svok: new applet (daemontools compat)

function                                             old     new   delta
svok_main                                              -     127    +127
packed_usage                                       32705   32757     +52
applet_names                                        2756    2761      +5
applet_main                                         1588    1592      +4
bb_banner                                             46      47      +1
sv                                                  1286    1284      -2
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 4/1 up/down: 189/-2)            Total: 187 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

examples/var_service/README_distro_proposal.txt

@@ -246,7 +246,8 @@ relative to the system-wide service directory.
 This proposal asks developers of other daemontools implementations
 to add "svc" command to their projects]
 
-The "svok DIR" tool exits 0 if service is running, and nonzero if not.
+The "svok DIR" tool exits 0 if service supervisor is running
+(with service itself either running or stopped), and nonzero if not.
 
 Other tools with different names and APIs may exist; however
 for portability scripts should use the above tools.

examples/var_service/ifplugd_if/run

@@ -16,7 +16,7 @@ exec \
 env - PATH="$PATH" \
 softlimit \
 setuidgid root \
-ifplugd -apqlns -t3 -u8 -d8 -i "$if" -r "$pwd/ifplugd_handler"
+ifplugd -aqlns -t3 -u8 -d8 -i "$if" -r "$pwd/ifplugd_handler"
 
 # We use -t3 to wake ifplugd up less often.
 # If after three tests (3*3=9 > 8) link state seen to be different,
@@ -24,6 +24,12 @@ ifplugd -apqlns -t3 -u8 -d8 -i "$if" -r "$pwd/ifplugd_handler"
 # IOW: short link losses will be ignored, longer ones
 # will trigger DHCP reconfiguration and such (see handler code).
 
+# -l makes ifplugd run either "up" or "down" script on startup.
+# For example, if wired eth cable is unplugged, this stops dhcp service
+# from pointlessly trying to get a lease.
+# -q means that stopping monitoring does not stop dhcp/zcip/etc:
+# presumably, admin decided to control them manually.
+
 #-a       Don't up interface automatically
 #-p       Don't run "up" script on startup
 #-q       Don't run "down" script on exit

runit/sv.c

@@ -163,7 +163,7 @@ Exit Codes
 //config:config SV_DEFAULT_SERVICE_DIR
 //config:	string "Default directory for services"
 //config:	default "/var/service"
-//config:	depends on SV
+//config:	depends on SV || SVC || SVOK
 //config:	help
 //config:	Default directory for services.
 //config:	Defaults to "/var/service"
@@ -173,13 +173,22 @@ Exit Codes
 //config:	default y
 //config:	help
 //config:	svc controls the state of services monitored by the runsv supervisor.
-//config:	It is comaptible with daemontools command with the same name.
+//config:	It is compatible with daemontools command with the same name.
+//config:
+//config:config SVOK
+//config:	bool "svok"
+//config:	default y
+//config:	help
+//config:	svok checks whether runsv supervisor is running.
+//config:	It is compatible with daemontools command with the same name.
 
-//applet:IF_SV( APPLET_NOEXEC(sv,  sv,  BB_DIR_USR_BIN, BB_SUID_DROP, sv ))
+//applet:IF_SV(  APPLET_NOEXEC(sv,   sv,   BB_DIR_USR_BIN, BB_SUID_DROP, sv  ))
-//applet:IF_SVC(APPLET_NOEXEC(svc, svc, BB_DIR_USR_BIN, BB_SUID_DROP, svc))
+//applet:IF_SVC( APPLET_NOEXEC(svc,  svc,  BB_DIR_USR_BIN, BB_SUID_DROP, svc ))
+//applet:IF_SVOK(APPLET_NOEXEC(svok, svok, BB_DIR_USR_BIN, BB_SUID_DROP, svok))
 
 //kbuild:lib-$(CONFIG_SV) += sv.o
 //kbuild:lib-$(CONFIG_SVC) += sv.o
+//kbuild:lib-$(CONFIG_SVOK) += sv.o
 
 #include <sys/file.h>
 #include "libbb.h"
@@ -615,7 +624,7 @@ static int sv(char **argv)
 	service = argv;
 	while ((x = *service) != NULL) {
 		if (x[0] != '/' && x[0] != '.'
-		 && x[0] != '\0' && x[strlen(x) - 1] != '/'
+		 && !last_char_is(x, '/')
 		) {
 			if (chdir(varservice) == -1)
 				goto chdir_failed_0;
@@ -742,3 +751,41 @@ int svc_main(int argc UNUSED_PARAM, char **argv)
 	return 0;
 }
 #endif
+
+//usage:#define svok_trivial_usage
+//usage:       "SERVICE_DIR"
+//usage:#define svok_full_usage "\n\n"
+//usage:       "Check whether runsv supervisor is running.\n"
+//usage:       "Exit code is 0 if it does, 100 if it does not,\n"
+//usage:       "111 (with error message) if SERVICE_DIR does not exist."
+#if ENABLE_SVOK
+int svok_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int svok_main(int argc UNUSED_PARAM, char **argv)
+{
+	const char *dir = argv[1];
+
+	if (!dir)
+		bb_show_usage();
+
+	xfunc_error_retval = 111;
+
+	/*
+	 * daemontools has no concept of "default service dir", runit does.
+	 * Let's act as runit.
+	 */
+	if (dir[0] != '/' && dir[0] != '.'
+	 && !last_char_is(dir, '/')
+	) {
+		xchdir(CONFIG_SV_DEFAULT_SERVICE_DIR);
+	}
+
+	xchdir(dir);
+	if (open("supervise/ok", O_WRONLY) < 0) {
+		if (errno == ENOENT || errno == ENXIO)
+			return 100;
+		bb_perror_msg_and_die("can't open '%s'", "supervise/ok");
+	}
+
+	return 0;
+}
+#endif