[PATCH v2 1/3] linux/termios: clear k_termios.c_cflag & CIBAUD for non-split speed [BZ 33340]

[H. Peter Anvin]

On 2025-09-10 14:36, H. Peter Anvin wrote:
> After getting more experience with the various broken direct-to-ioctl
> termios2 hacks using Fedora 43 beta, I have found a fair number of
> cases where the software would fail to set, or clear CIBAUD for
> non-split-speed operation.
> 
> Thus it seems will help improve compatibility to clear the kernel-side
> version of c_cflag & CIBAUD (having the same meaning to the Linux
> kernel as the speed 0 has for cfsetibaud(), i.e. force the input speed
> to equal the output speed) for non-split-speed operation, rather than
> having it explicitly equal the output speed in CBAUD.
> 
> When writing the code that went into glibc 2.42 I had considered this
> issue, and had to make an educated guess which way would be more
> likely to break fewer things.  Unfortunately, it appears I guessed
> wrong.
> 
> A third option would be to *always* set CIBAUD to __BOTHER, even for
> the standard baud rates.  However, that is an even bigger departure
> from legacy behavior, whereas this variant mostly preserves current
> behavior in terms of under what conditions buggy utilities will
> continue to work.
> 
> This change is in tcsetattr() rather than
> ___termios2_canonicalize_speeds(), as it should not be run for
> tcgetattr(); that would break split speed support for the legacy
> interface versions of cfgetispeed() and cfsetispeed().
> 
> [ v2: fixed comment style ]
> 

*Gentle ping*

	-hpa