gsi_driver_io(3) on Linux
The text fb8953fe65d4, as Debian 6.0 (Squeeze) shipped it.
The GSI driver behaves similar to the underlying transport driver with respect to reads and writes, except for the try-read and try-write operations (ie. The GSI driver behaves similar to the underlying transport driver with respect to reads and writes, except for the try-read and try-write operations (ie. waitforbytes ==0) which always return immediately. This is due to the fact that the security layer needs to read and write tokens of a certain minimal size and thus needs to rely on the underlying transport to handle greater than 0 reads/write which is not possible in 'try' mode.