qcow2: Split out guest cluster functions

qcow2-cluster.c contains all functions related to the management of guest
clusters, i.e. what the guest sees on its virtual disk. This code is about
mapping these guest clusters to host clusters in the image file using the
two-level lookup tables.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 754 insertions, 0 deletions

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
new file mode 100644
index 0000000..494cc91
--- /dev/null
+++ b/block/qcow2-cluster.c
@@ -0,0 +1,754 @@
+/*
+ * 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 <zlib.h>
+
+#include "qemu-common.h"
+#include "block_int.h"
+#include "block/qcow2.h"
+
+int grow_l1_table(BlockDriverState *bs, int min_size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int new_l1_size, new_l1_size2, ret, i;
+    uint64_t *new_l1_table;
+    uint64_t new_l1_table_offset;
+    uint8_t data[12];
+
+    new_l1_size = s->l1_size;
+    if (min_size <= new_l1_size)
+        return 0;
+    while (min_size > new_l1_size) {
+        new_l1_size = (new_l1_size * 3 + 1) / 2;
+    }
+#ifdef DEBUG_ALLOC2
+    printf("grow l1_table from %d to %d\n", s->l1_size, new_l1_size);
+#endif
+
+    new_l1_size2 = sizeof(uint64_t) * new_l1_size;
+    new_l1_table = qemu_mallocz(new_l1_size2);
+    memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
+
+    /* write new table (align to cluster) */
+    new_l1_table_offset = alloc_clusters(bs, new_l1_size2);
+
+    for(i = 0; i < s->l1_size; i++)
+        new_l1_table[i] = cpu_to_be64(new_l1_table[i]);
+    ret = bdrv_pwrite(s->hd, new_l1_table_offset, new_l1_table, new_l1_size2);
+    if (ret != new_l1_size2)
+        goto fail;
+    for(i = 0; i < s->l1_size; i++)
+        new_l1_table[i] = be64_to_cpu(new_l1_table[i]);
+
+    /* set new table */
+    cpu_to_be32w((uint32_t*)data, new_l1_size);
+    cpu_to_be64w((uint64_t*)(data + 4), new_l1_table_offset);
+    if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_size), data,
+                sizeof(data)) != sizeof(data))
+        goto fail;
+    qemu_free(s->l1_table);
+    free_clusters(bs, s->l1_table_offset, s->l1_size * sizeof(uint64_t));
+    s->l1_table_offset = new_l1_table_offset;
+    s->l1_table = new_l1_table;
+    s->l1_size = new_l1_size;
+    return 0;
+ fail:
+    qemu_free(s->l1_table);
+    return -EIO;
+}
+
+void l2_cache_reset(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+
+    memset(s->l2_cache, 0, s->l2_size * L2_CACHE_SIZE * sizeof(uint64_t));
+    memset(s->l2_cache_offsets, 0, L2_CACHE_SIZE * sizeof(uint64_t));
+    memset(s->l2_cache_counts, 0, L2_CACHE_SIZE * sizeof(uint32_t));
+}
+
+static inline int l2_cache_new_entry(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint32_t min_count;
+    int min_index, i;
+
+    /* find a new entry in the least used one */
+    min_index = 0;
+    min_count = 0xffffffff;
+    for(i = 0; i < L2_CACHE_SIZE; i++) {
+        if (s->l2_cache_counts[i] < min_count) {
+            min_count = s->l2_cache_counts[i];
+            min_index = i;
+        }
+    }
+    return min_index;
+}
+
+/*
+ * seek_l2_table
+ *
+ * seek l2_offset in the l2_cache table
+ * if not found, return NULL,
+ * if found,
+ *   increments the l2 cache hit count of the entry,
+ *   if counter overflow, divide by two all counters
+ *   return the pointer to the l2 cache entry
+ *
+ */
+
+static uint64_t *seek_l2_table(BDRVQcowState *s, uint64_t l2_offset)
+{
+    int i, j;
+
+    for(i = 0; i < L2_CACHE_SIZE; i++) {
+        if (l2_offset == s->l2_cache_offsets[i]) {
+            /* increment the hit count */
+            if (++s->l2_cache_counts[i] == 0xffffffff) {
+                for(j = 0; j < L2_CACHE_SIZE; j++) {
+                    s->l2_cache_counts[j] >>= 1;
+                }
+            }
+            return s->l2_cache + (i << s->l2_bits);
+        }
+    }
+    return NULL;
+}
+
+/*
+ * l2_load
+ *
+ * Loads a L2 table into memory. If the table is in the cache, the cache
+ * is used; otherwise the L2 table is loaded from the image file.
