iov_iter: Introduce fault_in_iov_iter_writeable

Introduce a new fault_in_iov_iter_writeable helper for safely faulting
in an iterator for writing.  Uses get_user_pages() to fault in the pages
without actually writing to them, which would be destructive.

We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that
the iterator passed to .read_iter isn't in memory.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

2 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9fe94f7a4f7e..2f7dd14083d9 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -736,6 +736,7 @@ extern void add_page_wait_queue(struct page *page, wait_queue_entry_t *waiter);
  * Fault in userspace address range.
  */
 size_t fault_in_writeable(char __user *uaddr, size_t size);
+size_t fault_in_safe_writeable(const char __user *uaddr, size_t size);
 size_t fault_in_readable(const char __user *uaddr, size_t size);
 
 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
diff --git a/include/linux/uio.h b/include/linux/uio.h
index d18458af6681..25d1c24fd829 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -134,6 +134,7 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset,
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 void iov_iter_revert(struct iov_iter *i, size_t bytes);
 size_t fault_in_iov_iter_readable(const struct iov_iter *i, size_t bytes);
+size_t fault_in_iov_iter_writeable(const struct iov_iter *i, size_t bytes);
 size_t iov_iter_single_seg_count(const struct iov_iter *i);
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);