getty: document bits we don't set - maybe we should set some of them?

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/loginutils/getty.c b/loginutils/getty.c
index 4e194c45fd2bb8304728bccccf39285e7daa1b71..2d2184a76b2cd02328ce54add0e8a74089facabe 100644 (file)
--- a/loginutils/getty.c
+++ b/loginutils/getty.c
@@ -264,10 +264,17 @@ static void termios_init(int speed)
        if (option_mask32 & F_RTSCTS)
                G.termios.c_cflag |= CRTSCTS; /* flow control using RTS/CTS pins */
 #endif
+       /* Other bits in c_cflag:
+        * CSTOPB 2 stop bits (1 otherwise)
+        * PARENB Enable parity bit
+        * PARODD Use odd parity (else even)
+        * LOBLK  Block job control output (??)
+        */
        G.termios.c_iflag = 0;
        G.termios.c_lflag = 0;
        /* non-raw output; add CR to each NL */
        G.termios.c_oflag = OPOST | ONLCR;
+
        G.termios.c_cc[VMIN] = 1; /* block reads if < 1 char is available */
        G.termios.c_cc[VTIME] = 0; /* no timeout (reads block forever) */
 #ifdef __linux__
@@ -281,18 +288,55 @@ static void termios_init(int speed)
 
 static void termios_final(void)
 {
-       /* software flow control on output; and on input */
+       /* software flow control on output (stop sending if XOFF is recvd);
+        * and on input (send XOFF when buffer is full)
+        */
        G.termios.c_iflag |= IXON | IXOFF;
        if (G.eol == '\r') {
                G.termios.c_iflag |= ICRNL; /* map CR on input to NL */
        }
-       /* non-raw input; enable SIGINT/QUIT/etc sigs; echo;
-        * echo erase character as BS-space-BS;
-        * echo NL on kill char;
-        * erase entire line via BS-space-BS on kill char */
+       /* Other bits in c_iflag:
+        * IXANY   Any recvd char enables output (any char is also a XON)
+        * INPCK   Enable parity check
+        * IGNPAR  Ignore parity errors (drop bad bytes)
+        * PARMRK  Mark parity errors with 0xff, 0x00 prefix
+        *         (else bad byte is received as 0x00)
+        * ISTRIP  Strip parity bit
+        * IGNBRK  Ignore break condition
+        * BRKINT  Send SIGINT on break - maybe set this?
+        * INLCR   Map NL to CR
+        * IGNCR   Ignore CR
+        * ICRNL   Map CR to NL
+        * IUCLC   Map uppercase to lowercase
+        * IMAXBEL Echo BEL on input line too long
+        * IUTF8   [Appears to affect tty's idea of char widths,
+        *         observed to improve backspacing through Unicode chars]
+         */
+
+       /* line buffered input (NL or EOL or EOF chars end a line);
+        * recognize INT/QUIT/SUSP chars;
+        * echo input chars;
+        * echo BS-SP-BS on erase character;
+        * echo kill char specially, not as ^c (ECHOKE controls how exactly);
+        * erase all input via BS-SP-BS on kill char (else go to next line)
+        */
        G.termios.c_lflag |= ICANON | ISIG | ECHO | ECHOE | ECHOK | ECHOKE;
-       /* echo ctrl chars as ^c; (what is ECHOPRT?) */
-       /* no longer in c_lflag: | ECHOCTL | ECHOPRT */
+       /* Other bits in c_lflag:
+        * XCASE   Map uppercase to \lowercase [tried, doesn't work]
+        * ECHONL  Echo NL even if ECHO is not set
+        * NOFLSH  Don't flush input buffer after interrupt or quit chars
+        * IEXTEN  Enable extended functions (??)
+        *         [glibc says it enables c_cc[LNEXT] "enter literal char"
+        *         and c_cc[VDISCARD] "toggle discard buffered output" chars]
+        * ECHOCTL Echo ctrl chars as ^c (else don't echo) - maybe set this?
+        * ECHOPRT On erase, echo erased chars
+        *         [qwe<BS><BS><BS> input looks like "qwe\ewq/" on screen]
+        * FLUSHO  Output being flushed (c_cc[VDISCARD] is in effect)
+        * PENDIN  Retype pending input at next read or input char
+        *         (c_cc[VREPRINT] is being processes)
+        * TOSTOP  Send SIGTTOU for background output
+        *         (why "stty sane" unsets this bit?)
+        */
 
        G.termios.c_cc[VINTR] = DEF_INTR;
        G.termios.c_cc[VQUIT] = DEF_QUIT;
@@ -305,6 +349,14 @@ static void termios_final(void)
        G.termios.c_cc[VSWTCH] = DEF_SWITCH;
 #endif
        G.termios.c_cc[VKILL] = DEF_KILL;
+       /* Other control chars:
+        * VEOL2
+        * VERASE, VWERASE - (word) erase. we may set VERASE in get_logname
+        * VREPRINT - reprint current input buffer
+        * VLNEXT, VDISCARD, VSTATUS
+        * VSUSP, VDSUSP - send (delayed) SIGTSTP
+        * VSTART, VSTOP - chars used for IXON/IXOFF
+        */
 
        if (tcsetattr_stdin_TCSANOW(&G.termios) < 0)
                bb_perror_msg_and_die("tcsetattr");