service: add optional controlling TTY via tty: stanza

Author: Ollie-Gutierrez

doc/config/service-opts.md

@@ -46,6 +46,7 @@ Other run/task/service options are:
   * `cgroup.NAME[,opts]` or `cgroup:opts` -- see the [Cgroups](cgroups.md) section
   * `env:[-]/path/to/env` -- see the [Service Environment](service-env.md) section
   * `log:...` -- see [Redirecting Output](logging.md#redirecting-output)
+  * `tty:<dev>` -- see [Controlling TTY](tty.md#controlling-tty)
   * `nowarn` -- see [Conditional Loading](services.md#conditional-loading)
   * `notify:...` -- see [Service Synchronization](service-sync.md)
   * `if:...` -- see [Conditional Execution](services.md#conditional-execution)

doc/config/tty.md

@@ -83,4 +83,31 @@ board bringup and system debugging it can come in handy.
 
 One can also use the `service` stanza to start a stand-alone shell:
 
-    service [12345] /bin/sh -l
+    service [12345] /bin/sh -l
+
+Controlling TTY for Services
+----------------------------
+
+The `tty:<dev>` option gives a `run`, `task`, or `service` a controlling
+terminal on the given device.  The device is opened, set as the
+controlling terminal for the session (after `setsid()`), and connected to
+the process's stdin, stdout, and stderr.  A default `TERM` environment
+variable is set based on the device type: `vt102` for serial lines and
+`linux` for virtual terminals.
+
+`<dev>` may be a device node like `/dev/ttyS0`, or the special keyword
+`@console` (see above).  Note that `@console` expands only to the
+first console, not all.
+
+When `tty:` is combined with `log:`, stdout and stderr are redirected
+to the log sink instead of the TTY, but stdin remains connected to the
+TTY device.
+
+> The `tty:<dev>` option is for `run`, `task`, and `service` stanzas only.
+> The `tty` directive itself (for getty/login) has its own syntax, see
+> above.
+
+**Example:**
+
+    service [2345] tty:/dev/ttyS0 /usr/sbin/foo -- Foo on serial console
+    task [S] tty:@console my-setup-script -- Board bringup on console

