From 207f43003ce81a67c71571b71255d0eb6f0c2281 Mon Sep 17 00:00:00 2001
From: Hallvard Furuseth <hallvard@openldap.org>
Date: Wed, 7 Dec 2016 19:06:11 +0100
Subject: [PATCH] mdbx: backport (comments) - MDB_CP_COMPACT comments.

Change-Id: I4965d5e511395fceafcd922f513dcf0d5050c9b8
---
 mdb.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mdb.c b/mdb.c
index 0208b73a..07cbeb9a 100644
--- a/mdb.c
+++ b/mdb.c
@@ -9057,7 +9057,10 @@ typedef struct mdb_copy {
 	HANDLE mc_fd;
 	int mc_toggle;			/**< Buffer number in provider */
 	int mc_new;				/**< (0-2 buffers to write) | (#MDB_EOF at end) */
-	volatile int mc_error;	/**< Error code, never cleared if set */
+	/** Error code.  Never cleared if set.  Both threads can set nonzero
+	 *	to fail the copy.  Not mutex-protected, LMDB expects atomic int.
+	 */
+	volatile int mc_error;
 } mdb_copy;
 
 	/** Dedicated writer thread for compacting copy. */
@@ -9135,7 +9138,11 @@ mdb_env_cthr_toggle(mdb_copy *my, int adjust)
 	return my->mc_error;
 }
 
-	/** Depth-first tree traversal for compacting copy. */
+	/** Depth-first tree traversal for compacting copy.
+	 * @param[in] my control structure.
+	 * @param[in,out] pg database root.
+	 * @param[in] flags includes #F_DUPDATA if it is a sorted-duplicate sub-DB.
+	 */
 static int __cold
 mdb_env_cwalk(mdb_copy *my, pgno_t *pg, int flags)
 {