// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013 Fusion IO.  All rights reserved.
 */

#include <linux/slab.h>
#include "btrfs-tests.h"
#include "../ctree.h"
#include "../disk-io.h"
#include "../free-space-cache.h"

#define BITS_PER_BITMAP         (PAGE_SIZE * 8UL)

/*
 * This test just does basic sanity checking, making sure we can add an extent
 * entry and remove space from either end and the middle, and make sure we can
 * remove space that covers adjacent extent entries.
 */
static int test_extents(struct btrfs_block_group_cache *cache)
{
        int ret = 0;

        test_msg("running extent only tests");

        /* First just make sure we can remove an entire entry */
        ret = btrfs_add_free_space(cache, 0, SZ_4M);
        if (ret) {
                test_err("error adding initial extents %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 0, SZ_4M);
        if (ret) {
                test_err("error removing extent %d", ret);
                return ret;
        }

        if (test_check_exists(cache, 0, SZ_4M)) {
                test_err("full remove left some lingering space");
                return -1;
        }

        /* Ok edge and middle cases now */
        ret = btrfs_add_free_space(cache, 0, SZ_4M);
        if (ret) {
                test_err("error adding half extent %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 3 * SZ_1M, SZ_1M);
        if (ret) {
                test_err("error removing tail end %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 0, SZ_1M);
        if (ret) {
                test_err("error removing front end %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, SZ_2M, 4096);
        if (ret) {
                test_err("error removing middle piece %d", ret);
                return ret;
        }

        if (test_check_exists(cache, 0, SZ_1M)) {
                test_err("still have space at the front");
                return -1;
        }

        if (test_check_exists(cache, SZ_2M, 4096)) {
                test_err("still have space in the middle");
                return -1;
        }

        if (test_check_exists(cache, 3 * SZ_1M, SZ_1M)) {
                test_err("still have space at the end");
                return -1;
        }

        /* Cleanup */
        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        return 0;
}

static int test_bitmaps(struct btrfs_block_group_cache *cache,
                        u32 sectorsize)
{
        u64 next_bitmap_offset;
        int ret;

        test_msg("running bitmap only tests");

        ret = test_add_free_space_entry(cache, 0, SZ_4M, 1);
        if (ret) {
                test_err("couldn't create a bitmap entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 0, SZ_4M);
        if (ret) {
                test_err("error removing bitmap full range %d", ret);
                return ret;
        }

        if (test_check_exists(cache, 0, SZ_4M)) {
                test_err("left some space in bitmap");
                return -1;
        }

        ret = test_add_free_space_entry(cache, 0, SZ_4M, 1);
        if (ret) {
                test_err("couldn't add to our bitmap entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, SZ_1M, SZ_2M);
        if (ret) {
                test_err("couldn't remove middle chunk %d", ret);
                return ret;
        }

        /*
         * The first bitmap we have starts at offset 0 so the next one is just
         * at the end of the first bitmap.
         */
        next_bitmap_offset = (u64)(BITS_PER_BITMAP * sectorsize);

        /* Test a bit straddling two bitmaps */
        ret = test_add_free_space_entry(cache, next_bitmap_offset - SZ_2M,
                                        SZ_4M, 1);
        if (ret) {
                test_err("couldn't add space that straddles two bitmaps %d",
                                ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, next_bitmap_offset - SZ_1M, SZ_2M);
        if (ret) {
                test_err("couldn't remove overlapping space %d", ret);
                return ret;
        }

        if (test_check_exists(cache, next_bitmap_offset - SZ_1M, SZ_2M)) {
                test_err("left some space when removing overlapping");
                return -1;
        }

        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        return 0;
}

/* This is the high grade jackassery */
static int test_bitmaps_and_extents(struct btrfs_block_group_cache *cache,
                                    u32 sectorsize)
{
        u64 bitmap_offset = (u64)(BITS_PER_BITMAP * sectorsize);
        int ret;

        test_msg("running bitmap and extent tests");

        /*
         * First let's do something simple, an extent at the same offset as the
         * bitmap, but the free space completely in the extent and then
         * completely in the bitmap.
         */
        ret = test_add_free_space_entry(cache, SZ_4M, SZ_1M, 1);
        if (ret) {
                test_err("couldn't create bitmap entry %d", ret);
                return ret;
        }

        ret = test_add_free_space_entry(cache, 0, SZ_1M, 0);
        if (ret) {
                test_err("couldn't add extent entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 0, SZ_1M);
        if (ret) {
                test_err("couldn't remove extent entry %d", ret);
                return ret;
        }

        if (test_check_exists(cache, 0, SZ_1M)) {
                test_err("left remnants after our remove");
                return -1;
        }

