Fix #81: Workaround for systems without SYSV shm IPC support

We should not let PID 1 fail on systems where Linux is built without
CONFIG_SYSVIPC, or the libc does not support shmget()/shmat().

This workaround implements a fallback to using calloc() for PID 1,
which means the initctl tool will not work properly.  A better fix
would be to refactor the shm implementation to instead have initctl
call Finit using api.c for each svc_t.  This has been added to the
TODO file as future work.

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

src/svc.c

@@ -35,14 +35,29 @@
 
 /* Each svc_t needs a unique job# */
 static int jobcounter = 1;
+static svc_t *workaround = NULL;
 
 static svc_t *__connect_shm(void)
 {
-	svc_t *list = finit_svc_connect();
+	svc_t *list;
+
+	list = finit_svc_connect();
+	if (!list) {
+		/* Linux not built with CONFIG_SYSVIPC, or libc does not support shmat()/shmget() */
+		if (ENOSYS == errno)
+			warn("Kernel does support SYSV shmat() IPC, error %d", errno);
+
+		/* Try to prevent PID 1 from aborting, issue #81 */
+		if (getpid() == 1) {
+			warn("Implementing PID 1 workaround, initctl tool will not work ...");
+			if (!workaround)
+				workaround = calloc(MAX_NUM_SVC, sizeof(svc_t));
+
+			list = workaround;
+		}
+	}
 
 	if (!list) {
-		/* This should never happen, but if it does we're probably
-		 * knee-deep in more serious problems already... */
 		warn("Failed connecting to shared memory, error %d", errno);
 		abort();
 	}