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Date: Thu, 13 Sep 2018 09:25:40 -0700
From: Benjamin Peterson <benjamin@...hon.org>
To: Rich Felker <dalias@...c.org>, musl@...ts.openwall.com
Subject: Re: [PATCH] return EBADF from ttyname_r
Thank you for the feedback.
On Thu, Sep 13, 2018, at 08:29, Rich Felker wrote:
> On Thu, Sep 13, 2018 at 10:53:14AM +0200, Szabolcs Nagy wrote:
> > * Benjamin Peterson <benjamin@...hon.org> [2018-09-12 17:34:24 -0700]:
> > > POSIX allows ttyname(_r) to return EBADF if passed file descriptor is invalid.
> >
> > i think EBADF is always a 'may fail' in posix, so not strictly required.
Right, I don't claim this patch fixes a bug; just makes the error reporting more precise.
> >
> > > - if (!isatty(fd)) return ENOTTY;
> > > + if (!isatty(fd)) {
> > > + if (errno == EBADF) return EBADF;
> > > + return ENOTTY;
> > > + }
> >
> > musl isatty uses __syscall which does not set errno so this is wrong.
Good point.
> >
> > note that on glibc isatty sets errno according what the kernel returns
> > however linux has different code paths in ioctl for different type of
> > fds and in some cases it can fail in interesting ways (iirc on a socket
> > fd it will fail with EINVAL or EFAULT at least on some linux versions
> > and it can even spuriously succeed on non-tty fds because the TCGETS
> > ioctl command was reused on some audio device to do different things)
>
> That's why we no longer use TCGETS but rather TIOCGWINSZ.
>
> > this means users cannot rely on errno value being sane,
> > so there is not much point trying to do something fancy here.
>
> I'm not sure this is actually an issue anymore, but if it is, we
> should simply translate anything other than EBADF to ENOTTY. There is
> no other meaningful error. Either the fd is valid or it's not, and if
> it is valid, either it is a tty or it's not.
I will send another patch to this effect.
>
> Rich
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