qcow2: Return 0/-errno in qcow2_alloc_compressed_cluster_offset()

qcow2_alloc_compressed_cluster_offset() used to return the cluster
offset for success and 0 for error. This doesn't only conflict with 0 as
a valid host offset, but also loses the error code.

Similar to the change made to qcow2_alloc_cluster_offset() for
uncompressed clusters in commit 148da7ea9d, make the function return
0/-errno and return the allocated cluster offset in a by-reference
parameter.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-cluster.c

@@ -736,19 +736,16 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset,
 /*
  * alloc_compressed_cluster_offset
  *
- * For a given offset of the disk image, return cluster offset in
- * qcow2 file.
- *
- * If the offset is not found, allocate a new compressed cluster.
- *
- * Return the cluster offset if successful,
- * Return 0, otherwise.
+ * For a given offset on the virtual disk, allocate a new compressed cluster
+ * and put the host offset of the cluster into *host_offset. If a cluster is
+ * already allocated at the offset, return an error.
  *
+ * Return 0 on success and -errno in error cases
  */
-
-uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
-                                               uint64_t offset,
-                                               int compressed_size)
+int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
+                                          uint64_t offset,
+                                          int compressed_size,
+                                          uint64_t *host_offset)
 {
     BDRVQcow2State *s = bs->opaque;
     int l2_index, ret;
@@ -758,7 +755,7 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
 
     ret = get_cluster_table(bs, offset, &l2_slice, &l2_index);
     if (ret < 0) {
-        return 0;
+        return ret;
     }
 
     /* Compression can't overwrite anything. Fail if the cluster was already
@@ -766,13 +763,13 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
     cluster_offset = be64_to_cpu(l2_slice[l2_index]);
     if (cluster_offset & L2E_OFFSET_MASK) {
         qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
-        return 0;
+        return -EIO;
     }
 
     cluster_offset = qcow2_alloc_bytes(bs, compressed_size);
     if (cluster_offset < 0) {
         qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
-        return 0;
+        return cluster_offset;
     }
 
     nb_csectors = ((cluster_offset + compressed_size - 1) >> 9) -
@@ -790,7 +787,8 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
     l2_slice[l2_index] = cpu_to_be64(cluster_offset);
     qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice);
 
-    return cluster_offset;
+    *host_offset = cluster_offset & s->cluster_offset_mask;
+    return 0;
 }
 
 static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)

block/qcow2.c

@@ -3896,17 +3896,16 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
     int ret;
     size_t out_len;
     uint8_t *buf, *out_buf;
-    int64_t cluster_offset;
+    uint64_t cluster_offset;
 
     if (bytes == 0) {
         /* align end of file to a sector boundary to ease reading with
            sector based I/Os */
-        cluster_offset = bdrv_getlength(bs->file->bs);
-        if (cluster_offset < 0) {
-            return cluster_offset;
+        int64_t len = bdrv_getlength(bs->file->bs);
+        if (len < 0) {
+            return len;
         }
-        return bdrv_co_truncate(bs->file, cluster_offset, PREALLOC_MODE_OFF,
-                                NULL);
+        return bdrv_co_truncate(bs->file, len, PREALLOC_MODE_OFF, NULL);
     }
 
     if (offset_into_cluster(s, offset)) {
@@ -3943,14 +3942,12 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
     }
 
     qemu_co_mutex_lock(&s->lock);
-    cluster_offset =
-        qcow2_alloc_compressed_cluster_offset(bs, offset, out_len);
-    if (!cluster_offset) {
+    ret = qcow2_alloc_compressed_cluster_offset(bs, offset, out_len,
+                                                &cluster_offset);
+    if (ret < 0) {
         qemu_co_mutex_unlock(&s->lock);
-        ret = -EIO;
         goto fail;
     }
-    cluster_offset &= s->cluster_offset_mask;
 
     ret = qcow2_pre_write_overlap_check(bs, 0, cluster_offset, out_len);
     qemu_co_mutex_unlock(&s->lock);

block/qcow2.h

@@ -647,9 +647,10 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
 int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
                                unsigned int *bytes, uint64_t *host_offset,
                                QCowL2Meta **m);
-uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
-                                         uint64_t offset,
-                                         int compressed_size);
+int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
+                                          uint64_t offset,
+                                          int compressed_size,
+                                          uint64_t *host_offset);
 
 int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m);
 void qcow2_alloc_cluster_abort(BlockDriverState *bs, QCowL2Meta *m);

tests/qemu-iotests/220.out

@@ -38,7 +38,7 @@ wrote 2097152/2097152 bytes at offset 37748736
 No errors were found on the image.
 image size 39845888
 == Trying to write compressed cluster ==
-write failed: Input/output error
+write failed: File too large
 image size 562949957615616
 == Writing normal cluster ==
 wrote 2097152/2097152 bytes at offset 0