doc/switchroot.md

@@ -61,7 +61,8 @@ For more complex setups (LUKS, LVM, etc.):
 
 ```
 # Unlock LUKS volume
-run [S] name:cryptsetup /sbin/cryptsetup open /dev/sda2 cryptroot -- Unlocking encrypted root
+# The tty:@console stanza is required so cryptsetup can prompt for a passphrase
+run [S] name:cryptsetup tty:@console /sbin/cryptsetup open /dev/sda2 cryptroot -- Unlocking encrypted root
 
 # Activate LVM
 run [S] name:lvm /sbin/lvm vgchange -ay -- Activating LVM volumes

man/finit.conf.5

@@ -744,6 +744,37 @@ is
 and the default
 .Cm tag
 identity is the basename of the service or run/task command.
+.It Cm tty:\&<dev>
+Give the
+.Cm run , task ,
+or
+.Cm service
+a controlling terminal on
+.Cm <dev> .
+The device is opened, set as the controlling terminal for the session
+(after
+.Fn setsid ) ,
+and connected to stdin, stdout, and stderr.
+A default
+.Ev TERM
+variable is set based on the device type:
+.Cm vt102
+for serial lines and
+.Cm linux
+for virtual terminals.
+.Cm <dev>
+may be a device node like
+.Pa /dev/ttyS0 ,
+or the special keyword
+.Cm @console
+(see TTYs and Consoles above).
+When combined with
+.Cm log: ,
+stdout and stderr are redirected to the log sink instead, but stdin
+remains connected to the TTY device.
+.Bd -unfilled -offset indent
+service [2345] tty:/dev/ttyS0 /usr/sbin/foo -- Foo on serial console
+.Ed
 .El
 .Sh RESCUE MODE
 Finit supports a rescue mode which is activated by the

src/service.c

@@ -29,10 +29,12 @@
 #include <sched.h>		/* sched_yield() */
 #include <string.h>
 #include <sys/reboot.h>
+#include <sys/ioctl.h>
 #include <sys/prctl.h>
 #include <sys/resource.h>
 #include <sys/un.h>
 #include <sys/wait.h>
+#include <linux/vt.h>
 #include <net/if.h>
 #ifdef _LIBITE_LITE
 # include <libite/lite.h>
@@ -387,6 +389,43 @@ static int lredirect(svc_t *svc)
 	return close(pipefd[1]);
 }
 
+/*
+ * Set up a controlling TTY for run/task/service.
+ * Opens the TTY device, dups to 0/1/2, resets termios to
+ * sane defaults, sets TERM env, and updates procname.
+ */
+static void svc_prepare_ctty(const char *tty, const char *procname, int log)
+{
+	int fd, dummy;
+
+	fd = open(tty, O_RDWR);
+	if (fd < 0) {
+		logit(LOG_ERR, "Failed opening %s: %s", tty, strerror(errno));
+		_exit(1);
+	}
+
+	/* Acquire as controlling terminal for the session */
+	ioctl(fd, TIOCSCTTY, 0);
+
+	dup2(fd, STDIN_FILENO);
+	if (!log) {
+		dup2(fd, STDOUT_FILENO);
+		dup2(fd, STDERR_FILENO);
+	}
+
+	/* Set default TERM */
+	if (ioctl(fd, VT_OPENQRY, &dummy) == -1)
+		setenv("TERM", "vt102", 1);	/* likely a serial line */
+	else
+		setenv("TERM", "linux", 1);
+
+	/* Reset to sane defaults */
+	stty(fd, B0);
+	close(fd);
+
+	prctl(PR_SET_NAME, procname, 0, 0, 0);
+}
+
 /*
  * Handle redirection of process output, if enabled
  */
@@ -946,6 +985,14 @@ static int service_start(svc_t *svc)
 
 		sig_unblock();
 
+		/*
+		 * If the stanza declared tty:<dev>, set up a controlling
+		 * terminal on that device now that we're a session leader.
+		 * Must run after setsid() to acquire the controlling TTY.
+		 */
+		if (!svc_is_tty(svc) && svc_has_ctty(svc))
+			svc_prepare_ctty(svc->log.ctty, svc->cmd, !!svc->log.enabled);
+
 		if (svc_is_runtask(svc))
 			status = exec_runtask(args[0], &args[1]);
 		else if (svc_is_tty(svc))
@@ -1795,6 +1842,7 @@ int service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 	char ident[MAX_IDENT_LEN];
 	char *ifstmt = NULL;
 	char *notify = NULL;
+	char *ctty = NULL;
 	struct tty tty = { 0 };
 	char *dev = NULL;
 	int respawn = 0;
@@ -1911,6 +1959,8 @@ int service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 			env = arg;
 		else if (MATCH_CMD(cmd, "caps:", arg))
 			caps = arg;
+		else if (MATCH_CMD(cmd, "tty:", arg))
+			ctty = arg;
 		/* catch both cgroup: and cgroup. handled in parse_cgroup() */
 		else if (MATCH_CMD(cmd, "cgroup", arg))
 			cgroup = arg;
@@ -2160,6 +2210,22 @@ int service_register(int type, char *cfg, struct rlimit rlimit[], char *file)
 		parse_caps(svc, caps);
 	else
 		memset(svc->capabilities, 0, sizeof(svc->capabilities));
+
+	if (!svc_is_tty(svc) && ctty) {
+		char *dev = ctty;
+
+		/* NOTE: @console expands only to first console, not all */
+		if (tty_isatcon(ctty))
+			dev = tty_atcon();
+		dev = tty_canonicalize(dev);
+		if (dev)
+			strlcpy(svc->log.ctty, dev, sizeof(svc->log.ctty));
+		else
+			logit(LOG_WARNING, "%s: tty: %s not found, skipping ctty", svc_ident(svc, NULL, 0), ctty);
+	} else if (!svc_is_tty(svc)) {
+		memset(svc->log.ctty, 0, sizeof(svc->log.ctty));
+	}
+
 	if (file)
 		strlcpy(svc->file, file, sizeof(svc->file));
 	else

src/svc.h

@@ -176,6 +176,7 @@ typedef struct svc {
 			char  file[64];
 			char  prio[20];
 			char  ident[20];
+			char  ctty[32];
 		} log;
 
 		/* Only for TTY type services */
@@ -291,6 +292,7 @@ static inline int svc_in_runlevel  (svc_t *svc, int runlevel) { return svc && IS
 static inline int svc_has_pidfile  (svc_t *svc) { return svc_is_daemon(svc) && svc->pidfile[0] != 0 && svc->pidfile[0] != '!'; }
 static inline int svc_has_pre      (svc_t *svc) { return svc->pre_script[0];  }
 static inline int svc_has_post     (svc_t *svc) { return svc->post_script[0]; }
+static inline int svc_has_ctty     (svc_t *svc) { return svc && svc->log.ctty[0]; }
 static inline int svc_has_ready    (svc_t *svc) { return svc->ready_script[0];}
 static inline int svc_has_cleanup  (svc_t *svc) { return svc->cleanup_script[0]; }