linux-kernel - [PATCH 2/6] folio: Add a function to change the private data attached to a folio

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Date:   Tue, 24 Aug 2021 14:24:59 +0100
From:   David Howells <dhowells@...hat.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     dhowells@...hat.com, Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-cachefs@...hat.com,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net, devel@...ts.orangefs.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] folio: Add a function to change the private data attached
 to a folio

Add a function, folio_change_private(), that will change the private data
attached to a folio, without the need to twiddle the private bit or the
refcount.  It assumes that folio_add_private() has already been called on
the page.

Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---

 include/linux/pagemap.h |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index f55d8d9001a9..c8d336e62177 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -229,6 +229,25 @@ static inline void folio_attach_private(struct folio *folio, void *data)
 	folio_set_private(folio);
 }
 
+/**
+ * folio_change_private - Change private data on a folio.
+ * @folio: Folio to change the data on.
+ * @data: Data to set on the folio.
+ *
+ * Change the private data attached to a folio and return the old
+ * data.  The page must previously have had data attached and the data
+ * must be detached before the folio will be freed.
+ *
+ * Return: Data that was previously attached to the folio.
+ */
+static inline void *folio_change_private(struct folio *folio, void *data)
+{
+	void *old = folio_get_private(folio);
+
+	folio->private = data;
+	return old;
+}
+
 /**
  * folio_detach_private - Detach private data from a folio.
  * @folio: Folio to detach data from.