diff --git a/block-qcow.c b/block-qcow.c
new file mode 100644
index 0000000..ed6359f
--- /dev/null
+++ b/block-qcow.c
@@ -0,0 +1,677 @@
+/*
+ * Block driver for the QCOW format
+ * 
+ * Copyright (c) 2004 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 "vl.h"
+#include "block_int.h"
+#include "zlib.h"
+#include "aes.h"
+
+/**************************************************************/
+/* QEMU COW block driver with compression and encryption support */
+
+#define QCOW_MAGIC (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
+#define QCOW_VERSION 1
+
+#define QCOW_CRYPT_NONE 0
+#define QCOW_CRYPT_AES  1
+
+#define QCOW_OFLAG_COMPRESSED (1LL << 63)
+
+typedef struct QCowHeader {
+    uint32_t magic;
+    uint32_t version;
+    uint64_t backing_file_offset;
+    uint32_t backing_file_size;
+    uint32_t mtime;
+    uint64_t size; /* in bytes */
+    uint8_t cluster_bits;
+    uint8_t l2_bits;
+    uint32_t crypt_method;
+    uint64_t l1_table_offset;
+} QCowHeader;
+
+#define L2_CACHE_SIZE 16
+
+typedef struct BDRVQcowState {
+    int fd;
+    int cluster_bits;
+    int cluster_size;
+    int cluster_sectors;
+    int l2_bits;
+    int l2_size;
+    int l1_size;
+    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;
+    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;
+} BDRVQcowState;
+
+static int decompress_cluster(BDRVQcowState *s, uint64_t cluster_offset);
+
+static int qcow_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    const QCowHeader *cow_header = (const void *)buf;
+
+    if (be32_to_cpu(cow_header->magic) == QCOW_MAGIC &&
+        be32_to_cpu(cow_header->version) == QCOW_VERSION) 
+        return 100;
+    else
+        return 0;
+}
+
+static int qcow_open(BlockDriverState *bs, const char *filename)
+{
+    BDRVQcowState *s = bs->opaque;
+    int fd, len, i, shift;
+    QCowHeader header;
+    
+    fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+    if (fd < 0) {
+        fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
+        if (fd < 0)
+            return -1;
+    }
+    s->fd = fd;
+    if (read(fd, &header, sizeof(header)) != sizeof(header))
+        goto fail;
+    be32_to_cpus(&header.magic);
+    be32_to_cpus(&header.version);
+    be64_to_cpus(&header.backing_file_offset);
+    be32_to_cpus(&header.backing_file_size);
+    be32_to_cpus(&header.mtime);
+    be64_to_cpus(&header.size);
+    be32_to_cpus(&header.crypt_method);
+    be64_to_cpus(&header.l1_table_offset);
+    
+    if (header.magic != QCOW_MAGIC || header.version != QCOW_VERSION)
+        goto fail;
+    if (header.size <= 1 || header.cluster_bits < 9)
+        goto fail;
+    if (header.crypt_method > QCOW_CRYPT_AES)
+        goto fail;
+    s->crypt_method_header = header.crypt_method;
+    if (s->crypt_method_header)
+        bs->encrypted = 1;
+    s->cluster_bits = header.cluster_bits;
+    s->cluster_size = 1 << s->cluster_bits;
+    s->cluster_sectors = 1 << (s->cluster_bits - 9);
+    s->l2_bits = header.l2_bits;
+    s->l2_size = 1 << s->l2_bits;
+    bs->total_sectors = header.size / 512;
+    s->cluster_offset_mask = (1LL << (63 - s->cluster_bits)) - 1;
