iov_iter_truncate()

Now It Can Be Done(tm) - we don't need to do iov_shorten() in
generic_file_direct_write() anymore, now that all ->direct_IO()
instances are converted to proper iov_iter methods and honour
iter->count and iter->iov_offset properly.

Get rid of count/ocount arguments of generic_file_direct_write(),
while we are at it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 4876e9f..532f59d 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -82,6 +82,12 @@
 	return i->count;
 }
 
+static inline void iov_iter_truncate(struct iov_iter *i, size_t count)
+{
+	if (i->count > count)
+		i->count = count;
+}
+
 int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 int memcpy_toiovec(struct iovec *iov, unsigned char *kdata, int len);