compression.c

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/*
 * 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.
 */

#include <linux/kernel.h>
#include <linux/bio.h>
#include <linux/buffer_head.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/mpage.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/bit_spinlock.h>
#include <linux/slab.h>
#include "compat.h"
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "volumes.h"
#include "ordered-data.h"
#include "compression.h"
#include "extent_io.h"
#include "extent_map.h"

struct compressed_bio {
    /* number of bios pending for this compressed extent */
    atomic_t pending_bios;

    /* the pages with the compressed data on them */
    struct page **compressed_pages;

    /* inode that owns this data */
    struct inode *inode;

    /* starting offset in the inode for our pages */
    u64 start;

    /* number of bytes in the inode we're working on */
    unsigned long len;

    /* number of bytes on disk */
    unsigned long compressed_len;

    /* the compression algorithm for this bio */
    int compress_type;

    /* number of compressed pages in the array */
    unsigned long nr_pages;

    /* IO errors */
    int errors;
    int mirror_num;

    /* for reads, this is the bio we are copying the data into */
    struct bio *orig_bio;

    /*
     * the start of a variable length array of checksums only
     * used by reads
     */
    u32 sums;
};

static inline int compressed_bio_size(struct btrfs_root *root,
                      unsigned long disk_size)
{
    u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);

    return sizeof(struct compressed_bio) +
        ((disk_size + root->sectorsize - 1) / root->sectorsize) *
        csum_size;
}

static struct bio *compressed_bio_alloc(struct block_device *bdev,
                    u64 first_byte, gfp_t gfp_flags)
{
    int nr_vecs;

    nr_vecs = bio_get_nr_vecs(bdev);
    return btrfs_bio_alloc(bdev, first_byte >> 9, nr_vecs, gfp_flags);
}

static int check_compressed_csum(struct inode *inode,
                 struct compressed_bio *cb,
                 u64 disk_start)
{
    int ret;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct page *page;
    unsigned long i;
    char *kaddr;
    u32 csum;
    u32 *cb_sum = &cb->sums;

    if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
        return 0;

    for (i = 0; i < cb->nr_pages; i++) {
        page = cb->compressed_pages[i];
        csum = ~(u32)0;

        kaddr = kmap_atomic(page);
        csum = btrfs_csum_data(root, kaddr, csum, PAGE_CACHE_SIZE);
        btrfs_csum_final(csum, (char *)&csum);
        kunmap_atomic(kaddr);

        if (csum != *cb_sum) {
            printk(KERN_INFO "btrfs csum failed ino %llu "
                   "extent %llu csum %u "
                   "wanted %u mirror %d\n",
                   (unsigned long long)btrfs_ino(inode),
                   (unsigned long long)disk_start,
                   csum, *cb_sum, cb->mirror_num);
            ret = -EIO;
            goto fail;
        }
        cb_sum++;

    }
    ret = 0;
fail:
    return ret;
}

/* when we finish reading compressed pages from the disk, we
 * decompress them and then run the bio end_io routines on the
 * decompressed pages (in the inode address space).
 *
 * This allows the checksumming and other IO error handling routines
 * to work normally
 *
 * The compressed pages are freed here, and it must be run
 * in process context
 */
static void end_compressed_bio_read(struct bio *bio, int err)
{
    struct compressed_bio *cb = bio->bi_private;
    struct inode *inode;
    struct page *page;
    unsigned long index;
    int ret;

    if (err)
        cb->errors = 1;

    /* if there are more bios still pending for this compressed
     * extent, just exit
     */
    if (!atomic_dec_and_test(&cb->pending_bios))
        goto out;

    inode = cb->inode;
    ret = check_compressed_csum(inode, cb, (u64)bio->bi_sector << 9);
    if (ret)
        goto csum_failed;

