getty: explain every bit in termios; remove redundant stuff in termios_final
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/loginutils/getty.c b/loginutils/getty.c
index b71d68a..29d889f 100644
--- a/loginutils/getty.c
+++ b/loginutils/getty.c
@@ -106,15 +106,15 @@
//usage:#define getty_full_usage "\n\n"
//usage: "Open a tty, prompt for a login name, then invoke /bin/login\n"
//usage: "\nOptions:"
-//usage: "\n -h Enable hardware (RTS/CTS) flow control"
-//usage: "\n -i Don't display /etc/issue"
-//usage: "\n -L Local line, set CLOCAL on it"
+//usage: "\n -h Enable hardware RTS/CTS flow control"
+//usage: "\n -L Set CLOCAL (ignore Carrier Detect state)"
//usage: "\n -m Get baud rate from modem's CONNECT status message"
+//usage: "\n -n Don't prompt for login name"
//usage: "\n -w Wait for CR or LF before sending /etc/issue"
-//usage: "\n -n Don't prompt for a login name"
+//usage: "\n -i Don't display /etc/issue"
//usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue"
//usage: "\n -l LOGIN Invoke LOGIN instead of /bin/login"
-//usage: "\n -t SEC Terminate after SEC if no username is read"
+//usage: "\n -t SEC Terminate after SEC if no login name is read"
//usage: "\n -I INITSTR Send INITSTR before anything else"
//usage: "\n -H HOST Log HOST into the utmp file as the hostname"
//usage: "\n"
@@ -251,20 +251,27 @@
* reads will be done in raw mode anyway. Errors will be dealt with
* later on.
*/
+ /* 8 bits; hangup (drop DTR) on last close; enable receive */
G.termios.c_cflag = CS8 | HUPCL | CREAD;
- if (option_mask32 & F_LOCAL)
+ if (option_mask32 & F_LOCAL) {
+ /* ignore Carrier Detect pin:
+ * opens don't block when CD is low,
+ * losing CD doesn't hang up processes whose ctty is this tty
+ */
G.termios.c_cflag |= CLOCAL;
- G.termios.c_iflag = 0;
- G.termios.c_lflag = 0;
- G.termios.c_oflag = OPOST | ONLCR;
- G.termios.c_cc[VMIN] = 1;
- G.termios.c_cc[VTIME] = 0;
-#ifdef __linux__
- G.termios.c_line = 0;
-#endif
+ }
#ifdef CRTSCTS
if (option_mask32 & F_RTSCTS)
- G.termios.c_cflag |= CRTSCTS;
+ G.termios.c_cflag |= CRTSCTS; /* flow control using RTS/CTS pins */
+#endif
+ 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__
+ G.termios.c_line = 0;
#endif
tcsetattr_stdin_TCSANOW(&G.termios);
@@ -274,12 +281,17 @@
static void termios_final(void)
{
- /* General terminal-independent stuff */
- G.termios.c_iflag |= IXON | IXOFF; /* 2-way flow control */
+ /* software flow control on output; and on input */
+ 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/ec sigs; echo; echo NL on kill char;
+ * erase entire line via BS-space-BS on kill char */
G.termios.c_lflag |= ICANON | ISIG | ECHO | ECHOE | ECHOK | ECHOKE;
- /* no longer in lflag: | ECHOCTL | ECHOPRT */
- G.termios.c_oflag |= OPOST;
- /* G.termios.c_cflag = 0; */
+ /* echo ctrl chars as ^c; (what is ECHOPRT?) */
+ /* no longer in c_lflag: | ECHOCTL | ECHOPRT */
+
G.termios.c_cc[VINTR] = DEF_INTR;
G.termios.c_cc[VQUIT] = DEF_QUIT;
G.termios.c_cc[VEOF] = DEF_EOF;
@@ -290,22 +302,8 @@
#ifdef VSWTCH
G.termios.c_cc[VSWTCH] = DEF_SWITCH;
#endif
-
- /* Account for special characters seen in input */
- if (G.eol == '\r') {
- G.termios.c_iflag |= ICRNL; /* map CR in input to NL */
- /* already done by termios_init */
- /* G.termios.c_oflag |= ONLCR; map NL in output to CR-NL */
- }
G.termios.c_cc[VKILL] = DEF_KILL;
-#ifdef CRTSCTS
- /* Optionally enable hardware flow control */
- if (option_mask32 & F_RTSCTS)
- G.termios.c_cflag |= CRTSCTS;
-#endif
-
- /* Finally, make the new settings effective */
if (tcsetattr_stdin_TCSANOW(&G.termios) < 0)
bb_perror_msg_and_die("tcsetattr");
}
@@ -330,11 +328,7 @@
* modem status messages is enabled.
*/
- /*
- * Don't block if input queue is empty.
- * Errors will be dealt with later on.
- */
- G.termios.c_cc[VMIN] = 0; /* don't block if queue empty */
+ G.termios.c_cc[VMIN] = 0; /* don't block reads (min read is 0 chars) */
tcsetattr_stdin_TCSANOW(&G.termios);
/*
@@ -538,6 +532,7 @@
/* Set the optional timer */
alarm(G.timeout); /* if 0, alarm is not set */
+//BUG: death by signal won't restore termios
/* Optionally wait for CR or LF before writing /etc/issue */
if (option_mask32 & F_WAITCRLF) {