contrib/qemu: Import qemu block source code

This qemu block format source code and its minimal
dependency files will be used in the next patch to implement
a qemu-block format translator.

Change-Id: Ic87638972f7ea9b3df84d7a0539512a250c11c1c
BUG: 986775
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5366
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

1 files changed, 1374 insertions, 0 deletions

diff --git a/contrib/qemu/block/qcow2-refcount.c b/contrib/qemu/block/qcow2-refcount.c
new file mode 100644
index 00000000000..1244693f39e
--- /dev/null
+++ b/contrib/qemu/block/qcow2-refcount.c
@@ -0,0 +1,1374 @@
+/*
+ * Block driver for the QCOW version 2 format
+ *
+ * Copyright (c) 2004-2006 Fabrice Bellard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu-common.h"
+#include "block/block_int.h"
+#include "block/qcow2.h"
+
+static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size);
+static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
+                            int64_t offset, int64_t length,
+                            int addend, enum qcow2_discard_type type);
+
+
+/*********************************************************/
+/* refcount handling */
+
+int qcow2_refcount_init(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret, refcount_table_size2, i;
+
+    refcount_table_size2 = s->refcount_table_size * sizeof(uint64_t);
+    s->refcount_table = g_malloc(refcount_table_size2);
+    if (s->refcount_table_size > 0) {
+        BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_LOAD);
+        ret = bdrv_pread(bs->file, s->refcount_table_offset,
+                         s->refcount_table, refcount_table_size2);
+        if (ret != refcount_table_size2)
+            goto fail;
+        for(i = 0; i < s->refcount_table_size; i++)
+            be64_to_cpus(&s->refcount_table[i]);
+    }
+    return 0;
+ fail:
+    return -ENOMEM;
+}
+
+void qcow2_refcount_close(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    g_free(s->refcount_table);
+}
+
+
+static int load_refcount_block(BlockDriverState *bs,
+                               int64_t refcount_block_offset,
+                               void **refcount_block)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret;
+
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_LOAD);
+    ret = qcow2_cache_get(bs, s->refcount_block_cache, refcount_block_offset,
+        refcount_block);
+
+    return ret;
+}
+
+/*
+ * Returns the refcount of the cluster given by its index. Any non-negative
+ * return value is the refcount of the cluster, negative values are -errno
+ * and indicate an error.
+ */
+static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
+{
+    BDRVQcowState *s = bs->opaque;
+    int refcount_table_index, block_index;
+    int64_t refcount_block_offset;
+    int ret;
+    uint16_t *refcount_block;
+    uint16_t refcount;
+
+    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+    if (refcount_table_index >= s->refcount_table_size)
+        return 0;
+    refcount_block_offset = s->refcount_table[refcount_table_index];
+    if (!refcount_block_offset)
+        return 0;
+
+    ret = qcow2_cache_get(bs, s->refcount_block_cache, refcount_block_offset,
+        (void**) &refcount_block);
+    if (ret < 0) {
+        return ret;
+    }
+
+    block_index = cluster_index &
+        ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+    refcount = be16_to_cpu(refcount_block[block_index]);
+
+    ret = qcow2_cache_put(bs, s->refcount_block_cache,
+        (void**) &refcount_block);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return refcount;
+}
+
+/*
+ * Rounds the refcount table size up to avoid growing the table for each single
+ * refcount block that is allocated.
+ */
+static unsigned int next_refcount_table_size(BDRVQcowState *s,
+    unsigned int min_size)
+{
+    unsigned int min_clusters = (min_size >> (s->cluster_bits - 3)) + 1;
+    unsigned int refcount_table_clusters =
+        MAX(1, s->refcount_table_size >> (s->cluster_bits - 3));
+
+    while (min_clusters > refcount_table_clusters) {
+        refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
+    }
+
+    return refcount_table_clusters << (s->cluster_bits - 3);
+}
+
+
+/* Checks if two offsets are described by the same refcount block */
+static int in_same_refcount_block(BDRVQcowState *s, uint64_t offset_a,
+    uint64_t offset_b)
+{
+    uint64_t block_a = offset_a >> (2 * s->cluster_bits - REFCOUNT_SHIFT);
+    uint64_t block_b = offset_b >> (2 * s->cluster_bits - REFCOUNT_SHIFT);
+
+    return (block_a == block_b);
+}
+
+/*
+ * Loads a refcount block. If it doesn't exist yet, it is allocated first
+ * (including growing the refcount table if needed).
+ *
+ * Returns 0 on success or -errno in error case
+ */
+static int alloc_refcount_block(BlockDriverState *bs,
+    int64_t cluster_index, uint16_t **refcount_block)
+{
+    BDRVQcowState *s = bs->opaque;
+    unsigned int refcount_table_index;
+    int ret;
+
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC);
+
+    /* Find the refcount block for the given cluster */
+    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+
+    if (refcount_table_index < s->refcount_table_size) {
+
+        uint64_t refcount_block_offset =
+            s->refcount_table[refcount_table_index] & REFT_OFFSET_MASK;
+
+        /* If it's already there, we're done */
+        if (refcount_block_offset) {
+             return load_refcount_block(bs, refcount_block_offset,
+                 (void**) refcount_block);
+        }
+    }
+
+    /*
+     * If we came here, we need to allocate something. Something is at least
+     * a cluster for the new refcount block. It may also include a new refcount
+     * table if the old refcount table is too small.
+     *
+     * Note that allocating clusters here needs some special care:
+     *
+     * - We can't use the normal qcow2_alloc_clusters(), it would try to
+     *   increase the refcount and very likely we would end up with an endless
+     *   recursion. Instead we must place the refcount blocks in a way that
+     *   they can describe them themselves.
