[Qemu-devel] [PATCH v6 01/11] qcow2: Calculate refcount block entry count

[Max Reitz <mreitz@redhat.com>]

The size of a refblock entry is (in theory) variable; calculate
therefore the number of entries per refblock and the according bit shift
(1 << x == entry count) when opening an image.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2.c | 3 +++
 block/qcow2.h | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 156a219..3c8b881 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -698,6 +698,9 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
 
     s->l2_bits = s->cluster_bits - 3; /* L2 is always one cluster */
     s->l2_size = 1 << s->l2_bits;
+    /* 2^(s->refcount_order - 3) is the refcount width in bytes */
+    s->refcount_block_bits = s->cluster_bits - (s->refcount_order - 3);
+    s->refcount_block_size = 1 << s->refcount_block_bits;
     bs->total_sectors = header.size / 512;
     s->csize_shift = (62 - (s->cluster_bits - 8));
     s->csize_mask = (1 << (s->cluster_bits - 8)) - 1;
diff --git a/block/qcow2.h b/block/qcow2.h
index 7d61e61..47cd4b3 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -223,6 +223,8 @@ typedef struct BDRVQcowState {
     int l2_size;
     int l1_size;
     int l1_vm_state_index;
+    int refcount_block_bits;
+    int refcount_block_size;
     int csize_shift;
     int csize_mask;
     uint64_t cluster_offset_mask;
-- 
2.1.2