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

From: Howard Chu
Date: Tue Jun 15 2010 - 15:54:58 EST

Alan Cox wrote:
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.

OK, since you mention it again down below I'll respond to this last.

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.

I'm grubbing around looking for a live Alpha system now, doesn't seem likely that I'll find one. Not sure what needs to match here, it's also unlikely that OSF/1 (or any other SVR4 platform) ever provided a definition for this bit. Looking at the telnet README:
This is a distribution of both client and server telnet. These programs
have been compiled on:
telnet telnetd
BSD 4.4 x x
BSD 4.3 Reno X X
BSDI 1.0 X X
Solaris 2.2 x x (no linemode in server)
Solaris 2.3 x x (no linemode in server)
SunOs 4.1.3 X X (no linemode in server)
Ultrix 4.3 X X (no linemode in server)
DYNIX V3.0.17.9 X X (no linemode in server)
HP-UX 8.0 x x (no linemode in server)

I doubt that anyone ever ported this feature over to those OSes.

+ 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)

Are you suggesting that this is completely unfixable/unworkable? Would it be sufficient to use kernel_termios_to_user_termios() ?

-- Howard Chu
CTO, Symas Corp.
Director, Highland Sun
Chief Architect, OpenLDAP
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