+     *
+     * - We need to consider that at this point we are inside update_refcounts
+     *   and doing the initial refcount increase. This means that some clusters
+     *   have already been allocated by the caller, but their refcount isn't
+     *   accurate yet. free_cluster_index tells us where this allocation ends
+     *   as long as we don't overwrite it by freeing clusters.
+     *
+     * - alloc_clusters_noref and qcow2_free_clusters may load a different
+     *   refcount block into the cache
+     */
+
+    *refcount_block = NULL;
+
+    /* We write to the refcount table, so we might depend on L2 tables */
+    ret = qcow2_cache_flush(bs, s->l2_table_cache);
+    if (ret < 0) {
+        return ret;
+    }
+
+    /* Allocate the refcount block itself and mark it as used */
+    int64_t new_block = alloc_clusters_noref(bs, s->cluster_size);
+    if (new_block < 0) {
+        return new_block;
+    }
+
+#ifdef DEBUG_ALLOC2
+    fprintf(stderr, "qcow2: Allocate refcount block %d for %" PRIx64
+        " at %" PRIx64 "\n",
+        refcount_table_index, cluster_index << s->cluster_bits, new_block);
+#endif
+
+    if (in_same_refcount_block(s, new_block, cluster_index << s->cluster_bits)) {
+        /* Zero the new refcount block before updating it */
+        ret = qcow2_cache_get_empty(bs, s->refcount_block_cache, new_block,
+            (void**) refcount_block);
+        if (ret < 0) {
+            goto fail_block;
+        }
+
+        memset(*refcount_block, 0, s->cluster_size);
+
+        /* The block describes itself, need to update the cache */
+        int block_index = (new_block >> s->cluster_bits) &
+            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+        (*refcount_block)[block_index] = cpu_to_be16(1);
+    } else {
+        /* Described somewhere else. This can recurse at most twice before we
+         * arrive at a block that describes itself. */
+        ret = update_refcount(bs, new_block, s->cluster_size, 1,
+                              QCOW2_DISCARD_NEVER);
+        if (ret < 0) {
+            goto fail_block;
+        }
+
+        ret = qcow2_cache_flush(bs, s->refcount_block_cache);
+        if (ret < 0) {
+            goto fail_block;
+        }
+
+        /* Initialize the new refcount block only after updating its refcount,
+         * update_refcount uses the refcount cache itself */
+        ret = qcow2_cache_get_empty(bs, s->refcount_block_cache, new_block,
+            (void**) refcount_block);
+        if (ret < 0) {
+            goto fail_block;
+        }
+
+        memset(*refcount_block, 0, s->cluster_size);
+    }
+
+    /* Now the new refcount block needs to be written to disk */
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_WRITE);
+    qcow2_cache_entry_mark_dirty(s->refcount_block_cache, *refcount_block);
+    ret = qcow2_cache_flush(bs, s->refcount_block_cache);
+    if (ret < 0) {
+        goto fail_block;
+    }
+
+    /* If the refcount table is big enough, just hook the block up there */
+    if (refcount_table_index < s->refcount_table_size) {
+        uint64_t data64 = cpu_to_be64(new_block);
+        BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_HOOKUP);
+        ret = bdrv_pwrite_sync(bs->file,
+            s->refcount_table_offset + refcount_table_index * sizeof(uint64_t),
+            &data64, sizeof(data64));
+        if (ret < 0) {
+            goto fail_block;
+        }
+
+        s->refcount_table[refcount_table_index] = new_block;
+        return 0;
+    }
+
+    ret = qcow2_cache_put(bs, s->refcount_block_cache, (void**) refcount_block);
+    if (ret < 0) {
+        goto fail_block;
+    }
+
+    /*
+     * If we come here, we need to grow the refcount table. Again, a new
+     * refcount table needs some space and we can't simply allocate to avoid
+     * endless recursion.
+     *
+     * Therefore let's grab new refcount blocks at the end of the image, which
+     * will describe themselves and the new refcount table. This way we can
+     * reference them only in the new table and do the switch to the new
+     * refcount table at once without producing an inconsistent state in
+     * between.
