Hardware flow control for serial ports falsely claims not to be supported.

[jpherbst]

I am using linux and whenever I try to enable hardware flow control on a serial port I get a boost::asio::error::operation_not_supported. If I enable flow control manually using termios everything works fine.

Some sifting through the source code has gotten me to the assumption that _BSD_SOURCE is not defined on my system which appears to gate the standard unix flow control setup in the asio code. According to this website, http://man7.org/tlpi/code/faq.html#use_default_source, use of _BSD_SOURCE is depricated and maybe was removed in glibc, but I'm not really sure what the correct fix is.

I am using Linux 4.9.48 with glibc 2.25. Please let me know if more information is needed.

[mossheim]

I also have this issue on macOS (10.13.6). Not sure of the implementation version, but the check in /usr/include/sys/termios.h that enables the control flag definitions is this:

#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define CCTS_OFLOW	0x00010000	/* CTS flow control of output */
#define CRTSCTS		(CCTS_OFLOW | CRTS_IFLOW)
#define CRTS_IFLOW	0x00020000	/* RTS flow control of input */
#define	CDTR_IFLOW	0x00040000	/* DTR flow control of input */
#define CDSR_OFLOW	0x00080000	/* DSR flow control of output */
#define	CCAR_OFLOW	0x00100000	/* DCD flow control of output */
#define	MDMBUF		0x00100000	/* old name for CCAR_OFLOW */
#endif

Of course, this is not correct according to https://linux.die.net/man/3/termios, but it would be nice if I didn't have to circumvent this library to get basic functionality, so I hope you'll consider adding a check to enable this.

[jpherbst]

This seems to be fixed for my condition at least as early as Boost 1.66.

[mossheim]

Not fixed for me in 1.66.0

[ghost]

This issue was moved by chriskohlhoff to chriskohlhoff/asio#592.