+ *
+ * Returns a pointer to the L2 table on success, or NULL if the read from
+ * the image file failed.
+ */
+
+static uint64_t *l2_load(BlockDriverState *bs, uint64_t l2_offset)
+{
+    BDRVQcowState *s = bs->opaque;
+    int min_index;
+    uint64_t *l2_table;
+
+    /* seek if the table for the given offset is in the cache */
+
+    l2_table = seek_l2_table(s, l2_offset);
+    if (l2_table != NULL)
+        return l2_table;
+
+    /* not found: load a new entry in the least used one */
+
+    min_index = l2_cache_new_entry(bs);
+    l2_table = s->l2_cache + (min_index << s->l2_bits);
+    if (bdrv_pread(s->hd, l2_offset, l2_table, s->l2_size * sizeof(uint64_t)) !=
+        s->l2_size * sizeof(uint64_t))
+        return NULL;
+    s->l2_cache_offsets[min_index] = l2_offset;
+    s->l2_cache_counts[min_index] = 1;
+
+    return l2_table;
+}
+
+/*
+ * l2_allocate
+ *
+ * Allocate a new l2 entry in the file. If l1_index points to an already
+ * used entry in the L2 table (i.e. we are doing a copy on write for the L2
+ * table) copy the contents of the old L2 table into the newly allocated one.
+ * Otherwise the new table is initialized with zeros.
+ *
+ */
+
+static uint64_t *l2_allocate(BlockDriverState *bs, int l1_index)
+{
+    BDRVQcowState *s = bs->opaque;
+    int min_index;
+    uint64_t old_l2_offset, tmp;
+    uint64_t *l2_table, l2_offset;
+
+    old_l2_offset = s->l1_table[l1_index];
+
+    /* allocate a new l2 entry */
+
+    l2_offset = alloc_clusters(bs, s->l2_size * sizeof(uint64_t));
+
+    /* update the L1 entry */
+
+    s->l1_table[l1_index] = l2_offset | QCOW_OFLAG_COPIED;
+
+    tmp = cpu_to_be64(l2_offset | QCOW_OFLAG_COPIED);
+    if (bdrv_pwrite(s->hd, s->l1_table_offset + l1_index * sizeof(tmp),
+                    &tmp, sizeof(tmp)) != sizeof(tmp))
+        return NULL;
+
+    /* allocate a new entry in the l2 cache */
+
+    min_index = l2_cache_new_entry(bs);
+    l2_table = s->l2_cache + (min_index << s->l2_bits);
+
+    if (old_l2_offset == 0) {
+        /* if there was no old l2 table, clear the new table */
+        memset(l2_table, 0, s->l2_size * sizeof(uint64_t));
+    } else {
+        /* if there was an old l2 table, read it from the disk */
+        if (bdrv_pread(s->hd, old_l2_offset,
+                       l2_table, s->l2_size * sizeof(uint64_t)) !=
+            s->l2_size * sizeof(uint64_t))
+            return NULL;
+    }
+    /* write the l2 table to the file */
+    if (bdrv_pwrite(s->hd, l2_offset,
+                    l2_table, s->l2_size * sizeof(uint64_t)) !=
+        s->l2_size * sizeof(uint64_t))
+        return NULL;
+
+    /* update the l2 cache entry */
+
+    s->l2_cache_offsets[min_index] = l2_offset;
+    s->l2_cache_counts[min_index] = 1;
+
+    return l2_table;
+}
+
+static int count_contiguous_clusters(uint64_t nb_clusters, int cluster_size,
+        uint64_t *l2_table, uint64_t start, uint64_t mask)
+{
+    int i;
+    uint64_t offset = be64_to_cpu(l2_table[0]) & ~mask;
+
+    if (!offset)
+        return 0;
+
+    for (i = start; i < start + nb_clusters; i++)
+        if (offset + i * cluster_size != (be64_to_cpu(l2_table[i]) & ~mask))
+            break;
+
+	return (i - start);
+}
+
+static int count_contiguous_free_clusters(uint64_t nb_clusters, uint64_t *l2_table)
+{
+    int i = 0;
+
+    while(nb_clusters-- && l2_table[i] == 0)
+        i++;
+
+    return i;
+}
+
