[01/10] include/linux/pagemap.h: introduce attach/detach_page_private

Commit Message

Guoqing Jiang May 17, 2020, 9:47 p.m. UTC

The logic in attach_page_buffers and  __clear_page_buffers are quite
paired, but

1. they are located in different files.

2. attach_page_buffers is implemented in buffer_head.h, so it could be
   used by other files. But __clear_page_buffers is static function in
   buffer.c and other potential users can't call the function, md-bitmap
   even copied the function.

So, introduce the new attach/detach_page_private to replace them. With
the new pair of function, we will remove the usage of attach_page_buffers
and  __clear_page_buffers in next patches. Thanks for suggestions about
the function name from Alexander Viro, Andreas Grünbacher, Christoph
Hellwig and Matthew Wilcox.

Suggested-by: Matthew Wilcox <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: "Darrick J. Wong" <[e-mail]>
Cc: William Kucharski <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Andreas Gruenbacher <[e-mail]>
Cc: Yang Shi <[e-mail]>
Cc: Yafang Shao <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: [e-mail]
Cc: Chris Mason <[e-mail]>
Cc: Josef Bacik <[e-mail]>
Cc: David Sterba <[e-mail]>
Cc: [e-mail]
Cc: Alexander Viro <[e-mail]>
Cc: Jaegeuk Kim <[e-mail]>
Cc: Chao Yu <[e-mail]>
Cc: [e-mail]
Cc: Christoph Hellwig <[e-mail]>
Cc: [e-mail]
Cc: Anton Altaparmakov <[e-mail]>
Cc: [e-mail]
Cc: Mike Marshall <[e-mail]>
Cc: Martin Brandenburg <[e-mail]>
Cc: [e-mail]
Cc: Thomas Gleixner <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Andreas Dilger <[e-mail]>
Signed-off-by: Guoqing Jiang <[e-mail]>
---
No change since RFC V3.

RFC V2 -> RFC V3:
1. rename clear_page_private to detach_page_private.
2. updated the comments for the two functions.

RFC -> RFC V2:  Address the comments from Christoph Hellwig
1. change function names to attach/clear_page_private and add comments.
2. change the return type of attach_page_private.

 include/linux/pagemap.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c6348c50136f..8e085713150c 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -208,6 +208,43 @@  static inline int page_cache_add_speculative(struct page *page, int count)
 	return __page_cache_add_speculative(page, count);
 }
 
+/**
+ * attach_page_private - Attach private data to a page.
+ * @page: Page to attach data to.
+ * @data: Data to attach to page.
+ *
+ * Attaching private data to a page increments the page's reference count.
+ * The data must be detached before the page will be freed.
+ */
+static inline void attach_page_private(struct page *page, void *data)
+{
+	get_page(page);
+	set_page_private(page, (unsigned long)data);
+	SetPagePrivate(page);
+}
+
+/**
+ * detach_page_private - Detach private data from a page.
+ * @page: Page to detach data from.
+ *
+ * Removes the data that was previously attached to the page and decrements
+ * the refcount on the page.
+ *
+ * Return: Data that was attached to the page.
+ */
+static inline void *detach_page_private(struct page *page)
+{
+	void *data = (void *)page_private(page);
+
+	if (!PagePrivate(page))
+		return NULL;
+	ClearPagePrivate(page);
+	set_page_private(page, 0);
+	put_page(page);
+
+	return data;
+}
+
 #ifdef CONFIG_NUMA
 extern struct page *__page_cache_alloc(gfp_t gfp);
 #else