[Qemu-devel] [PATCH 1/4] qcow2: Split out refcount handling

[Kevin Wolf <kwolf@redhat.com>]

qcow2-refcount.c contains all functions which are related to cluster
allocation and management in the image file. A large part of this is the
reference counting of these clusters.

Also a header file qcow2.h is introduced which will contain the interface of
the split qcow2 modules.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 Makefile               |    3 +-
 block/qcow2-refcount.c |  808 ++++++++++++++++++++++++++++++++++++++++++++
 block/qcow2.c          |  871 +-----------------------------------------------
 block/qcow2.h          |  154 +++++++++
 4 files changed, 966 insertions(+), 870 deletions(-)
 create mode 100644 block/qcow2-refcount.c
 create mode 100644 block/qcow2.h

diff --git a/Makefile b/Makefile
index d7b9985..5a0fdbe 100644
--- a/Makefile
+++ b/Makefile
@@ -68,7 +68,8 @@ recurse-all: $(SUBDIR_RULES)
 BLOCK_OBJS=cutils.o cache-utils.o qemu-malloc.o qemu-option.o module.o
 BLOCK_OBJS+=block/cow.o block/qcow.o aes.o block/vmdk.o block/cloop.o
 BLOCK_OBJS+=block/dmg.o block/bochs.o block/vpc.o block/vvfat.o
-BLOCK_OBJS+=block/qcow2.o block/parallels.o block/nbd.o
+BLOCK_OBJS+=block/qcow2.o block/qcow2-refcount.o
+BLOCK_OBJS+=block/parallels.o block/nbd.o
 BLOCK_OBJS+=nbd.o block.o aio.o
 
