Re: kern/58929: POSIX.1-2024 compliance: posix_close, POSIX_CLOSE_RESTART

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

Correction: Our current close() -- and probably all existing close()
implementations outside buggy proprietary Unix variants -- is not
compliant with POSIX.1-2024, because if some underlying I/O is
interrupted by a signal it can fail with EINTR even though the
descriptor is unconditionally closed.  That is now forbidden (emphasis
added):

> If close() is interrupted by a signal that is to be caught, then it
> is unspecified whether it returns -1 with errno set to [EINTR] and
> fildes _remaining open_, or returns -1 with errno set to
> [EINPROGRESS] and fildes being closed, or returns 0 to indicate
> successful completion[...]
> 
> RATIONALE
> 
> [...] Note that the standard requires that close() and posix_close()
> _must leave fildes open after [EINTR]_ (in the cases where [EINTR]
> is permitted)

So, in order to deal with POSIX.1-2024 having addressed the problem of
its own failure to adequately specify semantics by breaking
compatibility with every major OS on the planet, it looks like we'll
have to do some symbol magic under _POSIX_C_SOURCE -- something like
this:

/* include/unistd.h */

#if (_POSIX_C_SOURCE >= 202408L) && !defined(_NETBSD_SOURCE)
int	close(int) __RENAME(__posixly_correct_close);
int	posix_close(int, int);
#define	POSIX_CLOSE_RESTART	0
#else
int	close(int);
#endif

/* lib/libc/sys/posixly_correct_close.c */

int
__posixly_correct_close(int d)
{
	const int ret = close(d);

	if (ret == -1 && errno == EINTR)
		errno = EINPROGRESS;

	return ret;
}

int
posix_close(int d, int flag)
{
	const int ret = __posixly_correct_close(d);

	_DIAGASSERT(ret == 0 || errno != EINTR);

	if (ret == 0 && flag != 0) {
		errno = EINVAL;
		ret = -1;
	}
	return ret;
}

What a colossal waste of effort -- and attack surface for new bugs to
crawl onto -- to force everyone else to bend over backwards to
accommodate bugs in proprietary implementations of close().