typedef enum {


   MONGOC_READ_PRIMARY = (1 << 0),


   MONGOC_READ_SECONDARY = (1 << 1),


   MONGOC_READ_PRIMARY_PREFERRED = (1 << 2) | MONGOC_READ_PRIMARY,


   MONGOC_READ_SECONDARY_PREFERRED = (1 << 2) | MONGOC_READ_SECONDARY,


   MONGOC_READ_NEAREST = (1 << 3) | MONGOC_READ_SECONDARY,
} mongoc_read_mode_t;