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Subject: [PATCH v4 1/5] folio: Add a function to change the private data
 attached to a folio
From:   David Howells <dhowells@redhat.com>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     Jeff Layton <jlayton@kernel.org>,
        Dominique Martinet <asmadeus@codewreck.org>,
        kafs-testing@auristor.com, dhowells@redhat.com,
        Jeff Layton <jlayton@kernel.org>,
        Ilya Dryomov <idryomov@gmail.com>,
        Dominique Martinet <asmadeus@codewreck.org>,
        linux-fsdevel@vger.kernel.org, linux-cachefs@redhat.com,
        v9fs-developer@lists.sourceforge.net,
        linux-afs@lists.infradead.org, ceph-devel@vger.kernel.org,
        linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
        devel@lists.orangefs.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Date:   Tue, 09 Nov 2021 21:27:23 +0000
Message-ID: <163649324326.309189.17817587229450840783.stgit@warthog.procyon.org.uk>
In-Reply-To: <163649323416.309189.4637503793406396694.stgit@warthog.procyon.org.uk>
References: <163649323416.309189.4637503793406396694.stgit@warthog.procyon.org.uk>
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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@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Tested-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Dominique Martinet <asmadeus@codewreck.org>
Tested-by: kafs-testing@auristor.com
Link: https://lore.kernel.org/r/162981149911.1901565.17776700811659843340.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163005743485.2472992.5100702469503007023.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163584180781.4023316.5037526301198034310.stgit@warthog.procyon.org.uk/ # v3
---

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

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 6a30916b76e5..1f560aecd9b5 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -279,6 +279,25 @@ 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.