        /* Now to add back the extent entry and remove from the bitmap */
        ret = test_add_free_space_entry(cache, 0, SZ_1M, 0);
        if (ret) {
                test_err("couldn't re-add extent entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, SZ_4M, SZ_1M);
        if (ret) {
                test_err("couldn't remove from bitmap %d", ret);
                return ret;
        }

        if (test_check_exists(cache, SZ_4M, SZ_1M)) {
                test_err("left remnants in the bitmap");
                return -1;
        }

        /*
         * Ok so a little more evil, extent entry and bitmap at the same offset,
         * removing an overlapping chunk.
         */
        ret = test_add_free_space_entry(cache, SZ_1M, SZ_4M, 1);
        if (ret) {
                test_err("couldn't add to a bitmap %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, SZ_512K, 3 * SZ_1M);
        if (ret) {
                test_err("couldn't remove overlapping space %d", ret);
                return ret;
        }

        if (test_check_exists(cache, SZ_512K, 3 * SZ_1M)) {
                test_err("left over pieces after removing overlapping");
                return -1;
        }

        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        /* Now with the extent entry offset into the bitmap */
        ret = test_add_free_space_entry(cache, SZ_4M, SZ_4M, 1);
        if (ret) {
                test_err("couldn't add space to the bitmap %d", ret);
                return ret;
        }

        ret = test_add_free_space_entry(cache, SZ_2M, SZ_2M, 0);
        if (ret) {
                test_err("couldn't add extent to the cache %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, 3 * SZ_1M, SZ_4M);
        if (ret) {
                test_err("problem removing overlapping space %d", ret);
                return ret;
        }

        if (test_check_exists(cache, 3 * SZ_1M, SZ_4M)) {
                test_err("left something behind when removing space");
                return -1;
        }

        /*
         * This has blown up in the past, the extent entry starts before the
         * bitmap entry, but we're trying to remove an offset that falls
         * completely within the bitmap range and is in both the extent entry
         * and the bitmap entry, looks like this
         *
         *   [ extent ]
         *      [ bitmap ]
         *        [ del ]
         */
        __btrfs_remove_free_space_cache(cache->free_space_ctl);
        ret = test_add_free_space_entry(cache, bitmap_offset + SZ_4M, SZ_4M, 1);
        if (ret) {
                test_err("couldn't add bitmap %d", ret);
                return ret;
        }

        ret = test_add_free_space_entry(cache, bitmap_offset - SZ_1M,
                                        5 * SZ_1M, 0);
        if (ret) {
                test_err("couldn't add extent entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, bitmap_offset + SZ_1M, 5 * SZ_1M);
        if (ret) {
                test_err("failed to free our space %d", ret);
                return ret;
        }

        if (test_check_exists(cache, bitmap_offset + SZ_1M, 5 * SZ_1M)) {
                test_err("left stuff over");
                return -1;
        }

        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        /*
         * This blew up before, we have part of the free space in a bitmap and
         * then the entirety of the rest of the space in an extent.  This used
         * to return -EAGAIN back from btrfs_remove_extent, make sure this
         * doesn't happen.
         */
        ret = test_add_free_space_entry(cache, SZ_1M, SZ_2M, 1);
        if (ret) {
                test_err("couldn't add bitmap entry %d", ret);
                return ret;
        }

        ret = test_add_free_space_entry(cache, 3 * SZ_1M, SZ_1M, 0);
        if (ret) {
                test_err("couldn't add extent entry %d", ret);
                return ret;
        }

        ret = btrfs_remove_free_space(cache, SZ_1M, 3 * SZ_1M);
        if (ret) {
                test_err("error removing bitmap and extent overlapping %d", ret);
                return ret;
        }

        __btrfs_remove_free_space_cache(cache->free_space_ctl);
        return 0;
}

/* Used by test_steal_space_from_bitmap_to_extent(). */
static bool test_use_bitmap(struct btrfs_free_space_ctl *ctl,
                            struct btrfs_free_space *info)
{
        return ctl->free_extents > 0;
}

