Refactor, move speed parser from getty() to prepare_tty()

This patch relocates the speed parser so that exec.c can set the TTY
speed properly as soon as possible.  For external getty we make sure
to not touch the TTY speed.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/stty.c

@@ -21,10 +21,64 @@
  * THE SOFTWARE.
  */
 
+#include <errno.h>
+#include <stdlib.h>
 #include <unistd.h>	      /* _POSIX_VDISABLE */
 #include <sys/ttydefaults.h>  /* Not included by default in musl libc */
 #include <termios.h>
 
+speed_t stty_parse_speed(char *baud)
+{
+	char *ptr;
+	size_t i;
+	unsigned long val;
+	struct { unsigned long val; speed_t speed; } v2s[] = {
+		{       0, B0       },
+		{      50, B50      },
+		{      75, B75      },
+		{     110, B110     },
+		{     134, B134     },
+		{     150, B150     },
+		{     200, B200     },
+		{     300, B300     },
+		{     600, B600     },
+		{    1200, B1200    },
+		{    1800, B1800    },
+		{    2400, B2400    },
+		{    4800, B4800    },
+		{    9600, B9600    },
+		{   19200, B19200   },
+		{   38400, B38400   },
+		{   57600, B57600   },
+		{  115200, B115200  },
+		{  230400, B230400  },
+		{  460800, B460800  },
+		{  500000, B500000  },
+		{  576000, B576000  },
+		{  921600, B921600  },
+		{ 1000000, B1000000 },
+		{ 1152000, B1152000 },
+		{ 1500000, B1500000 },
+		{ 2000000, B2000000 },
+		{ 2500000, B2500000 },
+		{ 3000000, B3000000 },
+		{ 3500000, B3500000 },
+		{ 4000000, B4000000 },
+	};
+
+	errno = 0;
+	val = strtoul(baud, &ptr, 10);
+	if (errno || ptr == baud)
+		return B0;
+
+	for (i = 0; i < sizeof(v2s) / sizeof(v2s[0]); i++) {
+		if (v2s[i].val == val)
+			return v2s[i].speed;
+	}
+
+	return B0;
+}
+
 void stty(int fd, speed_t speed)
 {
 	struct termios term;
@@ -33,9 +87,11 @@ void stty(int fd, speed_t speed)
 	if (tcgetattr(fd, &term))
 		return;
 
-	cfsetispeed(&term, speed);
-	cfsetospeed(&term, speed);
-	tcsetattr(fd, TCSAFLUSH, &term);
+	if (speed != B0) {
+		cfsetispeed(&term, speed);
+		cfsetospeed(&term, speed);
+		tcsetattr(fd, TCSAFLUSH, &term);
+	}
 	tcflush(fd, TCIOFLUSH);
 
 	/* Disable modem specific flags */