vm: region: implement reading from a user-space vm-region into a kernel buffer

include/kernel/vm-region.h

@@ -122,6 +122,15 @@ extern virt_addr_t vm_region_get_base_address(const struct vm_region *region);
 
 extern void vm_region_dump(struct vm_region *region);
 
+/* read data from the user-space area of a vm-region into a kernel-mode buffer
+ */
+extern kern_status_t vm_region_read_kernel(
+	struct vm_region *src_region,
+	virt_addr_t src_ptr,
+	size_t count,
+	void *dest,
+	size_t *nr_read);
+
 extern kern_status_t vm_region_memmove(
 	struct vm_region *dest_region,
 	virt_addr_t dest_ptr,

vm/vm-region.c

@@ -1239,6 +1239,46 @@ virt_addr_t vm_region_get_base_address(const struct vm_region *region)
 	return entry_absolute_address(&region->vr_entry);
 }
 
+kern_status_t vm_region_read_kernel(
+	struct vm_region *src_region,
+	virt_addr_t src_ptr,
+	size_t count,
+	void *destp,
+	size_t *nr_read)
+{
+	struct vm_iterator src;
+	char *dest = destp;
+
+	vm_iterator_begin(
+		&src,
+		src_region,
+		src_ptr,
+		VM_PROT_READ | VM_PROT_USER);
+
+	kern_status_t status = KERN_OK;
+	size_t r = 0;
+
+	while (r < count && src.it_max) {
+		size_t remaining = count - r;
+		size_t to_move = MIN(src.it_max, remaining);
+		memmove(dest, src.it_buf, to_move);
+
+		status = vm_iterator_seek(&src, to_move);
+		if (status != KERN_OK) {
+			break;
+		}
+
+		r += to_move;
+		dest += to_move;
+	}
+
+	if (nr_read) {
+		*nr_read = r;
+	}
+
+	return status;
+}
+
 kern_status_t vm_region_memmove(
 	struct vm_region *dest_region,
 	virt_addr_t dest_ptr,