/* Used by test_steal_space_from_bitmap_to_extent(). */
static int
check_num_extents_and_bitmaps(const struct btrfs_block_group_cache *cache,
                              const int num_extents,
                              const int num_bitmaps)
{
        if (cache->free_space_ctl->free_extents != num_extents) {
                test_err(
                "incorrect # of extent entries in the cache: %d, expected %d",
                         cache->free_space_ctl->free_extents, num_extents);
                return -EINVAL;
        }
        if (cache->free_space_ctl->total_bitmaps != num_bitmaps) {
                test_err(
                "incorrect # of extent entries in the cache: %d, expected %d",
                         cache->free_space_ctl->total_bitmaps, num_bitmaps);
                return -EINVAL;
        }
        return 0;
}

/* Used by test_steal_space_from_bitmap_to_extent(). */
static int check_cache_empty(struct btrfs_block_group_cache *cache)
{
        u64 offset;
        u64 max_extent_size;

        /*
         * Now lets confirm that there's absolutely no free space left to
         * allocate.
         */
        if (cache->free_space_ctl->free_space != 0) {
                test_err("cache free space is not 0");
                return -EINVAL;
        }

        /* And any allocation request, no matter how small, should fail now. */
        offset = btrfs_find_space_for_alloc(cache, 0, 4096, 0,
                                            &max_extent_size);
        if (offset != 0) {
                test_err("space allocation did not fail, returned offset: %llu",
                         offset);
                return -EINVAL;
        }

        /* And no extent nor bitmap entries in the cache anymore. */
        return check_num_extents_and_bitmaps(cache, 0, 0);
}

/*
 * Before we were able to steal free space from a bitmap entry to an extent
 * entry, we could end up with 2 entries representing a contiguous free space.
 * One would be an extent entry and the other a bitmap entry. Since in order
 * to allocate space to a caller we use only 1 entry, we couldn't return that
 * whole range to the caller if it was requested. This forced the caller to
 * either assume ENOSPC or perform several smaller space allocations, which
 * wasn't optimal as they could be spread all over the block group while under
 * concurrency (extra overhead and fragmentation).
 *
 * This stealing approach is beneficial, since we always prefer to allocate
 * from extent entries, both for clustered and non-clustered allocation
 * requests.
 */
static int
test_steal_space_from_bitmap_to_extent(struct btrfs_block_group_cache *cache,
                                       u32 sectorsize)
{
        int ret;
        u64 offset;
        u64 max_extent_size;
        const struct btrfs_free_space_op test_free_space_ops = {
                .recalc_thresholds = cache->free_space_ctl->op->recalc_thresholds,
                .use_bitmap = test_use_bitmap,
        };
        const struct btrfs_free_space_op *orig_free_space_ops;

        test_msg("running space stealing from bitmap to extent tests");

        /*
         * For this test, we want to ensure we end up with an extent entry
         * immediately adjacent to a bitmap entry, where the bitmap starts
         * at an offset where the extent entry ends. We keep adding and
         * removing free space to reach into this state, but to get there
         * we need to reach a point where marking new free space doesn't
         * result in adding new extent entries or merging the new space
         * with existing extent entries - the space ends up being marked
         * in an existing bitmap that covers the new free space range.
         *
         * To get there, we need to reach the threshold defined set at
         * cache->free_space_ctl->extents_thresh, which currently is
         * 256 extents on a x86_64 system at least, and a few other
         * conditions (check free_space_cache.c). Instead of making the
         * test much longer and complicated, use a "use_bitmap" operation
         * that forces use of bitmaps as soon as we have at least 1
         * extent entry.
         */
        orig_free_space_ops = cache->free_space_ctl->op;
        cache->free_space_ctl->op = &test_free_space_ops;

        /*
         * Extent entry covering free space range [128Mb - 256Kb, 128Mb - 128Kb[
         */
        ret = test_add_free_space_entry(cache, SZ_128M - SZ_256K, SZ_128K, 0);
        if (ret) {
                test_err("couldn't add extent entry %d", ret);
                return ret;
        }

        /* Bitmap entry covering free space range [128Mb + 512Kb, 256Mb[ */
        ret = test_add_free_space_entry(cache, SZ_128M + SZ_512K,
                                        SZ_128M - SZ_512K, 1);
        if (ret) {
                test_err("couldn't add bitmap entry %d", ret);
                return ret;
        }

        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * Now make only the first 256Kb of the bitmap marked as free, so that
         * we end up with only the following ranges marked as free space:
         *
         * [128Mb - 256Kb, 128Mb - 128Kb[
         * [128Mb + 512Kb, 128Mb + 768Kb[
         */
        ret = btrfs_remove_free_space(cache,
                                      SZ_128M + 768 * SZ_1K,
                                      SZ_128M - 768 * SZ_1K);
        if (ret) {
                test_err("failed to free part of bitmap space %d", ret);
                return ret;
        }

