[Qemu-devel] [PATCH v2 01/21] qcow2: Add two new fields to BDRVQcowState

[Max Reitz <mreitz@redhat.com>]

Add two new fields regarding refcount information (the bit width of
every entry and the maximum refcount value) to the BDRVQcowState.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2-refcount.c | 2 +-
 block/qcow2.c          | 9 +++++++++
 block/qcow2.h          | 2 ++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 9afdb40..6016211 100644
--- a/block/qcow2-refcount.c
+++ b/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;
         }
diff --git a/block/qcow2.c b/block/qcow2.c
index d120494..f57aff9 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -684,6 +684,15 @@ 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;
+    if (s->refcount_order < 6) {
+        s->refcount_max = (UINT64_C(1) << s->refcount_bits) - 1;
+    } else {
+        /* The above shift would overflow with s->refcount_bits == 64;
+         * furthermore, we do not want to use UINT64_MAX because refcounts will
+         * be passed around in int64_ts (negative values for -errno) */
+        s->refcount_max = INT64_MAX;
+    }
 
     if (header.crypt_method > QCOW_CRYPT_AES) {
         error_setg(errp, "Unsupported encryption method: %" PRIu32,
diff --git a/block/qcow2.h b/block/qcow2.h
index 6e39a1b..4d8c902 100644
--- a/block/qcow2.h
+++ b/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];
 
-- 
1.9.3