+
+    /* read the level 1 table */
+    shift = s->cluster_bits + s->l2_bits;
+    s->l1_size = (header.size + (1LL << shift) - 1) >> shift;
+
+    s->l1_table_offset = header.l1_table_offset;
+    s->l1_table = qemu_malloc(s->l1_size * sizeof(uint64_t));
+    if (!s->l1_table)
+        goto fail;
+    lseek64(fd, s->l1_table_offset, SEEK_SET);
+    if (read(fd, s->l1_table, s->l1_size * sizeof(uint64_t)) != 
+        s->l1_size * sizeof(uint64_t))
+        goto fail;
+    for(i = 0;i < s->l1_size; i++) {
+        be64_to_cpus(&s->l1_table[i]);
+    }
+    /* alloc L2 cache */
+    s->l2_cache = qemu_malloc(s->l2_size * L2_CACHE_SIZE * sizeof(uint64_t));
+    if (!s->l2_cache)
+        goto fail;
+    s->cluster_cache = qemu_malloc(s->cluster_size);
+    if (!s->cluster_cache)
+        goto fail;
+    s->cluster_data = qemu_malloc(s->cluster_size);
+    if (!s->cluster_data)
+        goto fail;
+    s->cluster_cache_offset = -1;
+    
+    /* read the backing file name */
+    if (header.backing_file_offset != 0) {
+        len = header.backing_file_size;
+        if (len > 1023)
+            len = 1023;
+        lseek64(fd, header.backing_file_offset, SEEK_SET);
+        if (read(fd, bs->backing_file, len) != len)
+            goto fail;
+        bs->backing_file[len] = '\0';
+    }
+    return 0;
+
+ fail:
+    qemu_free(s->l1_table);
+    qemu_free(s->l2_cache);
+    qemu_free(s->cluster_cache);
+    qemu_free(s->cluster_data);
+    close(fd);
+    return -1;
+}
+
+static int qcow_set_key(BlockDriverState *bs, const char *key)
+{
+    BDRVQcowState *s = bs->opaque;
+    uint8_t keybuf[16];
+    int len, i;
+    
+    memset(keybuf, 0, 16);
+    len = strlen(key);
+    if (len > 16)
+        len = 16;
+    /* XXX: we could compress the chars to 7 bits to increase
+       entropy */
+    for(i = 0;i < len;i++) {
+        keybuf[i] = key[i];
+    }
+    s->crypt_method = s->crypt_method_header;
+
+    if (AES_set_encrypt_key(keybuf, 128, &s->aes_encrypt_key) != 0)
+        return -1;
+    if (AES_set_decrypt_key(keybuf, 128, &s->aes_decrypt_key) != 0)
+        return -1;
+#if 0
+    /* test */
+    {
+        uint8_t in[16];
+        uint8_t out[16];
+        uint8_t tmp[16];
+        for(i=0;i<16;i++)
+            in[i] = i;
+        AES_encrypt(in, tmp, &s->aes_encrypt_key);
+        AES_decrypt(tmp, out, &s->aes_decrypt_key);
+        for(i = 0; i < 16; i++)
+            printf(" %02x", tmp[i]);
+        printf("\n");
+        for(i = 0; i < 16; i++)
+            printf(" %02x", out[i]);
+        printf("\n");
+    }
+#endif
+    return 0;
+}
+
+/* The crypt function is compatible with the linux cryptoloop
+   algorithm for < 4 GB images. NOTE: out_buf == in_buf is
+   supported */
+static 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;
+    }
+}
+
+/* 'allocate' is:
+ *
+ * 0 to not allocate.
+ *
+ * 1 to allocate a normal cluster (for sector indexes 'n_start' to
+ * 'n_end')
+ *
+ * 2 to allocate a compressed cluster of size
+ * 'compressed_size'. 'compressed_size' must be > 0 and <
+ * cluster_size 
+ *
+ * return 0 if not allocated.