    /* ok, we're the last bio for this extent, lets start
     * the decompression.
     */
    ret = btrfs_decompress_biovec(cb->compress_type,
                      cb->compressed_pages,
                      cb->start,
                      cb->orig_bio->bi_io_vec,
                      cb->orig_bio->bi_vcnt,
                      cb->compressed_len);
csum_failed:
    if (ret)
        cb->errors = 1;

    /* release the compressed pages */
    index = 0;
    for (index = 0; index < cb->nr_pages; index++) {
        page = cb->compressed_pages[index];
        page->mapping = NULL;
        page_cache_release(page);
    }

    /* do io completion on the original bio */
    if (cb->errors) {
        bio_io_error(cb->orig_bio);
    } else {
        int bio_index = 0;
        struct bio_vec *bvec = cb->orig_bio->bi_io_vec;

        /*
         * we have verified the checksum already, set page
         * checked so the end_io handlers know about it
         */
        while (bio_index < cb->orig_bio->bi_vcnt) {
            SetPageChecked(bvec->bv_page);
            bvec++;
            bio_index++;
        }
        bio_endio(cb->orig_bio, 0);
    }

    /* finally free the cb struct */
    kfree(cb->compressed_pages);
    kfree(cb);
out:
    bio_put(bio);
}

/*
 * Clear the writeback bits on all of the file
 * pages for a compressed write
 */
static noinline void end_compressed_writeback(struct inode *inode, u64 start,
                          unsigned long ram_size)
{
    unsigned long index = start >> PAGE_CACHE_SHIFT;
    unsigned long end_index = (start + ram_size - 1) >> PAGE_CACHE_SHIFT;
    struct page *pages[16];
    unsigned long nr_pages = end_index - index + 1;
    int i;
    int ret;

    while (nr_pages > 0) {
        ret = find_get_pages_contig(inode->i_mapping, index,
                     min_t(unsigned long,
                     nr_pages, ARRAY_SIZE(pages)), pages);
        if (ret == 0) {
            nr_pages -= 1;
            index += 1;
            continue;
        }
        for (i = 0; i < ret; i++) {
            end_page_writeback(pages[i]);
            page_cache_release(pages[i]);
        }
        nr_pages -= ret;
        index += ret;
    }
    /* the inode may be gone now */
}

/*
 * do the cleanup once all the compressed pages hit the disk.
 * This will clear writeback on the file pages and free the compressed
 * pages.
 *
 * This also calls the writeback end hooks for the file pages so that
 * metadata and checksums can be updated in the file.
 */
static void end_compressed_bio_write(struct bio *bio, int err)
{
    struct extent_io_tree *tree;
    struct compressed_bio *cb = bio->bi_private;
    struct inode *inode;
    struct page *page;
    unsigned long index;

    if (err)
        cb->errors = 1;

    /* if there are more bios still pending for this compressed
     * extent, just exit
     */
    if (!atomic_dec_and_test(&cb->pending_bios))
        goto out;

    /* ok, we're the last bio for this extent, step one is to
     * call back into the FS and do all the end_io operations
     */
    inode = cb->inode;
    tree = &BTRFS_I(inode)->io_tree;
    cb->compressed_pages[0]->mapping = cb->inode->i_mapping;
    tree->ops->writepage_end_io_hook(cb->compressed_pages[0],
                     cb->start,
                     cb->start + cb->len - 1,
                     NULL, 1);
    cb->compressed_pages[0]->mapping = NULL;

    end_compressed_writeback(inode, cb->start, cb->len);
    /* note, our inode could be gone now */

    /*
     * release the compressed pages, these came from alloc_page and
     * are not attached to the inode at all
     */
    index = 0;
    for (index = 0; index < cb->nr_pages; index++) {
        page = cb->compressed_pages[index];
        page->mapping = NULL;
        page_cache_release(page);
    }

    /* finally free the cb struct */
    kfree(cb->compressed_pages);
    kfree(cb);
out:
    bio_put(bio);
}