 ifdef CONFIG_WIN32
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
new file mode 100644
index 0000000..b70afe9
--- /dev/null
+++ b/block/qcow2-refcount.c
@@ -0,0 +1,808 @@
+/*
+ * 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_int.h"
+#include "block/qcow2.h"
+
+static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size);
+static int update_refcount(BlockDriverState *bs,
+                            int64_t offset, int64_t length,
+                            int addend);
+
+/*********************************************************/
+/* refcount handling */
+
+int refcount_init(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret, refcount_table_size2, i;
+
+    s->refcount_block_cache = qemu_malloc(s->cluster_size);
+    refcount_table_size2 = s->refcount_table_size * sizeof(uint64_t);
+    s->refcount_table = qemu_malloc(refcount_table_size2);
+    if (s->refcount_table_size > 0) {
+        ret = bdrv_pread(s->hd, 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 refcount_close(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    qemu_free(s->refcount_block_cache);
+    qemu_free(s->refcount_table);
+}
+
+
+static int load_refcount_block(BlockDriverState *bs,
+                               int64_t refcount_block_offset)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret;
+    ret = bdrv_pread(s->hd, refcount_block_offset, s->refcount_block_cache,
+                     s->cluster_size);
+    if (ret != s->cluster_size)
+        return -EIO;
+    s->refcount_block_cache_offset = refcount_block_offset;
+    return 0;
+}
+
+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;
+
+    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;
+    if (refcount_block_offset != s->refcount_block_cache_offset) {
+        /* better than nothing: return allocated if read error */
+        if (load_refcount_block(bs, refcount_block_offset) < 0)
+            return 1;
+    }
+    block_index = cluster_index &
+        ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+    return be16_to_cpu(s->refcount_block_cache[block_index]);
+}
+
+static int grow_refcount_table(BlockDriverState *bs, int min_size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int new_table_size, new_table_size2, refcount_table_clusters, i, ret;
+    uint64_t *new_table;
+    int64_t table_offset;
+    uint8_t data[12];
+    int old_table_size;
+    int64_t old_table_offset;
+
+    if (min_size <= s->refcount_table_size)
+        return 0;
+    /* compute new table size */
+    refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
+    for(;;) {
+        if (refcount_table_clusters == 0) {
+            refcount_table_clusters = 1;
+        } else {
+            refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
+        }
+        new_table_size = refcount_table_clusters << (s->cluster_bits - 3);
+        if (min_size <= new_table_size)
+            break;
+    }
+#ifdef DEBUG_ALLOC2
+    printf("grow_refcount_table from %d to %d\n",
+           s->refcount_table_size,
+           new_table_size);
+#endif
+    new_table_size2 = new_table_size * sizeof(uint64_t);
+    new_table = qemu_mallocz(new_table_size2);
+    memcpy(new_table, s->refcount_table,
+           s->refcount_table_size * sizeof(uint64_t));
+    for(i = 0; i < s->refcount_table_size; i++)
+        cpu_to_be64s(&new_table[i]);
+    /* Note: we cannot update the refcount now to avoid recursion */
+    table_offset = alloc_clusters_noref(bs, new_table_size2);
+    ret = bdrv_pwrite(s->hd, table_offset, new_table, new_table_size2);
+    if (ret != new_table_size2)
+        goto fail;
+    for(i = 0; i < s->refcount_table_size; i++)
+        be64_to_cpus(&new_table[i]);
+
+    cpu_to_be64w((uint64_t*)data, table_offset);
+    cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters);
+    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
+                    data, sizeof(data)) != sizeof(data))
+        goto fail;
+    qemu_free(s->refcount_table);
+    old_table_offset = s->refcount_table_offset;
+    old_table_size = s->refcount_table_size;
+    s->refcount_table = new_table;
+    s->refcount_table_size = new_table_size;
+    s->refcount_table_offset = table_offset;
+
+    update_refcount(bs, table_offset, new_table_size2, 1);
+    free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t));
+    return 0;
+ fail:
+    free_clusters(bs, table_offset, new_table_size2);
+    qemu_free(new_table);
+    return -EIO;
+}
+
+
+static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t offset, refcount_block_offset;
+    int ret, refcount_table_index;
+    uint64_t data64;
+
+    /* Find L1 index and grow refcount table if needed */
+    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+    if (refcount_table_index >= s->refcount_table_size) {
+        ret = grow_refcount_table(bs, refcount_table_index + 1);
+        if (ret < 0)
+            return ret;
+    }
+
+    /* Load or allocate the refcount block */
+    refcount_block_offset = s->refcount_table[refcount_table_index];
+    if (!refcount_block_offset) {
+        /* create a new refcount block */
+        /* Note: we cannot update the refcount now to avoid recursion */
+        offset = alloc_clusters_noref(bs, s->cluster_size);
+        memset(s->refcount_block_cache, 0, s->cluster_size);
+        ret = bdrv_pwrite(s->hd, offset, s->refcount_block_cache, s->cluster_size);
+        if (ret != s->cluster_size)
+            return -EINVAL;
+        s->refcount_table[refcount_table_index] = offset;
+        data64 = cpu_to_be64(offset);
+        ret = bdrv_pwrite(s->hd, s->refcount_table_offset +
+                          refcount_table_index * sizeof(uint64_t),
+                          &data64, sizeof(data64));
+        if (ret != sizeof(data64))
+            return -EINVAL;
+
+        refcount_block_offset = offset;
+        s->refcount_block_cache_offset = offset;
+        update_refcount(bs, offset, s->cluster_size, 1);
+    } else {
+        if (refcount_block_offset != s->refcount_block_cache_offset) {
+            if (load_refcount_block(bs, refcount_block_offset) < 0)
+                return -EIO;
+        }
+    }
+
+    return refcount_block_offset;
+}
+
+/* XXX: cache several refcount block clusters ? */
+static int update_refcount(BlockDriverState *bs,
+                            int64_t offset, int64_t length,
+                            int addend)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t start, last, cluster_offset;
+    int64_t refcount_block_offset = 0;
+    int64_t table_index = -1, old_table_index;
+    int first_index = -1, last_index = -1;
+
+#ifdef DEBUG_ALLOC2
+    printf("update_refcount: offset=%lld size=%lld addend=%d\n",
+           offset, length, addend);
+#endif
+    if (length <= 0)
+        return -EINVAL;
+    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;
+
+        /* Only write refcount block to disk when we are done with it */
+        old_table_index = table_index;
+        table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+        if ((old_table_index >= 0) && (table_index != old_table_index)) {
+            size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
+            if (bdrv_pwrite(s->hd,
+                refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+                &s->refcount_block_cache[first_index], size) != size)
+            {
+                return -EIO;
+            }
+
+            first_index = -1;
+            last_index = -1;
+        }
+
+        /* Load the refcount block and allocate it if needed */
+        refcount_block_offset = alloc_refcount_block(bs, cluster_index);
+        if (refcount_block_offset < 0) {
+            return refcount_block_offset;
+        }
+
+        /* we can update the count and save it */
+        block_index = cluster_index &
+            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+        if (first_index == -1 || block_index < first_index) {
+            first_index = block_index;
+        }
+        if (block_index > last_index) {
+            last_index = block_index;
+        }
+
+        refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
+        refcount += addend;
+        if (refcount < 0 || refcount > 0xffff)
+            return -EINVAL;
+        if (refcount == 0 && cluster_index < s->free_cluster_index) {
+            s->free_cluster_index = cluster_index;
+        }
+        s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
+    }
+
+    /* Write last changed block to disk */
+    if (refcount_block_offset != 0) {
+        size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
+        if (bdrv_pwrite(s->hd,
+            refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+            &s->refcount_block_cache[first_index], size) != size)
+        {
+            return -EIO;
+        }
+    }
+
+    return 0;
+}
+
+/* addend must be 1 or -1 */
+static int update_cluster_refcount(BlockDriverState *bs,
+                                   int64_t cluster_index,
+                                   int addend)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret;
+
+    ret = update_refcount(bs, cluster_index << s->cluster_bits, 1, addend);
+    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;
+
+    nb_clusters = size_to_clusters(s, size);
+retry:
+    for(i = 0; i < nb_clusters; i++) {
+        int64_t i = s->free_cluster_index++;
+        if (get_refcount(bs, i) != 0)
+            goto retry;
+    }
+#ifdef DEBUG_ALLOC2
+    printf("alloc_clusters: size=%lld -> %lld\n",
+            size,
+            (s->free_cluster_index - nb_clusters) << s->cluster_bits);
+#endif
+    return (s->free_cluster_index - nb_clusters) << s->cluster_bits;
+}
+
+int64_t alloc_clusters(BlockDriverState *bs, int64_t size)
+{
+    int64_t offset;
+
+    offset = alloc_clusters_noref(bs, size);
+    update_refcount(bs, offset, size, 1);
+    return offset;
+}
+
+/* only used to allocate compressed sectors. We try to allocate
+   contiguous sectors. size must be <= cluster_size */
+int64_t alloc_bytes(BlockDriverState *bs, int size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t offset, cluster_offset;
+    int free_in_cluster;
+
+    assert(size > 0 && size <= s->cluster_size);
+    if (s->free_byte_offset == 0) {
+        s->free_byte_offset = alloc_clusters(bs, s->cluster_size);
+    }
+ 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);
+    } else {
+        offset = alloc_clusters(bs, s->cluster_size);
+        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);
+            s->free_byte_offset += size;
+        } else {
+            s->free_byte_offset = offset;
+            goto redo;
+        }
+    }
+    return offset;
+}
+
+void free_clusters(BlockDriverState *bs,
+                          int64_t offset, int64_t size)
+{
+    update_refcount(bs, offset, size, -1);
+}
+
+
+
+/*********************************************************/
+/* snapshots and image creation */
+
+
+
+void create_refcount_update(QCowCreateState *s, int64_t offset, int64_t size)
+{
