Implement utime() along with a naive /bin/touch.

This synchronous approach to inodes is silly, obviously. I need to rework
it so that the in-memory CoreInode object is the canonical inode, and then
we just need a sync() that flushes pending changes to disk.

Userland/.gitignore

@@ -21,3 +21,4 @@ ft2
 strsignal
 fgrep
 mkdir
+touch

Userland/Makefile

@@ -19,7 +19,8 @@ OBJS = \
        strsignal.o \
        fgrep.o \
        tty.o \
-       mkdir.o
+       mkdir.o \
+       touch.o
 
 APPS = \
        id \
@@ -42,7 +43,8 @@ APPS = \
        strsignal \
        fgrep \
        tty \
-       mkdir
+       mkdir \
+       touch
 
 ARCH_FLAGS =
 STANDARD_FLAGS = -std=c++17 -nostdinc++ -nostdlib -nostdinc
@@ -125,6 +127,9 @@ strsignal: strsignal.o
 mkdir: mkdir.o
 	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
 
+touch: touch.o
+	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
+
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
 

Userland/ls.cpp

@@ -152,6 +152,8 @@ int do_dir(const char* path)
 
         printf(" %10u  ", st.st_size);
 
+        printf(" %10u  ", st.st_mtime);
+
         print_name(st, de->d_name, pathbuf);
 
         printf("\n");

Userland/touch.cpp

@@ -0,0 +1,16 @@
+#include <stdio.h>
+#include <utime.h>
+#include <sys/types.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "usage: touch <path>\n");
+        return 1;
+    }
+    int rc = utime(argv[1], nullptr);
+    if (rc < 0)
+        perror("utime");
+    return 0;
+}
+