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Add an explicitly numeric interface for baudrate setting. For glibc, this only announces what is a fair accompli, but this is a plausible way forward for standardization, and may be possible to infill on non-compliant systems. The POSIX committee has stated: [https://www.austingroupbugs.net/view.php?id=1916#c7135] A future version of this standard is expected to add at least the following symbolic constants for use as values of objects of type speed_t: B57600, B115200, B230400, B460800, and B921600. Implementations are encouraged to propose additional interfaces which will make it possible to set and query a wider range of speeds than just those enumerated by the constants beginning with B. If a set of common interfaces emerges between several implementations, a future version of this standard will likely add those interfaces. This is exactly that interface. The use of the term "baud" is due to the need to have a term contrasting "speed", and it is already well established as a legacy term -- including in the names of the legacy Bxxx constants. Futhermore, it *is* valid from the point of view that the termios interface fundamentally emulates an RS-232 serial port as far as the application software is concerned. The documentation states that for the current version of glibc, speed_t == baud_t, but explicitly declares that this may not be the case in the future. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>