add readahead size option (#1146)

db/c.cc

@@ -2127,6 +2127,11 @@ void rocksdb_readoptions_set_tailing(
   opt->rep.tailing = v;
 }
 
+void rocksdb_readoptions_set_readahead_size(
+    rocksdb_readoptions_t* opt, size_t v) {
+  opt->rep.readahead_size = v;
+}
+
 rocksdb_writeoptions_t* rocksdb_writeoptions_create() {
   return new rocksdb_writeoptions_t;
 }

include/rocksdb/c.h

@@ -819,6 +819,8 @@ extern ROCKSDB_LIBRARY_API void rocksdb_readoptions_set_read_tier(
     rocksdb_readoptions_t*, int);
 extern ROCKSDB_LIBRARY_API void rocksdb_readoptions_set_tailing(
     rocksdb_readoptions_t*, unsigned char);
+extern ROCKSDB_LIBRARY_API void rocksdb_readoptions_set_readahead_size(
+    rocksdb_readoptions_t*, size_t);
 
 /* Write options */