Re: kern/57259: ucom serial ports cannot be re-opened "too quickly" with O_NONBLOCK

[Jason Thorpe <thorpej%me.com@localhost>]

The following reply was made to PR kern/57259; it has been noted by GNATS.

From: Jason Thorpe <thorpej%me.com@localhost>
To: Taylor Campbell <riastradh%NetBSD.org@localhost>
Cc: "gnats-bugs%netbsd.org@localhost" <gnats-bugs%NetBSD.org@localhost>
Subject: Re: kern/57259: ucom serial ports cannot be re-opened "too quickly"
	with O_NONBLOCK
Date: Sun, 5 Mar 2023 04:46:26 -0800

 > On Mar 5, 2023, at 4:39 AM, Taylor R Campbell <riastradh%NetBSD.org@localhost> =
 wrote:
 >=20
 >> - Even suppressing EWOULDBLOCK (resulting in an ERESTART), it would
 >>  simply fail with a spurious EINTR that I couldn't determine where
 >>  that was coming from (clearly from some higher-up layer).
 >=20
 > EINTR should only happen if a signal is delivered.  If you're not sure
 > where that was coming from it bears further investigation.  I don't
 > think tty(9) or condvar(9) will fabricate EINTR when there's no signal
 > pending.
 
 Nope, you=E2=80=99re wrong.  I found where it=E2=80=99s coming from:
 
         error =3D vn_open(dvp, pb, TRYEMULROOT, flags, cmode,
             &vp, &dupfd_move, &dupfd);
         if (error !=3D 0) {
                 fd_abort(p, fp, indx);
                 if (error =3D=3D ERESTART)
                         error =3D EINTR;
                 return error;
         }
 
 That=E2=80=99s in do_open().  So the logic to return ERESTART here is =
 just wrong, and it could have never worked as written.
 
 -- thorpej