qcow2: Convert qcow2_alloc_cluster_offset() into qcow2_alloc_host_offset()

qcow2_alloc_cluster_offset() takes an (unaligned) guest offset and
returns the (aligned) offset of the corresponding cluster in the qcow2
image.

In practice none of the callers need to know where the cluster starts
so this patch makes the function calculate and return the final host
offset directly. The function is also renamed accordingly.

See 388e581615 for a similar change to qcow2_get_cluster_offset().

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <9bfef50ec9200d752413be4fc2aeb22a28378817.1599833007.git.berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

3 files changed, 26 insertions, 30 deletions

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 1a67b2d..9acc6ce 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1719,6 +1719,10 @@ out:
  * clusters (or subclusters) if necessary. The result can span a
  * combination of allocated and previously unallocated clusters.
  *
+ * Note that offset may not be cluster aligned. In this case, the returned
+ * *host_offset points to exact byte referenced by offset and therefore
+ * isn't cluster aligned as well.
+ *
  * On return, @host_offset is set to the beginning of the requested
  * area. This area is guaranteed to be contiguous on the qcow2 file
  * but it can be smaller than initially requested. In this case @bytes
@@ -1736,9 +1740,9 @@ out:
  *
  * Return 0 on success and -errno in error cases
  */
-int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
-                               unsigned int *bytes, uint64_t *host_offset,
-                               QCowL2Meta **m)
+int qcow2_alloc_host_offset(BlockDriverState *bs, uint64_t offset,
+                            unsigned int *bytes, uint64_t *host_offset,
+                            QCowL2Meta **m)
 {
     BDRVQcow2State *s = bs->opaque;
     uint64_t start, remaining;
@@ -1759,7 +1763,7 @@ again:
     while (true) {
 
         if (*host_offset == INV_OFFSET && cluster_offset != INV_OFFSET) {
-            *host_offset = start_of_cluster(s, cluster_offset);
+            *host_offset = cluster_offset;
         }
 
         assert(remaining >= cur_bytes);
@@ -1842,6 +1846,8 @@ again:
     *bytes -= remaining;
     assert(*bytes > 0);
     assert(*host_offset != INV_OFFSET);
+    assert(offset_into_cluster(s, *host_offset) ==
+           offset_into_cluster(s, offset));
 
     return 0;
 }
diff --git a/block/qcow2.c b/block/qcow2.c
index 1cb5daf..b055127 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2559,7 +2559,7 @@ static coroutine_fn int qcow2_co_pwritev_part(
     int offset_in_cluster;
     int ret;
     unsigned int cur_bytes; /* number of sectors in current iteration */
-    uint64_t cluster_offset;
+    uint64_t host_offset;
     QCowL2Meta *l2meta = NULL;
     AioTaskPool *aio = NULL;
 
@@ -2580,16 +2580,13 @@ static coroutine_fn int qcow2_co_pwritev_part(
 
         qemu_co_mutex_lock(&s->lock);
 
-        ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
-                                         &cluster_offset, &l2meta);
+        ret = qcow2_alloc_host_offset(bs, offset, &cur_bytes,
+                                      &host_offset, &l2meta);
         if (ret < 0) {
             goto out_locked;
         }
 
-        assert(offset_into_cluster(s, cluster_offset) == 0);
-
-        ret = qcow2_pre_write_overlap_check(bs, 0,
-                                            cluster_offset + offset_in_cluster,
+        ret = qcow2_pre_write_overlap_check(bs, 0, host_offset,
                                             cur_bytes, true);
         if (ret < 0) {
             goto out_locked;
@@ -2601,7 +2598,7 @@ static coroutine_fn int qcow2_co_pwritev_part(
             aio = aio_task_pool_new(QCOW2_MAX_WORKERS);
         }
         ret = qcow2_add_task(bs, aio, qcow2_co_pwritev_task_entry, 0,
-                             cluster_offset + offset_in_cluster, offset,
+                             host_offset, offset,
                              cur_bytes, qiov, qiov_offset, l2meta);
         l2meta = NULL; /* l2meta is consumed by qcow2_co_pwritev_task() */
         if (ret < 0) {
@@ -3129,13 +3126,12 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
 
     while (bytes) {
         cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size));
-        ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
-                                         &host_offset, &meta);
+        ret = qcow2_alloc_host_offset(bs, offset, &cur_bytes,
+                                      &host_offset, &meta);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Allocating clusters failed");
             goto out;
         }
-        host_offset += offset_into_cluster(s, offset);
 
         for (m = meta; m != NULL; m = m->next) {
             m->prealloc = true;
@@ -4043,10 +4039,9 @@ qcow2_co_copy_range_to(BlockDriverState *bs,
                        BdrvRequestFlags write_flags)
 {
     BDRVQcow2State *s = bs->opaque;
-    int offset_in_cluster;
     int ret;
     unsigned int cur_bytes; /* number of sectors in current iteration */
-    uint64_t cluster_offset;
+    uint64_t host_offset;
     QCowL2Meta *l2meta = NULL;
 
     assert(!bs->encrypted);
@@ -4057,31 +4052,26 @@ qcow2_co_copy_range_to(BlockDriverState *bs,
 
         l2meta = NULL;
 
-        offset_in_cluster = offset_into_cluster(s, dst_offset);
         cur_bytes = MIN(bytes, INT_MAX);
 
         /* TODO:
          * If src->bs == dst->bs, we could simply copy by incrementing
          * the refcnt, without copying user data.
          * Or if src->bs == dst->bs->backing->bs, we could copy by discarding. */
-        ret = qcow2_alloc_cluster_offset(bs, dst_offset, &cur_bytes,
-                                         &cluster_offset, &l2meta);
+        ret = qcow2_alloc_host_offset(bs, dst_offset, &cur_bytes,
+                                      &host_offset, &l2meta);
         if (ret < 0) {
             goto fail;
         }
 
-        assert(offset_into_cluster(s, cluster_offset) == 0);
-
-        ret = qcow2_pre_write_overlap_check(bs, 0,
-                cluster_offset + offset_in_cluster, cur_bytes, true);
+        ret = qcow2_pre_write_overlap_check(bs, 0, host_offset, cur_bytes,
+                                            true);
         if (ret < 0) {
             goto fail;
         }
 
         qemu_co_mutex_unlock(&s->lock);
-        ret = bdrv_co_copy_range_to(src, src_offset,
-                                    s->data_file,
-                                    cluster_offset + offset_in_cluster,
+        ret = bdrv_co_copy_range_to(src, src_offset, s->data_file, host_offset,
                                     cur_bytes, read_flags, write_flags);
         qemu_co_mutex_lock(&s->lock);
         if (ret < 0) {
diff --git a/block/qcow2.h b/block/qcow2.h
index b73a4cf..b71e444 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -901,9 +901,9 @@ int qcow2_encrypt_sectors(BDRVQcow2State *s, int64_t sector_num,
 int qcow2_get_host_offset(BlockDriverState *bs, uint64_t offset,
                           unsigned int *bytes, uint64_t *host_offset,
                           QCow2SubclusterType *subcluster_type);
-int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
-                               unsigned int *bytes, uint64_t *host_offset,
-                               QCowL2Meta **m);
+int qcow2_alloc_host_offset(BlockDriverState *bs, uint64_t offset,
+                            unsigned int *bytes, uint64_t *host_offset,
+                            QCowL2Meta **m);
 int qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
                                           uint64_t offset,
                                           int compressed_size,