+    int refcount;
+    int64_t start, last, cluster_offset;
+    uint16_t *p;
+
+    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) {
+        p = &s->refcount_block[cluster_offset >> s->cluster_bits];
+        refcount = be16_to_cpu(*p);
+        refcount++;
+        *p = cpu_to_be16(refcount);
+    }
+}
+
+/* update the refcounts of snapshots and the copied flag */
+int 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 l2_size, i, j, l1_modified, l2_modified, nb_csectors, refcount;
+
+    l2_cache_reset(bs);
+
+    l2_table = NULL;
+    l1_table = NULL;
+    l1_size2 = l1_size * sizeof(uint64_t);
+    l1_allocated = 0;
+    if (l1_table_offset != s->l1_table_offset) {
+        l1_table = qemu_malloc(l1_size2);
+        l1_allocated = 1;
+        if (bdrv_pread(s->hd, l1_table_offset,
+                       l1_table, l1_size2) != l1_size2)
+            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;
+    }
+
+    l2_size = s->l2_size * sizeof(uint64_t);
+    l2_table = qemu_malloc(l2_size);
+    l1_modified = 0;
+    for(i = 0; i < l1_size; i++) {
+        l2_offset = l1_table[i];
+        if (l2_offset) {
+            old_l2_offset = l2_offset;
+            l2_offset &= ~QCOW_OFLAG_COPIED;
+            l2_modified = 0;
+            if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
+                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)
+                            update_refcount(bs, (offset & s->cluster_offset_mask) & ~511,
+                                            nb_csectors * 512, addend);
+                        /* compressed clusters are never modified */
+                        refcount = 2;
+                    } else {
+                        if (addend != 0) {
+                            refcount = update_cluster_refcount(bs, offset >> s->cluster_bits, addend);
+                        } else {
+                            refcount = get_refcount(bs, offset >> s->cluster_bits);
+                        }
+                    }
+
+                    if (refcount == 1) {
+                        offset |= QCOW_OFLAG_COPIED;
+                    }
+                    if (offset != old_offset) {
+                        l2_table[j] = cpu_to_be64(offset);
+                        l2_modified = 1;
+                    }
+                }
+            }
+            if (l2_modified) {
+                if (bdrv_pwrite(s->hd,
+                                l2_offset, l2_table, l2_size) != l2_size)
+                    goto fail;
+            }
+
+            if (addend != 0) {
+                refcount = update_cluster_refcount(bs, l2_offset >> s->cluster_bits, addend);
+            } else {
+                refcount = get_refcount(bs, l2_offset >> s->cluster_bits);
+            }
+            if (refcount == 1) {
+                l2_offset |= QCOW_OFLAG_COPIED;
+            }
+            if (l2_offset != old_l2_offset) {
+                l1_table[i] = l2_offset;
+                l1_modified = 1;
+            }
+        }
+    }
+    if (l1_modified) {
+        for(i = 0; i < l1_size; i++)
+            cpu_to_be64s(&l1_table[i]);
+        if (bdrv_pwrite(s->hd, l1_table_offset, l1_table,
+                        l1_size2) != l1_size2)
+            goto fail;
+        for(i = 0; i < l1_size; i++)
+            be64_to_cpus(&l1_table[i]);
+    }
+    if (l1_allocated)
+        qemu_free(l1_table);
+    qemu_free(l2_table);
+    return 0;
+ fail:
+    if (l1_allocated)
+        qemu_free(l1_table);
+    qemu_free(l2_table);
+    return -EIO;
+}
+
+
+
+
+/*********************************************************/
+/* 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.
+ *
+ * Returns the number of errors in the image that were found
+ */
+static int inc_refcounts(BlockDriverState *bs,
+                          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;
+    int errors = 0;
+
+    if (size <= 0)
+        return 0;
+
+    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 || k >= refcount_table_size) {
+            fprintf(stderr, "ERROR: invalid cluster offset=0x%" PRIx64 "\n",
+                cluster_offset);
+            errors++;
+        } else {
+            if (++refcount_table[k] == 0) {
+                fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64
+                    "\n", cluster_offset);
+                errors++;
+            }
+        }
+    }
+
+    return errors;
+}
+
+/*
+ * 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,
+    uint16_t *refcount_table, int refcount_table_size, int64_t l2_offset,
+    int check_copied)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t *l2_table, offset;
+    int i, l2_size, nb_csectors, refcount;
+    int errors = 0;
+
+    /* Read L2 table from disk */
+    l2_size = s->l2_size * sizeof(uint64_t);
+    l2_table = qemu_malloc(l2_size);
+
+    if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
+        goto fail;
+
+    /* Do the actual checks */
+    for(i = 0; i < s->l2_size; i++) {
+        offset = be64_to_cpu(l2_table[i]);
+        if (offset != 0) {
+            if (offset & QCOW_OFLAG_COMPRESSED) {
+                /* Compressed clusters don't have QCOW_OFLAG_COPIED */
+                if (offset & QCOW_OFLAG_COPIED) {
+                    fprintf(stderr, "ERROR: cluster %" PRId64 ": "
+                        "copied flag must never be set for compressed "
+                        "clusters\n", offset >> s->cluster_bits);
+                    offset &= ~QCOW_OFLAG_COPIED;
+                    errors++;
+                }
+
+                /* Mark cluster as used */
+                nb_csectors = ((offset >> s->csize_shift) &
+                               s->csize_mask) + 1;
+                offset &= s->cluster_offset_mask;
+                errors += inc_refcounts(bs, refcount_table,
+                              refcount_table_size,
+                              offset & ~511, nb_csectors * 512);
+            } else {
+                /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
+                if (check_copied) {
+                    uint64_t entry = offset;
+                    offset &= ~QCOW_OFLAG_COPIED;
+                    refcount = get_refcount(bs, offset >> s->cluster_bits);
+                    if ((refcount == 1) != ((entry & QCOW_OFLAG_COPIED) != 0)) {
+                        fprintf(stderr, "ERROR OFLAG_COPIED: offset=%"
+                            PRIx64 " refcount=%d\n", entry, refcount);
+                        errors++;
+                    }
+                }
+
+                /* Mark cluster as used */
+                offset &= ~QCOW_OFLAG_COPIED;
+                errors += inc_refcounts(bs, 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);
+                    errors++;
+                }
+            }
+        }
+    }
+
+    qemu_free(l2_table);
+    return errors;
+
+fail:
+    fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
+    qemu_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,
+                              uint16_t *refcount_table,
+                              int refcount_table_size,
+                              int64_t l1_table_offset, int l1_size,
+                              int check_copied)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint64_t *l1_table, l2_offset, l1_size2;
+    int i, refcount, ret;
+    int errors = 0;
+
+    l1_size2 = l1_size * sizeof(uint64_t);
+
+    /* Mark L1 table as used */
+    errors += inc_refcounts(bs, refcount_table, refcount_table_size,
+                  l1_table_offset, l1_size2);
+
+    /* Read L1 table entries from disk */
+    l1_table = qemu_malloc(l1_size2);
+    if (bdrv_pread(s->hd, 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 (check_copied) {
+                refcount = get_refcount(bs, (l2_offset & ~QCOW_OFLAG_COPIED)
+                    >> s->cluster_bits);
+                if ((refcount == 1) != ((l2_offset & QCOW_OFLAG_COPIED) != 0)) {
+                    fprintf(stderr, "ERROR OFLAG_COPIED: l2_offset=%" PRIx64
+                        " refcount=%d\n", l2_offset, refcount);
+                    errors++;
+                }
+            }
+
+            /* Mark L2 table as used */
+            l2_offset &= ~QCOW_OFLAG_COPIED;
+            errors += inc_refcounts(bs, 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);
+                errors++;
+            }
+
+            /* Process and check L2 entries */
+            ret = check_refcounts_l2(bs, refcount_table, refcount_table_size,
+                l2_offset, check_copied);
+            if (ret < 0) {
+                goto fail;
+            }
+            errors += ret;
+        }
+    }
+    qemu_free(l1_table);
+    return errors;
+
+fail:
+    fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
+    qemu_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 occured.
+ */
+int check_refcounts(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    int64_t size;
+    int nb_clusters, refcount1, refcount2, i;
+    QCowSnapshot *sn;
+    uint16_t *refcount_table;
+    int ret, errors = 0;
+
+    size = bdrv_getlength(s->hd);
+    nb_clusters = size_to_clusters(s, size);
+    refcount_table = qemu_mallocz(nb_clusters * sizeof(uint16_t));
+
+    /* header */
+    errors += inc_refcounts(bs, refcount_table, nb_clusters,
+                  0, s->cluster_size);
+
+    /* current L1 table */
+    ret = check_refcounts_l1(bs, refcount_table, nb_clusters,
+                       s->l1_table_offset, s->l1_size, 1);
+    if (ret < 0) {
+        return ret;
+    }
+    errors += ret;
+
+    /* snapshots */
+    for(i = 0; i < s->nb_snapshots; i++) {
+        sn = s->snapshots + i;
+        check_refcounts_l1(bs, refcount_table, nb_clusters,
+                           sn->l1_table_offset, sn->l1_size, 0);
+    }
+    errors += inc_refcounts(bs, refcount_table, nb_clusters,
+                  s->snapshots_offset, s->snapshots_size);
+
+    /* refcount data */
+    errors += inc_refcounts(bs, refcount_table, nb_clusters,
+                  s->refcount_table_offset,
+                  s->refcount_table_size * sizeof(uint64_t));
+    for(i = 0; i < s->refcount_table_size; i++) {
+        int64_t offset;
+        offset = s->refcount_table[i];
+        if (offset != 0) {
+            errors += inc_refcounts(bs, refcount_table, nb_clusters,
+                          offset, s->cluster_size);
+        }
+    }
+
+    /* compare ref counts */
+    for(i = 0; i < nb_clusters; i++) {
+        refcount1 = get_refcount(bs, i);
+        refcount2 = refcount_table[i];
+        if (refcount1 != refcount2) {
+            fprintf(stderr, "ERROR cluster %d refcount=%d reference=%d\n",
+                   i, refcount1, refcount2);
+            errors++;
+        }
+    }
+
+    qemu_free(refcount_table);
+
+    return errors;
+}
+
diff --git a/block/qcow2.c b/block/qcow2.c
index d1611d1..f9ff44f 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -26,6 +26,7 @@
 #include "module.h"
 #include <zlib.h>
 #include "aes.h"
+#include "block/qcow2.h"
 
