Follow-up to issue #81: remove SysV shared memory IPC altogether

This change removes a long standing kernel requirement and architectural
mishap in the design of Finit v1.  It is no longer necessary to include
CONFIG_SYSVIPC in the kernel to use Finit and its command line tool
initctl.  It is also no longer possible to connect to the internals of
PID 1 using shmat(), the initctl tool has already been updated to use
the domain socket API.

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

doc/TODO.md

@@ -21,9 +21,6 @@ can also be used.
 General
 -------
 
-* Remove shm, let `initctl` call `api.c` for each `svc_t` instead of
-  opening up the inner parts of PID 1 to other processes.  Also, this
-  would prevent issues like #81 from happening.
 * Add support for timed shutdown in Finit, including cancelled shutdown.
 * SysV init and systemd use SIGUSR1 to restart their FIFO/D-Bus.  Add
   API restart to SIGHUP callback for the same functionality in Finit.

src/finit.c

@@ -378,10 +378,6 @@ int main(int argc, char* argv[])
 	makedir("/dev/pts", 0755);
 	mount("devpts", "/dev/pts", "devpts", 0, "gid=5,mode=620");
 
-	makedir("/dev/shm", 0755);
-	if (!fismnt("/dev/shm"))
-		mount("shm", "/dev/shm", "tmpfs", 0, NULL);
-
 	/*
 	 * New tmpfs based /run for volatile runtime data
 	 * For details, see http://lwn.net/Articles/436012/

src/svc.c

@@ -35,37 +35,20 @@
 
 /* Each svc_t needs a unique job# */
 static int jobcounter = 1;
-static svc_t *workaround = NULL;
+static svc_t *svc_list = NULL;
 
 static svc_t *__connect_shm(void)
 {
-	svc_t *list;
+	if (svc_list)
+		return svc_list;
 
-	list = finit_svc_connect();
-	if (!list) {
-		if (workaround)
-			return workaround;
-
-		/* 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) {
-			warnx("Implementing PID 1 workaround, initctl tool will not work ...");
-			if (!workaround)
-				workaround = calloc(MAX_NUM_SVC, sizeof(svc_t));
-
-			list = workaround;
-		}
-	}
-
-	if (!list) {
-		warn("Failed connecting to shared memory, error %d", errno);
+	svc_list = calloc(MAX_NUM_SVC, sizeof(svc_t));
+	if (!svc_list) {
+		warn("Failed allocating static list of services, error %d", errno);
 		abort();
 	}
 
-	return list;
+	return svc_list;
 }
 
 /**

src/svc.h

@@ -27,7 +27,6 @@
 
 #include <sys/ipc.h>		/* IPC_CREAT */
 #include <sys/resource.h>
-#include <sys/shm.h>		/* shmat() */
 #include <sys/types.h>		/* pid_t */
 #include <lite/lite.h>
 
@@ -66,7 +65,6 @@ typedef enum {
 	SVC_BLOCK_RESTARTING,
 } svc_block_t;
 
-#define FINIT_SHM_ID     0x494E4954  /* "INIT", see ascii(7) */
 #define MAX_ARG_LEN      64
 #define MAX_STR_LEN      64
 #define MAX_COND_LEN     (MAX_ARG_LEN * 3)
@@ -129,23 +127,6 @@ typedef struct svc {
 	void           (*timer_cb)(struct svc *svc);
 } svc_t;
 
-typedef struct svc_map svc_map_t;
-
-/* Put services array in shm */
-static inline svc_t *finit_svc_connect(void)
-{
-	static void *ptr = (void *)-1;
-
-	if ((void *)-1 == ptr) {
-		ptr = shmat(shmget(FINIT_SHM_ID, sizeof(svc_t) * MAX_NUM_SVC,
-				   0600 | IPC_CREAT), NULL, 0);
-		if ((void *)-1 == ptr)
-			return NULL;
-	}
-
-	return (svc_t *)ptr;
-}
-
 svc_t      *svc_new                (char *cmd, int id, int type);
 int	    svc_del	           (svc_t *svc);