        /* Confirm that only those 2 ranges are marked as free. */
        if (!test_check_exists(cache, SZ_128M - SZ_256K, SZ_128K)) {
                test_err("free space range missing");
                return -ENOENT;
        }
        if (!test_check_exists(cache, SZ_128M + SZ_512K, SZ_256K)) {
                test_err("free space range missing");
                return -ENOENT;
        }

        /*
         * Confirm that the bitmap range [128Mb + 768Kb, 256Mb[ isn't marked
         * as free anymore.
         */
        if (test_check_exists(cache, SZ_128M + 768 * SZ_1K,
                              SZ_128M - 768 * SZ_1K)) {
                test_err("bitmap region not removed from space cache");
                return -EINVAL;
        }

        /*
         * Confirm that the region [128Mb + 256Kb, 128Mb + 512Kb[, which is
         * covered by the bitmap, isn't marked as free.
         */
        if (test_check_exists(cache, SZ_128M + SZ_256K, SZ_256K)) {
                test_err("invalid bitmap region marked as free");
                return -EINVAL;
        }

        /*
         * Confirm that the region [128Mb, 128Mb + 256Kb[, which is covered
         * by the bitmap too, isn't marked as free either.
         */
        if (test_check_exists(cache, SZ_128M, SZ_256K)) {
                test_err("invalid bitmap region marked as free");
                return -EINVAL;
        }

        /*
         * Now lets mark the region [128Mb, 128Mb + 512Kb[ as free too. But,
         * lets make sure the free space cache marks it as free in the bitmap,
         * and doesn't insert a new extent entry to represent this region.
         */
        ret = btrfs_add_free_space(cache, SZ_128M, SZ_512K);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }
        /* Confirm the region is marked as free. */
        if (!test_check_exists(cache, SZ_128M, SZ_512K)) {
                test_err("bitmap region not marked as free");
                return -ENOENT;
        }

        /*
         * Confirm that no new extent entries or bitmap entries were added to
         * the cache after adding that free space region.
         */
        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * Now lets add a small free space region to the right of the previous
         * one, which is not contiguous with it and is part of the bitmap too.
         * The goal is to test that the bitmap entry space stealing doesn't
         * steal this space region.
         */
        ret = btrfs_add_free_space(cache, SZ_128M + SZ_16M, sectorsize);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }

        /*
         * Confirm that no new extent entries or bitmap entries were added to
         * the cache after adding that free space region.
         */
        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * Now mark the region [128Mb - 128Kb, 128Mb[ as free too. This will
         * expand the range covered by the existing extent entry that represents
         * the free space [128Mb - 256Kb, 128Mb - 128Kb[.
         */
        ret = btrfs_add_free_space(cache, SZ_128M - SZ_128K, SZ_128K);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }
        /* Confirm the region is marked as free. */
        if (!test_check_exists(cache, SZ_128M - SZ_128K, SZ_128K)) {
                test_err("extent region not marked as free");
                return -ENOENT;
        }

        /*
         * Confirm that our extent entry didn't stole all free space from the
         * bitmap, because of the small 4Kb free space region.
         */
        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * So now we have the range [128Mb - 256Kb, 128Mb + 768Kb[ as free
         * space. Without stealing bitmap free space into extent entry space,
         * we would have all this free space represented by 2 entries in the
         * cache:
         *
         * extent entry covering range: [128Mb - 256Kb, 128Mb[
         * bitmap entry covering range: [128Mb, 128Mb + 768Kb[
         *
         * Attempting to allocate the whole free space (1Mb) would fail, because
         * we can't allocate from multiple entries.
         * With the bitmap free space stealing, we get a single extent entry
         * that represents the 1Mb free space, and therefore we're able to
         * allocate the whole free space at once.
         */
        if (!test_check_exists(cache, SZ_128M - SZ_256K, SZ_1M)) {
                test_err("expected region not marked as free");
                return -ENOENT;
        }

        if (cache->free_space_ctl->free_space != (SZ_1M + sectorsize)) {
                test_err("cache free space is not 1Mb + %u", sectorsize);
                return -EINVAL;
        }

        offset = btrfs_find_space_for_alloc(cache,
                                            0, SZ_1M, 0,
                                            &max_extent_size);
        if (offset != (SZ_128M - SZ_256K)) {
                test_err(
        "failed to allocate 1Mb from space cache, returned offset is: %llu",
                         offset);
                return -EINVAL;
        }