 /*
   Differences with QCOW:
@@ -47,40 +48,6 @@
 //#define DEBUG_ALLOC2
 //#define DEBUG_EXT
 
-#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
-#define QCOW_VERSION 2
-
-#define QCOW_CRYPT_NONE 0
-#define QCOW_CRYPT_AES  1
-
-#define QCOW_MAX_CRYPT_CLUSTERS 32
-
-/* indicate that the refcount of the referenced cluster is exactly one. */
-#define QCOW_OFLAG_COPIED     (1LL << 63)
-/* indicate that the cluster is compressed (they never have the copied flag) */
-#define QCOW_OFLAG_COMPRESSED (1LL << 62)
-
-#define REFCOUNT_SHIFT 1 /* refcount size is 2 bytes */
-
-#define MIN_CLUSTER_BITS 9
-#define MAX_CLUSTER_BITS 16
-
-typedef struct QCowHeader {
-    uint32_t magic;
-    uint32_t version;
-    uint64_t backing_file_offset;
-    uint32_t backing_file_size;
-    uint32_t cluster_bits;
-    uint64_t size; /* in bytes */
-    uint32_t crypt_method;
-    uint32_t l1_size; /* XXX: save number of clusters instead ? */
-    uint64_t l1_table_offset;
-    uint64_t refcount_table_offset;
-    uint32_t refcount_table_clusters;
-    uint32_t nb_snapshots;
-    uint64_t snapshots_offset;
-} QCowHeader;
-
 
 typedef struct {
     uint32_t magic;
@@ -110,77 +77,12 @@ typedef struct __attribute__((packed)) QCowSnapshotHeader {
     /* name follows  */
 } QCowSnapshotHeader;
 
-#define L2_CACHE_SIZE 16
-
-typedef struct QCowSnapshot {
-    uint64_t l1_table_offset;
-    uint32_t l1_size;
-    char *id_str;
-    char *name;
-    uint32_t vm_state_size;
-    uint32_t date_sec;
-    uint32_t date_nsec;
-    uint64_t vm_clock_nsec;
-} QCowSnapshot;
-
-typedef struct BDRVQcowState {
-    BlockDriverState *hd;
-    int cluster_bits;
-    int cluster_size;
-    int cluster_sectors;
-    int l2_bits;
-    int l2_size;
-    int l1_size;
-    int l1_vm_state_index;
-    int csize_shift;
-    int csize_mask;
-    uint64_t cluster_offset_mask;
-    uint64_t l1_table_offset;
-    uint64_t *l1_table;
-    uint64_t *l2_cache;
-    uint64_t l2_cache_offsets[L2_CACHE_SIZE];
-    uint32_t l2_cache_counts[L2_CACHE_SIZE];
-    uint8_t *cluster_cache;
-    uint8_t *cluster_data;
-    uint64_t cluster_cache_offset;
-
-    uint64_t *refcount_table;
-    uint64_t refcount_table_offset;
-    uint32_t refcount_table_size;
-    uint64_t refcount_block_cache_offset;
-    uint16_t *refcount_block_cache;
-    int64_t free_cluster_index;
-    int64_t free_byte_offset;
-
-    uint32_t crypt_method; /* current crypt method, 0 if no key yet */
-    uint32_t crypt_method_header;
-    AES_KEY aes_encrypt_key;
-    AES_KEY aes_decrypt_key;
-    uint64_t snapshots_offset;
-    int snapshots_size;
-    int nb_snapshots;
-    QCowSnapshot *snapshots;
-} BDRVQcowState;
 
 static int decompress_cluster(BDRVQcowState *s, uint64_t cluster_offset);
 static int qcow_read(BlockDriverState *bs, int64_t sector_num,
                      uint8_t *buf, int nb_sectors);
 static int qcow_read_snapshots(BlockDriverState *bs);
 static void qcow_free_snapshots(BlockDriverState *bs);
-static int refcount_init(BlockDriverState *bs);
-static void refcount_close(BlockDriverState *bs);
-static int get_refcount(BlockDriverState *bs, int64_t cluster_index);
-static int update_cluster_refcount(BlockDriverState *bs,
-                                   int64_t cluster_index,
-                                   int addend);
-static int update_refcount(BlockDriverState *bs,
-                            int64_t offset, int64_t length,
-                            int addend);
-static int64_t alloc_clusters(BlockDriverState *bs, int64_t size);
-static int64_t alloc_bytes(BlockDriverState *bs, int size);
-static void free_clusters(BlockDriverState *bs,
-                          int64_t offset, int64_t size);
-static int check_refcounts(BlockDriverState *bs);
 
 static int qcow_probe(const uint8_t *buf, int buf_size, const char *filename)
 {
@@ -482,7 +384,7 @@ static int copy_sectors(BlockDriverState *bs, uint64_t start_sect,
     return 0;
 }
 
-static void l2_cache_reset(BlockDriverState *bs)
+void l2_cache_reset(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
 
@@ -691,11 +593,6 @@ static uint64_t *l2_allocate(BlockDriverState *bs, int l1_index)
     return l2_table;
 }
 
