block-qcow.c - third_party/qemu - Git at Google

 /*
  * 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 (buf_size >= sizeof(QCowHeader) &&
         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;
     lseek(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;
         lseek(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 = lseek(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);
         lseek(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 = lseek(s->fd, 0, SEEK_END);
             cluster_offset = (cluster_offset + s->cluster_size - 1) &
                 ~(s->cluster_size - 1);
             /* write the cluster content */
             lseek(s->fd, cluster_offset, SEEK_SET);
             if (write(s->fd, s->cluster_cache, s->cluster_size) !=
                 s->cluster_size)
                 return -1;
         } else {
             cluster_offset = lseek(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);
                             lseek(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;
         lseek(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);
         lseek(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 {
             lseek(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;
         lseek(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 void 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) {
 	if (strcmp(backing_file, "fat:")) {
 	    const char *p;
 	    /* XXX: this is a hack: we do not attempt to check for URL
 	       like syntax */
 	    p = strchr(backing_file, ':');
 	    if (p && (p - backing_file) >= 2) {
 		/* URL like but exclude "c:" like filenames */
 		pstrcpy(backing_filename, sizeof(backing_filename),
 			backing_file);
 	    } else {
 		realpath(backing_file, backing_filename);
 		if (stat(backing_filename, &st) != 0) {
 		    return -1;
 		}
 	    }
 	    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;
 	} else
 	    backing_file = NULL;
         header.mtime = cpu_to_be32(st.st_mtime);
         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_make_empty(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     uint32_t l1_length = s->l1_size * sizeof(uint64_t);

     memset(s->l1_table, 0, l1_length);
     lseek(s->fd, s->l1_table_offset, SEEK_SET);
     if (write(s->fd, s->l1_table, l1_length) < 0)
 	return -1;
     ftruncate(s->fd, s->l1_table_offset + l1_length);

     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));

     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;
         lseek(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;
 }

 static void qcow_flush(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
     fsync(s->fd);
 }

 BlockDriver bdrv_qcow = {
     "qcow",
     sizeof(BDRVQcowState),
     qcow_probe,
     qcow_open,
     qcow_read,
     qcow_write,
     qcow_close,
     qcow_create,
     qcow_flush,
     qcow_is_allocated,
     qcow_set_key,
     qcow_make_empty
 };
	/*
	* 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 (buf_size >= sizeof(QCowHeader) &&
	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;
	lseek(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;
	lseek(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 = lseek(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);
	lseek(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 = lseek(s->fd, 0, SEEK_END);
	cluster_offset = (cluster_offset + s->cluster_size - 1) &
	~(s->cluster_size - 1);
	/* write the cluster content */
	lseek(s->fd, cluster_offset, SEEK_SET);
	if (write(s->fd, s->cluster_cache, s->cluster_size) !=
	s->cluster_size)
	return -1;
	} else {
	cluster_offset = lseek(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);
	lseek(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;
	lseek(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);
	lseek(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 {
	lseek(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;
	lseek(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 void 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) {
	if (strcmp(backing_file, "fat:")) {
	const char *p;
	/* XXX: this is a hack: we do not attempt to check for URL
	like syntax */
	p = strchr(backing_file, ':');
	if (p && (p - backing_file) >= 2) {
	/* URL like but exclude "c:" like filenames */
	pstrcpy(backing_filename, sizeof(backing_filename),
	backing_file);
	} else {
	realpath(backing_file, backing_filename);
	if (stat(backing_filename, &st) != 0) {
	return -1;
	}
	}
	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;
	} else
	backing_file = NULL;
	header.mtime = cpu_to_be32(st.st_mtime);
	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_make_empty(BlockDriverState *bs)
	{
	BDRVQcowState *s = bs->opaque;
	uint32_t l1_length = s->l1_size * sizeof(uint64_t);

	memset(s->l1_table, 0, l1_length);
	lseek(s->fd, s->l1_table_offset, SEEK_SET);
	if (write(s->fd, s->l1_table, l1_length) < 0)
	return -1;
	ftruncate(s->fd, s->l1_table_offset + l1_length);

	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));

	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;
	lseek(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;
	}

	static void qcow_flush(BlockDriverState *bs)
	{
	BDRVQcowState *s = bs->opaque;
	fsync(s->fd);
	}

	BlockDriver bdrv_qcow = {
	"qcow",
	sizeof(BDRVQcowState),
	qcow_probe,
	qcow_open,
	qcow_read,
	qcow_write,
	qcow_close,
	qcow_create,
	qcow_flush,
	qcow_is_allocated,
	qcow_set_key,
	qcow_make_empty
	};