Status of kernel

[Samuel Thibault]

Okash Khawaja, on Tue 15 Nov 2016 06:58:24 +0000, wrote:
>     On Tue, Nov 15, 2016 at 6:36 AM, Samuel Thibault <[2]
>     samuel.thibault at ens-lyon.org> wrote:
>         > And how will /dev/ttyx be used?
> 
>         It won't be used. As a line discipline speakup will plug higher in the
>         stack.
> 
>     Could you explain this more? May be a concrete example?
> I mean is this something that a user space application will read from?

Normally what happens, for instance when running a serial mouse driver,
is that a userland program opens /dev/ttyS0, calls an ioctl to set the
N_MOUSE line discipline, and then leaves /dev/ttyS0 alone. All the work
is done by the line discipline, userland doesn't do any read/write on
the device. I.e. the line discipline catches the data before it reaches
userland.

> If so, what is the specific advantage of speakup being line
> discipline?

It's simply because that's the way things work for all other drivers
"over serial lines", like mice, joysticks ppp, gsm, etc. There is then
no risk for speakup to break at all, these have been working for decades
without a fuss. And they will work with anything that looks more or less
like a serial port, be it ISA, PCI, USB, bluetooth, irda, whatever.

> Please add any links/documentation that will help
> understand this. Thanks

Unfortunately line disciplines are a rather obscure area not many people
work on.

There is linux/Documentation/serial/tty.txt

>         > Also is there a link to where you pasted your idea from?
> 
>         I wrote it.
> 
>     Of course. I mean a link to full discussion to get more context.

There is a thread starting here:

http://www.spinics.net/lists/linux-serial/msg21752.html

Samuel