-static int size_to_clusters(BDRVQcowState *s, int64_t size)
-{
-    return (size + (s->cluster_size - 1)) >> s->cluster_bits;
-}
-
 static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,
         uint64_t *l2_table, uint64_t start, uint64_t mask)
 {
@@ -1522,35 +1419,6 @@ static void qcow_close(BlockDriverState *bs)
     bdrv_delete(s->hd);
 }
 
-/* XXX: use std qcow open function ? */
-typedef struct QCowCreateState {
-    int cluster_size;
-    int cluster_bits;
-    uint16_t *refcount_block;
-    uint64_t *refcount_table;
-    int64_t l1_table_offset;
-    int64_t refcount_table_offset;
-    int64_t refcount_block_offset;
-} QCowCreateState;
-
-static void create_refcount_update(QCowCreateState *s,
-                                   int64_t offset, int64_t size)
-{
-    int refcount;
-    int64_t start, last, cluster_offset;
-    uint16_t *p;
-
-    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) {
-        p = &s->refcount_block[cluster_offset >> s->cluster_bits];
-        refcount = be16_to_cpu(*p);
-        refcount++;
-        *p = cpu_to_be16(refcount);
-    }
-}
-
 static int get_bits_from_size(size_t size)
 {
     int res = 0;
@@ -1834,117 +1702,6 @@ static int qcow_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
 /*********************************************************/
 /* snapshot support */
 
-/* update the refcounts of snapshots and the copied flag */
-static int 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 l2_size, i, j, l1_modified, l2_modified, nb_csectors, refcount;
-
-    l2_cache_reset(bs);
-
-    l2_table = NULL;
-    l1_table = NULL;
-    l1_size2 = l1_size * sizeof(uint64_t);
-    l1_allocated = 0;
-    if (l1_table_offset != s->l1_table_offset) {
-        l1_table = qemu_malloc(l1_size2);
-        l1_allocated = 1;
-        if (bdrv_pread(s->hd, l1_table_offset,
-                       l1_table, l1_size2) != l1_size2)
-            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;
-    }
-
-    l2_size = s->l2_size * sizeof(uint64_t);
-    l2_table = qemu_malloc(l2_size);
-    l1_modified = 0;
-    for(i = 0; i < l1_size; i++) {
-        l2_offset = l1_table[i];
-        if (l2_offset) {
-            old_l2_offset = l2_offset;
-            l2_offset &= ~QCOW_OFLAG_COPIED;
-            l2_modified = 0;
-            if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
-                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)
-                            update_refcount(bs, (offset & s->cluster_offset_mask) & ~511,
-                                            nb_csectors * 512, addend);
-                        /* compressed clusters are never modified */
-                        refcount = 2;
-                    } else {
-                        if (addend != 0) {
-                            refcount = update_cluster_refcount(bs, offset >> s->cluster_bits, addend);
-                        } else {
-                            refcount = get_refcount(bs, offset >> s->cluster_bits);
-                        }
-                    }
-
-                    if (refcount == 1) {
-                        offset |= QCOW_OFLAG_COPIED;
-                    }
-                    if (offset != old_offset) {
-                        l2_table[j] = cpu_to_be64(offset);
-                        l2_modified = 1;
-                    }
-                }
-            }
-            if (l2_modified) {
-                if (bdrv_pwrite(s->hd,
-                                l2_offset, l2_table, l2_size) != l2_size)
-                    goto fail;
-            }
-
-            if (addend != 0) {
-                refcount = update_cluster_refcount(bs, l2_offset >> s->cluster_bits, addend);
-            } else {
-                refcount = get_refcount(bs, l2_offset >> s->cluster_bits);
-            }
-            if (refcount == 1) {
-                l2_offset |= QCOW_OFLAG_COPIED;
-            }
-            if (l2_offset != old_l2_offset) {
-                l1_table[i] = l2_offset;
-                l1_modified = 1;
-            }
-        }
-    }
-    if (l1_modified) {
-        for(i = 0; i < l1_size; i++)
-            cpu_to_be64s(&l1_table[i]);
-        if (bdrv_pwrite(s->hd, l1_table_offset, l1_table,
-                        l1_size2) != l1_size2)
-            goto fail;
-        for(i = 0; i < l1_size; i++)
-            be64_to_cpus(&l1_table[i]);
-    }
-    if (l1_allocated)
-        qemu_free(l1_table);
-    qemu_free(l2_table);
-    return 0;
- fail:
-    if (l1_allocated)
-        qemu_free(l1_table);
-    qemu_free(l2_table);
-    return -EIO;
-}
 
 static void qcow_free_snapshots(BlockDriverState *bs)
 {
@@ -2306,630 +2063,6 @@ static int qcow_snapshot_list(BlockDriverState *bs,
     return s->nb_snapshots;
 }
 
