Re: RFC: Serial port DTR/RTS - O_<something>

[Ned Ulbricht]

On 11/18/25 10:05, H. Peter Anvin wrote:

> > "(O_EXCL|O_NOFOLLOW)" provokes a thought...
> >
> > As essential context, fs/open.c build_open_flags() has:
> >
> > if (flags & O_CREAT) {
> >      op->intent |= LOOKUP_CREATE;
> >      if (flags & O_EXCL) {
> >          op->intent |= LOOKUP_EXCL;
> >          flags |= O_NOFOLLOW;
> >      }
> > }

[snip]

> I had missed the bit in the spec that says that O_CREAT|O_EXCL is required to
> imply O_NOFOLLOW (as Linux indeed does as seen above.)

Fwiw, earlier today I had an ultimately unsuccessful series of searches
using the Austin Group Issue tracker at:

https://austingroupbugs.net/view_all_bug_page.php

Searched (serially): "O_EXCL", "O_NOFOLLOW", "EEXIST", "ELOOP"; all with
no other filter refinements.  Then searched filtering by 'Section'
(multiple adjacent selections): 'open' .. 'openat'. In all results,
simply eyeball-scanned 'Summary' (w/o opening most).

Apparent upshot, unless I'm mistaken, is that the exact error return is
a trivial conflict with no appreciable impact on higher levels.


In roughly same vein, FreeBSD open(2) man page, specifically at
"[EMLINK]" and "STANDARDS", might possibly be stretched to read as
implicitly encouraging that assessment.

https://man.freebsd.org/cgi/man.cgi?query=open&manpath=FreeBSD+16.0-CURRENT

Alhough I don't have a FreeBSD box available to actually test
(O_CREAT|O_EXCL|O_NOFOLLOW) symlink behavior on that platform.  (Maybe
that combo's wired to detonate tnt nasal daemons? Dunno;-)


Unfortunately, this does prompt a close re-scrutinization of linux's
open(2) man page. Notwithstanding the damn spec, the linux man page
should precisely and accurately reflect the observed error return?


Ned