kernel: add functions for iterating through an array of iovecs

kernel/iovec.c

@@ -0,0 +1,59 @@
+#include <kernel/iovec.h>
+#include <kernel/libc/string.h>
+#include <kernel/util.h>
+
+void iovec_iterator_begin(
+	struct iovec_iterator *it,
+	const struct iovec *vecs,
+	size_t nr_vecs)
+{
+	memset(it, 0x0, sizeof *it);
+	it->it_vecs = vecs;
+	it->it_nr_vecs = nr_vecs;
+
+	while (it->it_vec_ptr < nr_vecs) {
+		if (vecs[it->it_vec_ptr].io_len > 0) {
+			break;
+		}
+
+		it->it_vec_ptr++;
+	}
+
+	if (it->it_vec_ptr >= nr_vecs) {
+		return;
+	}
+
+	it->it_base = vecs[it->it_vec_ptr].io_base;
+	it->it_len = vecs[it->it_vec_ptr].io_len;
+}
+
+void iovec_iterator_seek(struct iovec_iterator *it, size_t nr_bytes)
+{
+	while (nr_bytes > 0) {
+		size_t to_seek = MIN(nr_bytes, it->it_len);
+
+		if (to_seek < it->it_len) {
+			it->it_len -= to_seek;
+			it->it_base += to_seek;
+			break;
+		}
+
+		nr_bytes -= to_seek;
+
+		it->it_vec_ptr++;
+		while (it->it_vec_ptr < it->it_nr_vecs) {
+			if (it->it_vecs[it->it_vec_ptr].io_len > 0) {
+				break;
+			}
+
+			it->it_vec_ptr++;
+		}
+
+		if (it->it_vec_ptr >= it->it_nr_vecs) {
+			return;
+		}
+
+		it->it_base = it->it_vecs[it->it_vec_ptr].io_base;
+		it->it_len = it->it_vecs[it->it_vec_ptr].io_len;
+	}
+}