mm: buffered write iterator

Add an iterator data structure to operate over an iovec.  Add usercopy
operators needed by generic_file_buffered_write, and convert that function
over.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 500ffc0e4ac7..86ce27c72554 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -401,6 +401,39 @@ struct page;
 struct address_space;
 struct writeback_control;
 
+struct iov_iter {
+        const struct iovec *iov;
+        unsigned long nr_segs;
+        size_t iov_offset;
+        size_t count;
+};
+
+size_t iov_iter_copy_from_user_atomic(struct page *page,
+                struct iov_iter *i, unsigned long offset, size_t bytes);
+size_t iov_iter_copy_from_user(struct page *page,
+                struct iov_iter *i, unsigned long offset, size_t bytes);
+void iov_iter_advance(struct iov_iter *i, size_t bytes);
+int iov_iter_fault_in_readable(struct iov_iter *i);
+size_t iov_iter_single_seg_count(struct iov_iter *i);
+
+static inline void iov_iter_init(struct iov_iter *i,
+                        const struct iovec *iov, unsigned long nr_segs,
+                        size_t count, size_t written)
+{
+        i->iov = iov;
+        i->nr_segs = nr_segs;
+        i->iov_offset = 0;
+        i->count = count + written;
+
+        iov_iter_advance(i, written);
+}
+
+static inline size_t iov_iter_count(struct iov_iter *i)
+{
+        return i->count;
+}
+
+
 struct address_space_operations {
         int (*writepage)(struct page *page, struct writeback_control *wbc);
         int (*readpage)(struct file *, struct page *);