-/*********************************************************/
-/* refcount handling */
-
-static int refcount_init(BlockDriverState *bs)
-{
-    BDRVQcowState *s = bs->opaque;
-    int ret, refcount_table_size2, i;
-
-    s->refcount_block_cache = qemu_malloc(s->cluster_size);
-    refcount_table_size2 = s->refcount_table_size * sizeof(uint64_t);
-    s->refcount_table = qemu_malloc(refcount_table_size2);
-    if (s->refcount_table_size > 0) {
-        ret = bdrv_pread(s->hd, 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;
-}
-
-static void refcount_close(BlockDriverState *bs)
-{
-    BDRVQcowState *s = bs->opaque;
-    qemu_free(s->refcount_block_cache);
-    qemu_free(s->refcount_table);
-}
-
-
-static int load_refcount_block(BlockDriverState *bs,
-                               int64_t refcount_block_offset)
-{
-    BDRVQcowState *s = bs->opaque;
-    int ret;
-    ret = bdrv_pread(s->hd, refcount_block_offset, s->refcount_block_cache,
-                     s->cluster_size);
-    if (ret != s->cluster_size)
-        return -EIO;
-    s->refcount_block_cache_offset = refcount_block_offset;
-    return 0;
-}
-
-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;
-
-    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;
-    if (refcount_block_offset != s->refcount_block_cache_offset) {
-        /* better than nothing: return allocated if read error */
-        if (load_refcount_block(bs, refcount_block_offset) < 0)
-            return 1;
-    }
-    block_index = cluster_index &
-        ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
-    return be16_to_cpu(s->refcount_block_cache[block_index]);
-}
-
-/* return < 0 if error */
-static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size)
-{
-    BDRVQcowState *s = bs->opaque;
-    int i, nb_clusters;
-
-    nb_clusters = size_to_clusters(s, size);
-retry:
-    for(i = 0; i < nb_clusters; i++) {
-        int64_t i = s->free_cluster_index++;
-        if (get_refcount(bs, i) != 0)
-            goto retry;
-    }
-#ifdef DEBUG_ALLOC2
-    printf("alloc_clusters: size=%lld -> %lld\n",
-            size,
-            (s->free_cluster_index - nb_clusters) << s->cluster_bits);
-#endif
-    return (s->free_cluster_index - nb_clusters) << s->cluster_bits;
-}
-
-static int64_t alloc_clusters(BlockDriverState *bs, int64_t size)
-{
-    int64_t offset;
-
-    offset = alloc_clusters_noref(bs, size);
-    update_refcount(bs, offset, size, 1);
-    return offset;
-}
-
-/* only used to allocate compressed sectors. We try to allocate
-   contiguous sectors. size must be <= cluster_size */
-static int64_t alloc_bytes(BlockDriverState *bs, int size)
-{
-    BDRVQcowState *s = bs->opaque;
-    int64_t offset, cluster_offset;
-    int free_in_cluster;
-
-    assert(size > 0 && size <= s->cluster_size);
-    if (s->free_byte_offset == 0) {
-        s->free_byte_offset = alloc_clusters(bs, s->cluster_size);
-    }
- 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);
-    } else {
-        offset = alloc_clusters(bs, s->cluster_size);
-        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);
-            s->free_byte_offset += size;
-        } else {
-            s->free_byte_offset = offset;
-            goto redo;
-        }
-    }
-    return offset;
-}
-
-static void free_clusters(BlockDriverState *bs,
-                          int64_t offset, int64_t size)
-{
-    update_refcount(bs, offset, size, -1);
-}
-
-static int grow_refcount_table(BlockDriverState *bs, int min_size)
-{
-    BDRVQcowState *s = bs->opaque;
-    int new_table_size, new_table_size2, refcount_table_clusters, i, ret;
-    uint64_t *new_table;
-    int64_t table_offset;
-    uint8_t data[12];
-    int old_table_size;
-    int64_t old_table_offset;
-
-    if (min_size <= s->refcount_table_size)
-        return 0;
-    /* compute new table size */
-    refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
-    for(;;) {
-        if (refcount_table_clusters == 0) {
-            refcount_table_clusters = 1;
-        } else {
-            refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
-        }
-        new_table_size = refcount_table_clusters << (s->cluster_bits - 3);
-        if (min_size <= new_table_size)
-            break;
-    }
-#ifdef DEBUG_ALLOC2
-    printf("grow_refcount_table from %d to %d\n",
-           s->refcount_table_size,
-           new_table_size);
-#endif
-    new_table_size2 = new_table_size * sizeof(uint64_t);
-    new_table = qemu_mallocz(new_table_size2);
-    memcpy(new_table, s->refcount_table,
-           s->refcount_table_size * sizeof(uint64_t));
-    for(i = 0; i < s->refcount_table_size; i++)
-        cpu_to_be64s(&new_table[i]);
-    /* Note: we cannot update the refcount now to avoid recursion */
-    table_offset = alloc_clusters_noref(bs, new_table_size2);
-    ret = bdrv_pwrite(s->hd, table_offset, new_table, new_table_size2);
-    if (ret != new_table_size2)
-        goto fail;
-    for(i = 0; i < s->refcount_table_size; i++)
-        be64_to_cpus(&new_table[i]);
-
-    cpu_to_be64w((uint64_t*)data, table_offset);
-    cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters);
-    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
-                    data, sizeof(data)) != sizeof(data))
-        goto fail;
-    qemu_free(s->refcount_table);
-    old_table_offset = s->refcount_table_offset;
-    old_table_size = s->refcount_table_size;
-    s->refcount_table = new_table;
-    s->refcount_table_size = new_table_size;
-    s->refcount_table_offset = table_offset;
-
-    update_refcount(bs, table_offset, new_table_size2, 1);
-    free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t));
-    return 0;
- fail:
-    free_clusters(bs, table_offset, new_table_size2);
-    qemu_free(new_table);
-    return -EIO;
-}
-
-
-static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index)
-{
-    BDRVQcowState *s = bs->opaque;
-    int64_t offset, refcount_block_offset;
-    int ret, refcount_table_index;
-    uint64_t data64;
-
-    /* Find L1 index and grow refcount table if needed */
-    refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
-    if (refcount_table_index >= s->refcount_table_size) {
-        ret = grow_refcount_table(bs, refcount_table_index + 1);
-        if (ret < 0)
-            return ret;
-    }
-
-    /* Load or allocate the refcount block */
-    refcount_block_offset = s->refcount_table[refcount_table_index];
-    if (!refcount_block_offset) {
-        /* create a new refcount block */
-        /* Note: we cannot update the refcount now to avoid recursion */
-        offset = alloc_clusters_noref(bs, s->cluster_size);
-        memset(s->refcount_block_cache, 0, s->cluster_size);
-        ret = bdrv_pwrite(s->hd, offset, s->refcount_block_cache, s->cluster_size);
-        if (ret != s->cluster_size)
-            return -EINVAL;
-        s->refcount_table[refcount_table_index] = offset;
-        data64 = cpu_to_be64(offset);
-        ret = bdrv_pwrite(s->hd, s->refcount_table_offset +
-                          refcount_table_index * sizeof(uint64_t),
-                          &data64, sizeof(data64));
-        if (ret != sizeof(data64))
-            return -EINVAL;
-
-        refcount_block_offset = offset;
-        s->refcount_block_cache_offset = offset;
