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qcow2: Support reading zero clusters 

This adds support for reading zero clusters in version 3 images.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2012-03-16 15:02:38 +01:00
parent 6744cbab8c
commit 6377af48b0
4 changed files with 33 additions and 4 deletions
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17
block/qcow2-cluster.c
View File

@ -453,6 +453,12 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
c = 1;
*cluster_offset &= L2E_COMPRESSED_OFFSET_SIZE_MASK;
break;
case QCOW2_CLUSTER_ZERO:
c = count_contiguous_clusters(nb_clusters, s->cluster_size,
&l2_table[l2_index], 0,
QCOW_OFLAG_COMPRESSED | QCOW_OFLAG_ZERO);
*cluster_offset = 0;
break;
case QCOW2_CLUSTER_UNALLOCATED:
/* how many empty clusters ? */
c = count_contiguous_free_clusters(nb_clusters, &l2_table[l2_index]);
@ -461,7 +467,8 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
case QCOW2_CLUSTER_NORMAL:
/* how many allocated clusters ? */
c = count_contiguous_clusters(nb_clusters, s->cluster_size,
&l2_table[l2_index], 0, QCOW_OFLAG_COMPRESSED);
&l2_table[l2_index], 0,
QCOW_OFLAG_COMPRESSED | QCOW_OFLAG_ZERO);
*cluster_offset &= L2E_OFFSET_MASK;
break;
}
@ -720,6 +727,7 @@ static int count_cow_clusters(BDRVQcowState *s, int nb_clusters,
break;
case QCOW2_CLUSTER_UNALLOCATED:
case QCOW2_CLUSTER_COMPRESSED:
case QCOW2_CLUSTER_ZERO:
break;
default:
abort();
@ -868,9 +876,10 @@ again:
&& (cluster_offset & QCOW_OFLAG_COPIED))
{
/* We keep all QCOW_OFLAG_COPIED clusters */
keep_clusters = count_contiguous_clusters(nb_clusters, s->cluster_size,
&l2_table[l2_index], 0,
QCOW_OFLAG_COPIED);
keep_clusters =
count_contiguous_clusters(nb_clusters, s->cluster_size,
&l2_table[l2_index], 0,
QCOW_OFLAG_COPIED | QCOW_OFLAG_ZERO);
assert(keep_clusters <= nb_clusters);
nb_clusters -= keep_clusters;
} else {

7
block/qcow2-refcount.c
View File

@ -703,6 +703,7 @@ void qcow2_free_any_clusters(BlockDriverState *bs,
nb_clusters << s->cluster_bits);
break;
case QCOW2_CLUSTER_UNALLOCATED:
case QCOW2_CLUSTER_ZERO:
break;
default:
abort();
@ -973,6 +974,12 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
l2_entry & ~511, nb_csectors * 512);
break;
case QCOW2_CLUSTER_ZERO:
if ((l2_entry & L2E_OFFSET_MASK) == 0) {
break;
}
/* fall through */
case QCOW2_CLUSTER_NORMAL:
{
/* QCOW_OFLAG_COPIED must be set iff refcount == 1 */

8
block/qcow2.c
View File

@ -536,6 +536,14 @@ static coroutine_fn int qcow2_co_readv(BlockDriverState *bs, int64_t sector_num,
}
break;
case QCOW2_CLUSTER_ZERO:
if (s->qcow_version < 3) {
ret = -EIO;
goto fail;
}
qemu_iovec_memset(&hd_qiov, 0, 512 * cur_nr_sectors);
break;
case QCOW2_CLUSTER_COMPRESSED:
/* add AIO support for compressed blocks ? */
ret = qcow2_decompress_cluster(bs, cluster_offset);

5
block/qcow2.h
View File

@ -43,6 +43,8 @@
#define QCOW_OFLAG_COPIED (1LL << 63)
/* indicate that the cluster is compressed (they never have the copied flag) */
#define QCOW_OFLAG_COMPRESSED (1LL << 62)
/* The cluster reads as all zeros */
#define QCOW_OFLAG_ZERO (1LL << 0)
#define REFCOUNT_SHIFT 1 /* refcount size is 2 bytes */
@ -184,6 +186,7 @@ enum {
QCOW2_CLUSTER_UNALLOCATED,
QCOW2_CLUSTER_NORMAL,
QCOW2_CLUSTER_COMPRESSED,
QCOW2_CLUSTER_ZERO
};
#define L1E_OFFSET_MASK 0x00ffffffffffff00ULL
@ -213,6 +216,8 @@ static inline int qcow2_get_cluster_type(uint64_t l2_entry)
{
if (l2_entry & QCOW_OFLAG_COMPRESSED) {
return QCOW2_CLUSTER_COMPRESSED;
} else if (l2_entry & QCOW_OFLAG_ZERO) {
return QCOW2_CLUSTER_ZERO;
} else if (!(l2_entry & L2E_OFFSET_MASK)) {
return QCOW2_CLUSTER_UNALLOCATED;
} else {