openvt: fix gross mismatch between us and "standard" openvt.

  standard one even has different syntax!
  std: "openvt -c 12", we: "openvt 12"
  std: "openvt top", we: complain that "top" is not a number.
openvt: implement -c -w -s (-l -f -v are also accepted but ingnored)

openvt_main                                          188     343    +155
vfork_child                                            -      67     +67
not_vt_fd                                              -      23     +23
packed_usage                                       23932   23952     +20
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 2/0 up/down: 265/0)             Total: 265 bytes
   text    data     bss     dec     hex filename
 801344     641    7380  809365   c5995 busybox_old
 801617     641    7380  809638   c5aa6 busybox_unstripped

1 files changed, 148 insertions, 13 deletions

diff --git a/console-tools/openvt.c b/console-tools/openvt.c
index 39b9859..6f2aa19 100644
--- a/console-tools/openvt.c
+++ b/console-tools/openvt.c
@@ -8,29 +8,164 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
-/* getopt not needed */
-
+#include <linux/vt.h>
 #include "libbb.h"
 
+/* "Standard" openvt's man page (we do not support all of this):
+
+openvt [-c NUM] [-fsulv] [--] [command [args]]
+
+Find the first available VT, and run command on it. Stdio is directed
+to that VT. If no command is specified then $SHELL is used.
+
+-c NUM
+    Use the given VT number, not the first free one.
+-f
+    Force opening a VT: don't try to check if VT is already in use.
+-s
+    Switch to the new VT when starting the command.
+    The VT of the new command will be made the new current VT.
+-u
+    Figure out the owner of the current VT, and run login as that user.
+    Suitable to be called by init. Shouldn't be used with -c or -l.
+-l
+    Make the command a login shell: a "-" is prepended to the argv[0]
+    when command is executed.
+-v
+    Verbose.
+-w
+    Wait for command to complete. If -w and -s are used together,
+    switch back to the controlling terminal when the command completes.
+
+bbox:
+-u: not implemented
+-f: always in effect
+-l: not implemented, ignored
+-v: ignored
+-ws: does NOT switch back
+*/
+
+/* Helper: does this fd understand VT_xxx? */
+static int not_vt_fd(int fd)
+{
+	struct vt_stat vtstat;
+	return ioctl(fd, VT_GETSTATE, &vtstat); /* !0: error, it's not VT fd */
+}
+
+/* Helper: get a fd suitable for VT_xxx */
+static int get_vt_fd(void)
+{
+	int fd;
+
+	/* Do we, by chance, already have it? */
+	for (fd = 0; fd < 3; fd++)
+		if (!not_vt_fd(fd))
+    			return fd;
+	/* _only_ O_NONBLOCK: ask for neither read not write perms */
+	fd = open(DEV_CONSOLE, O_NONBLOCK);
+	if (fd >= 0 && !not_vt_fd(fd))
+		return fd;
+	bb_error_msg_and_die("can't find open VT");
+}
+
+static int find_free_vtno(void)
+{
+	int vtno;
+	int fd = get_vt_fd();
+
+ 	errno = 0;
+	/*xfunc_error_retval = 3; - do we need compat? */
+	if (ioctl(fd, VT_OPENQRY, &vtno) != 0 || vtno <= 0)
+		bb_perror_msg_and_die("can't find open VT");
+// Not really needed, grep for DAEMON_ONLY_SANITIZE
+//	if (fd > 2)
+//		close(fd);
+	return vtno;
+}
+
+/* vfork scares gcc, it generates bigger code.
+ * Keep it away from main program.
+ * TODO: move to libbb; or adapt existing libbb's spawn().
+ */
+static NOINLINE void vfork_child(char **argv)
+{
+	if (vfork() == 0) {
+		/* CHILD */
+		/* Try to make this VT our controlling tty */
+		setsid(); /* lose old ctty */
+		ioctl(0, TIOCSCTTY, 0 /* 0: don't forcibly steal */);
+		//bb_error_msg("our sid %d", getsid(0));
+		//bb_error_msg("our pgrp %d", getpgrp());
+		//bb_error_msg("VT's sid %d", tcgetsid(0));
+		//bb_error_msg("VT's pgrp %d", tcgetpgrp(0));
+		BB_EXECVP(argv[0], argv);
+		bb_perror_msg_and_die("exec %s", argv[0]);
+	}
+}
+
 int openvt_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int openvt_main(int argc, char **argv)
+int openvt_main(int argc ATTRIBUTE_UNUSED, char **argv)
 {
-	char vtname[sizeof(VC_FORMAT) + 2];
+	char vtname[sizeof(VC_FORMAT) + sizeof(int)*3];
+	char *str_c;
+	int vtno;
+	int flags;
+	enum {
+		OPT_c = (1 << 0),
+		OPT_w = (1 << 1),
+		OPT_s = (1 << 2),
+		OPT_l = (1 << 3),
+		OPT_f = (1 << 4),
+		OPT_v = (1 << 5),
+	};
 
-	if (argc < 3)
-		bb_show_usage();
+	/* "+" - stop on first non-option */
+	flags = getopt32(argv, "+c:wslfv", &str_c);
+	argv += optind;
 
-	/* check for illegal vt number: < 1 or > 63 */
-	sprintf(vtname, VC_FORMAT, (int)xatou_range(argv[1], 1, 63));
+	if (flags & OPT_c) {
+		/* Check for illegal vt number: < 1 or > 63 */
+		vtno = xatou_range(str_c, 1, 63);
+	} else {
+		vtno = find_free_vtno();
+	}
 
-	bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
-	/* grab new one */
+	/* Grab new VT */
+	sprintf(vtname, VC_FORMAT, vtno);
+	/* (Try to) clean up stray open fds above fd 2 */
+	bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS | DAEMON_ONLY_SANITIZE, NULL);
 	close(0);
+	/*setsid(); - BAD IDEA: after we exit, child is SIGHUPed... */
 	xopen(vtname, O_RDWR);
+
+	if (flags & OPT_s) {
+		xioctl(0, VT_ACTIVATE, (void*)(ptrdiff_t)vtno);
+		xioctl(0, VT_WAITACTIVE, (void*)(ptrdiff_t)vtno);
+	}
+
+	if (!argv[0]) {
+		argv--;
+		argv[0] = getenv("SHELL");
+		if (!argv[0])
+			argv[0] = (char *) DEFAULT_SHELL;
+		/*argv[1] = NULL; - already is */
+	}
+
 	xdup2(0, STDOUT_FILENO);
 	xdup2(0, STDERR_FILENO);
 
-	argv += 2;
-	BB_EXECVP(argv[0], argv);
-	_exit(1);
+#ifdef BLOAT
+	/* Handle -l (login shell) option */
+	const char *prog = argv[0];
+	if (flags & OPT_l)
+		argv[0] = xasprintf("-%s", argv[0]);
+#endif
+
+	vfork_child(argv);
+	if (flags & OPT_w) {
+		wait(NULL);
+// TODO: -ws handling should be here
+	}
+
+	return EXIT_SUCCESS;
 }