Re: [PATCH] tty: Add EXTPROC support for LINEMODE

From: Alan Cox
Date: Tue Jun 15 2010 - 15:26:20 EST

> bit set, and the data will be the contents of a struct termios.
> This allows the process on the server side of the pty to know
> when the state of the terminal has changed, and what the new
> state is.

First problem - the kernel and user idea of struct termios don't match.

> diff --git a/arch/alpha/include/asm/termbits.h b/arch/alpha/include/asm/termbits.h
> index ad854a4..879dd35 100644
> --- a/arch/alpha/include/asm/termbits.h
> +++ b/arch/alpha/include/asm/termbits.h
> @@ -180,6 +180,7 @@ struct ktermios {
> #define FLUSHO 0x00800000
> #define PENDIN 0x20000000
> #define IEXTEN 0x00000400
> +#define EXTPROC 0x10000000

For Alpha this value should match OSF if possible.

> + if (cs & TIOCPKT_IOCTL) {
> + c = sizeof(struct termios);
> + if (c > nr)
> + c = nr;
> + copy_to_user(b, tty->link->termios, c);
> + nr -= c;
> + b += c;
> + }

This is where the wheels come off the bus.

The kernel use struct ktermios which is what tty->link->termios is

The C library presents this via struct termios which is a glibc invention
dependant on the C library and which is converted by libc from struct
termios or struct termios2 depending on your C library

How you fix that given a broken by design historic Unix interface which
pastes arbitary struct termios objects into the data stream is an
interesting question - doubly so when like most Unixen we have also have
extended terminal attributes as well (termiox)

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