+     */
+    BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_GROW);
+
+    /* Calculate the number of refcount blocks needed so far */
+    uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT);
+    uint64_t blocks_used = (s->free_cluster_index +
+        refcount_block_clusters - 1) / refcount_block_clusters;
+
+    /* And now we need at least one block more for the new metadata */
+    uint64_t table_size = next_refcount_table_size(s, blocks_used + 1);
+    uint64_t last_table_size;
+    uint64_t blocks_clusters;
+    do {
+        uint64_t table_clusters =
+            size_to_clusters(s, table_size * sizeof(uint64_t));
+        blocks_clusters = 1 +
+            ((table_clusters + refcount_block_clusters - 1)
+            / refcount_block_clusters);
+        uint64_t meta_clusters = table_clusters + blocks_clusters;
+
+        last_table_size = table_size;
+        table_size = next_refcount_table_size(s, blocks_used +
+            ((meta_clusters + refcount_block_clusters - 1)
+            / refcount_block_clusters));
+
+    } while (last_table_size != table_size);
+
+#ifdef DEBUG_ALLOC2
+    fprintf(stderr, "qcow2: Grow refcount table %" PRId32 " => %" PRId64 "\n",
+        s->refcount_table_size, table_size);
+#endif
+
+    /* Create the new refcount table and blocks */
+    uint64_t meta_offset = (blocks_used * refcount_block_clusters) *
+        s->cluster_size;
+    uint64_t table_offset = meta_offset + blocks_clusters * s->cluster_size;
+    uint16_t *new_blocks = g_malloc0(blocks_clusters * s->cluster_size);
+    uint64_t *new_table = g_malloc0(table_size * sizeof(uint64_t));
+
+    assert(meta_offset >= (s->free_cluster_index * s->cluster_size));
+
+    /* Fill the new refcount table */
+    memcpy(new_table, s->refcount_table,
+        s->refcount_table_size * sizeof(uint64_t));
+    new_table[refcount_table_index] = new_block;
+
+    int i;
+    for (i = 0; i < blocks_clusters; i++) {
+        new_table[blocks_used + i] = meta_offset + (i * s->cluster_size);
+    }
+
+    /* Fill the refcount blocks */
+    uint64_t table_clusters = size_to_clusters(s, table_size * sizeof(uint64_t));
+    int block = 0;
+    for (i = 0; i < table_clusters + blocks_clusters; i++) {
+        new_blocks[block++] = cpu_to_be16(1);
+    }
+
+    /* Write refcount blocks to disk */
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_WRITE_BLOCKS);
+    ret = bdrv_pwrite_sync(bs->file, meta_offset, new_blocks,
+        blocks_clusters * s->cluster_size);
+    g_free(new_blocks);
+    if (ret < 0) {
+        goto fail_table;
+    }
+
+    /* Write refcount table to disk */
+    for(i = 0; i < table_size; i++) {
+        cpu_to_be64s(&new_table[i]);
+    }
+
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_WRITE_TABLE);
+    ret = bdrv_pwrite_sync(bs->file, table_offset, new_table,
+        table_size * sizeof(uint64_t));
+    if (ret < 0) {
+        goto fail_table;
+    }
+
+    for(i = 0; i < table_size; i++) {
+        be64_to_cpus(&new_table[i]);
+    }
+
+    /* Hook up the new refcount table in the qcow2 header */
+    uint8_t data[12];
+    cpu_to_be64w((uint64_t*)data, table_offset);
+    cpu_to_be32w((uint32_t*)(data + 8), table_clusters);
+    BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_SWITCH_TABLE);
+    ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, refcount_table_offset),
+        data, sizeof(data));
+    if (ret < 0) {
+        goto fail_table;
+    }
+
+    /* And switch it in memory */
+    uint64_t old_table_offset = s->refcount_table_offset;
+    uint64_t old_table_size = s->refcount_table_size;
+
+    g_free(s->refcount_table);
+    s->refcount_table = new_table;
+    s->refcount_table_size = table_size;
+    s->refcount_table_offset = table_offset;
+
+    /* Free old table. Remember, we must not change free_cluster_index */
+    uint64_t old_free_cluster_index = s->free_cluster_index;
+    qcow2_free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t),
+                        QCOW2_DISCARD_OTHER);
+    s->free_cluster_index = old_free_cluster_index;
+
+    ret = load_refcount_block(bs, new_block, (void**) refcount_block);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return 0;
+
+fail_table:
+    g_free(new_table);
+fail_block:
+    if (*refcount_block != NULL) {
+        qcow2_cache_put(bs, s->refcount_block_cache, (void**) refcount_block);
+    }
+    return ret;
+}
+
+void qcow2_process_discards(BlockDriverState *bs, int ret)
+{
+    BDRVQcowState *s = bs->opaque;
+    Qcow2DiscardRegion *d, *next;
+
+    QTAILQ_FOREACH_SAFE(d, &s->discards, next, next) {
+        QTAILQ_REMOVE(&s->discards, d, next);
+
+        /* Discard is optional, ignore the return value */
+        if (ret >= 0) {
+            bdrv_discard(bs->file,
+                         d->offset >> BDRV_SECTOR_BITS,
+                         d->bytes >> BDRV_SECTOR_BITS);
+        }
+
+        g_free(d);
+    }
+}
+
+static void update_refcount_discard(BlockDriverState *bs,
+                                    uint64_t offset, uint64_t length)
+{
+    BDRVQcowState *s = bs->opaque;
+    Qcow2DiscardRegion *d, *p, *next;
+
+    QTAILQ_FOREACH(d, &s->discards, next) {
+        uint64_t new_start = MIN(offset, d->offset);
+        uint64_t new_end = MAX(offset + length, d->offset + d->bytes);
+
+        if (new_end - new_start <= length + d->bytes) {
+            /* There can't be any overlap, areas ending up here have no
+             * references any more and therefore shouldn't get freed another
+             * time. */
+            assert(d->bytes + length == new_end - new_start);
+            d->offset = new_start;
+            d->bytes = new_end - new_start;
+            goto found;
+        }
+    }
+
+    d = g_malloc(sizeof(*d));
+    *d = (Qcow2DiscardRegion) {
+        .bs     = bs,
+        .offset = offset,
+        .bytes  = length,
+    };
+    QTAILQ_INSERT_TAIL(&s->discards, d, next);
+
+found:
