linux-kernel - Re: [PATCH] tty: Add EXTPROC support for LINEMODE

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Date:	Tue, 15 Jun 2010 20:29:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	hyc@...as.com
Cc:	linux-kernel@...r.kernel.org, <greg@...ah.com>, Alan@...as.com,
	Cox@...as.com, Greg@...as.com, KH@...as.com
Subject: Re: [PATCH] tty: Add EXTPROC support for LINEMODE

>      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)

Alan
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