qcow2: compressed read: simplify cluster descriptor passing

Let's pass the whole L2 entry and not bother with
L2E_COMPRESSED_OFFSET_SIZE_MASK.

It also helps further refactoring that adds generic
qcow2_parse_compressed_l2_entry() helper.

Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: Alberto Garcia <[email protected]>
Reviewed-by: Hanna Reitz <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Hanna Reitz <[email protected]>

Author: Vladimir Sementsov-Ogievskiy

block/qcow2-cluster.c

@@ -556,8 +556,7 @@ static int coroutine_fn do_perform_cow_write(BlockDriverState *bs,
  * offset needs to be aligned to a cluster boundary.
  *
  * If the cluster is unallocated then *host_offset will be 0.
- * If the cluster is compressed then *host_offset will contain the
- * complete compressed cluster descriptor.
+ * If the cluster is compressed then *host_offset will contain the l2 entry.
  *
  * On entry, *bytes is the maximum number of contiguous bytes starting at
  * offset that we are interested in.
@@ -660,7 +659,7 @@ int qcow2_get_host_offset(BlockDriverState *bs, uint64_t offset,
             ret = -EIO;
             goto fail;
         }
-        *host_offset = l2_entry & L2E_COMPRESSED_OFFSET_SIZE_MASK;
+        *host_offset = l2_entry;
         break;
     case QCOW2_SUBCLUSTER_ZERO_PLAIN:
     case QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN:

block/qcow2.c

@@ -74,7 +74,7 @@ typedef struct {
 
 static int coroutine_fn
 qcow2_co_preadv_compressed(BlockDriverState *bs,
-                           uint64_t cluster_descriptor,
+                           uint64_t l2_entry,
                            uint64_t offset,
                            uint64_t bytes,
                            QEMUIOVector *qiov,
@@ -2205,7 +2205,7 @@ typedef struct Qcow2AioTask {
 
     BlockDriverState *bs;
     QCow2SubclusterType subcluster_type; /* only for read */
-    uint64_t host_offset; /* or full descriptor in compressed clusters */
+    uint64_t host_offset; /* or l2_entry for compressed read */
     uint64_t offset;
     uint64_t bytes;
     QEMUIOVector *qiov;
@@ -4693,7 +4693,7 @@ qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
 
 static int coroutine_fn
 qcow2_co_preadv_compressed(BlockDriverState *bs,
-                           uint64_t cluster_descriptor,
+                           uint64_t l2_entry,
                            uint64_t offset,
                            uint64_t bytes,
                            QEMUIOVector *qiov,
@@ -4705,8 +4705,10 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
     uint8_t *buf, *out_buf;
     int offset_in_cluster = offset_into_cluster(s, offset);
 
-    coffset = cluster_descriptor & s->cluster_offset_mask;
-    nb_csectors = ((cluster_descriptor >> s->csize_shift) & s->csize_mask) + 1;
+    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_MASK);
 

block/qcow2.h

@@ -588,7 +588,6 @@ typedef enum QCow2MetadataOverlap {
 
 #define L1E_OFFSET_MASK 0x00fffffffffffe00ULL
 #define L2E_OFFSET_MASK 0x00fffffffffffe00ULL
-#define L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
 
 #define REFT_OFFSET_MASK 0xfffffffffffffe00ULL