+    /* Merge discard requests if they are adjacent now */
+    QTAILQ_FOREACH_SAFE(p, &s->discards, next, next) {
+        if (p == d
+            || p->offset > d->offset + d->bytes
+            || d->offset > p->offset + p->bytes)
+        {
+            continue;
+        }
+
+        /* Still no overlap possible */
+        assert(p->offset == d->offset + d->bytes
+            || d->offset == p->offset + p->bytes);
+
+        QTAILQ_REMOVE(&s->discards, p, next);
+        d->offset = MIN(d->offset, p->offset);
+        d->bytes += p->bytes;
+    }
+}
+
+/* XXX: cache several refcount block clusters ? */
+static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
+    int64_t offset, int64_t length, int addend, enum qcow2_discard_type type)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t start, last, cluster_offset;
+    uint16_t *refcount_block = NULL;
+    int64_t old_table_index = -1;
+    int ret;
+
+#ifdef DEBUG_ALLOC2
+    fprintf(stderr, "update_refcount: offset=%" PRId64 " size=%" PRId64 " addend=%d\n",
+           offset, length, addend);
+#endif
+    if (length < 0) {
+        return -EINVAL;
+    } else if (length == 0) {
+        return 0;
+    }
+
+    if (addend < 0) {
+        qcow2_cache_set_dependency(bs, s->refcount_block_cache,
+            s->l2_table_cache);
+    }
+
+    start = offset & ~(s->cluster_size - 1);
+    last = (offset + length - 1) & ~(s->cluster_size - 1);
+    for(cluster_offset = start; cluster_offset <= last;
+        cluster_offset += s->cluster_size)
+    {
+        int block_index, refcount;
+        int64_t cluster_index = cluster_offset >> s->cluster_bits;
+        int64_t table_index =
+            cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+
+        /* Load the refcount block and allocate it if needed */
+        if (table_index != old_table_index) {
+            if (refcount_block) {
+                ret = qcow2_cache_put(bs, s->refcount_block_cache,
+                    (void**) &refcount_block);
+                if (ret < 0) {
+                    goto fail;
+                }
+            }
+
+            ret = alloc_refcount_block(bs, cluster_index, &refcount_block);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+        old_table_index = table_index;
+
+        qcow2_cache_entry_mark_dirty(s->refcount_block_cache, refcount_block);
+
+        /* we can update the count and save it */
+        block_index = cluster_index &
+            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+
+        refcount = be16_to_cpu(refcount_block[block_index]);
+        refcount += addend;
+        if (refcount < 0 || refcount > 0xffff) {
+            ret = -EINVAL;
+            goto fail;
+        }
+        if (refcount == 0 && cluster_index < s->free_cluster_index) {
+            s->free_cluster_index = cluster_index;
+        }
+        refcount_block[block_index] = cpu_to_be16(refcount);
+
+        if (refcount == 0 && s->discard_passthrough[type]) {
+            update_refcount_discard(bs, cluster_offset, s->cluster_size);
+        }
+    }
+
+    ret = 0;
+fail:
+    if (!s->cache_discards) {
+        qcow2_process_discards(bs, ret);
+    }
+
+    /* Write last changed block to disk */
+    if (refcount_block) {
+        int wret;
+        wret = qcow2_cache_put(bs, s->refcount_block_cache,
+            (void**) &refcount_block);
+        if (wret < 0) {
+            return ret < 0 ? ret : wret;
+        }
+    }
+
+    /*
+     * Try do undo any updates if an error is returned (This may succeed in
+     * some cases like ENOSPC for allocating a new refcount block)
+     */
+    if (ret < 0) {
+        int dummy;
+        dummy = update_refcount(bs, offset, cluster_offset - offset, -addend,
+                                QCOW2_DISCARD_NEVER);
+        (void)dummy;
+    }
+
+    return ret;
+}
+
+/*
+ * Increases or decreases the refcount of a given cluster by one.
+ * addend must be 1 or -1.
+ *
+ * If the return value is non-negative, it is the new refcount of the cluster.
+ * If it is negative, it is -errno and indicates an error.
+ */
+static int update_cluster_refcount(BlockDriverState *bs,
+                                   int64_t cluster_index,
+                                   int addend,
+                                   enum qcow2_discard_type type)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret;
+
+    ret = update_refcount(bs, cluster_index << s->cluster_bits, 1, addend,
+                          type);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return get_refcount(bs, cluster_index);
+}
+
+
+
+/*********************************************************/
+/* cluster allocation functions */
+
+
+
+/* return < 0 if error */
+static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int i, nb_clusters, refcount;
+
+    nb_clusters = size_to_clusters(s, size);
+retry:
+    for(i = 0; i < nb_clusters; i++) {
+        int64_t next_cluster_index = s->free_cluster_index++;
+        refcount = get_refcount(bs, next_cluster_index);
+
+        if (refcount < 0) {
+            return refcount;
+        } else if (refcount != 0) {
+            goto retry;
+        }
+    }
+#ifdef DEBUG_ALLOC2
+    fprintf(stderr, "alloc_clusters: size=%" PRId64 " -> %" PRId64 "\n",
+            size,
+            (s->free_cluster_index - nb_clusters) << s->cluster_bits);
+#endif
+    return (s->free_cluster_index - nb_clusters) << s->cluster_bits;
+}
+
+int64_t qcow2_alloc_clusters(BlockDriverState *bs, int64_t size)
+{
+    int64_t offset;
+    int ret;
+
+    BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC);
+    offset = alloc_clusters_noref(bs, size);
+    if (offset < 0) {
+        return offset;
+    }
+
+    ret = update_refcount(bs, offset, size, 1, QCOW2_DISCARD_NEVER);
+    if (ret < 0) {
+        return ret;
+    }
+
+    return offset;
+}
+
+int qcow2_alloc_clusters_at(BlockDriverState *bs, uint64_t offset,
