Christoph Hellwig [off-list ref] writes:

From: Milosz Tanski <redacted>

New syscalls that take an flag argument. This change does not add any
specific flags.

So, it looks like file systems that don't implement read_iter/write_iter
won't get the flags argument passed along.  I don't think that's a big
deal, as such file systems seem to be in-memory file systems, but I
think it warrants mention in the changelog.

Also, I think you added a stray newline below:

+static long do_compat_pwritev64(unsigned long fd,
 				   const struct compat_iovec __user *vec,
-				   unsigned long vlen, loff_t pos)
+				   unsigned long vlen, loff_t pos, int flags)
 {
 	struct fd f;
 	ssize_t ret;
 
 	if (pos < 0)
 		return -EINVAL;
+
 	f = fdget(fd);
 	if (!f.file)
 		return -EBADF;
 	ret = -ESPIPE;
 	if (f.file->f_mode & FMODE_PWRITE)
-		ret = compat_writev(f.file, vec, vlen, &pos);
+		ret = compat_writev(f.file, vec, vlen, &pos, flags);
 	fdput(f);
 	return ret;
 }

Cheers,
Jeff