        /*
         * All that remains is a sectorsize free space region in a bitmap.
         * Confirm.
         */
        ret = check_num_extents_and_bitmaps(cache, 1, 1);
        if (ret)
                return ret;

        if (cache->free_space_ctl->free_space != sectorsize) {
                test_err("cache free space is not %u", sectorsize);
                return -EINVAL;
        }

        offset = btrfs_find_space_for_alloc(cache,
                                            0, sectorsize, 0,
                                            &max_extent_size);
        if (offset != (SZ_128M + SZ_16M)) {
                test_err("failed to allocate %u, returned offset : %llu",
                         sectorsize, offset);
                return -EINVAL;
        }

        ret = check_cache_empty(cache);
        if (ret)
                return ret;

        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        /*
         * Now test a similar scenario, but where our extent entry is located
         * to the right of the bitmap entry, so that we can check that stealing
         * space from a bitmap to the front of an extent entry works.
         */

        /*
         * Extent entry covering free space range [128Mb + 128Kb, 128Mb + 256Kb[
         */
        ret = test_add_free_space_entry(cache, SZ_128M + SZ_128K, SZ_128K, 0);
        if (ret) {
                test_err("couldn't add extent entry %d", ret);
                return ret;
        }

        /* Bitmap entry covering free space range [0, 128Mb - 512Kb[ */
        ret = test_add_free_space_entry(cache, 0, SZ_128M - SZ_512K, 1);
        if (ret) {
                test_err("couldn't add bitmap entry %d", ret);
                return ret;
        }

        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * Now make only the last 256Kb of the bitmap marked as free, so that
         * we end up with only the following ranges marked as free space:
         *
         * [128Mb + 128b, 128Mb + 256Kb[
         * [128Mb - 768Kb, 128Mb - 512Kb[
         */
        ret = btrfs_remove_free_space(cache, 0, SZ_128M - 768 * SZ_1K);
        if (ret) {
                test_err("failed to free part of bitmap space %d", ret);
                return ret;
        }

        /* Confirm that only those 2 ranges are marked as free. */
        if (!test_check_exists(cache, SZ_128M + SZ_128K, SZ_128K)) {
                test_err("free space range missing");
                return -ENOENT;
        }
        if (!test_check_exists(cache, SZ_128M - 768 * SZ_1K, SZ_256K)) {
                test_err("free space range missing");
                return -ENOENT;
        }

        /*
         * Confirm that the bitmap range [0, 128Mb - 768Kb[ isn't marked
         * as free anymore.
         */
        if (test_check_exists(cache, 0, SZ_128M - 768 * SZ_1K)) {
                test_err("bitmap region not removed from space cache");
                return -EINVAL;
        }

        /*
         * Confirm that the region [128Mb - 512Kb, 128Mb[, which is
         * covered by the bitmap, isn't marked as free.
         */
        if (test_check_exists(cache, SZ_128M - SZ_512K, SZ_512K)) {
                test_err("invalid bitmap region marked as free");
                return -EINVAL;
        }

        /*
         * Now lets mark the region [128Mb - 512Kb, 128Mb[ as free too. But,
         * lets make sure the free space cache marks it as free in the bitmap,
         * and doesn't insert a new extent entry to represent this region.
         */
        ret = btrfs_add_free_space(cache, SZ_128M - SZ_512K, SZ_512K);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }
        /* Confirm the region is marked as free. */
        if (!test_check_exists(cache, SZ_128M - SZ_512K, SZ_512K)) {
                test_err("bitmap region not marked as free");
                return -ENOENT;
        }

        /*
         * Confirm that no new extent entries or bitmap entries were added to
         * the cache after adding that free space region.
         */
        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * Now lets add a small free space region to the left of the previous
         * one, which is not contiguous with it and is part of the bitmap too.
         * The goal is to test that the bitmap entry space stealing doesn't
         * steal this space region.
         */
        ret = btrfs_add_free_space(cache, SZ_32M, 2 * sectorsize);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }

        /*
         * Now mark the region [128Mb, 128Mb + 128Kb[ as free too. This will
         * expand the range covered by the existing extent entry that represents
         * the free space [128Mb + 128Kb, 128Mb + 256Kb[.
         */
        ret = btrfs_add_free_space(cache, SZ_128M, SZ_128K);
        if (ret) {
                test_err("error adding free space: %d", ret);
                return ret;
        }
        /* Confirm the region is marked as free. */
        if (!test_check_exists(cache, SZ_128M, SZ_128K)) {
                test_err("extent region not marked as free");
                return -ENOENT;
        }

