writev and some fixes

kernel/include/uio.h

@@ -0,0 +1,27 @@
+#ifndef __UIO_H
+#define __UIO_H
+
+struct iovec
+{
+	void *iov_base;	/* BSD uses caddr_t (1003.1g requires void *) */
+	size_t iov_len; /* Must be size_t (1003.1g) */
+};
+
+/*
+ * Total number of bytes covered by an iovec.
+ *
+ * NOTE that it is not safe to use this function until all the iovec's
+ * segment lengths have been validated.  Because the individual lengths can
+ * overflow a size_t when added together.
+ */
+static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
+{
+	unsigned long seg;
+	size_t ret = 0;
+
+	for (seg = 0; seg < nr_segs; seg++)
+		ret += iov[seg].iov_len;
+	return ret;
+}
+
+#endif