[PATCH v2 2/7] block-copy: improve documentation of BlockCopyTask and BlockCopyState types and functions

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

As done in BlockCopyCallState, categorize BlockCopyTask
and BlockCopyState in IN, State and OUT fields.
This is just to understand which field has to be protected with a lock.

BlockCopyTask .zeroes is a special case, because it is only initialized
and then read by the coroutine in block_copy_task_entry.

Also set block_copy_task_create as coroutine_fn because:
1) it is static and only invoked by coroutine functions
2) next patches will introduce and use a CoMutex lock there

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/block-copy.c | 49 ++++++++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 15 deletions(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index 10ce51a244..d2d3839dec 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -67,13 +67,28 @@ typedef struct BlockCopyCallState {
 typedef struct BlockCopyTask {
     AioTask task;
 
+    /*
+     * IN parameters. Initialized in block_copy_task_create()
+     * and never changed.
+     */
     BlockCopyState *s;
     BlockCopyCallState *call_state;
     int64_t offset;
-    int64_t bytes;
+    int64_t bytes; /* only re-set in task_shrink, before running the task */
+
+    /*
+     * "local" parameter: used only to communicate between
+     * the caller (block_copy_dirty_clusters) and the aiotask
+     * coroutine running block_copy_task_entry
+     */
     bool zeroes;
-    QLIST_ENTRY(BlockCopyTask) list;
+
+    /* State */
     CoQueue wait_queue; /* coroutines blocked on this task */
+
+    /* To reference all call states from BlockCopyState */
+    QLIST_ENTRY(BlockCopyTask) list;
+
 } BlockCopyTask;
 
 static int64_t task_end(BlockCopyTask *task)
@@ -89,15 +104,25 @@ typedef struct BlockCopyState {
      */
     BdrvChild *source;
     BdrvChild *target;
-    BdrvDirtyBitmap *copy_bitmap;
+
+    /* State */
     int64_t in_flight_bytes;
-    int64_t cluster_size;
     BlockCopyMethod method;
-    int64_t max_transfer;
-    uint64_t len;
     QLIST_HEAD(, BlockCopyTask) tasks; /* All tasks from all block-copy calls */
     QLIST_HEAD(, BlockCopyCallState) calls;
+    /* State fields that use a thread-safe API */
+    BdrvDirtyBitmap *copy_bitmap;
+    ProgressMeter *progress;
+    SharedResource *mem;
+    RateLimit rate_limit;
 
+    /*
+     * IN parameters. Initialized in block_copy_state_new()
+     * and never changed.
+     */
+    int64_t cluster_size;
+    int64_t max_transfer;
+    uint64_t len;
     BdrvRequestFlags write_flags;
 
     /*
@@ -115,12 +140,6 @@ typedef struct BlockCopyState {
      * block_copy_reset_unallocated() every time it does.
      */
     bool skip_unallocated;
-
-    ProgressMeter *progress;
-
-    SharedResource *mem;
-
-    RateLimit rate_limit;
 } BlockCopyState;
 
 static BlockCopyTask *find_conflicting_task(BlockCopyState *s,
@@ -176,9 +195,9 @@ static inline int64_t block_copy_chunk_size(BlockCopyState *s)
  * Search for the first dirty area in offset/bytes range and create task at
  * the beginning of it.
  */
-static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
-                                             BlockCopyCallState *call_state,
-                                             int64_t offset, int64_t bytes)
+static coroutine_fn BlockCopyTask *block_copy_task_create(BlockCopyState *s,
+                                                BlockCopyCallState *call_state,
+                                                int64_t offset, int64_t bytes)
 {
     BlockCopyTask *task;
     int64_t max_chunk = block_copy_chunk_size(s);
-- 
2.30.2