+    int nb_clusters)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t cluster_index;
+    uint64_t old_free_cluster_index;
+    int i, refcount, ret;
+
+    /* Check how many clusters there are free */
+    cluster_index = offset >> s->cluster_bits;
+    for(i = 0; i < nb_clusters; i++) {
+        refcount = get_refcount(bs, cluster_index++);
+
+        if (refcount < 0) {
+            return refcount;
+        } else if (refcount != 0) {
+            break;
+        }
+    }
+
+    /* And then allocate them */
+    old_free_cluster_index = s->free_cluster_index;
+    s->free_cluster_index = cluster_index + i;
+
+    ret = update_refcount(bs, offset, i << s->cluster_bits, 1,
+                          QCOW2_DISCARD_NEVER);
+    if (ret < 0) {
+        return ret;
+    }
+
+    s->free_cluster_index = old_free_cluster_index;
+
+    return i;
+}
+
+/* only used to allocate compressed sectors. We try to allocate
+   contiguous sectors. size must be <= cluster_size */
+int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t offset, cluster_offset;
+    int free_in_cluster;
+
+    BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_BYTES);
+    assert(size > 0 && size <= s->cluster_size);
+    if (s->free_byte_offset == 0) {
+        offset = qcow2_alloc_clusters(bs, s->cluster_size);
+        if (offset < 0) {
+            return offset;
+        }
+        s->free_byte_offset = offset;
+    }
+ redo:
+    free_in_cluster = s->cluster_size -
+        (s->free_byte_offset & (s->cluster_size - 1));
+    if (size <= free_in_cluster) {
+        /* enough space in current cluster */
+        offset = s->free_byte_offset;
+        s->free_byte_offset += size;
+        free_in_cluster -= size;
+        if (free_in_cluster == 0)
+            s->free_byte_offset = 0;
+        if ((offset & (s->cluster_size - 1)) != 0)
+            update_cluster_refcount(bs, offset >> s->cluster_bits, 1,
+                                    QCOW2_DISCARD_NEVER);
+    } else {
+        offset = qcow2_alloc_clusters(bs, s->cluster_size);
+        if (offset < 0) {
+            return offset;
+        }
+        cluster_offset = s->free_byte_offset & ~(s->cluster_size - 1);
+        if ((cluster_offset + s->cluster_size) == offset) {
+            /* we are lucky: contiguous data */
+            offset = s->free_byte_offset;
+            update_cluster_refcount(bs, offset >> s->cluster_bits, 1,
+                                    QCOW2_DISCARD_NEVER);
+            s->free_byte_offset += size;
+        } else {
+            s->free_byte_offset = offset;
+            goto redo;
+        }
+    }
+
+    /* The cluster refcount was incremented, either by qcow2_alloc_clusters()
+     * or explicitly by update_cluster_refcount().  Refcount blocks must be
+     * flushed before the caller's L2 table updates.
+     */
+    qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache);
+    return offset;
+}
+
+void qcow2_free_clusters(BlockDriverState *bs,
+                          int64_t offset, int64_t size,
+                          enum qcow2_discard_type type)
+{
+    int ret;
+
+    BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_FREE);
+    ret = update_refcount(bs, offset, size, -1, type);
+    if (ret < 0) {
+        fprintf(stderr, "qcow2_free_clusters failed: %s\n", strerror(-ret));
+        /* TODO Remember the clusters to free them later and avoid leaking */
+    }
+}
+
+/*
+ * Free a cluster using its L2 entry (handles clusters of all types, e.g.
+ * normal cluster, compressed cluster, etc.)
+ */
+void qcow2_free_any_clusters(BlockDriverState *bs, uint64_t l2_entry,
+                             int nb_clusters, enum qcow2_discard_type type)
+{
+    BDRVQcowState *s = bs->opaque;
+
+    switch (qcow2_get_cluster_type(l2_entry)) {
+    case QCOW2_CLUSTER_COMPRESSED:
+        {
+            int nb_csectors;
+            nb_csectors = ((l2_entry >> s->csize_shift) &
+                           s->csize_mask) + 1;
+            qcow2_free_clusters(bs,
+                (l2_entry & s->cluster_offset_mask) & ~511,
+                nb_csectors * 512, type);
+        }
+        break;
+    case QCOW2_CLUSTER_NORMAL:
+        qcow2_free_clusters(bs, l2_entry & L2E_OFFSET_MASK,
+                            nb_clusters << s->cluster_bits, type);
+        break;
+    case QCOW2_CLUSTER_UNALLOCATED:
+    case QCOW2_CLUSTER_ZERO:
+        break;
+    default:
+        abort();
+    }
+}
+
+
+
+/*********************************************************/
+/* snapshots and image creation */
+
+
+
+/* update the refcounts of snapshots and the copied flag */
+int qcow2_update_snapshot_refcount(BlockDriverState *bs,
+    int64_t l1_table_offset, int l1_size, int addend)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2, l1_allocated;
+    int64_t old_offset, old_l2_offset;
+    int i, j, l1_modified = 0, nb_csectors, refcount;
+    int ret;
+
+    l2_table = NULL;
+    l1_table = NULL;
+    l1_size2 = l1_size * sizeof(uint64_t);
+
+    s->cache_discards = true;
+
+    /* WARNING: qcow2_snapshot_goto relies on this function not using the
+     * l1_table_offset when it is the current s->l1_table_offset! Be careful
+     * when changing this! */
+    if (l1_table_offset != s->l1_table_offset) {
+        l1_table = g_malloc0(align_offset(l1_size2, 512));
+        l1_allocated = 1;
+
+        ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        for(i = 0;i < l1_size; i++)
+            be64_to_cpus(&l1_table[i]);
+    } else {
+        assert(l1_size == s->l1_size);
+        l1_table = s->l1_table;
+        l1_allocated = 0;
+    }
+
+    for(i = 0; i < l1_size; i++) {
+        l2_offset = l1_table[i];
+        if (l2_offset) {
+            old_l2_offset = l2_offset;
+            l2_offset &= L1E_OFFSET_MASK;
+
+            ret = qcow2_cache_get(bs, s->l2_table_cache, l2_offset,
+                (void**) &l2_table);
+            if (ret < 0) {
+                goto fail;
+            }
+