+/* The crypt function is compatible with the linux cryptoloop
+   algorithm for < 4 GB images. NOTE: out_buf == in_buf is
+   supported */
+void encrypt_sectors(BDRVQcowState *s, int64_t sector_num,
+                     uint8_t *out_buf, const uint8_t *in_buf,
+                     int nb_sectors, int enc,
+                     const AES_KEY *key)
+{
+    union {
+        uint64_t ll[2];
+        uint8_t b[16];
+    } ivec;
+    int i;
+
+    for(i = 0; i < nb_sectors; i++) {
+        ivec.ll[0] = cpu_to_le64(sector_num);
+        ivec.ll[1] = 0;
+        AES_cbc_encrypt(in_buf, out_buf, 512, key,
+                        ivec.b, enc);
+        sector_num++;
+        in_buf += 512;
+        out_buf += 512;
+    }
+}
+
+
+static int qcow_read(BlockDriverState *bs, int64_t sector_num,
+                     uint8_t *buf, int nb_sectors)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret, index_in_cluster, n, n1;
+    uint64_t cluster_offset;
+
+    while (nb_sectors > 0) {
+        n = nb_sectors;
+        cluster_offset = get_cluster_offset(bs, sector_num << 9, &n);
+        index_in_cluster = sector_num & (s->cluster_sectors - 1);
+        if (!cluster_offset) {
+            if (bs->backing_hd) {
+                /* read from the base image */
+                n1 = backing_read1(bs->backing_hd, sector_num, buf, n);
+                if (n1 > 0) {
+                    ret = bdrv_read(bs->backing_hd, sector_num, buf, n1);
+                    if (ret < 0)
+                        return -1;
+                }
+            } else {
+                memset(buf, 0, 512 * n);
+            }
+        } else if (cluster_offset & QCOW_OFLAG_COMPRESSED) {
+            if (decompress_cluster(s, cluster_offset) < 0)
+                return -1;
+            memcpy(buf, s->cluster_cache + index_in_cluster * 512, 512 * n);
+        } else {
+            ret = bdrv_pread(s->hd, cluster_offset + index_in_cluster * 512, buf, n * 512);
+            if (ret != n * 512)
+                return -1;
+            if (s->crypt_method) {
+                encrypt_sectors(s, sector_num, buf, buf, n, 0,
+                                &s->aes_decrypt_key);
+            }
+        }
+        nb_sectors -= n;
+        sector_num += n;
+        buf += n * 512;
+    }
+    return 0;
+}
+
+static int copy_sectors(BlockDriverState *bs, uint64_t start_sect,
+                        uint64_t cluster_offset, int n_start, int n_end)
+{
+    BDRVQcowState *s = bs->opaque;
+    int n, ret;
+
+    n = n_end - n_start;
+    if (n <= 0)
+        return 0;
+    ret = qcow_read(bs, start_sect + n_start, s->cluster_data, n);
+    if (ret < 0)
+        return ret;
+    if (s->crypt_method) {
+        encrypt_sectors(s, start_sect + n_start,
+                        s->cluster_data,
+                        s->cluster_data, n, 1,
+                        &s->aes_encrypt_key);
+    }
+    ret = bdrv_write(s->hd, (cluster_offset >> 9) + n_start,
+                     s->cluster_data, n);
+    if (ret < 0)
+        return ret;
+    return 0;
+}
+
+
+/*
+ * get_cluster_offset
+ *
+ * For a given offset of the disk image, return cluster offset in
+ * qcow2 file.
+ *
+ * on entry, *num is the number of contiguous clusters we'd like to
+ * access following offset.
+ *
+ * on exit, *num is the number of contiguous clusters we can read.
+ *
+ * Return 1, if the offset is found
+ * Return 0, otherwise.
