netdev - [PATCH v2 bpf-next 1/2] lib/scatterlist: add sg_init

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Message-Id: <20180330002100.5724-2-bhole_prashant_q7@lab.ntt.co.jp>
Date:   Fri, 30 Mar 2018 09:20:59 +0900
From:   Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org
Subject: [PATCH v2 bpf-next 1/2] lib/scatterlist: add sg_init_marker() helper

sg_init_marker initializes sg_magic in the sg table and calls
sg_mark_end() on the last entry of the table. This can be useful to
avoid memset in sg_init_table() when scatterlist is already zeroed out

For example: when scatterlist is embedded inside other struct and that
container struct is zeroed out

Suggested-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
---
 include/linux/scatterlist.h | 18 ++++++++++++++++++
 lib/scatterlist.c           |  9 +--------
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 22b2131bcdcd..aa5d4eb725f5 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -248,6 +248,24 @@ static inline void *sg_virt(struct scatterlist *sg)
 	return page_address(sg_page(sg)) + sg->offset;
 }
 
+/**
+ * sg_init_marker - Initialize markers in sg table
+ * @sgl:	   The SG table
+ * @nents:	   Number of entries in table
+ *
+ **/
+static inline void sg_init_marker(struct scatterlist *sgl,
+				  unsigned int nents)
+{
+#ifdef CONFIG_DEBUG_SG
+	unsigned int i;
+
+	for (i = 0; i < nents; i++)
+		sgl[i].sg_magic = SG_MAGIC;
+#endif
+	sg_mark_end(&sgl[nents - 1]);
+}
+
 int sg_nents(struct scatterlist *sg);
 int sg_nents_for_len(struct scatterlist *sg, u64 len);
 struct scatterlist *sg_next(struct scatterlist *);
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 53728d391d3a..06dad7a072fd 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -132,14 +132,7 @@ EXPORT_SYMBOL(sg_last);
 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 {
 	memset(sgl, 0, sizeof(*sgl) * nents);
-#ifdef CONFIG_DEBUG_SG
-	{
-		unsigned int i;
-		for (i = 0; i < nents; i++)
-			sgl[i].sg_magic = SG_MAGIC;
-	}
-#endif
-	sg_mark_end(&sgl[nents - 1]);
+	sg_init_marker(sgl, nents);
 }
 EXPORT_SYMBOL(sg_init_table);
 
-- 
2.14.3