Extended IPC Support added.

Benefits & Facts:
- Messages up to 2 kilobytes may be sent.
- Both parties may use non-disjoint user buffers. E.g. any userspace address.
- Userspace buffers can page fault.
- Page faults punish timeslice of only the faulting thread.
- Any number of extended ipcs can take place at any one time, since
  only ktcbs of ipc parties are engaged. No global buffer is used.
  - This also provides smp-safety benefit.

Disadvantages:
- There is triple copying penalty. This has to be done:
  - Sender buffer to sender ktcb
  - Sender ktcb to receiver ktcb
  - Receiver ktcb to receiver buffer.
  This is due to the fact that buffers can be on non-disjoint userspace addresses.

If you want to avoid disadvantages and lose some of the benefits,
(e.g. address freedom, shorter copy size) use FULL IPC.

tasks/test0/src/ipctest.c

@@ -89,7 +89,8 @@ void ipc_extended_test(void)
 	 */
 	ipcbuf = base + PAGE_SIZE - L4_IPC_EXTENDED_MAX_SIZE / 2;
 
-	if (!child) {
+	/* Child sending message */
+	if (child == 0) {
 		/* Child creates a string of maximum extended ipc size */
 		for (int i = 0; i < L4_IPC_EXTENDED_MAX_SIZE; i++) {
 			ipcbuf[i] = 'A' + i % 20;
@@ -107,6 +108,7 @@ void ipc_extended_test(void)
 			goto out_err;
 		}
 
+	/* Parent receiving message */
 	} else {
 		/*
 		 * Parent receives on the buffer - we are sure that the
@@ -125,11 +127,16 @@ void ipc_extended_test(void)
 		printf("(%d): Message received from child: %s\n",
 		       getpid(), ipcbuf);
 
-		/* Check that child string is there */
-		for (int i = 0; i < L4_IPC_EXTENDED_MAX_SIZE; i++) {
+		/* Check that string received from child is an exact match */
+		for (int i = 0; i < L4_IPC_EXTENDED_MAX_SIZE - 2; i++) {
 			if (ipcbuf[i] != ('A' + i % 20))
 				goto out_err;
 		}
+		if (ipcbuf[L4_IPC_EXTENDED_MAX_SIZE - 2] != '\n')
+			goto out_err;
+		if (ipcbuf[L4_IPC_EXTENDED_MAX_SIZE - 1] != '\0')
+			goto out_err;
+
 		printf("EXTENDED IPC TEST: -- PASSED --\n");
 	}
 	return;