-        update_refcount(bs, offset, s->cluster_size, 1);
-    } else {
-        if (refcount_block_offset != s->refcount_block_cache_offset) {
-            if (load_refcount_block(bs, refcount_block_offset) < 0)
-                return -EIO;
-        }
-    }
-
-    return refcount_block_offset;
-}
-
-/* addend must be 1 or -1 */
-static int update_cluster_refcount(BlockDriverState *bs,
-                                   int64_t cluster_index,
-                                   int addend)
-{
-    BDRVQcowState *s = bs->opaque;
-    int ret;
-
-    ret = update_refcount(bs, cluster_index << s->cluster_bits, 1, addend);
-    if (ret < 0) {
-        return ret;
-    }
-
-    return get_refcount(bs, cluster_index);
-}
-
-/* XXX: cache several refcount block clusters ? */
-static int update_refcount(BlockDriverState *bs,
-                            int64_t offset, int64_t length,
-                            int addend)
-{
-    BDRVQcowState *s = bs->opaque;
-    int64_t start, last, cluster_offset;
-    int64_t refcount_block_offset = 0;
-    int64_t table_index = -1, old_table_index;
-    int first_index = -1, last_index = -1;
-
-#ifdef DEBUG_ALLOC2
-    printf("update_refcount: offset=%lld size=%lld addend=%d\n",
-           offset, length, addend);
-#endif
-    if (length <= 0)
-        return -EINVAL;
-    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;
-
-        /* Only write refcount block to disk when we are done with it */
-        old_table_index = table_index;
-        table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
-        if ((old_table_index >= 0) && (table_index != old_table_index)) {
-            size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
-            if (bdrv_pwrite(s->hd,
-                refcount_block_offset + (first_index << REFCOUNT_SHIFT),
-                &s->refcount_block_cache[first_index], size) != size)
-            {
-                return -EIO;
-            }
-
-            first_index = -1;
-            last_index = -1;
-        }
-
-        /* Load the refcount block and allocate it if needed */
-        refcount_block_offset = alloc_refcount_block(bs, cluster_index);
-        if (refcount_block_offset < 0) {
-            return refcount_block_offset;
-        }
-
-        /* we can update the count and save it */
-        block_index = cluster_index &
-            ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
-        if (first_index == -1 || block_index < first_index) {
-            first_index = block_index;
-        }
-        if (block_index > last_index) {
-            last_index = block_index;
-        }
-
-        refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
-        refcount += addend;
-        if (refcount < 0 || refcount > 0xffff)
-            return -EINVAL;
-        if (refcount == 0 && cluster_index < s->free_cluster_index) {
-            s->free_cluster_index = cluster_index;
-        }
-        s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
-    }
-
-    /* Write last changed block to disk */
-    if (refcount_block_offset != 0) {
-        size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
-        if (bdrv_pwrite(s->hd,
-            refcount_block_offset + (first_index << REFCOUNT_SHIFT),
-            &s->refcount_block_cache[first_index], size) != size)
-        {
-            return -EIO;
-        }
-    }
-
-    return 0;
-}
-
-/*
- * 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.
- *
- * Returns the number of errors in the image that were found
- */
-static int inc_refcounts(BlockDriverState *bs,
-                          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;
-    int errors = 0;
-
-    if (size <= 0)
-        return 0;
-
-    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 || k >= refcount_table_size) {
-            fprintf(stderr, "ERROR: invalid cluster offset=0x%" PRIx64 "\n",
-                cluster_offset);
-            errors++;
-        } else {
-            if (++refcount_table[k] == 0) {
-                fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64
-                    "\n", cluster_offset);
-                errors++;
-            }
-        }
-    }
-
-    return errors;
-}
-
-/*
- * 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,
-    uint16_t *refcount_table, int refcount_table_size, int64_t l2_offset,
-    int check_copied)
-{
-    BDRVQcowState *s = bs->opaque;
-    uint64_t *l2_table, offset;
-    int i, l2_size, nb_csectors, refcount;
-    int errors = 0;
-
-    /* Read L2 table from disk */
-    l2_size = s->l2_size * sizeof(uint64_t);
-    l2_table = qemu_malloc(l2_size);
-
-    if (bdrv_pread(s->hd, l2_offset, l2_table, l2_size) != l2_size)
-        goto fail;
-
-    /* Do the actual checks */
-    for(i = 0; i < s->l2_size; i++) {
-        offset = be64_to_cpu(l2_table[i]);
-        if (offset != 0) {
-            if (offset & QCOW_OFLAG_COMPRESSED) {
-                /* Compressed clusters don't have QCOW_OFLAG_COPIED */
-                if (offset & QCOW_OFLAG_COPIED) {
-                    fprintf(stderr, "ERROR: cluster %" PRId64 ": "
-                        "copied flag must never be set for compressed "
-                        "clusters\n", offset >> s->cluster_bits);
-                    offset &= ~QCOW_OFLAG_COPIED;
-                    errors++;
-                }
-
-                /* Mark cluster as used */
-                nb_csectors = ((offset >> s->csize_shift) &
-                               s->csize_mask) + 1;
-                offset &= s->cluster_offset_mask;
-                errors += inc_refcounts(bs, refcount_table,
-                              refcount_table_size,
-                              offset & ~511, nb_csectors * 512);
-            } else {
-                /* QCOW_OFLAG_COPIED must be set iff refcount == 1 */
-                if (check_copied) {
-                    uint64_t entry = offset;
-                    offset &= ~QCOW_OFLAG_COPIED;
-                    refcount = get_refcount(bs, offset >> s->cluster_bits);
-                    if ((refcount == 1) != ((entry & QCOW_OFLAG_COPIED) != 0)) {
-                        fprintf(stderr, "ERROR OFLAG_COPIED: offset=%"
-                            PRIx64 " refcount=%d\n", entry, refcount);
-                        errors++;
-                    }
-                }
-
-                /* Mark cluster as used */
-                offset &= ~QCOW_OFLAG_COPIED;
-                errors += inc_refcounts(bs, 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);
-                    errors++;
-                }
-            }
-        }
-    }
-
-    qemu_free(l2_table);
-    return errors;
-
-fail:
-    fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
-    qemu_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,
-                              uint16_t *refcount_table,
-                              int refcount_table_size,
-                              int64_t l1_table_offset, int l1_size,
-                              int check_copied)
-{
-    BDRVQcowState *s = bs->opaque;
-    uint64_t *l1_table, l2_offset, l1_size2;
-    int i, refcount, ret;
-    int errors = 0;
-
-    l1_size2 = l1_size * sizeof(uint64_t);
-
-    /* Mark L1 table as used */
-    errors += inc_refcounts(bs, refcount_table, refcount_table_size,