+ */
+static uint64_t get_cluster_offset(BlockDriverState *bs,
+                                   uint64_t offset, int allocate,
+                                   int compressed_size,
+                                   int n_start, int n_end)
+{
+    BDRVQcowState *s = bs->opaque;
+    int min_index, i, j, l1_index, l2_index;
+    uint64_t l2_offset, *l2_table, cluster_offset, tmp;
+    uint32_t min_count;
+    int new_l2_table;
+    
+    l1_index = offset >> (s->l2_bits + s->cluster_bits);
+    l2_offset = s->l1_table[l1_index];
+    new_l2_table = 0;
+    if (!l2_offset) {
+        if (!allocate)
+            return 0;
+        /* allocate a new l2 entry */
+        l2_offset = lseek64(s->fd, 0, SEEK_END);
+        /* round to cluster size */
+        l2_offset = (l2_offset + s->cluster_size - 1) & ~(s->cluster_size - 1);
+        /* update the L1 entry */
+        s->l1_table[l1_index] = l2_offset;
+        tmp = cpu_to_be64(l2_offset);
+        lseek64(s->fd, s->l1_table_offset + l1_index * sizeof(tmp), SEEK_SET);
+        if (write(s->fd, &tmp, sizeof(tmp)) != sizeof(tmp))
+            return 0;
+        new_l2_table = 1;
+    }
+    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;
+                }
+            }
+            l2_table = s->l2_cache + (i << s->l2_bits);
+            goto found;
+        }
+    }
+    /* not found: load 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;
+        }
+    }
+    l2_table = s->l2_cache + (min_index << s->l2_bits);
+    lseek(s->fd, l2_offset, SEEK_SET);
+    if (new_l2_table) {
+        memset(l2_table, 0, s->l2_size * sizeof(uint64_t));
+        if (write(s->fd, l2_table, s->l2_size * sizeof(uint64_t)) !=
+            s->l2_size * sizeof(uint64_t))
+            return 0;
+    } else {
+        if (read(s->fd, l2_table, s->l2_size * sizeof(uint64_t)) != 
+            s->l2_size * sizeof(uint64_t))
+            return 0;
+    }
+    s->l2_cache_offsets[min_index] = l2_offset;
+    s->l2_cache_counts[min_index] = 1;
+ found:
+    l2_index = (offset >> s->cluster_bits) & (s->l2_size - 1);
+    cluster_offset = be64_to_cpu(l2_table[l2_index]);
+    if (!cluster_offset || 
+        ((cluster_offset & QCOW_OFLAG_COMPRESSED) && allocate == 1)) {
+        if (!allocate)
+            return 0;
+        /* allocate a new cluster */
+        if ((cluster_offset & QCOW_OFLAG_COMPRESSED) &&
+            (n_end - n_start) < s->cluster_sectors) {
+            /* if the cluster is already compressed, we must
+               decompress it in the case it is not completely
+               overwritten */
+            if (decompress_cluster(s, cluster_offset) < 0)
+                return 0;
+            cluster_offset = lseek64(s->fd, 0, SEEK_END);
+            cluster_offset = (cluster_offset + s->cluster_size - 1) & 
+                ~(s->cluster_size - 1);
+            /* write the cluster content */
+            lseek64(s->fd, cluster_offset, SEEK_SET);
+            if (write(s->fd, s->cluster_cache, s->cluster_size) != 
+                s->cluster_size)
+                return -1;
+        } else {
+            cluster_offset = lseek64(s->fd, 0, SEEK_END);
+            if (allocate == 1) {
+                /* round to cluster size */
+                cluster_offset = (cluster_offset + s->cluster_size - 1) & 
+                    ~(s->cluster_size - 1);
+                ftruncate(s->fd, cluster_offset + s->cluster_size);
+                /* if encrypted, we must initialize the cluster
+                   content which won't be written */
+                if (s->crypt_method && 
+                    (n_end - n_start) < s->cluster_sectors) {
+                    uint64_t start_sect;
+                    start_sect = (offset & ~(s->cluster_size - 1)) >> 9;
+                    memset(s->cluster_data + 512, 0xaa, 512);
+                    for(i = 0; i < s->cluster_sectors; i++) {
+                        if (i < n_start || i >= n_end) {
+                            encrypt_sectors(s, start_sect + i, 
+                                            s->cluster_data, 
+                                            s->cluster_data + 512, 1, 1,
+                                            &s->aes_encrypt_key);
+                            lseek64(s->fd, cluster_offset + i * 512, SEEK_SET);
