Re: [Boost-users] Boost ASIO 1.66 serial port open seem to never fail opening (at least the way i'm using it)

Subject: Re: [Boost-users] Boost ASIO 1.66 serial port open seem to never fail opening (at least the way i'm using it)
From: Klebsch, Mario (Mario.Klebsch_at_[hidden])
Date: 2018-01-11 14:08:10

Hello,

this probably is a linux issue.

> i'm using boost asio 1.66 serial port on a Ubuntu Mate 64 machine, and
> I facing the fact that open("port name", error_code) command on an
> already openned port do not return an error.
> 
> My test sequence :
> 
> On the same machine I pre-open /dev/ttsS0 on minicom : minicom -D
> /dev/ttyS0 and check that is indeed open by sending some chars.

You could use /dev/cua*-devices for this instead of /dev/ttyS*.

/dev/cua*-Devicess take exclusive use of the serial port, while /dev/ttyS* are intended for being used in interactive sessions (with a serial terminal attached).

Until recently, the linux kernel included a file Documentation/devices.txt (It was there in Linux-4.9.72) saying /dev/cua* are major 5, minor 64 and up. Newer kernels describe the cua*-devices in Documentation/admin-guide/devices.rst.

> Now while minicom still openned, I try openning a second minicom on
> same
> /dev/ttyS0 and this return an error : "device /dev/ttyS0 locked" as
> expected.

This works, because minicom uses additional locking with a lock-file. If you strace minicom, you will see, that minicom not even tried to open /dev/ttyS0.

The locking procedure for serial ports also is described in Documentation/admin-guide/devices.rst.

73, Mario
-- 
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