On 2019-08-03 18:14, Theo de Raadt wrote:
Adam Thompson <athom...@athompso.net> wrote:
Summary: I open cua0 with cu(1), quit cu(1), try to re-open with
cu(1) but now it immediately fails with EBUSY. *Usually* doesn't
happen with USB-to-serial (cuaU[0-9]) but have still seen it once or
twice.
[...]
You are observing the forcing-down of DTR and RTS for a long enough
period that the other side of the link notices the event.
Therefore it is not suprising you are finding this behaviour very
similar in many drivers and operating systems.
Thanks!
I feel as though I'm seeing something that's slightly off (see below),
but I was focused on the open() end of things not the close() end - I
now need to do more reading.
FWIW, things that don't *feel* right about this:
* "long enough" doesn't typically describe multiple days, in DTE/DCE
signalling. Far-end device is the same when testing using cua00 vs.
cuaU0.
* isn't cua(4) supposed to be the device we use to ignore line signals?
Why would closing it fiddle with line status? Maybe I'm reading too
much into hupcl in stty(1) manpage...
* and now I'm wondering if cu(1) fiddles with [-]clocal and/or [-]hupcl
As I said, more reading now you've given me a direction and I'll
probably come back with at least one or two of my own answers.
-Adam
