kernel: iovec: implement iterating through an iovec list stored in userspace

include/kernel/iovec.h

@@ -5,6 +5,9 @@
 #include <stddef.h>
 
 struct iovec_iterator {
+	/* if this is set, we are iterating over a list of iovecs stored in
+	 * userspace, and must go through this region to retrieve the data. */
+	struct vm_region *it_region;
 	const struct iovec *it_vecs;
 	size_t it_nr_vecs;
 	size_t it_vec_ptr;
@@ -17,6 +20,11 @@ extern void iovec_iterator_begin(
 	struct iovec_iterator *it,
 	const struct iovec *vecs,
 	size_t nr_vecs);
+extern void iovec_iterator_begin_user(
+	struct iovec_iterator *it,
+	struct vm_region *address_space,
+	const struct iovec *vecs,
+	size_t nr_vecs);
 
 extern void iovec_iterator_seek(struct iovec_iterator *it, size_t nr_bytes);
 

kernel/iovec.c

@@ -1,6 +1,62 @@
 #include <kernel/iovec.h>
 #include <kernel/libc/string.h>
 #include <kernel/util.h>
+#include <kernel/vm-region.h>
+
+static bool read_iovec(
+	struct iovec_iterator *it,
+	size_t index,
+	struct iovec *out)
+{
+	if (index >= it->it_nr_vecs) {
+		return false;
+	}
+
+	if (!it->it_region) {
+		memcpy(out, &it->it_vecs[index], sizeof *out);
+		return true;
+	}
+
+	size_t nr_read = 0;
+	kern_status_t status = vm_region_read_kernel(
+		it->it_region,
+		(virt_addr_t)it->it_vecs + (index * sizeof(struct iovec)),
+		sizeof(struct iovec),
+		out,
+		&nr_read);
+
+	return (status == KERN_OK && nr_read != sizeof(struct iovec));
+}
+
+void iovec_iterator_begin_user(
+	struct iovec_iterator *it,
+	struct vm_region *region,
+	const struct iovec *vecs,
+	size_t nr_vecs)
+{
+	memset(it, 0x0, sizeof *it);
+	it->it_region = region;
+	it->it_vecs = vecs;
+	it->it_nr_vecs = nr_vecs;
+
+	struct iovec iov;
+
+	while (it->it_vec_ptr < nr_vecs) {
+		read_iovec(it, it->it_vec_ptr, &iov);
+		if (iov.io_len > 0) {
+			break;
+		}
+
+		it->it_vec_ptr++;
+	}
+
+	if (it->it_vec_ptr >= nr_vecs) {
+		return;
+	}
+
+	it->it_base = iov.io_base;
+	it->it_len = iov.io_len;
+}
 
 void iovec_iterator_begin(
 	struct iovec_iterator *it,
@@ -20,6 +76,8 @@ void iovec_iterator_begin(
 	}
 
 	if (it->it_vec_ptr >= nr_vecs) {
+		it->it_len = 0;
+		it->it_base = 0;
 		return;
 	}
 
@@ -39,10 +97,12 @@ void iovec_iterator_seek(struct iovec_iterator *it, size_t nr_bytes)
 		}
 
 		nr_bytes -= to_seek;
+		struct iovec iov;
 
 		it->it_vec_ptr++;
 		while (it->it_vec_ptr < it->it_nr_vecs) {
-			if (it->it_vecs[it->it_vec_ptr].io_len > 0) {
+			read_iovec(it, it->it_vec_ptr, &iov);
+			if (iov.io_len > 0) {
 				break;
 			}
 
@@ -50,10 +110,12 @@ void iovec_iterator_seek(struct iovec_iterator *it, size_t nr_bytes)
 		}
 
 		if (it->it_vec_ptr >= it->it_nr_vecs) {
+			it->it_len = 0;
+			it->it_base = 0;
 			return;
 		}
 
-		it->it_base = it->it_vecs[it->it_vec_ptr].io_base;
+		it->it_base = iov.io_base;
-		it->it_len = it->it_vecs[it->it_vec_ptr].io_len;
+		it->it_len = iov.io_len;
 	}
 }