+ *
+ */
+
+uint64_t get_cluster_offset(BlockDriverState *bs, uint64_t offset, int *num)
+{
+    BDRVQcowState *s = bs->opaque;
+    int l1_index, l2_index;
+    uint64_t l2_offset, *l2_table, cluster_offset;
+    int l1_bits, c;
+    int index_in_cluster, nb_available, nb_needed, nb_clusters;
+
+    index_in_cluster = (offset >> 9) & (s->cluster_sectors - 1);
+    nb_needed = *num + index_in_cluster;
+
+    l1_bits = s->l2_bits + s->cluster_bits;
+
+    /* compute how many bytes there are between the offset and
+     * the end of the l1 entry
+     */
+
+    nb_available = (1 << l1_bits) - (offset & ((1 << l1_bits) - 1));
+
+    /* compute the number of available sectors */
+
+    nb_available = (nb_available >> 9) + index_in_cluster;
+
+    if (nb_needed > nb_available) {
+        nb_needed = nb_available;
+    }
+
+    cluster_offset = 0;
+
+    /* seek the the l2 offset in the l1 table */
+
+    l1_index = offset >> l1_bits;
+    if (l1_index >= s->l1_size)
+        goto out;
+
+    l2_offset = s->l1_table[l1_index];
+
+    /* seek the l2 table of the given l2 offset */
+
+    if (!l2_offset)
+        goto out;
+
+    /* load the l2 table in memory */
+
+    l2_offset &= ~QCOW_OFLAG_COPIED;
+    l2_table = l2_load(bs, l2_offset);
+    if (l2_table == NULL)
+        return 0;
+
+    /* find the cluster offset for the given disk offset */
+
+    l2_index = (offset >> s->cluster_bits) & (s->l2_size - 1);
+    cluster_offset = be64_to_cpu(l2_table[l2_index]);
+    nb_clusters = size_to_clusters(s, nb_needed << 9);
+
+    if (!cluster_offset) {
+        /* how many empty clusters ? */
+        c = count_contiguous_free_clusters(nb_clusters, &l2_table[l2_index]);
+    } else {
+        /* how many allocated clusters ? */
+        c = count_contiguous_clusters(nb_clusters, s->cluster_size,
+                &l2_table[l2_index], 0, QCOW_OFLAG_COPIED);
+    }
+
+   nb_available = (c * s->cluster_sectors);
+out:
+    if (nb_available > nb_needed)
+        nb_available = nb_needed;
+
+    *num = nb_available - index_in_cluster;
+
+    return cluster_offset & ~QCOW_OFLAG_COPIED;
+}
+
+/*
+ * get_cluster_table
+ *
+ * for a given disk offset, load (and allocate if needed)
+ * the l2 table.
+ *
+ * the l2 table offset in the qcow2 file and the cluster index
+ * in the l2 table are given to the caller.
+ *
+ */
+
+static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
+                             uint64_t **new_l2_table,
+                             uint64_t *new_l2_offset,
+                             int *new_l2_index)
+{
+    BDRVQcowState *s = bs->opaque;
+    int l1_index, l2_index, ret;
+    uint64_t l2_offset, *l2_table;
+
+    /* seek the the l2 offset in the l1 table */
+
+    l1_index = offset >> (s->l2_bits + s->cluster_bits);
+    if (l1_index >= s->l1_size) {
+        ret = grow_l1_table(bs, l1_index + 1);
+        if (ret < 0)
+            return 0;
+    }
+    l2_offset = s->l1_table[l1_index];
+
+    /* seek the l2 table of the given l2 offset */
+
+    if (l2_offset & QCOW_OFLAG_COPIED) {
+        /* load the l2 table in memory */
+        l2_offset &= ~QCOW_OFLAG_COPIED;
+        l2_table = l2_load(bs, l2_offset);
+        if (l2_table == NULL)
+            return 0;
+    } else {
+        if (l2_offset)
+            free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t));
+        l2_table = l2_allocate(bs, l1_index);
+        if (l2_table == NULL)
+            return 0;
+        l2_offset = s->l1_table[l1_index] & ~QCOW_OFLAG_COPIED;
+    }
+
+    /* find the cluster offset for the given disk offset */
+
+    l2_index = (offset >> s->cluster_bits) & (s->l2_size - 1);
+
+    *new_l2_table = l2_table;
+    *new_l2_offset = l2_offset;
+    *new_l2_index = l2_index;
+
+    return 1;
+}
+
+/*
+ * alloc_compressed_cluster_offset
+ *
+ * For a given offset of the disk image, return cluster offset in
+ * qcow2 file.
+ *
+ * If the offset is not found, allocate a new compressed cluster.
+ *
+ * Return the cluster offset if successful,
+ * Return 0, otherwise.
