Implement basic chmod() syscall and /bin/chmod helper.

Only raw octal modes are supported right now.
This patch also changes mode_t from 32-bit to 16-bit to match the on-disk
type used by Ext2FS.

I also ran into EPERM being errno=0 which was confusing, so I inserted an
ESUCCESS in its place.

Userland/.gitignore

@@ -28,3 +28,4 @@ rm
 cp
 rmdir
 dmesg
+chmod

Userland/Makefile

@@ -25,6 +25,7 @@ OBJS = \
        cp.o \
        rmdir.o \
        dmesg.o \
+       chmod.o \
        rm.o
 
 APPS = \
@@ -55,6 +56,7 @@ APPS = \
        cp \
        rmdir \
        dmesg \
+       chmod \
        rm
 
 ARCH_FLAGS =
@@ -159,6 +161,9 @@ rm: rm.o
 rmdir: rmdir.o
 	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
 
+chmod: chmod.o
+	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
+
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
 

Userland/chmod.cpp

@@ -0,0 +1,27 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <string.h>
+
+int main(int argc, char **argv)
+{
+    if (argc != 3) {
+        printf("usage: chmod <octal-mode> <path>\n");
+        return 1;
+    }
+
+    mode_t mode;
+    int rc = sscanf(argv[1], "%o", &mode);
+    if (rc != 1) {
+        perror("sscanf");
+        return 1;
+    }
+
+    rc = chmod(argv[2], mode);
+    if (rc < 0) {
+        perror("chmod");
+        return 1;
+    }
+
+    return 0;
+}