[PATCH v2 2/5] mm: Add file_offset_of_ helpers

[Matthew Wilcox <willy@infradead.org>]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

The page_offset function is badly named for people reading the functions
which call it.  The natural meaning of a function with this name would
be 'offset within a page', not 'page offset in bytes within a file'.
Dave Chinner suggests file_offset_of_page() as a replacement function
name and I'm also adding file_offset_of_next_page() as a helper for the
large page work.  Also add kernel-doc for these functions so they show
up in the kernel API book.

page_offset() is retained as a compatibility define for now.
---
 include/linux/pagemap.h | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2728f20fbc49..84f341109710 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -436,14 +436,33 @@ static inline pgoff_t page_to_pgoff(struct page *page)
 	return page_to_index(page);
 }
 
-/*
- * Return byte-offset into filesystem object for page.
+/**
+ * file_offset_of_page - File offset of this page.
+ * @page: Page cache page.
+ *
+ * Context: Any context.
+ * Return: The offset of the first byte of this page.
  */
-static inline loff_t page_offset(struct page *page)
+static inline loff_t file_offset_of_page(struct page *page)
 {
 	return ((loff_t)page->index) << PAGE_SHIFT;
 }
 
+/* Legacy; please convert callers */
+#define page_offset(page)	file_offset_of_page(page)
+
+/**
+ * file_offset_of_next_page - File offset of the next page.
+ * @page: Page cache page.
+ *
+ * Context: Any context.
+ * Return: The offset of the first byte after this page.
+ */
+static inline loff_t file_offset_of_next_page(struct page *page)
+{
+	return ((loff_t)page->index + compound_nr(page)) << PAGE_SHIFT;
+}
+
 static inline loff_t page_file_offset(struct page *page)
 {
 	return ((loff_t)page_index(page)) << PAGE_SHIFT;
-- 
2.23.0.rc1