[ILUG] Serial Port Problem

[Kenn Humborg]

> Hi Friends,
>     How to lock a serial Port ?  I have used the following procedure
> to lock a serial port.
>    1. set group-execute bit off
>    2. group-ID bit on
>     This reflectes a Mandatory locking.  Then I am using
> fcntl function with appropricate parameters to lock the port
> 
> But the problem is ,  even after this procedure I am not able
> to give an exclusive access to Serial Port.  Utilities like
> minicom 'open, write and read' the Serial port which is locked.
> 
> If once a port is opened and locked,  then all successive
> opens to that port must fail, until the port is close/unlocked.
> 
> 
> How can I do it ?

Serial port locking is implemented by a lockfile convention.
For example, /var/lock/uucp/LCK..ttyS0 is a lock file for
ttyS0.  (Or maybe it's /var/lock/LCK..ttyS0).

When I was writing my portserver app, I stole the locking
code from pppd.  I'd suggest that you look at the pppd
sources or at 

   ftp://ftp.bluetree.ie/pub/portserver/portserver-0.1.5.tar.gz

Later,
Kenn