+ * fault_in_writeable - fault in userspace address range for writing
+ * @uaddr: start of address range
+ * @size: size of address range
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_writeable(char __user *uaddr, size_t size)
+{
+ char __user *start = uaddr, *end;
+
+ if (unlikely(size == 0))
+ return 0;
+ if (!PAGE_ALIGNED(uaddr)) {
+ if (unlikely(__put_user(0, uaddr) != 0))
+ return size;
+ uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
+ }
+ end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
+ if (unlikely(end < start))
+ end = NULL;
+ while (uaddr != end) {
+ if (unlikely(__put_user(0, uaddr) != 0))
+ goto out;
+ uaddr += PAGE_SIZE;
+ }
+
+out:
+ if (size > uaddr - start)
+ return size - (uaddr - start);
+ return 0;
+}
+EXPORT_SYMBOL(fault_in_writeable);
+
+/*
+ * fault_in_safe_writeable - fault in an address range for writing
+ * @uaddr: start of address range
+ * @size: length of address range
+ *
+ * Faults in an address range for writing. This is primarily useful when we
+ * already know that some or all of the pages in the address range aren't in
+ * memory.
+ *
+ * Unlike fault_in_writeable(), this function is non-destructive.
+ *
+ * Note that we don't pin or otherwise hold the pages referenced that we fault
+ * in. There's no guarantee that they'll stay in memory for any duration of
+ * time.
+ *
+ * Returns the number of bytes not faulted in, like copy_to_user() and
+ * copy_from_user().
+ */
+size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
+{
+ unsigned long start = (unsigned long)uaddr, end;
+ struct mm_struct *mm = current->mm;
+ bool unlocked = false;
+
+ if (unlikely(size == 0))
+ return 0;
+ end = PAGE_ALIGN(start + size);
+ if (end < start)
+ end = 0;
+
+ mmap_read_lock(mm);
+ do {
+ if (fixup_user_fault(mm, start, FAULT_FLAG_WRITE, &unlocked))
+ break;
+ start = (start + PAGE_SIZE) & PAGE_MASK;
+ } while (start != end);
+ mmap_read_unlock(mm);
+
+ if (size > (unsigned long)uaddr - start)
+ return size - ((unsigned long)uaddr - start);
+ return 0;
+}
+EXPORT_SYMBOL(fault_in_safe_writeable);
+
+/**
+ * fault_in_readable - fault in userspace address range for reading
+ * @uaddr: start of user address range
+ * @size: size of user address range
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_readable(const char __user *uaddr, size_t size)
+{
+ const char __user *start = uaddr, *end;
+ volatile char c;
+
+ if (unlikely(size == 0))
+ return 0;
+ if (!PAGE_ALIGNED(uaddr)) {
+ if (unlikely(__get_user(c, uaddr) != 0))
+ return size;
+ uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
+ }
+ end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
+ if (unlikely(end < start))
+ end = NULL;
+ while (uaddr != end) {
+ if (unlikely(__get_user(c, uaddr) != 0))
+ goto out;
+ uaddr += PAGE_SIZE;
+ }
+
+out:
+ (void)c;
+ if (size > uaddr - start)
+ return size - (uaddr - start);
+ return 0;
+}
+EXPORT_SYMBOL(fault_in_readable);
+
+/**