From: valdis.kletnieks@vt.edu
To: noloader@gmail.com
Cc: kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: How to make /dev/ttyACM0 (and friends) exclusive?
Date: Sun, 03 Mar 2019 00:55:50 -0500 [thread overview]
Message-ID: <8247.1551592550@turing-police> (raw)
In-Reply-To: <CAH8yC8kkwZLD+get-V-kp1jYMmG7ovYTnQVJdis-DdCyVGTzdw@mail.gmail.com>
On Sat, 02 Mar 2019 14:36:12 -0500, Jeffrey Walton said:
> I feel like I am missing something... Does Linux consider the modem a
> shared resource instead of an exclusive resource? What use cases
> support two different programs sending commands to the modem at the
> same time?
The Linux kernel has exactly zero clue what a "modem" is. It's talking to a
serial port, and doesn't care where the other end of the serial cable is. If
you have a onboard modem, that cable may be all of 2 mm long and consist of a
bunch of traces between two chips on a PCB, or even internal connections
between two sides of a chip, but it's still there.
So the correct question is "what use cases have two programs talking to the
same serial port"?
And the answer is: A lot. For a long time, there were these things called
"terminals", that the younger folk may not have encountered. And a very common
use case was to login via a terminal. At that point, you usually had a login
shell like bash or similar running and often doing I/O to the terminal - and if
you ran any sub-processes, they also would do I/O to the terminal. So consider
the following bash one-liner:
% for i in `seq 1 10`; do echo "Loop number $i"; date; sleep 1; done
How and why does this work? (Hint 1: 'echo' is a bash builtin, Hint 2:
think about how a shell handles stdin/out for child processes)
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next prev parent reply other threads:[~2019-03-03 5:56 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-02 4:29 How to make /dev/ttyACM0 (and friends) exclusive? Jeffrey Walton
2019-03-02 7:50 ` Greg KH
2019-03-02 18:45 ` valdis.kletnieks
2019-03-02 19:36 ` Jeffrey Walton
2019-03-03 5:55 ` valdis.kletnieks [this message]
2019-03-03 8:55 ` Jeffrey Walton
2019-03-03 11:00 ` Greg KH
2019-03-04 13:04 ` Jeffrey Walton
2019-03-04 13:20 ` Greg KH
2019-03-04 15:38 ` Yann Droneaud
2019-03-04 22:01 ` valdis.kletnieks
2020-10-06 20:41 ` Daniel Santos
2020-10-11 14:52 ` linux lover
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