/*
 * worker function to build and submit bios for previously compressed pages.
 * The corresponding pages in the inode should be marked for writeback
 * and the compressed pages should have a reference on them for dropping
 * when the IO is complete.
 *
 * This also checksums the file bytes and gets things ready for
 * the end io hooks.
 */
int btrfs_submit_compressed_write(struct inode *inode, u64 start,
                 unsigned long len, u64 disk_start,
                 unsigned long compressed_len,
                 struct page **compressed_pages,
                 unsigned long nr_pages)
{
    struct bio *bio = NULL;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    struct compressed_bio *cb;
    unsigned long bytes_left;
    struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
    int pg_index = 0;
    struct page *page;
    u64 first_byte = disk_start;
    struct block_device *bdev;
    int ret;
    int skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;

    WARN_ON(start & ((u64)PAGE_CACHE_SIZE - 1));
    cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
    if (!cb)
        return -ENOMEM;
    atomic_set(&cb->pending_bios, 0);
    cb->errors = 0;
    cb->inode = inode;
    cb->start = start;
    cb->len = len;
    cb->mirror_num = 0;
    cb->compressed_pages = compressed_pages;
    cb->compressed_len = compressed_len;
    cb->orig_bio = NULL;
    cb->nr_pages = nr_pages;

    bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;

    bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
    if(!bio) {
        kfree(cb);
        return -ENOMEM;
    }
    bio->bi_private = cb;
    bio->bi_end_io = end_compressed_bio_write;
    atomic_inc(&cb->pending_bios);

    /* create and submit bios for the compressed pages */
    bytes_left = compressed_len;
    for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
        page = compressed_pages[pg_index];
        page->mapping = inode->i_mapping;
        if (bio->bi_size)
            ret = io_tree->ops->merge_bio_hook(page, 0,
                               PAGE_CACHE_SIZE,
                               bio, 0);
        else
            ret = 0;

        page->mapping = NULL;
        if (ret || bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) <
            PAGE_CACHE_SIZE) {
            bio_get(bio);

            /*
             * inc the count before we submit the bio so
             * we know the end IO handler won't happen before
             * we inc the count.  Otherwise, the cb might get
             * freed before we're done setting it up
             */
            atomic_inc(&cb->pending_bios);
            ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
            BUG_ON(ret); /* -ENOMEM */

            if (!skip_sum) {
                ret = btrfs_csum_one_bio(root, inode, bio,
                             start, 1);
                BUG_ON(ret); /* -ENOMEM */
            }

            ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
            BUG_ON(ret); /* -ENOMEM */

            bio_put(bio);

            bio = compressed_bio_alloc(bdev, first_byte, GFP_NOFS);
            BUG_ON(!bio);
            bio->bi_private = cb;
            bio->bi_end_io = end_compressed_bio_write;
            bio_add_page(bio, page, PAGE_CACHE_SIZE, 0);
        }
        if (bytes_left < PAGE_CACHE_SIZE) {
            printk("bytes left %lu compress len %lu nr %lu\n",
                   bytes_left, cb->compressed_len, cb->nr_pages);
        }
        bytes_left -= PAGE_CACHE_SIZE;
        first_byte += PAGE_CACHE_SIZE;
        cond_resched();
    }
    bio_get(bio);

    ret = btrfs_bio_wq_end_io(root->fs_info, bio, 0);
    BUG_ON(ret); /* -ENOMEM */

    if (!skip_sum) {
        ret = btrfs_csum_one_bio(root, inode, bio, start, 1);
        BUG_ON(ret); /* -ENOMEM */
    }

    ret = btrfs_map_bio(root, WRITE, bio, 0, 1);
    BUG_ON(ret); /* -ENOMEM */

    bio_put(bio);
    return 0;
}

static noinline int add_ra_bio_pages(struct inode *inode,
                     u64 compressed_end,
                     struct compressed_bio *cb)
{
    unsigned long end_index;
    unsigned long pg_index;
    u64 last_offset;
    u64 isize = i_size_read(inode);
    int ret;
    struct page *page;
    unsigned long nr_pages = 0;
    struct extent_map *em;
    struct address_space *mapping = inode->i_mapping;
    struct extent_map_tree *em_tree;
    struct extent_io_tree *tree;
    u64 end;
    int misses = 0;