        /*
         * Confirm that our extent entry didn't stole all free space from the
         * bitmap, because of the small 2 * sectorsize free space region.
         */
        ret = check_num_extents_and_bitmaps(cache, 2, 1);
        if (ret)
                return ret;

        /*
         * So now we have the range [128Mb - 768Kb, 128Mb + 256Kb[ as free
         * space. Without stealing bitmap free space into extent entry space,
         * we would have all this free space represented by 2 entries in the
         * cache:
         *
         * extent entry covering range: [128Mb, 128Mb + 256Kb[
         * bitmap entry covering range: [128Mb - 768Kb, 128Mb[
         *
         * Attempting to allocate the whole free space (1Mb) would fail, because
         * we can't allocate from multiple entries.
         * With the bitmap free space stealing, we get a single extent entry
         * that represents the 1Mb free space, and therefore we're able to
         * allocate the whole free space at once.
         */
        if (!test_check_exists(cache, SZ_128M - 768 * SZ_1K, SZ_1M)) {
                test_err("expected region not marked as free");
                return -ENOENT;
        }

        if (cache->free_space_ctl->free_space != (SZ_1M + 2 * sectorsize)) {
                test_err("cache free space is not 1Mb + %u", 2 * sectorsize);
                return -EINVAL;
        }

        offset = btrfs_find_space_for_alloc(cache, 0, SZ_1M, 0,
                                            &max_extent_size);
        if (offset != (SZ_128M - 768 * SZ_1K)) {
                test_err(
        "failed to allocate 1Mb from space cache, returned offset is: %llu",
                         offset);
                return -EINVAL;
        }

        /*
         * All that remains is 2 * sectorsize free space region
         * in a bitmap. Confirm.
         */
        ret = check_num_extents_and_bitmaps(cache, 1, 1);
        if (ret)
                return ret;

        if (cache->free_space_ctl->free_space != 2 * sectorsize) {
                test_err("cache free space is not %u", 2 * sectorsize);
                return -EINVAL;
        }

        offset = btrfs_find_space_for_alloc(cache,
                                            0, 2 * sectorsize, 0,
                                            &max_extent_size);
        if (offset != SZ_32M) {
                test_err("failed to allocate %u, offset: %llu",
                         2 * sectorsize, offset);
                return -EINVAL;
        }

        ret = check_cache_empty(cache);
        if (ret)
                return ret;

        cache->free_space_ctl->op = orig_free_space_ops;
        __btrfs_remove_free_space_cache(cache->free_space_ctl);

        return 0;
}

int btrfs_test_free_space_cache(u32 sectorsize, u32 nodesize)
{
        struct btrfs_fs_info *fs_info;
        struct btrfs_block_group_cache *cache;
        struct btrfs_root *root = NULL;
        int ret = -ENOMEM;

        test_msg("running btrfs free space cache tests");
        fs_info = btrfs_alloc_dummy_fs_info(nodesize, sectorsize);
        if (!fs_info) {
                test_std_err(TEST_ALLOC_FS_INFO);
                return -ENOMEM;
        }

        /*
         * For ppc64 (with 64k page size), bytes per bitmap might be
         * larger than 1G.  To make bitmap test available in ppc64,
         * alloc dummy block group whose size cross bitmaps.
         */
        cache = btrfs_alloc_dummy_block_group(fs_info,
                                      BITS_PER_BITMAP * sectorsize + PAGE_SIZE);
        if (!cache) {
                test_std_err(TEST_ALLOC_BLOCK_GROUP);
                btrfs_free_dummy_fs_info(fs_info);
                return 0;
        }

        root = btrfs_alloc_dummy_root(fs_info);
        if (IS_ERR(root)) {
                test_std_err(TEST_ALLOC_ROOT);
                ret = PTR_ERR(root);
                goto out;
        }

        root->fs_info->extent_root = root;

        ret = test_extents(cache);
        if (ret)
                goto out;
        ret = test_bitmaps(cache, sectorsize);
        if (ret)
                goto out;
        ret = test_bitmaps_and_extents(cache, sectorsize);
        if (ret)
                goto out;

        ret = test_steal_space_from_bitmap_to_extent(cache, sectorsize);
out:
        btrfs_free_dummy_block_group(cache);
        btrfs_free_dummy_root(root);
        btrfs_free_dummy_fs_info(fs_info);
        return ret;
}