;
                else
                        buf_offset = 0;

                bytes = min(PAGE_CACHE_SIZE - pg_offset,
                            PAGE_CACHE_SIZE - buf_offset);
                bytes = min(bytes, bytes_left);

                kaddr = kmap_atomic(dest_page, KM_USER0);
                memcpy(kaddr + pg_offset, workspace->buf + buf_offset, bytes);
                kunmap_atomic(kaddr, KM_USER0);

                pg_offset += bytes;
                bytes_left -= bytes;
next:
                workspace->inf_strm.next_out = workspace->buf;
                workspace->inf_strm.avail_out = PAGE_CACHE_SIZE;
        }

        if (ret != Z_STREAM_END && bytes_left != 0)
                ret = -1;
        else
                ret = 0;

        zlib_inflateEnd(&workspace->inf_strm);
out:
        free_workspace(workspace);
        return ret;
}

void btrfs_zlib_exit(void)
{
    free_workspaces();
}