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

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

1 files changed, 59 insertions, 7 deletions

diff --git a/loginutils/getty.c b/loginutils/getty.c
index 4e194c45f..2d2184a76 100644
--- 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");