Re: [PATCH] n_tty: Remove LINEMODE support

[Peter Hurley <peter@hurleysoftware.com>]

On 01/19/2015 11:36 AM, Howard Chu wrote:
> Peter Hurley wrote:

[...]

>> A description of how the pty master uses EXTPROC to implement line mode would
>> be very helpful, especially to people working in the tty code (eg., me, although
>> I don't need it now).
> 
> The original patch submission carried this description
> http://lkml.iu.edu/hypermail/linux/kernel/1006.2/02428.html

[from linked source]

> Paraphrased from the 1989 BSD patch by David Borman @ cray.com:
> 
> These are the changes needed for the kernel to support
> LINEMODE in the server.
> 
> There is a new bit in the termios local flag word, EXTPROC.
> When this bit is set, several aspects of the terminal driver
> are disabled. Input line editing, character echo, and mapping
> of signals are all disabled. This allows the telnetd to turn
> off these functions when in linemode, but still keep track of
> what state the user wants the terminal to be in.

Ok, but this should go on to describe at least the basics of
transparent local/remote line editing. Even mentioning that
it should be transparent is important.

> New ioctl:
> TIOCSIG Generate a signal to processes in the
> current process group of the pty.

Yes, but documentation should describe why this is important/required/useful.
That is, how this supports client signal handling.

> There is a new mode for packet driver, the TIOCPKT_IOCTL bit.
> When packet mode is turned on in the pty, and the EXTPROC bit
> is set, then whenever the state of the pty is changed, the
> next read on the master side of the pty will have the TIOCPKT_IOCTL
> bit set. This allows the process on the server side of the pty
> to know when the state of the terminal has changed; it can then
> issue the appropriate ioctl to retrieve the new state.

... and go on to outline in a sentence or two what the pty master
process does with this information.

IOW, _how_ does this kernel interface support LINEMODE?

Regards,
Peter Hurley