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termios: add new baud_t interface, defined to be explicitly numeric

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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>
This commit is contained in:
H. Peter Anvin (Intel)
2025-06-11 18:35:42 -07:00
committed by Adhemerval Zanella
parent 98aeca349a
commit 5f138519eb
45 changed files with 400 additions and 27 deletions
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4
sysdeps/unix/sysv/linux/speed.c
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@ -263,6 +263,7 @@ __cfgetospeed (const struct termios *termios_p)
{
return termios_p->c_ospeed;
}
libc_hidden_def (__cfgetospeed)
versioned_symbol (libc, __cfgetospeed, cfgetospeed, GLIBC_2_42);
/* Return the input baud rate stored in *TERMIOS_P. */
@ -271,6 +272,7 @@ __cfgetispeed (const struct termios *termios_p)
{
return termios_p->c_ispeed;
}
libc_hidden_def (__cfgetispeed)
versioned_symbol (libc, __cfgetispeed, cfgetispeed, GLIBC_2_42);
/* Set the output baud rate stored in *TERMIOS_P to SPEED. */
@ -285,6 +287,7 @@ __cfsetospeed (struct termios *termios_p, speed_t speed)
return 0;
}
libc_hidden_def (__cfsetospeed)
versioned_symbol (libc, __cfsetospeed, cfsetospeed, GLIBC_2_42);
/* Set the input baud rate stored in *TERMIOS_P to SPEED. */
@ -299,6 +302,7 @@ __cfsetispeed (struct termios *termios_p, speed_t speed)
return 0;
}
libc_hidden_def (__cfsetispeed)
versioned_symbol (libc, __cfsetispeed, cfsetispeed, GLIBC_2_42);
#if _TERMIOS_OLD_COMPAT