+ *
+ */
+
+uint64_t alloc_compressed_cluster_offset(BlockDriverState *bs,
+                                         uint64_t offset,
+                                         int compressed_size)
+{
+    BDRVQcowState *s = bs->opaque;
+    int l2_index, ret;
+    uint64_t l2_offset, *l2_table, cluster_offset;
+    int nb_csectors;
+
+    ret = get_cluster_table(bs, offset, &l2_table, &l2_offset, &l2_index);
+    if (ret == 0)
+        return 0;
+
+    cluster_offset = be64_to_cpu(l2_table[l2_index]);
+    if (cluster_offset & QCOW_OFLAG_COPIED)
+        return cluster_offset & ~QCOW_OFLAG_COPIED;
+
+    if (cluster_offset)
+        free_any_clusters(bs, cluster_offset, 1);
+
+    cluster_offset = alloc_bytes(bs, compressed_size);
+    nb_csectors = ((cluster_offset + compressed_size - 1) >> 9) -
+                  (cluster_offset >> 9);
+
+    cluster_offset |= QCOW_OFLAG_COMPRESSED |
+                      ((uint64_t)nb_csectors << s->csize_shift);
+
+    /* update L2 table */
+
+    /* compressed clusters never have the copied flag */
+
+    l2_table[l2_index] = cpu_to_be64(cluster_offset);
+    if (bdrv_pwrite(s->hd,
+                    l2_offset + l2_index * sizeof(uint64_t),
+                    l2_table + l2_index,
+                    sizeof(uint64_t)) != sizeof(uint64_t))
+        return 0;
+
+    return cluster_offset;
+}
+
+int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset,
+    QCowL2Meta *m)
+{
+    BDRVQcowState *s = bs->opaque;
+    int i, j = 0, l2_index, ret;
+    uint64_t *old_cluster, start_sect, l2_offset, *l2_table;
+
+    if (m->nb_clusters == 0)
+        return 0;
+
+    old_cluster = qemu_malloc(m->nb_clusters * sizeof(uint64_t));
+
+    /* copy content of unmodified sectors */
+    start_sect = (m->offset & ~(s->cluster_size - 1)) >> 9;
+    if (m->n_start) {
+        ret = copy_sectors(bs, start_sect, cluster_offset, 0, m->n_start);
+        if (ret < 0)
+            goto err;
+    }
+
+    if (m->nb_available & (s->cluster_sectors - 1)) {
+        uint64_t end = m->nb_available & ~(uint64_t)(s->cluster_sectors - 1);
+        ret = copy_sectors(bs, start_sect + end, cluster_offset + (end << 9),
+                m->nb_available - end, s->cluster_sectors);
+        if (ret < 0)
+            goto err;
+    }
+
+    ret = -EIO;
+    /* update L2 table */
+    if (!get_cluster_table(bs, m->offset, &l2_table, &l2_offset, &l2_index))
+        goto err;
+
+    for (i = 0; i < m->nb_clusters; i++) {
+        /* if two concurrent writes happen to the same unallocated cluster
+	 * each write allocates separate cluster and writes data concurrently.
+	 * The first one to complete updates l2 table with pointer to its
+	 * cluster the second one has to do RMW (which is done above by
+	 * copy_sectors()), update l2 table with its cluster pointer and free
+	 * old cluster. This is what this loop does */
+        if(l2_table[l2_index + i] != 0)
+            old_cluster[j++] = l2_table[l2_index + i];
+
+        l2_table[l2_index + i] = cpu_to_be64((cluster_offset +
+                    (i << s->cluster_bits)) | QCOW_OFLAG_COPIED);
+     }
+
+    if (bdrv_pwrite(s->hd, l2_offset + l2_index * sizeof(uint64_t),
+                l2_table + l2_index, m->nb_clusters * sizeof(uint64_t)) !=
+            m->nb_clusters * sizeof(uint64_t))
+        goto err;
+
+    for (i = 0; i < j; i++)
+        free_any_clusters(bs, be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED,
+                          1);
+
+    ret = 0;
+err:
+    qemu_free(old_cluster);
+    return ret;
+ }
+
+/*
+ * alloc_cluster_offset
+ *
+ * For a given offset of the disk image, return cluster offset in
+ * qcow2 file.
+ *
+ * If the offset is not found, allocate a new cluster.
+ *
+ * Return the cluster offset if successful,
+ * Return 0, otherwise.