+            for(j = 0; j < s->l2_size; j++) {
+                offset = be64_to_cpu(l2_table[j]);
+                if (offset != 0) {
+                    old_offset = offset;
+                    offset &= ~QCOW_OFLAG_COPIED;
+                    if (offset & QCOW_OFLAG_COMPRESSED) {
+                        nb_csectors = ((offset >> s->csize_shift) &
+                                       s->csize_mask) + 1;
+                        if (addend != 0) {
+                            int ret;
+                            ret = update_refcount(bs,
+                                (offset & s->cluster_offset_mask) & ~511,
+                                nb_csectors * 512, addend,
+                                QCOW2_DISCARD_SNAPSHOT);
+                            if (ret < 0) {
+                                goto fail;
+                            }
+                        }
+                        /* compressed clusters are never modified */
+                        refcount = 2;
+                    } else {
+                        uint64_t cluster_index = (offset & L2E_OFFSET_MASK) >> s->cluster_bits;
+                        if (addend != 0) {
+                            refcount = update_cluster_refcount(bs, cluster_index, addend,
+                                                               QCOW2_DISCARD_SNAPSHOT);
+                        } else {
+                            refcount = get_refcount(bs, cluster_index);
+                        }
+
+                        if (refcount < 0) {
+                            ret = refcount;
+                            goto fail;
+                        }
+                    }
+
+                    if (refcount == 1) {
+                        offset |= QCOW_OFLAG_COPIED;
+                    }
+                    if (offset != old_offset) {
+                        if (addend > 0) {
+                            qcow2_cache_set_dependency(bs, s->l2_table_cache,
+                                s->refcount_block_cache);
+                        }
+                        l2_table[j] = cpu_to_be64(offset);
+                        qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
+                    }
+                }
+            }
+
+            ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
+            if (ret < 0) {
+                goto fail;
+            }
+
+
+            if (addend != 0) {
+                refcount = update_cluster_refcount(bs, l2_offset >> s->cluster_bits, addend,
+                                                   QCOW2_DISCARD_SNAPSHOT);
+            } else {
+                refcount = get_refcount(bs, l2_offset >> s->cluster_bits);
+            }
+            if (refcount < 0) {
+                ret = refcount;
+                goto fail;
+            } else if (refcount == 1) {
+                l2_offset |= QCOW_OFLAG_COPIED;
+            }
+            if (l2_offset != old_l2_offset) {
+                l1_table[i] = l2_offset;
+                l1_modified = 1;
+            }
+        }
+    }
+
+    ret = bdrv_flush(bs);
+fail:
+    if (l2_table) {
+        qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
+    }
+
+    s->cache_discards = false;
+    qcow2_process_discards(bs, ret);
+
+    /* Update L1 only if it isn't deleted anyway (addend = -1) */
+    if (ret == 0 && addend >= 0 && l1_modified) {
+        for (i = 0; i < l1_size; i++) {
+            cpu_to_be64s(&l1_table[i]);
+        }
+
+        ret = bdrv_pwrite_sync(bs->file, l1_table_offset, l1_table, l1_size2);
+
+        for (i = 0; i < l1_size; i++) {
+            be64_to_cpus(&l1_table[i]);
+        }
+    }
+    if (l1_allocated)
+        g_free(l1_table);
+    return ret;
+}
+
+
+
+
+/*********************************************************/
+/* refcount checking functions */
+
+
+
+/*
+ * Increases the refcount for a range of clusters in a given refcount table.
+ * This is used to construct a temporary refcount table out of L1 and L2 tables
+ * which can be compared the the refcount table saved in the image.
+ *
+ * Modifies the number of errors in res.
+ */
+static void inc_refcounts(BlockDriverState *bs,
+                          BdrvCheckResult *res,
+                          uint16_t *refcount_table,
+                          int refcount_table_size,
+                          int64_t offset, int64_t size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t start, last, cluster_offset;
+    int k;
+
+    if (size <= 0)
+        return;
+
+    start = offset & ~(s->cluster_size - 1);
+    last = (offset + size - 1) & ~(s->cluster_size - 1);
+    for(cluster_offset = start; cluster_offset <= last;
+        cluster_offset += s->cluster_size) {
+        k = cluster_offset >> s->cluster_bits;
+        if (k < 0) {
+            fprintf(stderr, "ERROR: invalid cluster offset=0x%" PRIx64 "\n",
+                cluster_offset);
+            res->corruptions++;
+        } else if (k >= refcount_table_size) {
+            fprintf(stderr, "Warning: cluster offset=0x%" PRIx64 " is after "
+                "the end of the image file, can't properly check refcounts.\n",
+                cluster_offset);
+            res->check_errors++;
+        } else {
+            if (++refcount_table[k] == 0) {
+                fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64
+                    "\n", cluster_offset);
+                res->corruptions++;
+            }
+        }
+    }
+}
+
+/* Flags for check_refcounts_l1() and check_refcounts_l2() */
+enum {
+    CHECK_OFLAG_COPIED = 0x1,   /* check QCOW_OFLAG_COPIED matches refcount */
+    CHECK_FRAG_INFO = 0x2,      /* update BlockFragInfo counters */
+};
+
+/*
+ * Increases the refcount in the given refcount table for the all clusters
+ * referenced in the L2 table. While doing so, performs some checks on L2
+ * entries.
+ *
+ * Returns the number of errors found by the checks or -errno if an internal
+ * error occurred.