    page = cb->orig_bio->bi_io_vec[cb->orig_bio->bi_vcnt - 1].bv_page;
    last_offset = (page_offset(page) + PAGE_CACHE_SIZE);
    em_tree = &BTRFS_I(inode)->extent_tree;
    tree = &BTRFS_I(inode)->io_tree;

    if (isize == 0)
        return 0;

    end_index = (i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT;

    while (last_offset < compressed_end) {
        pg_index = last_offset >> PAGE_CACHE_SHIFT;

        if (pg_index > end_index)
            break;

        rcu_read_lock();
        page = radix_tree_lookup(&mapping->page_tree, pg_index);
        rcu_read_unlock();
        if (page) {
            misses++;
            if (misses > 4)
                break;
            goto next;
        }

        page = __page_cache_alloc(mapping_gfp_mask(mapping) &
                                ~__GFP_FS);
        if (!page)
            break;

        if (add_to_page_cache_lru(page, mapping, pg_index,
                                GFP_NOFS)) {
            page_cache_release(page);
            goto next;
        }

        end = last_offset + PAGE_CACHE_SIZE - 1;
        /*
         * at this point, we have a locked page in the page cache
         * for these bytes in the file.  But, we have to make
         * sure they map to this compressed extent on disk.
         */
        set_page_extent_mapped(page);
        lock_extent(tree, last_offset, end);
        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, last_offset,
                       PAGE_CACHE_SIZE);
        read_unlock(&em_tree->lock);

        if (!em || last_offset < em->start ||
            (last_offset + PAGE_CACHE_SIZE > extent_map_end(em)) ||
            (em->block_start >> 9) != cb->orig_bio->bi_sector) {
            free_extent_map(em);
            unlock_extent(tree, last_offset, end);
            unlock_page(page);
            page_cache_release(page);
            break;
        }
        free_extent_map(em);

        if (page->index == end_index) {
            char *userpage;
            size_t zero_offset = isize & (PAGE_CACHE_SIZE - 1);

            if (zero_offset) {
                int zeros;
                zeros = PAGE_CACHE_SIZE - zero_offset;
                userpage = kmap_atomic(page);
                memset(userpage + zero_offset, 0, zeros);
                flush_dcache_page(page);
                kunmap_atomic(userpage);
            }
        }

        ret = bio_add_page(cb->orig_bio, page,
                   PAGE_CACHE_SIZE, 0);

        if (ret == PAGE_CACHE_SIZE) {
            nr_pages++;
            page_cache_release(page);
        } else {
            unlock_extent(tree, last_offset, end);
            unlock_page(page);
            page_cache_release(page);
            break;
        }
next:
        last_offset += PAGE_CACHE_SIZE;
    }
    return 0;
}

/*
 * for a compressed read, the bio we get passed has all the inode pages
 * in it.  We don't actually do IO on those pages but allocate new ones
 * to hold the compressed pages on disk.
 *
 * bio->bi_sector points to the compressed extent on disk
 * bio->bi_io_vec points to all of the inode pages
 * bio->bi_vcnt is a count of pages
 *
 * After the compressed pages are read, we copy the bytes into the
 * bio we were passed and then call the bio end_io calls
 */
int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
                 int mirror_num, unsigned long bio_flags)
{
    struct extent_io_tree *tree;
    struct extent_map_tree *em_tree;
    struct compressed_bio *cb;
    struct btrfs_root *root = BTRFS_I(inode)->root;
    unsigned long uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
    unsigned long compressed_len;
    unsigned long nr_pages;
    unsigned long pg_index;
    struct page *page;
    struct block_device *bdev;
    struct bio *comp_bio;
    u64 cur_disk_byte = (u64)bio->bi_sector << 9;
    u64 em_len;
    u64 em_start;
    struct extent_map *em;
    int ret = -ENOMEM;
    int faili = 0;
    u32 *sums;

    tree = &BTRFS_I(inode)->io_tree;
    em_tree = &BTRFS_I(inode)->extent_tree;