+ *
+ */
+
+uint64_t alloc_cluster_offset(BlockDriverState *bs,
+                              uint64_t offset,
+                              int n_start, int n_end,
+                              int *num, QCowL2Meta *m)
+{
+    BDRVQcowState *s = bs->opaque;
+    int l2_index, ret;
+    uint64_t l2_offset, *l2_table, cluster_offset;
+    int nb_clusters, i = 0;
+
+    ret = get_cluster_table(bs, offset, &l2_table, &l2_offset, &l2_index);
+    if (ret == 0)
+        return 0;
+
+    nb_clusters = size_to_clusters(s, n_end << 9);
+
+    nb_clusters = MIN(nb_clusters, s->l2_size - l2_index);
+
+    cluster_offset = be64_to_cpu(l2_table[l2_index]);
+
+    /* We keep all QCOW_OFLAG_COPIED clusters */
+
+    if (cluster_offset & QCOW_OFLAG_COPIED) {
+        nb_clusters = count_contiguous_clusters(nb_clusters, s->cluster_size,
+                &l2_table[l2_index], 0, 0);
+
+        cluster_offset &= ~QCOW_OFLAG_COPIED;
+        m->nb_clusters = 0;
+
+        goto out;
+    }
+
+    /* for the moment, multiple compressed clusters are not managed */
+
+    if (cluster_offset & QCOW_OFLAG_COMPRESSED)
+        nb_clusters = 1;
+
+    /* how many available clusters ? */
+
+    while (i < nb_clusters) {
+        i += count_contiguous_clusters(nb_clusters - i, s->cluster_size,
+                &l2_table[l2_index], i, 0);
+
+        if(be64_to_cpu(l2_table[l2_index + i]))
+            break;
+
+        i += count_contiguous_free_clusters(nb_clusters - i,
+                &l2_table[l2_index + i]);
+
+        cluster_offset = be64_to_cpu(l2_table[l2_index + i]);
+
+        if ((cluster_offset & QCOW_OFLAG_COPIED) ||
+                (cluster_offset & QCOW_OFLAG_COMPRESSED))
+            break;
+    }
+    nb_clusters = i;
+
+    /* allocate a new cluster */
+
+    cluster_offset = alloc_clusters(bs, nb_clusters * s->cluster_size);
+
+    /* save info needed for meta data update */
+    m->offset = offset;
+    m->n_start = n_start;
+    m->nb_clusters = nb_clusters;
+
+out:
+    m->nb_available = MIN(nb_clusters << (s->cluster_bits - 9), n_end);
+
+    *num = m->nb_available - n_start;
+
+    return cluster_offset;
+}
+
+static int decompress_buffer(uint8_t *out_buf, int out_buf_size,
+                             const uint8_t *buf, int buf_size)
+{
+    z_stream strm1, *strm = &strm1;
+    int ret, out_len;
+
+    memset(strm, 0, sizeof(*strm));
+
+    strm->next_in = (uint8_t *)buf;
+    strm->avail_in = buf_size;
+    strm->next_out = out_buf;
+    strm->avail_out = out_buf_size;
+
+    ret = inflateInit2(strm, -12);
+    if (ret != Z_OK)
+        return -1;
+    ret = inflate(strm, Z_FINISH);
+    out_len = strm->next_out - out_buf;
+    if ((ret != Z_STREAM_END && ret != Z_BUF_ERROR) ||
+        out_len != out_buf_size) {
+        inflateEnd(strm);
+        return -1;
+    }
+    inflateEnd(strm);
+    return 0;
+}
+
+int decompress_cluster(BDRVQcowState *s, uint64_t cluster_offset)
+{
+    int ret, csize, nb_csectors, sector_offset;
+    uint64_t coffset;
+
+    coffset = cluster_offset & s->cluster_offset_mask;
+    if (s->cluster_cache_offset != coffset) {
+        nb_csectors = ((cluster_offset >> s->csize_shift) & s->csize_mask) + 1;
+        sector_offset = coffset & 511;
+        csize = nb_csectors * 512 - sector_offset;
+        ret = bdrv_read(s->hd, coffset >> 9, s->cluster_data, nb_csectors);
+        if (ret < 0) {
+            return -1;
+        }
+        if (decompress_buffer(s->cluster_cache, s->cluster_size,
+                              s->cluster_data + sector_offset, csize) < 0) {
+            return -1;
+        }
+        s->cluster_cache_offset = coffset;
+    }
+    return 0;
+}