From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F2419148833; Wed, 24 Jul 2024 10:15:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721816143; cv=none; b=qgujJDC48Kx2/kuNJERtW+5XpOzxoigbPPj5cBYgrrcfhif5z5bZgqhBfyqS2ECOMNzwVFcvMEcP2vZuBz90Al7lUcmY7BRcxa8+8S1nl0Xk/mJpYfci2Cxeh8VOONQRsfvN9QkriDzuZBXw1uHw/aW+ymExilI3N7fhmzL5A1M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721816143; c=relaxed/simple; bh=sFMZIf2ihav5KWBNwZUG6rIsjfc4DYBGazgFV+3l1/g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HBzqq0OX65vS8JMtPUFzKB4iJtKUxJsUqxZlS+slw/2zC1leEGl2PQUqM6rTtd1IeM3vG2nJuN/+kp3F18nhq8PKs1yqafTWkluc4A3F+IDI2us0AklGQQz0J90M44t5DuHSNlF0+YrKJscgS0AXh8Penya/KhS62sBloDa3qTE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=LkJJVW8y; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="LkJJVW8y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A759C32782; Wed, 24 Jul 2024 10:15:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1721816142; bh=sFMZIf2ihav5KWBNwZUG6rIsjfc4DYBGazgFV+3l1/g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LkJJVW8yjty5etW7/zx/HPuSXPnlwzRZP9v1mNIRtVMswIB4cxHU8xH7WASSdWQXF Huh2T+ejAiI84ecqRcxrgfX7avp75rZrd8aqubDY8+ywDOqETCkKV9I01gyzlwkGc2 UOQDN8bn8R0nMQX/NGN2R4567egXJyHEFzewpJp8= Date: Wed, 24 Jul 2024 12:15:39 +0200 From: Greg KH To: stsp Cc: linux-serial@vger.kernel.org, Linux kernel , Herbert Xu , Johan Hovold Subject: Re: [regression] ENOTTY returned for tty fds Message-ID: <2024072401-obtain-heap-6d8d@gregkh> References: <2024072452-pegboard-undying-4245@gregkh> <2024072401-spearfish-gnarly-a09e@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Jul 24, 2024 at 12:55:22PM +0300, stsp wrote: > 24.07.2024 12:08, Greg KH пишет: > > On Wed, Jul 24, 2024 at 11:07:32AM +0300, stsp wrote: > > > 24.07.2024 09:51, Greg KH пишет: > > > > What caused this change/regression? > > > I have absolutely no idea. > > > I've found it by debugging userspace, > > > and wrote a test-case to make sure the > > > problem is not in user-space. > > So this has always worked this way? Or has it changed? If changed, > > when did it work before? > > OK, I did some extensive digging, and > now am pretty sure its this one: > > commit 1b8b20868a6d64cfe8174a21b25b74367bdf0560 > Author:     Johan Hovold > AuthorDate: Wed Apr 7 11:52:02 2021 +0200 > Commit:     Greg Kroah-Hartman > CommitDate: Sat Apr 10 10:36:34 2021 +0200 > >     tty: fix return value for unsupported ioctls > >     Drivers should return -ENOTTY ("Inappropriate I/O control operation") >     when an ioctl isn't supported, while -EINVAL is used for invalid >     arguments. > > > > > And does any real-world programs > > > > rely on this? > > > dosemu > > It does this today or wants to do this in the future? > > It does so since 2003/03/15, according > to a change-log (so for 21 year now). > Adding Herbert Xu to CC as an author of > that feature. > > > > > What exactly are you trying to determine with this ioctl > > > > test? > > > Whether it is a PTS (Pseudo-Tty-Slave), or > > > a real comport with MSR signalling. > > Why is that needed? > > To fake modem status lines, mustly DCD. > > > > And why not do it how other programs (like stty) > > does it? > > I am not sure stty is interested in faking > modem status lines. It doesn't seem to be > using TIOCM ioctls at all. > > > > > Is there a different way to determine that? > > > I am not aware of any "canonical" way > > > of determining this. Maybe you tell me. :) > > > So far the only fix I know, is to stop checking > > > errno. But you return ENOTTY for a tty-associated > > > fd (isatty(fd)==1), so I believe this is a > > > bug in a kernel. > > isatty() is a libc provided function, not a kernel call. > It seems to be using TCGETS ioctl() and looks > for it to not return an error. > I still think returning ENOTTY where TCGETS > succeeds, is more than strange. > I looked at the tty code of current linux kernel, > and it returns EOPNOTSUPP in most such cases. > At least that makes sense, but ENOTTY? -ENOTTY is the documented result of invalid ioctl arguments sent, I am pretty sure POSIX requires this somewhere. So this was fixing a requirement here... thanks, greg k-h