Add a simple shell

this is the kiss command, the
Keep It Simple Stupid
shell. Used for debug on riscv.

Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>

sys/src/cmd/build.json

@@ -58,6 +58,7 @@
 			"init.c",
 			"join.c",
 			"kbmap.c",
+		        "kiss.c",
 			"ktrace.c",
 			"lens.c",
 			"lnfs.c",

sys/src/cmd/kiss.c

@@ -0,0 +1,77 @@
+/*
+ * This file is part of the UCB release of Plan 9. It is subject to the license
+ * terms in the LICENSE file found in the top-level directory of this
+ * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
+ * part of the UCB release of Plan 9, including this file, may be copied,
+ * modified, propagated, or distributed except according to the terms contained
+ * in the LICENSE file.
+ */
+
+/* This is the Keep It Simple, Stupid shell. It is written
+ * to have as little c library usage as possible. It's handy
+ * for bootstrapping broken harvey ports. You can make it the
+ * boot command in your config. It tries to open /dev/cons and
+ * if that fails #P/cons, which is useful if your namespace
+ * is really not working. */
+#include <u.h>
+#include <libc.h>
+
+static char line[512];
+static char *argv[512];
+static int argc;
+static char err[] = "Can't open /dev/cons or #P/cons; continuing\n";
+void
+main(int _, char *__)
+{
+	int i, amt;
+	int fd;
+
+	fd = open("#P/cons", ORDWR);
+	if (fd < 0)
+		write(1, err, sizeof(err)-1);
+	else {
+		if (fd != 0)
+			dup(fd, 0);
+		dup(fd, 1);
+		dup(fd, 2);
+	}
+
+	argv0 = "kiss";
+	i = 0;
+	argv[0] = line;
+	while (1) {
+		if (amt = read(0, &line[i], 1) < 1) {
+			print("read: %r\n");
+			break;
+		}
+		if (line[i] == '\n') {
+			line[i] = 0;
+			switch(fork()) {
+			default:
+				wait();
+				break;
+			case 0:
+				exec(argv[0], argv);
+				exits("exec failed");
+				break;
+			case -1:
+				print("rfork failed: %r\n");
+				break;
+			}
+			i = 0;
+			argc = 0;
+			memset(argv, 0, sizeof(argv));
+			memset(line, 0, sizeof(line));
+			argv[0] = line;
+		} else if (line[i] == ' ') {
+				line[i] = 0;
+				argc++, i++;
+				argv[argc] = &line[i];
+		} else {
+			i++;
+		}
+
+	}
+	exits(0);
+}
+