netdev - [PATCH 03/13] scatterlist: Add sg_set

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Message-Id: <20230621164557.3510324-4-willy@infradead.org>
Date: Wed, 21 Jun 2023 17:45:47 +0100
From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
To: linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	intel-gfx@...ts.freedesktop.org,
	linux-afs@...ts.infradead.org,
	linux-nfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH 03/13] scatterlist: Add sg_set_folio()

This wrapper for sg_set_page() lets drivers add folios to a scatterlist
more easily.  We could, perhaps, do better by using a different page
in the folio if offset is larger than UINT_MAX, but let's hope we get
a better data structure than this before we need to care about such
large folios.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
---
 include/linux/scatterlist.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index ec46d8e8e49d..77df3d7b18a6 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -141,6 +141,30 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
 	sg->length = len;
 }
 
+/**
+ * sg_set_folio - Set sg entry to point at given folio
+ * @sg:		 SG entry
+ * @folio:	 The folio
+ * @len:	 Length of data
+ * @offset:	 Offset into folio
+ *
+ * Description:
+ *   Use this function to set an sg entry pointing at a folio, never assign
+ *   the folio directly. We encode sg table information in the lower bits
+ *   of the folio pointer. See sg_page() for looking up the page belonging
+ *   to an sg entry.
+ *
+ **/
+static inline void sg_set_folio(struct scatterlist *sg, struct folio *folio,
+			       size_t len, size_t offset)
+{
+	WARN_ON_ONCE(len > UINT_MAX);
+	WARN_ON_ONCE(offset > UINT_MAX);
+	sg_assign_page(sg, &folio->page);
+	sg->offset = offset;
+	sg->length = len;
+}
+
 static inline struct page *sg_page(struct scatterlist *sg)
 {
 #ifdef CONFIG_DEBUG_SG
-- 
2.39.2