+ */
+static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
+    uint16_t *refcount_table, int refcount_table_size, int64_t l2_offset,
+    int flags)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t *l2_table, l2_entry;
+    uint64_t next_contiguous_offset = 0;
+    int i, l2_size, nb_csectors, refcount;
+
+    /* Read L2 table from disk */
+    l2_size = s->l2_size * sizeof(uint64_t);
+    l2_table = g_malloc(l2_size);
+
+    if (bdrv_pread(bs->file, l2_offset, l2_table, l2_size) != l2_size)
+        goto fail;
+
+    /* Do the actual checks */
+    for(i = 0; i < s->l2_size; i++) {
+        l2_entry = be64_to_cpu(l2_table[i]);
+
+        switch (qcow2_get_cluster_type(l2_entry)) {
+        case QCOW2_CLUSTER_COMPRESSED:
+            /* Compressed clusters don't have QCOW_OFLAG_COPIED */
+            if (l2_entry & QCOW_OFLAG_COPIED) {
+                fprintf(stderr, "ERROR: cluster %" PRId64 ": "
+                    "copied flag must never be set for compressed "
+                    "clusters\n", l2_entry >> s->cluster_bits);
+                l2_entry &= ~QCOW_OFLAG_COPIED;
+                res->corruptions++;
+            }
+
+            /* Mark cluster as used */
+            nb_csectors = ((l2_entry >> s->csize_shift) &
+                           s->csize_mask) + 1;
+            l2_entry &= s->cluster_offset_mask;
+            inc_refcounts(bs, res, refcount_table, refcount_table_size,
+                l2_entry & ~511, nb_csectors * 512);
+
+            if (flags & CHECK_FRAG_INFO) {
+                res->bfi.allocated_clusters++;
+                res->bfi.compressed_clusters++;
+
+                /* Compressed clusters are fragmented by nature.  Since they
+                 * take up sub-sector space but we only have sector granularity
+                 * I/O we need to re-read the same sectors even for adjacent
+                 * compressed clusters.
+                 */
+                res->bfi.fragmented_clusters++;
+            }
+            break;
+
+        case QCOW2_CLUSTER_ZERO:
+            if ((l2_entry & L2E_OFFSET_MASK) == 0) {
+                break;
+            }
+            /* fall through */
+
+        case QCOW2_CLUSTER_NORMAL:
+        {
+            /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
+            uint64_t offset = l2_entry & L2E_OFFSET_MASK;
+
+            if (flags & CHECK_OFLAG_COPIED) {
+                refcount = get_refcount(bs, offset >> s->cluster_bits);
+                if (refcount < 0) {
+                    fprintf(stderr, "Can't get refcount for offset %"
+                        PRIx64 ": %s\n", l2_entry, strerror(-refcount));
+                    goto fail;
+                }
+                if ((refcount == 1) != ((l2_entry & QCOW_OFLAG_COPIED) != 0)) {
+                    fprintf(stderr, "ERROR OFLAG_COPIED: offset=%"
+                        PRIx64 " refcount=%d\n", l2_entry, refcount);
+                    res->corruptions++;
+                }
+            }
+
+            if (flags & CHECK_FRAG_INFO) {
+                res->bfi.allocated_clusters++;
+                if (next_contiguous_offset &&
+                    offset != next_contiguous_offset) {
+                    res->bfi.fragmented_clusters++;
+                }
+                next_contiguous_offset = offset + s->cluster_size;
+            }
+
+            /* Mark cluster as used */
+            inc_refcounts(bs, res, refcount_table,refcount_table_size,
+                offset, s->cluster_size);
+
+            /* Correct offsets are cluster aligned */
+            if (offset & (s->cluster_size - 1)) {
+                fprintf(stderr, "ERROR offset=%" PRIx64 ": Cluster is not "
+                    "properly aligned; L2 entry corrupted.\n", offset);
+                res->corruptions++;
+            }
+            break;
+        }
+
+        case QCOW2_CLUSTER_UNALLOCATED:
+            break;
+
+        default:
+            abort();
+        }
+    }
+
+    g_free(l2_table);
+    return 0;
+
+fail:
+    fprintf(stderr, "ERROR: I/O error in check_refcounts_l2\n");
+    g_free(l2_table);
+    return -EIO;
+}
+
+/*
+ * Increases the refcount for the L1 table, its L2 tables and all referenced
+ * clusters in the given refcount table. While doing so, performs some checks
+ * on L1 and L2 entries.
+ *
+ * Returns the number of errors found by the checks or -errno if an internal
+ * error occurred.
+ */
+static int check_refcounts_l1(BlockDriverState *bs,
+                              BdrvCheckResult *res,
+                              uint16_t *refcount_table,
+                              int refcount_table_size,
+                              int64_t l1_table_offset, int l1_size,
+                              int flags)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t *l1_table, l2_offset, l1_size2;
+    int i, refcount, ret;
+
+    l1_size2 = l1_size * sizeof(uint64_t);
+
+    /* Mark L1 table as used */
+    inc_refcounts(bs, res, refcount_table, refcount_table_size,
+        l1_table_offset, l1_size2);
+
+    /* Read L1 table entries from disk */
+    if (l1_size2 == 0) {
+        l1_table = NULL;
+    } else {
+        l1_table = g_malloc(l1_size2);
+        if (bdrv_pread(bs->file, l1_table_offset,
+                       l1_table, l1_size2) != l1_size2)
+            goto fail;
+        for(i = 0;i < l1_size; i++)
+            be64_to_cpus(&l1_table[i]);
+    }
+
+    /* Do the actual checks */
+    for(i = 0; i < l1_size; i++) {
+        l2_offset = l1_table[i];
+        if (l2_offset) {
+            /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
+            if (flags & CHECK_OFLAG_COPIED) {
+                refcount = get_refcount(bs, (l2_offset & ~QCOW_OFLAG_COPIED)
+                    >> s->cluster_bits);
+                if (refcount < 0) {
+                    fprintf(stderr, "Can't get refcount for l2_offset %"
+                        PRIx64 ": %s\n", l2_offset, strerror(-refcount));
+                    goto fail;
+                }
+                if ((refcount == 1) != ((l2_offset & QCOW_OFLAG_COPIED) != 0)) {
+                    fprintf(stderr, "ERROR OFLAG_COPIED: l2_offset=%" PRIx64
+                        " refcount=%d\n", l2_offset, refcount);
+                    res->corruptions++;
+                }
+            }
+
+            /* Mark L2 table as used */
+            l2_offset &= L1E_OFFSET_MASK;
+            inc_refcounts(bs, res, refcount_table, refcount_table_size,
+                l2_offset, s->cluster_size);
+
+            /* L2 tables are cluster aligned */
+            if (l2_offset & (s->cluster_size - 1)) {
+                fprintf(stderr, "ERROR l2_offset=%" PRIx64 ": Table is not "
+                    "cluster aligned; L1 entry corrupted\n", l2_offset);
+                res->corruptions++;
+            }
+
+            /* Process and check L2 entries */
+            ret = check_refcounts_l2(bs, res, refcount_table,
+                                     refcount_table_size, l2_offset, flags);
+            if (ret < 0) {
+                goto fail;
+            }
+        }
+    }
+    g_free(l1_table);
+    return 0;
+
+fail:
+    fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
+    res->check_errors++;
+    g_free(l1_table);
+    return -EIO;
+}
+
+/*
+ * Checks an image for refcount consistency.
