glibc/sysdeps/unix/sysv/linux/cfsetspeed.c

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linux: implement arbitrary and split speeds in termios Linux has supported arbitrary speeds and split speeds in the kernel since 2008 on all platforms except Alpha (fixed in 2020), but glibc was never updated to match. This is further complicated by POSIX uses of macros for the cf[gs]et[io]speed interfaces, rather than plain numbers, as it really ought to have. On most platforms, the glibc ABI includes the c_[io]speed fields in struct termios, but they are incorrectly used. On MIPS and SPARC, they are entirely missing. For backwards compatibility, the kernel will still use the legacy speed fields unless they are set to BOTHER, and will use the legacy output speed as the input speed if the latter is 0 (== B0). However, the specific encoding used is visible to user space applications, including ones other than the one running. - SPARC and MIPS get a new struct termios, and tc[gs]etattr() is versioned accordingly. However, the new struct termios is set to be a strict extension of the old one, which means that cf* interfaces other than the speed-related ones do not need versioning. - The Bxxx constants are redefined as equivalent to their integer values and the legacy Bxxx constants are renamed __Bxxx. - cf[gs]et[io]speed() and cfsetspeed() are versioned accordingly. - tcgetattr() and cfset[io]speed() are adjusted to always keep the c_[io]speed fields correct (unlike earlier versions), but to canonicalize the representation to ALSO configure the legacy fields if a valid legacy representation exists. - tcsetattr(), too, canonicalizes the representation in this way before passing it to the kernel, to maximize compatibility with older applications/tools. - The old IBAUD0 hack is removed; it is no longer necessary since even the legacy c_cflag baud rate fields have had separate input values for a long time. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2025-06-12 01:35:36 +00:00
/* cfsetspeed(), Linux version.
Copyright (C) 1991-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <termios_internals.h>
/* Set both the input and output baud rates stored in *TERMIOS_P to SPEED. */
int
__cfsetspeed (struct termios *termios_p, speed_t speed)
{
tcflag_t cbaud = ___speed_to_cbaud (speed);
termios_p->c_ospeed = speed;
termios_p->c_ispeed = speed;
termios_p->c_cflag &= ~(CBAUD | CIBAUD);
termios_p->c_cflag |= cbaud | (cbaud << IBSHIFT);
return 0;
}
termios: add new baud_t interface, defined to be explicitly numeric 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>
2025-06-12 01:35:42 +00:00
libc_hidden_def (__cfsetspeed)
linux: implement arbitrary and split speeds in termios Linux has supported arbitrary speeds and split speeds in the kernel since 2008 on all platforms except Alpha (fixed in 2020), but glibc was never updated to match. This is further complicated by POSIX uses of macros for the cf[gs]et[io]speed interfaces, rather than plain numbers, as it really ought to have. On most platforms, the glibc ABI includes the c_[io]speed fields in struct termios, but they are incorrectly used. On MIPS and SPARC, they are entirely missing. For backwards compatibility, the kernel will still use the legacy speed fields unless they are set to BOTHER, and will use the legacy output speed as the input speed if the latter is 0 (== B0). However, the specific encoding used is visible to user space applications, including ones other than the one running. - SPARC and MIPS get a new struct termios, and tc[gs]etattr() is versioned accordingly. However, the new struct termios is set to be a strict extension of the old one, which means that cf* interfaces other than the speed-related ones do not need versioning. - The Bxxx constants are redefined as equivalent to their integer values and the legacy Bxxx constants are renamed __Bxxx. - cf[gs]et[io]speed() and cfsetspeed() are versioned accordingly. - tcgetattr() and cfset[io]speed() are adjusted to always keep the c_[io]speed fields correct (unlike earlier versions), but to canonicalize the representation to ALSO configure the legacy fields if a valid legacy representation exists. - tcsetattr(), too, canonicalizes the representation in this way before passing it to the kernel, to maximize compatibility with older applications/tools. - The old IBAUD0 hack is removed; it is no longer necessary since even the legacy c_cflag baud rate fields have had separate input values for a long time. Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
2025-06-12 01:35:36 +00:00
versioned_symbol (libc, __cfsetspeed, cfsetspeed, GLIBC_2_42);
#if _TERMIOS_OLD_COMPAT
int
attribute_compat_text_section
__old_cfsetspeed (old_termios_t *termios_p, speed_t speed)
{
speed_t real_speed = ___cbaud_to_speed (speed, -1);
if (real_speed == (speed_t)-1)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (EINVAL);
#if !_HAVE_STRUCT_OLD_TERMIOS
/* Otherwise these fields don't exist in old_termios_t */
termios_p->c_ospeed = real_speed;
termios_p->c_ispeed = real_speed;
#endif
termios_p->c_cflag &= ~(CBAUD | CIBAUD);
termios_p->c_cflag |= speed | (speed << IBSHIFT);
return 0;
}
compat_symbol (libc, __old_cfsetspeed, cfsetspeed, GLIBC_2_0);
#endif /* _TERMIOS_OLD_COMPAT */