    /* we need the actual starting offset of this extent in the file */
    read_lock(&em_tree->lock);
    em = lookup_extent_mapping(em_tree,
                   page_offset(bio->bi_io_vec->bv_page),
                   PAGE_CACHE_SIZE);
    read_unlock(&em_tree->lock);
    if (!em)
        return -EIO;

    compressed_len = em->block_len;
    cb = kmalloc(compressed_bio_size(root, compressed_len), GFP_NOFS);
    if (!cb)
        goto out;

    atomic_set(&cb->pending_bios, 0);
    cb->errors = 0;
    cb->inode = inode;
    cb->mirror_num = mirror_num;
    sums = &cb->sums;

    cb->start = em->orig_start;
    em_len = em->len;
    em_start = em->start;

    free_extent_map(em);
    em = NULL;

    cb->len = uncompressed_len;
    cb->compressed_len = compressed_len;
    cb->compress_type = extent_compress_type(bio_flags);
    cb->orig_bio = bio;

    nr_pages = (compressed_len + PAGE_CACHE_SIZE - 1) /
                 PAGE_CACHE_SIZE;
    cb->compressed_pages = kzalloc(sizeof(struct page *) * nr_pages,
                       GFP_NOFS);
    if (!cb->compressed_pages)
        goto fail1;

    bdev = BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev;

    for (pg_index = 0; pg_index < nr_pages; pg_index++) {
        cb->compressed_pages[pg_index] = alloc_page(GFP_NOFS |
                                  __GFP_HIGHMEM);
        if (!cb->compressed_pages[pg_index]) {
            faili = pg_index - 1;
            ret = -ENOMEM;
            goto fail2;
        }
    }
    faili = nr_pages - 1;
    cb->nr_pages = nr_pages;

    add_ra_bio_pages(inode, em_start + em_len, cb);

    /* include any pages we added in add_ra-bio_pages */
    uncompressed_len = bio->bi_vcnt * PAGE_CACHE_SIZE;
    cb->len = uncompressed_len;

    comp_bio = compressed_bio_alloc(bdev, cur_disk_byte, GFP_NOFS);
    if (!comp_bio)
        goto fail2;
    comp_bio->bi_private = cb;
    comp_bio->bi_end_io = end_compressed_bio_read;
    atomic_inc(&cb->pending_bios);

    for (pg_index = 0; pg_index < nr_pages; pg_index++) {
        page = cb->compressed_pages[pg_index];
        page->mapping = inode->i_mapping;
        page->index = em_start >> PAGE_CACHE_SHIFT;

        if (comp_bio->bi_size)
            ret = tree->ops->merge_bio_hook(page, 0,
                            PAGE_CACHE_SIZE,
                            comp_bio, 0);
        else
            ret = 0;

        page->mapping = NULL;
        if (ret || bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0) <
            PAGE_CACHE_SIZE) {
            bio_get(comp_bio);

            ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
            BUG_ON(ret); /* -ENOMEM */

            /*
             * inc the count before we submit the bio so
             * we know the end IO handler won't happen before
             * we inc the count.  Otherwise, the cb might get
             * freed before we're done setting it up
             */
            atomic_inc(&cb->pending_bios);

            if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
                ret = btrfs_lookup_bio_sums(root, inode,
                            comp_bio, sums);
                BUG_ON(ret); /* -ENOMEM */
            }
            sums += (comp_bio->bi_size + root->sectorsize - 1) /
                root->sectorsize;

            ret = btrfs_map_bio(root, READ, comp_bio,
                        mirror_num, 0);
            BUG_ON(ret); /* -ENOMEM */

            bio_put(comp_bio);

            comp_bio = compressed_bio_alloc(bdev, cur_disk_byte,
                            GFP_NOFS);
            BUG_ON(!comp_bio);
            comp_bio->bi_private = cb;
            comp_bio->bi_end_io = end_compressed_bio_read;

