[PATCH] cttyhack: print detected ctty name when called without parameters

[Alexander Shishkin]

Sometimes there's a need to figure out the controlling tty from a shell
script, for example, to obtain a line for getty. In this case it's easier
to call cttyhack than trying to repeat some of the cttyhack's logic.

function                                             old     new   delta
cttyhack_main                                        324     320      -4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-4)               Total: -4 bytes

Signed-off-by: Alexander Shishkin <virtuoso at slind.org>
---
 shell/cttyhack.c |   40 +++++++++++++++++++++-------------------
 1 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/shell/cttyhack.c b/shell/cttyhack.c
index 6241c76..772f8b8 100644
--- a/shell/cttyhack.c
+++ b/shell/cttyhack.c
@@ -50,6 +50,9 @@
 //config:
 //config:	  # exec setsid sh -c 'exec sh </dev/tty1 >/dev/tty1 2>&1'
 //config:
+//config:	  Starting getty on a controlling tty from a shell script:
+//config:
+//config:	  # getty $(cttyhack) 115200
 
 //usage:#define cttyhack_trivial_usage
 //usage:       "PROG ARGS"
@@ -108,14 +111,10 @@ int cttyhack_main(int argc UNUSED_PARAM, char **argv)
 		char paranoia[sizeof(struct serial_struct) * 3];
 	} u;
 
-	if (!*++argv) {
-		bb_show_usage();
-	}
-
 	strcpy(console, "/dev/tty");
 	fd = open(console, O_RDWR);
 	if (fd >= 0) {
-		/* We already have ctty, nothing to do */
+		/* We already have ctty, don't try to detect it. */
 		close(fd);
 	} else {
 		/* We don't have ctty (or don't have "/dev/tty" node...) */
@@ -145,24 +144,27 @@ int cttyhack_main(int argc UNUSED_PARAM, char **argv)
 			}
 #endif
 			/* nope, could not find it */
-			goto ret;
+			console[0] = '\0';
 		} while (0);
+	}
 
-		fd = open_or_warn(console, O_RDWR);
-		if (fd < 0)
-			goto ret;
-		//bb_error_msg("switching to '%s'", console);
-		dup2(fd, 0);
-		dup2(fd, 1);
-		dup2(fd, 2);
-		while (fd > 2)
-			close(fd--);
-		/* Some other session may have it as ctty,
-		 * steal it from them:
-		 */
-		ioctl(0, TIOCSCTTY, 1);
+	if (!*++argv) {
+		puts(console);
+		return EXIT_SUCCESS;
 	}
 
+	/* If it's a /dev/tty, still make sure it's wired to std{in,out,err} */
+	fd = open_or_warn(console, O_RDWR);
+	if (fd < 0)
+		goto ret;
+	//bb_error_msg("switching to '%s'", console);
+	dup2(fd, STDIN_FILENO);
+	dup2(fd, STDOUT_FILENO);
+	xmove_fd(fd, STDERR_FILENO);
+	/* Some other session may have it as ctty,
+	 * steal it from them:
+	 */
+	ioctl(0, TIOCSCTTY, 1);
 ret:
 	BB_EXECVP_or_die(argv);
 }
-- 
1.7.2.1.45.gb66c2