Re: stty: problem if IXON enabled and DC3 char was received

[Pádraig Brady]

On 04/01/16 08:06, Tomas Krcka wrote:
> Hi,
>   I had a problem with setting baudrate of serial line by stty command.
> I tried to change the baudrate, but the stty went to frozen state.
> I found out that problem is that kernel has IXON enabled as default
> and before change of speed the line received DC3 char. It's illegal
> character in this situation, it happens once per 100 starts of the
> system.
> 
> Example situation:
>    IXON is enabled in kernel by default and a serial line received DC3
> char and then you can not disable IXON. There is waiting for empty
> buffer in kernel but sending is stopped because of DC3 char.
> 
> If TCSADRAIN is changed to TCSANOW then it's correct.
> 
> Do you have any opinion about the situation ? Is it possible to change
> TCSADRAIN to TCSANOW or create a new parameter of stty to change the
> serial line settings immediately ?

Interesting. I see that Red Hat systems for the last 6 years
have unconditionally used TCSANOW rather than TCSADRAIN due to:
https://bugzilla.redhat.com/504798

I see a similar 13 year old request to debian:
https://bugs.debian.org/210475

I see that FreeBSD uses TCSANOW (well the equivalent 0 value).

Now it's tempting to use TCSANOW unconditionally
though it does seem safer to drain pending output before changing settings,
so an option like you suggest seems appropriate.

thanks,
Pádraig