Write tests and fixes for utimensat()

libc/calls/utimensat.c

@@ -24,25 +24,45 @@
 #include "libc/dce.h"
 #include "libc/intrin/asan.internal.h"
 #include "libc/intrin/describeflags.internal.h"
+#include "libc/sysv/consts/at.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/zipos/zipos.internal.h"
 
 /**
  * Sets atime/mtime on file, the modern way.
  *
+ * This is two functions in one. If `path` is null then this function
+ * becomes the same as `futimens(dirfd, ts)`.
+ *
+ * XNU and RHEL5 only have microsecond accuracy and there's no `dirfd`
+ * relative support.
+ *
+ * @param dirfd should AT_FDCWD
  * @param ts is atime/mtime, or null for current time
  * @param flags can have AT_SYMLINK_NOFOLLOW
- * @note no xnu/rhel5 support if dirfd≠AT_FDCWD∨flags≠0
+ * @raise ENOSYS on RHEL5 if path is NULL
+ * @raise EINVAL if flags had unrecognized bits
+ * @raise EINVAL if path is NULL and flags has AT_SYMLINK_NOFOLLOW
+ * @raise EBADF if dirfd isn't a valid fd or AT_FDCWD
+ * @raise EFAULT if path or ts memory was invalid
+ * @raise EROFS if file system is read-only
+ * @raise ENAMETOOLONG
+ * @raise EPERM
+ * @see futimens()
  * @asyncsignalsafe
  */
 int utimensat(int dirfd, const char *path, const struct timespec ts[2],
               int flags) {
   int rc;
   char buf[12];
-  if (IsAsan() && (!__asan_is_valid(path, 1) ||
+  if (IsAsan() && ((dirfd == AT_FDCWD && !__asan_is_valid(path, 1)) ||
                    (ts && (!__asan_is_valid_timespec(ts + 0) ||
                            !__asan_is_valid_timespec(ts + 1))))) {
-    rc = efault();
+    rc = efault();  // bad memory
+  } else if ((flags & ~AT_SYMLINK_NOFOLLOW)) {
+    rc = einval();  // unsupported flag
+  } else if (!path && flags) {
+    rc = einval();  // futimens() doesn't take flags
   } else if (weaken(__zipos_notat) && (rc = __zipos_notat(dirfd, path)) == -1) {
     STRACE("zipos mkdirat not supported yet");
   } else if (!IsWindows()) {