+                            if (write(s->fd, s->cluster_data, 512) != 512)
+                                return -1;
+                        }
+                    }
+                }
+            } else {
+                cluster_offset |= QCOW_OFLAG_COMPRESSED | 
+                    (uint64_t)compressed_size << (63 - s->cluster_bits);
+            }
+        }
+        /* update L2 table */
+        tmp = cpu_to_be64(cluster_offset);
+        l2_table[l2_index] = tmp;
+        lseek64(s->fd, l2_offset + l2_index * sizeof(tmp), SEEK_SET);
+        if (write(s->fd, &tmp, sizeof(tmp)) != sizeof(tmp))
+            return 0;
+    }
+    return cluster_offset;
+}
+
+static int qcow_is_allocated(BlockDriverState *bs, int64_t sector_num, 
+                             int nb_sectors, int *pnum)
+{
+    BDRVQcowState *s = bs->opaque;
+    int index_in_cluster, n;
+    uint64_t cluster_offset;
+
+    cluster_offset = get_cluster_offset(bs, sector_num << 9, 0, 0, 0, 0);
+    index_in_cluster = sector_num & (s->cluster_sectors - 1);
+    n = s->cluster_sectors - index_in_cluster;
+    if (n > nb_sectors)
+        n = nb_sectors;
+    *pnum = n;
+    return (cluster_offset != 0);
+}
+
+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;
+}
+                              
+static int decompress_cluster(BDRVQcowState *s, uint64_t cluster_offset)
+{
+    int ret, csize;
+    uint64_t coffset;
+
+    coffset = cluster_offset & s->cluster_offset_mask;
+    if (s->cluster_cache_offset != coffset) {
+        csize = cluster_offset >> (63 - s->cluster_bits);
+        csize &= (s->cluster_size - 1);
+        lseek64(s->fd, coffset, SEEK_SET);
+        ret = read(s->fd, s->cluster_data, csize);
+        if (ret != csize) 
+            return -1;
+        if (decompress_buffer(s->cluster_cache, s->cluster_size,
+                              s->cluster_data, csize) < 0) {
+            return -1;
+        }
+        s->cluster_cache_offset = coffset;
+    }
+    return 0;
+}
+
+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;
+    uint64_t cluster_offset;
+    
+    while (nb_sectors > 0) {
+        cluster_offset = get_cluster_offset(bs, sector_num << 9, 0, 0, 0, 0);
+        index_in_cluster = sector_num & (s->cluster_sectors - 1);
+        n = s->cluster_sectors - index_in_cluster;
+        if (n > nb_sectors)
+            n = nb_sectors;
+        if (!cluster_offset) {
+            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 {
+            lseek64(s->fd, cluster_offset + index_in_cluster * 512, SEEK_SET);
+            ret = read(s->fd, 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 qcow_write(BlockDriverState *bs, int64_t sector_num, 
+                     const uint8_t *buf, int nb_sectors)
+{
+    BDRVQcowState *s = bs->opaque;
+    int ret, index_in_cluster, n;
+    uint64_t cluster_offset;
+    
+    while (nb_sectors > 0) {
+        index_in_cluster = sector_num & (s->cluster_sectors - 1);
+        n = s->cluster_sectors - index_in_cluster;
+        if (n > nb_sectors)
+            n = nb_sectors;
+        cluster_offset = get_cluster_offset(bs, sector_num << 9, 1, 0, 
+                                            index_in_cluster, 
+                                            index_in_cluster + n);
+        if (!cluster_offset)
+            return -1;
+        lseek64(s->fd, cluster_offset + index_in_cluster * 512, SEEK_SET);
+        if (s->crypt_method) {
+            encrypt_sectors(s, sector_num, s->cluster_data, buf, n, 1,
+                            &s->aes_encrypt_key);
+            ret = write(s->fd, s->cluster_data, n * 512);
+        } else {
+            ret = write(s->fd, buf, n * 512);
+        }
+        if (ret != n * 512) 
+            return -1;
+        nb_sectors -= n;
+        sector_num += n;
+        buf += n * 512;
+    }
+    s->cluster_cache_offset = -1; /* disable compressed cache */
+    return 0;
+}
+
+static int qcow_close(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    qemu_free(s->l1_table);
+    qemu_free(s->l2_cache);
+    qemu_free(s->cluster_cache);
+    qemu_free(s->cluster_data);
+    close(s->fd);
+}
+
+static int qcow_create(const char *filename, int64_t total_size,
+                      const char *backing_file, int flags)
