qcow2: introduce qcow2_parse_compressed_l2_entry() helper

Add helper to parse compressed l2_entry and use it everywhere instead
of open-coding.

Note, that in most places we move to precise coffset/csize instead of
sector-aligned. Still it should work good enough for updating
refcounts.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210914122454.141075-4-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 3d53657c26..4ebb49a087 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -2480,3 +2480,18 @@ fail:
     g_free(l1_table);
     return ret;
 }
+
+void qcow2_parse_compressed_l2_entry(BlockDriverState *bs, uint64_t l2_entry,
+                                     uint64_t *coffset, int *csize)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int nb_csectors;
+
+    assert(qcow2_get_cluster_type(bs, l2_entry) == QCOW2_CLUSTER_COMPRESSED);
+
+    *coffset = l2_entry & s->cluster_offset_mask;
+
+    nb_csectors = ((l2_entry >> s->csize_shift) & s->csize_mask) + 1;
+    *csize = nb_csectors * QCOW2_COMPRESSED_SECTOR_SIZE -
+        (*coffset & (QCOW2_COMPRESSED_SECTOR_SIZE - 1));
+}