Tweaks for MDB_MULTIPLE

Terminate loop on intermediate failures, return count of written items,
document usage.

libraries/liblmdb/lmdb.h

@@ -309,7 +309,7 @@ typedef void (MDB_rel_func)(MDB_val *item, void *oldptr, void *newptr, void *rel
 #define MDB_APPEND	0x20000
 /** Duplicate data is being appended, don't split full pages. */
 #define MDB_APPENDDUP	0x40000
-/** Store multiple data items in one call. */
+/** Store multiple data items in one call. Only for #MDB_DUPFIXED. */
 #define MDB_MULTIPLE	0x80000
 /*	@} */
 
@@ -1210,6 +1210,16 @@ int  mdb_cursor_get(MDB_cursor *cursor, MDB_val *key, MDB_val *data,
 	 *		correct order. Loading unsorted keys with this flag will cause
 	 *		data corruption.
 	 *	<li>#MDB_APPENDDUP - as above, but for sorted dup data.
+	 *	<li>#MDB_MULTIPLE - store multiple contiguous data elements in a
+	 *		single request. This flag may only be specified if the database
+	 *		was opened with #MDB_DUPFIXED. The \b data argument must be an
+	 *		array of two MDB_vals. The mv_size of the first MDB_val must be
+	 *		the size of a single data element. The mv_data of the first MDB_val
+	 *		must point to the beginning of the array of contiguous data elements.
+	 *		The mv_size of the second MDB_val must be the count of the number
+	 *		of data elements to store. On return this field will be set to
+	 *		the count of the number of elements actually written. The mv_data
+	 *		of the second MDB_val is unused.
 	 * </ul>
 	 * @return A non-zero error value on failure and 0 on success. Some possible
 	 * errors are:

libraries/liblmdb/mdb.c

@@ -4969,7 +4969,7 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 	MDB_page	*fp;
 	MDB_db dummy;
 	int do_sub = 0, insert = 0;
-	unsigned int mcount = 0;
+	unsigned int mcount = 0, dcount;
 	size_t nsize;
 	int rc, rc2;
 	MDB_pagebuf pbuf;
@@ -4977,6 +4977,16 @@ mdb_cursor_put(MDB_cursor *mc, MDB_val *key, MDB_val *data,
 	unsigned int nflags;
 	DKBUF;
 
+	/* Check this first so counter will always be zero on any
+	 * early failures.
+	 */
+	if (flags & MDB_MULTIPLE) {
+		dcount = data[1].mv_size;
+		data[1].mv_size = 0;
+		if (!F_ISSET(mc->mc_db->md_flags, MDB_DUPFIXED))
+			return EINVAL;
+	}
+
 	if (F_ISSET(mc->mc_txn->mt_flags, MDB_TXN_RDONLY))
 		return EACCES;
 
@@ -5357,13 +5367,17 @@ put_sub:
 		if (!rc && !(flags & MDB_CURRENT))
 			mc->mc_db->md_entries++;
 		if (flags & MDB_MULTIPLE) {
+			if (!rc) {
 				mcount++;
-			if (mcount < data[1].mv_size) {
+				if (mcount < dcount) {
 					data[0].mv_data = (char *)data[0].mv_data + data[0].mv_size;
 					leaf = NODEPTR(mc->mc_pg[mc->mc_top], mc->mc_ki[mc->mc_top]);
 					goto more;
 				}
 			}
+			/* let caller know how many succeeded, if any */
+			data[1].mv_size = mcount;
+		}
 	}
 done:
 	/* If we succeeded and the key didn't exist before, make sure