Enhancing pty driver to act like a serial port?

Enhancing pty driver to act like a serial port?

[Grant Edwards]

The question of emulating a serial port in user-space has come
up a number of times in various contexts during the past few
years.  

The current pty driver isn't really sufficient when the
application actually expects to be connected to a physical
serial port: you can't set parity or word length, and the modem
control/status ioctl() calls fail.

That means that many applications just won't run when told to
use a pty instead of a normal serial port.

If one were to enhance the pty driver to support the same
operations as a serial port, would the "powers that be" be
amenable to accepting such changes into the main pty driver
sources?

Or is this even the right place to discuss the pty driver?

-- 
Grant

Enhancing pty driver to act like a serial port?

[Peter Åstrand]

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>The question of emulating a serial port in user-space has come
>up a number of times in various contexts during the past few
>years.  
>
>The current pty driver isn't really sufficient when the
>application actually expects to be connected to a physical
>serial port: 

A better userspace solution would be great. I'm maintaining 
cyclades-serial-client. It relies on LD_PRELOAD, which is not very 
elegant. 



>you can't set parity or word length, and the modem
>control/status ioctl() calls fail.

Oh. I was just investigating why it's not possible to set "cs7" on the 
pty. stty fails with:

$ stty cs7 -F /my/pty
stty: /my/pty: unable to perform all requested operations

I guess this explains it. 



Best regards, 
---
Peter Åstrand		ThinLinc Chief Developer
Cendio AB		http://www.cendio.se
Wallenbergs gata 4
583 30 Linköping	Phone: +46-13-21 46 00
---
Open Source Developers wanted - http://www.cendio.com/about-cendio/career

Re: Enhancing pty driver to act like a serial port?

[Grant Edwards]

On 2008-06-22, Peter Åstrand <astrand@cendio.se> wrote:
>
>>The question of emulating a serial port in user-space has come
>>up a number of times in various contexts during the past few
>>years.  
>>
>>The current pty driver isn't really sufficient when the
>>application actually expects to be connected to a physical
>>serial port: 
>
> A better userspace solution would be great. I'm maintaining 
> cyclades-serial-client. It relies on LD_PRELOAD, which is not
> very elegant. 

I can imagine.   (I used a few Cyclades 8-port boards many
years ago, and always liked Cyclades' product lines).

>>you can't set parity or word length, and the modem
>>control/status ioctl() calls fail.
>
> Oh. I was just investigating why it's not possible to set
> "cs7" on the pty. stty fails with:
>
> $ stty cs7 -F /my/pty
> stty: /my/pty: unable to perform all requested operations
>
> I guess this explains it. 

Yup.  It wouldn't be difficult at all to make the pty driver
act like a serial device, but there's a huge difference between
something being easy to change and getting those changes
accepted.  Judging by the silence I got in response to my query
the chances of such a change being accepted are pretty much
zero.

-- 
Grant Edwards                   grante             Yow!  The PINK SOCKS were
                                  at               ORIGINALLY from 1952!! But
                               visi.com            they went to MARS around
                                                   1953!!

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