            bio_add_page(comp_bio, page, PAGE_CACHE_SIZE, 0);
        }
        cur_disk_byte += PAGE_CACHE_SIZE;
    }
    bio_get(comp_bio);

    ret = btrfs_bio_wq_end_io(root->fs_info, comp_bio, 0);
    BUG_ON(ret); /* -ENOMEM */

    if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
        ret = btrfs_lookup_bio_sums(root, inode, comp_bio, sums);
        BUG_ON(ret); /* -ENOMEM */
    }

    ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
    BUG_ON(ret); /* -ENOMEM */

    bio_put(comp_bio);
    return 0;

fail2:
    while (faili >= 0) {
        __free_page(cb->compressed_pages[faili]);
        faili--;
    }

    kfree(cb->compressed_pages);
fail1:
    kfree(cb);
out:
    free_extent_map(em);
    return ret;
}

static struct list_head comp_idle_workspace[BTRFS_COMPRESS_TYPES];
static spinlock_t comp_workspace_lock[BTRFS_COMPRESS_TYPES];
static int comp_num_workspace[BTRFS_COMPRESS_TYPES];
static atomic_t comp_alloc_workspace[BTRFS_COMPRESS_TYPES];
static wait_queue_head_t comp_workspace_wait[BTRFS_COMPRESS_TYPES];

struct btrfs_compress_op *btrfs_compress_op[] = {
    &btrfs_zlib_compress,
    &btrfs_lzo_compress,
};

void __init btrfs_init_compress(void)
{
    int i;

    for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
        INIT_LIST_HEAD(&comp_idle_workspace[i]);
        spin_lock_init(&comp_workspace_lock[i]);
        atomic_set(&comp_alloc_workspace[i], 0);
        init_waitqueue_head(&comp_workspace_wait[i]);
    }
}

/*
 * this finds an available workspace or allocates a new one
 * ERR_PTR is returned if things go bad.
 */
static struct list_head *find_workspace(int type)
{
    struct list_head *workspace;
    int cpus = num_online_cpus();
    int idx = type - 1;

    struct list_head *idle_workspace    = &comp_idle_workspace[idx];
    spinlock_t *workspace_lock      = &comp_workspace_lock[idx];
    atomic_t *alloc_workspace       = &comp_alloc_workspace[idx];
    wait_queue_head_t *workspace_wait   = &comp_workspace_wait[idx];
    int *num_workspace          = &comp_num_workspace[idx];
again:
    spin_lock(workspace_lock);
    if (!list_empty(idle_workspace)) {
        workspace = idle_workspace->next;
        list_del(workspace);
        (*num_workspace)--;
        spin_unlock(workspace_lock);
        return workspace;

    }
    if (atomic_read(alloc_workspace) > cpus) {
        DEFINE_WAIT(wait);

        spin_unlock(workspace_lock);
        prepare_to_wait(workspace_wait, &wait, TASK_UNINTERRUPTIBLE);
        if (atomic_read(alloc_workspace) > cpus && !*num_workspace)
            schedule();
        finish_wait(workspace_wait, &wait);
        goto again;
    }
    atomic_inc(alloc_workspace);
    spin_unlock(workspace_lock);

    workspace = btrfs_compress_op[idx]->alloc_workspace();
    if (IS_ERR(workspace)) {
        atomic_dec(alloc_workspace);
        wake_up(workspace_wait);
    }
    return workspace;
}