+ *
+ * Returns 0 if no errors are found, the number of errors in case the image is
+ * detected as corrupted, and -errno when an internal error occurred.
+ */
+int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res,
+                          BdrvCheckMode fix)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t size, i, highest_cluster;
+    int nb_clusters, refcount1, refcount2;
+    QCowSnapshot *sn;
+    uint16_t *refcount_table;
+    int ret;
+
+    size = bdrv_getlength(bs->file);
+    nb_clusters = size_to_clusters(s, size);
+    refcount_table = g_malloc0(nb_clusters * sizeof(uint16_t));
+
+    res->bfi.total_clusters =
+        size_to_clusters(s, bs->total_sectors * BDRV_SECTOR_SIZE);
+
+    /* header */
+    inc_refcounts(bs, res, refcount_table, nb_clusters,
+        0, s->cluster_size);
+
+    /* current L1 table */
+    ret = check_refcounts_l1(bs, res, refcount_table, nb_clusters,
+                             s->l1_table_offset, s->l1_size,
+                             CHECK_OFLAG_COPIED | CHECK_FRAG_INFO);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    /* snapshots */
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn = s->snapshots + i;
+        ret = check_refcounts_l1(bs, res, refcount_table, nb_clusters,
+            sn->l1_table_offset, sn->l1_size, 0);
+        if (ret < 0) {
+            goto fail;
+        }
+    }
+    inc_refcounts(bs, res, refcount_table, nb_clusters,
+        s->snapshots_offset, s->snapshots_size);
+
+    /* refcount data */
+    inc_refcounts(bs, res, refcount_table, nb_clusters,
+        s->refcount_table_offset,
+        s->refcount_table_size * sizeof(uint64_t));
+
+    for(i = 0; i < s->refcount_table_size; i++) {
+        uint64_t offset, cluster;
+        offset = s->refcount_table[i];
+        cluster = offset >> s->cluster_bits;
+
+        /* Refcount blocks are cluster aligned */
+        if (offset & (s->cluster_size - 1)) {
+            fprintf(stderr, "ERROR refcount block %" PRId64 " is not "
+                "cluster aligned; refcount table entry corrupted\n", i);
+            res->corruptions++;
+            continue;
+        }
+
+        if (cluster >= nb_clusters) {
+            fprintf(stderr, "ERROR refcount block %" PRId64
+                    " is outside image\n", i);
+            res->corruptions++;
+            continue;
+        }
+
+        if (offset != 0) {
+            inc_refcounts(bs, res, refcount_table, nb_clusters,
+                offset, s->cluster_size);
+            if (refcount_table[cluster] != 1) {
+                fprintf(stderr, "ERROR refcount block %" PRId64
+                    " refcount=%d\n",
+                    i, refcount_table[cluster]);
+                res->corruptions++;
+            }
+        }
+    }
+
+    /* compare ref counts */
+    for (i = 0, highest_cluster = 0; i < nb_clusters; i++) {
+        refcount1 = get_refcount(bs, i);
+        if (refcount1 < 0) {
+            fprintf(stderr, "Can't get refcount for cluster %" PRId64 ": %s\n",
+                i, strerror(-refcount1));
+            res->check_errors++;
+            continue;
+        }
+
+        refcount2 = refcount_table[i];
+
+        if (refcount1 > 0 || refcount2 > 0) {
+            highest_cluster = i;
+        }
+
+        if (refcount1 != refcount2) {
+
+            /* Check if we're allowed to fix the mismatch */
+            int *num_fixed = NULL;
+            if (refcount1 > refcount2 && (fix & BDRV_FIX_LEAKS)) {
+                num_fixed = &res->leaks_fixed;
+            } else if (refcount1 < refcount2 && (fix & BDRV_FIX_ERRORS)) {
+                num_fixed = &res->corruptions_fixed;
+            }
+
+            fprintf(stderr, "%s cluster %" PRId64 " refcount=%d reference=%d\n",
+                   num_fixed != NULL     ? "Repairing" :
+                   refcount1 < refcount2 ? "ERROR" :
+                                           "Leaked",
+                   i, refcount1, refcount2);
+
+            if (num_fixed) {
+                ret = update_refcount(bs, i << s->cluster_bits, 1,
+                                      refcount2 - refcount1,
+                                      QCOW2_DISCARD_ALWAYS);
+                if (ret >= 0) {
+                    (*num_fixed)++;
+                    continue;
+                }
+            }
+
+            /* And if we couldn't, print an error */
+            if (refcount1 < refcount2) {
+                res->corruptions++;
+            } else {
+                res->leaks++;
+            }
+        }
+    }
+
+    res->image_end_offset = (highest_cluster + 1) * s->cluster_size;
+    ret = 0;
+
+fail:
+    g_free(refcount_table);
+
+    return ret;
+}
+