qcow2: Add two new fields to BDRVQcowState

Add two new fields regarding refcount information (the bit width of
every entry and the maximum refcount value) to the BDRVQcowState.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

@@ -584,7 +584,7 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
 
         refcount = be16_to_cpu(refcount_block[block_index]);
         refcount += addend;
-        if (refcount < 0 || refcount > 0xffff) {
+        if (refcount < 0 || refcount > s->refcount_max) {
             ret = -EINVAL;
             goto fail;
         }
@@ -775,7 +775,7 @@ int64_t qcow2_alloc_bytes(BlockDriverState *bs, int size)
             return refcount;
         }
 
-        if (refcount == 0xffff) {
+        if (refcount == s->refcount_max) {
             offset = 0;
         }
     }

block/qcow2.c

@@ -684,6 +684,9 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
     s->refcount_order = header.refcount_order;
+    s->refcount_bits = 1 << s->refcount_order;
+    s->refcount_max = UINT64_C(1) << (s->refcount_bits - 1);
+    s->refcount_max += s->refcount_max - 1;
 
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "Unsupported encryption method: %" PRIu32,

block/qcow2.h

@@ -258,6 +258,8 @@ typedef struct BDRVQcowState {
     int qcow_version;
     bool use_lazy_refcounts;
     int refcount_order;
+    int refcount_bits;
+    uint64_t refcount_max;
 
     bool discard_passthrough[QCOW2_DISCARD_MAX];