Re: tty loop-back device

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2013-09-28, Matwey V. Kornilov <matwey.kornilov@gmail.com> wrote:
> 28.09.2013 21:21, Matwey V. Kornilov ?????:
>> It seems that BSD and Unix98 pty's may coexist in pty.c. So, there is a
>> chance that it is possible to add support of Extended pty not breaking
>> existing things. One need to be a brave to change something in pty.c, It
>> is quite critical part.
>
> It seems that we need new line discipline to allow async notification of 
> master tty when the client changes tty->termios. poll() has to be 
> reimplemented to generate POLLPRI, when tty->termios handling required 
> on the master side, then master may use special ioctl to read 
> tty->termios requested.

I was thinking about initially just creating a blocking ioctl() call
that the master can use to wait for either a termios configuration
change or a modem control line change.  I admit that's not as elegent:
it would mean a master would need multiple threads in most cases (one
for data and one for config and modem status).  But, it may be a less
intrusive change [I haven't looked at the poll implementation in any
detail, so perhaps the poll change isn't as bad as I fear.]

Having to use multiple threads in a master sounds ugly at first, but
it's still orders of magnitude easier than implementing a serial
driver in kernel space that uses network I/O to communicate with the
physical UART.

-- 
Grant