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 <johan@xxxxxxxxxx>
AuthorDate: Wed Apr 7 11:52:02 2021 +0200
Commit: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
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?