/*
 * put a workspace struct back on the list or free it if we have enough
 * idle ones sitting around
 */
static void free_workspace(int type, struct list_head *workspace)
{
    int idx = type - 1;
    struct list_head *idle_workspace    = &comp_idle_workspace[idx];
    spinlock_t *workspace_lock      = &comp_workspace_lock[idx];
    atomic_t *alloc_workspace       = &comp_alloc_workspace[idx];
    wait_queue_head_t *workspace_wait   = &comp_workspace_wait[idx];
    int *num_workspace          = &comp_num_workspace[idx];

    spin_lock(workspace_lock);
    if (*num_workspace < num_online_cpus()) {
        list_add_tail(workspace, idle_workspace);
        (*num_workspace)++;
        spin_unlock(workspace_lock);
        goto wake;
    }
    spin_unlock(workspace_lock);

    btrfs_compress_op[idx]->free_workspace(workspace);
    atomic_dec(alloc_workspace);
wake:
    smp_mb();
    if (waitqueue_active(workspace_wait))
        wake_up(workspace_wait);
}

/*
 * cleanup function for module exit
 */
static void free_workspaces(void)
{
    struct list_head *workspace;
    int i;

    for (i = 0; i < BTRFS_COMPRESS_TYPES; i++) {
        while (!list_empty(&comp_idle_workspace[i])) {
            workspace = comp_idle_workspace[i].next;
            list_del(workspace);
            btrfs_compress_op[i]->free_workspace(workspace);
            atomic_dec(&comp_alloc_workspace[i]);
        }
    }
}

/*
 * 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_compress_pages(int type, 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)
{
    struct list_head *workspace;
    int ret;

    workspace = find_workspace(type);
    if (IS_ERR(workspace))
        return -1;

    ret = btrfs_compress_op[type-1]->compress_pages(workspace, mapping,
                              start, len, pages,
                              nr_dest_pages, out_pages,
                              total_in, total_out,
                              max_out);
    free_workspace(type, 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_decompress_biovec(int type, struct page **pages_in, u64 disk_start,
                struct bio_vec *bvec, int vcnt, size_t srclen)
{
    struct list_head *workspace;
    int ret;

    workspace = find_workspace(type);
    if (IS_ERR(workspace))
        return -ENOMEM;

    ret = btrfs_compress_op[type-1]->decompress_biovec(workspace, pages_in,
                             disk_start,
                             bvec, vcnt, srclen);
    free_workspace(type, 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_decompress(int type, unsigned char *data_in, struct page *dest_page,
             unsigned long start_byte, size_t srclen, size_t destlen)
{
    struct list_head *workspace;
    int ret;

    workspace = find_workspace(type);
    if (IS_ERR(workspace))
        return -ENOMEM;

    ret = btrfs_compress_op[type-1]->decompress(workspace, data_in,
                          dest_page, start_byte,
                          srclen, destlen);

    free_workspace(type, workspace);
    return ret;
}

void btrfs_exit_compress(void)
{
    free_workspaces();
}

/*
 * Copy uncompressed data from working buffer to pages.
 *
 * buf_start is the byte offset we're of the start of our workspace buffer.
 *
 * total_out is the last byte of the buffer
 */
int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
                  unsigned long total_out, u64 disk_start,
                  struct bio_vec *bvec, int vcnt,
                  unsigned long *pg_index,
                  unsigned long *pg_offset)
{
    unsigned long buf_offset;
    unsigned long current_buf_start;
    unsigned long start_byte;
    unsigned long working_bytes = total_out - buf_start;
    unsigned long bytes;
    char *kaddr;
    struct page *page_out = bvec[*pg_index].bv_page;

    /*
     * 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;

    /* we haven't yet hit data corresponding to this page */
    if (total_out <= start_byte)
        return 1;

    /*
     * 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);
        memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
        kunmap_atomic(kaddr);
        flush_dcache_page(page_out);

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

        /* check if we need to pick another page */
        if (*pg_offset == PAGE_CACHE_SIZE) {
            (*pg_index)++;
            if (*pg_index >= vcnt)
                return 0;

            page_out = bvec[*pg_index].bv_page;
            *pg_offset = 0;
            start_byte = page_offset(page_out) - disk_start;

            /*
             * make sure our new page is covered by this
             * working buffer
             */
            if (total_out <= start_byte)
                return 1;

            /*
             * 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;
            }
        }
    }

    return 1;
}