-                  l1_table_offset, l1_size2);
-
-    /* Read L1 table entries from disk */
-    l1_table = qemu_malloc(l1_size2);
-    if (bdrv_pread(s->hd, 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 (check_copied) {
-                refcount = get_refcount(bs, (l2_offset & ~QCOW_OFLAG_COPIED)
-                    >> s->cluster_bits);
-                if ((refcount == 1) != ((l2_offset & QCOW_OFLAG_COPIED) != 0)) {
-                    fprintf(stderr, "ERROR OFLAG_COPIED: l2_offset=%" PRIx64
-                        " refcount=%d\n", l2_offset, refcount);
-                    errors++;
-                }
-            }
-
-            /* Mark L2 table as used */
-            l2_offset &= ~QCOW_OFLAG_COPIED;
-            errors += inc_refcounts(bs, 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);
-                errors++;
-            }
-
-            /* Process and check L2 entries */
-            ret = check_refcounts_l2(bs, refcount_table, refcount_table_size,
-                l2_offset, check_copied);
-            if (ret < 0) {
-                goto fail;
-            }
-            errors += ret;
-        }
-    }
-    qemu_free(l1_table);
-    return errors;
-
-fail:
-    fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
-    qemu_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 occured.
- */
-static int check_refcounts(BlockDriverState *bs)
-{
-    BDRVQcowState *s = bs->opaque;
-    int64_t size;
-    int nb_clusters, refcount1, refcount2, i;
-    QCowSnapshot *sn;
-    uint16_t *refcount_table;
-    int ret, errors = 0;
-
-    size = bdrv_getlength(s->hd);
-    nb_clusters = size_to_clusters(s, size);
-    refcount_table = qemu_mallocz(nb_clusters * sizeof(uint16_t));
-
-    /* header */
-    errors += inc_refcounts(bs, refcount_table, nb_clusters,
-                  0, s->cluster_size);
-
-    /* current L1 table */
-    ret = check_refcounts_l1(bs, refcount_table, nb_clusters,
-                       s->l1_table_offset, s->l1_size, 1);
-    if (ret < 0) {
-        return ret;
-    }
-    errors += ret;
-
-    /* snapshots */
-    for(i = 0; i < s->nb_snapshots; i++) {
-        sn = s->snapshots + i;
-        check_refcounts_l1(bs, refcount_table, nb_clusters,
-                           sn->l1_table_offset, sn->l1_size, 0);
-    }
-    errors += inc_refcounts(bs, refcount_table, nb_clusters,
-                  s->snapshots_offset, s->snapshots_size);
-
-    /* refcount data */
-    errors += inc_refcounts(bs, refcount_table, nb_clusters,
-                  s->refcount_table_offset,
-                  s->refcount_table_size * sizeof(uint64_t));
-    for(i = 0; i < s->refcount_table_size; i++) {
-        int64_t offset;
-        offset = s->refcount_table[i];
-        if (offset != 0) {
-            errors += inc_refcounts(bs, refcount_table, nb_clusters,
-                          offset, s->cluster_size);
-        }
-    }
-
-    /* compare ref counts */
-    for(i = 0; i < nb_clusters; i++) {
-        refcount1 = get_refcount(bs, i);
-        refcount2 = refcount_table[i];
-        if (refcount1 != refcount2) {
-            fprintf(stderr, "ERROR cluster %d refcount=%d reference=%d\n",
-                   i, refcount1, refcount2);
-            errors++;
-        }
-    }
-
-    qemu_free(refcount_table);
-
-    return errors;
-}
-
 static int qcow_check(BlockDriverState *bs)
 {
     return check_refcounts(bs);
diff --git a/block/qcow2.h b/block/qcow2.h
new file mode 100644
index 0000000..3a34212
--- /dev/null
+++ b/block/qcow2.h
@@ -0,0 +1,154 @@
+/*
+ * 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.
+ */
+
+#ifndef BLOCK_QCOW2_H
+#define BLOCK_QCOW2_H
+
+#include "aes.h"
+
+#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
+#define QCOW_VERSION 2
+
+#define QCOW_CRYPT_NONE 0
+#define QCOW_CRYPT_AES  1
+
+#define QCOW_MAX_CRYPT_CLUSTERS 32
+
+/* indicate that the refcount of the referenced cluster is exactly one. */
+#define QCOW_OFLAG_COPIED     (1LL << 63)
+/* indicate that the cluster is compressed (they never have the copied flag) */
+#define QCOW_OFLAG_COMPRESSED (1LL << 62)
+
+#define REFCOUNT_SHIFT 1 /* refcount size is 2 bytes */
+
+#define MIN_CLUSTER_BITS 9
+#define MAX_CLUSTER_BITS 16
+
+#define L2_CACHE_SIZE 16
+
+typedef struct QCowHeader {
+    uint32_t magic;
+    uint32_t version;
+    uint64_t backing_file_offset;
+    uint32_t backing_file_size;
+    uint32_t cluster_bits;
+    uint64_t size; /* in bytes */
+    uint32_t crypt_method;
+    uint32_t l1_size; /* XXX: save number of clusters instead ? */
+    uint64_t l1_table_offset;
+    uint64_t refcount_table_offset;
+    uint32_t refcount_table_clusters;
+    uint32_t nb_snapshots;
+    uint64_t snapshots_offset;
+} QCowHeader;
+
+typedef struct QCowSnapshot {
+    uint64_t l1_table_offset;
+    uint32_t l1_size;
+    char *id_str;
+    char *name;
+    uint32_t vm_state_size;
+    uint32_t date_sec;
+    uint32_t date_nsec;
+    uint64_t vm_clock_nsec;
+} QCowSnapshot;
+
+typedef struct BDRVQcowState {
+    BlockDriverState *hd;
+    int cluster_bits;
+    int cluster_size;
+    int cluster_sectors;
+    int l2_bits;
+    int l2_size;
+    int l1_size;
+    int l1_vm_state_index;
+    int csize_shift;
+    int csize_mask;
+    uint64_t cluster_offset_mask;
+    uint64_t l1_table_offset;
+    uint64_t *l1_table;
+    uint64_t *l2_cache;
+    uint64_t l2_cache_offsets[L2_CACHE_SIZE];
+    uint32_t l2_cache_counts[L2_CACHE_SIZE];
+    uint8_t *cluster_cache;
+    uint8_t *cluster_data;
+    uint64_t cluster_cache_offset;
+
+    uint64_t *refcount_table;
+    uint64_t refcount_table_offset;
+    uint32_t refcount_table_size;
+    uint64_t refcount_block_cache_offset;
+    uint16_t *refcount_block_cache;
+    int64_t free_cluster_index;
+    int64_t free_byte_offset;
+
+    uint32_t crypt_method; /* current crypt method, 0 if no key yet */
+    uint32_t crypt_method_header;
+    AES_KEY aes_encrypt_key;
+    AES_KEY aes_decrypt_key;
+    uint64_t snapshots_offset;
+    int snapshots_size;
+    int nb_snapshots;
+    QCowSnapshot *snapshots;
+} BDRVQcowState;
+
+/* XXX: use std qcow open function ? */
+typedef struct QCowCreateState {
+    int cluster_size;
+    int cluster_bits;
+    uint16_t *refcount_block;
+    uint64_t *refcount_table;
+    int64_t l1_table_offset;
+    int64_t refcount_table_offset;
+    int64_t refcount_block_offset;
+} QCowCreateState;
+
+static int size_to_clusters(BDRVQcowState *s, int64_t size)
+{
+    return (size + (s->cluster_size - 1)) >> s->cluster_bits;
+}
+
+// FIXME Need qcow2_ prefix to global functions
+
+/* qcow2.c functions */
+void l2_cache_reset(BlockDriverState *bs);
+
+/* qcow2-refcount.c functions */
+int refcount_init(BlockDriverState *bs);
+void refcount_close(BlockDriverState *bs);
+
+int64_t alloc_clusters(BlockDriverState *bs, int64_t size);
+int64_t alloc_bytes(BlockDriverState *bs, int size);
+void free_clusters(BlockDriverState *bs,
+                          int64_t offset, int64_t size);
+
+void create_refcount_update(QCowCreateState *s, int64_t offset, int64_t size);
+int update_snapshot_refcount(BlockDriverState *bs,
+                             int64_t l1_table_offset,
+                             int l1_size,
+                             int addend);
+
+int check_refcounts(BlockDriverState *bs);
+
+#endif
-- 
1.6.0.6