Re: [PATCH v2] agetty: don't put the VC into canonical mode

[Karel Zak <kzak@redhat.com>]

On Tue, Oct 16, 2018 at 08:41:49AM +0200, Lubomir Rintel wrote:
> The wait_for_term_input()'s select() needs to be tripped when the user
> starts typing. Otherwise the reloads can abort an already in-progress login.
> 
> Coupled with \4 and \6 expansions that happen to be there on Fedora Server,
> this means reload on every netlink event. With a couple of IPv6 routers
> announcing their networks and temporary addresses in use can make it
> sometimes virtually impossible to log in.

It's too late for v2.33. It also seems we need to wait for Stanislav's
work on this issue -- his idea is to complete disable the reload
notification when user start typing, and it also requires to switch
to non-canonical mode.

This is definitely something we need to fix in v2.34 and v2.33.1.

> Seems like zero lflags do the job just fine on a Linux VT. Reset it to
> canonical mode before running login.

What about Del/Backspace keys when user is typing login name? :-)

    Karel

> Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
> 
> ---
> Changes since v1:
> - Unreversed the logic in termio_final()/reset_vc() conditional
> 
> Tested on a vc and serial console on a stock Fedora installation:
> 
>   /sbin/agetty -o -p -- \u --noclear tty1 linux
>   /sbin/agetty -o -p -- \u --keep-baud 115200,38400,9600 ttyS2 vt220
> 
>  term-utils/agetty.c | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/term-utils/agetty.c b/term-utils/agetty.c
> index 3c87ec64e..3834813f1 100644
> --- a/term-utils/agetty.c
> +++ b/term-utils/agetty.c
> @@ -303,7 +303,7 @@ static void parse_speeds(struct options *op, char *arg);
>  static void update_utmp(struct options *op);
>  static void open_tty(char *tty, struct termios *tp, struct options *op);
>  static void termio_init(struct options *op, struct termios *tp);
> -static void reset_vc (const struct options *op, struct termios *tp);
> +static void reset_vc(const struct options *op, struct termios *tp, int canon);
>  static void auto_baud(struct termios *tp);
>  static void list_speeds(void);
>  static void output_special_char (unsigned char c, struct options *op,
> @@ -485,13 +485,14 @@ int main(int argc, char **argv)
>  	if (options.timeout)
>  		alarm(0);
>  
> -	if ((options.flags & F_VCONSOLE) == 0) {
> -		/* Finalize the termios settings. */
> +	/* Finalize the termios settings. */
> +	if ((options.flags & F_VCONSOLE) == 0)
>  		termio_final(&options, &termios, &chardata);
> +	else
> +		reset_vc(&options, &termios, 1);
>  
> -		/* Now the newline character should be properly written. */
> -		write_all(STDOUT_FILENO, "\r\n", 2);
> -	}
> +	/* Now the newline character should be properly written. */
> +	write_all(STDOUT_FILENO, "\r\n", 2);
>  
>  	sigaction(SIGQUIT, &sa_quit, NULL);
>  	sigaction(SIGINT, &sa_int, NULL);
> @@ -1234,7 +1235,7 @@ static void termio_init(struct options *op, struct termios *tp)
>  		setlocale(LC_CTYPE, "POSIX");
>  		op->flags &= ~F_UTF8;
>  #endif
> -		reset_vc(op, tp);
> +		reset_vc(op, tp, 0);
>  
>  		if ((tp->c_cflag & (CS8|PARODD|PARENB)) == CS8)
>  			op->flags |= F_EIGHTBITS;
> @@ -1344,7 +1345,7 @@ static void termio_init(struct options *op, struct termios *tp)
>  }
>  
>  /* Reset virtual console on stdin to its defaults */
> -static void reset_vc(const struct options *op, struct termios *tp)
> +static void reset_vc(const struct options *op, struct termios *tp, int canon)
>  {
>  	int fl = 0;
>  
> @@ -1353,6 +1354,15 @@ static void reset_vc(const struct options *op, struct termios *tp)
>  
>  	reset_virtual_console(tp, fl);
>  
> +#ifdef AGETTY_RELOAD
> +	/*
> +	 * Discard all the flags that makes the line go canonical with echoing.
> +	 * We need to know when the user starts typing.
> +	 */
> +	if (canon == 0)
> +		tp->c_lflag = 0;
> +#endif
> +
>  	if (tcsetattr(STDIN_FILENO, TCSADRAIN, tp))
>  		log_warn(_("setting terminal attributes failed: %m"));
>  
> -- 
> 2.19.1
> 

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com