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.

Kernel/Process.cpp

@@ -1079,6 +1079,30 @@ int Process::sys$close(int fd)
     return rc;
 }
 
+int Process::sys$utime(const char* pathname, const Unix::utimbuf* buf)
+{
+    if (!validate_read_str(pathname))
+        return -EFAULT;
+    if (buf && !validate_read_typed(buf))
+        return -EFAULT;
+    String path(pathname);
+    int error;
+    auto descriptor = VFS::the().open(move(path), error, 0, cwd_inode()->identifier());
+    if (!descriptor)
+        return error;
+    Unix::time_t atime;
+    Unix::time_t mtime;
+    if (buf) {
+        atime = buf->actime;
+        mtime = buf->modtime;
+    } else {
+        auto now = RTC::now();
+        mtime = now;
+        atime = now;
+    }
+    return descriptor->set_atime_and_mtime(atime, mtime);
+}
+
 int Process::sys$access(const char* pathname, int mode)
 {
     (void) mode;

Kernel/Process.h

@@ -173,6 +173,7 @@ public:
     int sys$ioctl(int fd, unsigned request, unsigned arg);
     int sys$mkdir(const char* pathname, mode_t mode);
     Unix::clock_t sys$times(Unix::tms*);
+    int sys$utime(const char* pathname, const struct Unix::utimbuf*);
 
     static void initialize();
 

Kernel/Syscall.cpp

@@ -177,6 +177,8 @@ static dword handle(RegisterDump& regs, dword function, dword arg1, dword arg2,
         return current->sys$mkdir((const char*)arg1, (mode_t)arg2);
     case Syscall::SC_times:
         return current->sys$times((Unix::tms*)arg1);
+    case Syscall::SC_utime:
+        return current->sys$utime((const char*)arg1, (const Unix::utimbuf*)arg2);
     default:
         kprintf("<%u> int0x80: Unknown function %u requested {%x, %x, %x}\n", current->pid(), function, arg1, arg2, arg3);
         break;

Kernel/Syscall.h

@@ -64,6 +64,7 @@
     __ENUMERATE_SYSCALL(ioctl) \
     __ENUMERATE_SYSCALL(mkdir) \
     __ENUMERATE_SYSCALL(times) \
+    __ENUMERATE_SYSCALL(utime) \
 
 
 #define DO_SYSCALL_A0(function) Syscall::invoke((dword)(function))

Kernel/sync.sh

@@ -30,6 +30,7 @@ cp -v ../Userland/kill mnt/bin/kill
 cp -v ../Userland/tty mnt/bin/tty
 cp -v ../Userland/strsignal mnt/bin/strsignal
 cp -v ../Userland/mkdir mnt/bin/mkdir
+cp -v ../Userland/touch mnt/bin/touch
 sh sync-local.sh
 cp -v kernel.map mnt/
 ln -s dir_a mnt/dir_cur