vm: region: add a function to write data from a kernel buffer to a vm-region

include/kernel/vm-region.h

@@ -157,6 +157,15 @@ extern kern_status_t vm_region_read_kernel(
 	void *dest,
 	size_t *nr_read);
 
+/* write data to the user-space area of a vm-region from a kernel-mode buffer
+ */
+extern kern_status_t vm_region_write_kernel(
+	struct vm_region *dst_region,
+	virt_addr_t dst_ptr,
+	size_t count,
+	const void *src,
+	size_t *nr_written);
+
 extern kern_status_t vm_region_memmove(
 	struct vm_region *dest_region,
 	virt_addr_t dest_ptr,

vm/vm-region.c

@@ -1713,6 +1713,52 @@ kern_status_t vm_region_read_kernel(
 	return status;
 }
 
+kern_status_t vm_region_write_kernel(
+	struct vm_region *dst_region,
+	virt_addr_t dst_ptr,
+	size_t count,
+	const void *srcp,
+	size_t *nr_written)
+{
+	if (dst_region->vr_status != VM_REGION_ONLINE) {
+		return KERN_BAD_STATE;
+	}
+
+	struct vm_iterator dst;
+	const char *src = srcp;
+
+	vm_iterator_begin(
+		&dst,
+		dst_region,
+		dst_ptr,
+		VM_PROT_WRITE | VM_PROT_USER);
+
+	kern_status_t status = KERN_OK;
+	size_t r = 0;
+
+	while (r < count && dst.it_max) {
+		size_t remaining = count - r;
+		size_t to_move = MIN(dst.it_max, remaining);
+		memmove(dst.it_buf, src, to_move);
+
+		status = vm_iterator_seek(&dst, to_move);
+		if (status != KERN_OK) {
+			break;
+		}
+
+		r += to_move;
+		src += to_move;
+	}
+
+	vm_iterator_finish(&dst);
+
+	if (nr_written) {
+		*nr_written = r;
+	}
+
+	return status;
+}
+
 kern_status_t vm_region_memmove(
 	struct vm_region *dest_region,
 	virt_addr_t dest_ptr,