[PATCH v3 2/5] block-copy: improve comments of BlockCopyTask and BlockCopyState types and functions

[Emanuele Giuseppe Esposito]

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.

.sleep_state is handled in the series "coroutine: new sleep/wake API"
and thus here left as TODO.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/block-copy.c | 47 ++++++++++++++++++++++++++++++----------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index d58051288b..b3533a3003 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -56,25 +56,33 @@ typedef struct BlockCopyCallState {
     QLIST_ENTRY(BlockCopyCallState) list;
 
     /* State */
-    int ret;
     bool finished;
-    QemuCoSleep sleep;
-    bool cancelled;
+    QemuCoSleep sleep; /* TODO: protect API with a lock */
 
     /* OUT parameters */
+    bool cancelled;
     bool error_is_read;
+    int ret;
 } 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;
-    BlockCopyMethod method;
-    QLIST_ENTRY(BlockCopyTask) list;
+    int64_t bytes; /* only re-set in task_shrink, before running the task */
+    BlockCopyMethod method; /* initialized in block_copy_dirty_clusters() */
+
+    /* 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)
@@ -90,15 +98,25 @@ 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;
 
     /*
@@ -114,14 +132,11 @@ typedef struct BlockCopyState {
      * In this case, block_copy() will query the source’s allocation status,
      * skip unallocated regions, clear them in the copy_bitmap, and invoke
      * block_copy_reset_unallocated() every time it does.
+     *
+     * This field is set in backup_run() before coroutines are run,
+     * therefore is an IN.
      */
     bool skip_unallocated;
-
-    ProgressMeter *progress;
-
-    SharedResource *mem;
-
-    RateLimit rate_limit;
 } BlockCopyState;
 
 static BlockCopyTask *find_conflicting_task(BlockCopyState *s,
-- 
2.30.2