+{
+    int fd, header_size, backing_filename_len, l1_size, i, shift;
+    QCowHeader header;
+    char backing_filename[1024];
+    uint64_t tmp;
+    struct stat st;
+
+    fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY | O_LARGEFILE, 
+              0644);
+    if (fd < 0)
+        return -1;
+    memset(&header, 0, sizeof(header));
+    header.magic = cpu_to_be32(QCOW_MAGIC);
+    header.version = cpu_to_be32(QCOW_VERSION);
+    header.size = cpu_to_be64(total_size * 512);
+    header_size = sizeof(header);
+    backing_filename_len = 0;
+    if (backing_file) {
+        realpath(backing_file, backing_filename);
+        if (stat(backing_filename, &st) != 0) {
+            return -1;
+        }
+        header.mtime = cpu_to_be32(st.st_mtime);
+        header.backing_file_offset = cpu_to_be64(header_size);
+        backing_filename_len = strlen(backing_filename);
+        header.backing_file_size = cpu_to_be32(backing_filename_len);
+        header_size += backing_filename_len;
+        header.cluster_bits = 9; /* 512 byte cluster to avoid copying
+                                    unmodifyed sectors */
+        header.l2_bits = 12; /* 32 KB L2 tables */
+    } else {
+        header.cluster_bits = 12; /* 4 KB clusters */
+        header.l2_bits = 9; /* 4 KB L2 tables */
+    }
+    header_size = (header_size + 7) & ~7;
+    shift = header.cluster_bits + header.l2_bits;
+    l1_size = ((total_size * 512) + (1LL << shift) - 1) >> shift;
+
+    header.l1_table_offset = cpu_to_be64(header_size);
+    if (flags) {
+        header.crypt_method = cpu_to_be32(QCOW_CRYPT_AES);
+    } else {
+        header.crypt_method = cpu_to_be32(QCOW_CRYPT_NONE);
+    }
+    
+    /* write all the data */
+    write(fd, &header, sizeof(header));
+    if (backing_file) {
+        write(fd, backing_filename, backing_filename_len);
+    }
+    lseek(fd, header_size, SEEK_SET);
+    tmp = 0;
+    for(i = 0;i < l1_size; i++) {
+        write(fd, &tmp, sizeof(tmp));
+    }
+    close(fd);
+    return 0;
+}
+
+int qcow_get_cluster_size(BlockDriverState *bs)
+{
+    BDRVQcowState *s = bs->opaque;
+    if (bs->drv != &bdrv_qcow)
+        return -1;
+    return s->cluster_size;
+}
+
+/* XXX: put compressed sectors first, then all the cluster aligned
+   tables to avoid losing bytes in alignment */
+int qcow_compress_cluster(BlockDriverState *bs, int64_t sector_num, 
+                          const uint8_t *buf)
+{
+    BDRVQcowState *s = bs->opaque;
+    z_stream strm;
+    int ret, out_len;
+    uint8_t *out_buf;
+    uint64_t cluster_offset;
+
+    if (bs->drv != &bdrv_qcow)
+        return -1;
+
+    out_buf = qemu_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
+    if (!out_buf)
+        return -1;
+
+    /* best compression, small window, no zlib header */
+    memset(&strm, 0, sizeof(strm));
+    ret = deflateInit2(&strm, Z_DEFAULT_COMPRESSION,
+                       Z_DEFLATED, -12, 
+                       9, Z_DEFAULT_STRATEGY);
+    if (ret != 0) {
+        qemu_free(out_buf);
+        return -1;
+    }
+
+    strm.avail_in = s->cluster_size;
+    strm.next_in = (uint8_t *)buf;
+    strm.avail_out = s->cluster_size;
+    strm.next_out = out_buf;
+
+    ret = deflate(&strm, Z_FINISH);
+    if (ret != Z_STREAM_END && ret != Z_OK) {
+        qemu_free(out_buf);
+        deflateEnd(&strm);
+        return -1;
+    }
+    out_len = strm.next_out - out_buf;
+
+    deflateEnd(&strm);
+
+    if (ret != Z_STREAM_END || out_len >= s->cluster_size) {
+        /* could not compress: write normal cluster */
+        qcow_write(bs, sector_num, buf, s->cluster_sectors);
+    } else {
+        cluster_offset = get_cluster_offset(bs, sector_num << 9, 2, 
+                                            out_len, 0, 0);
+        cluster_offset &= s->cluster_offset_mask;
+        lseek64(s->fd, cluster_offset, SEEK_SET);
+        if (write(s->fd, out_buf, out_len) != out_len) {
+            qemu_free(out_buf);
+            return -1;
+        }
+    }
+    
+    qemu_free(out_buf);
+    return 0;
+}
+
+BlockDriver bdrv_qcow = {
+    "qcow",
+    sizeof(BDRVQcowState),
+    qcow_probe,
+    qcow_open,
+    qcow_read,
+    qcow_write,
+    qcow_close,
+    qcow_create,
+    qcow_is_allocated,
+    qcow_set_key,
+};
+
+