netdev - [bpf-next PATCH 4/7] net: do_tcp_sendpages flag to avoid SKBTX_SHARED

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Date:   Fri, 12 Jan 2018 10:10:55 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     borkmann@...earbox.net, john.fastabend@...il.com, ast@...nel.org
Cc:     netdev@...r.kernel.org, kafai@...com
Subject: [bpf-next PATCH 4/7] net: do_tcp_sendpages flag to avoid
 SKBTX_SHARED_FRAG

When calling do_tcp_sendpages() from in kernel and we know the data
has no references from user side we can omit SKBTX_SHARED_FRAG flag.
This patch adds an internal flag, NO_SKBTX_SHARED_FRAG that can be used
to omit setting SKBTX_SHARED_FRAG.

Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 include/linux/socket.h |    1 +
 net/ipv4/tcp.c         |    4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 9286a5a..add9360 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -287,6 +287,7 @@ struct ucred {
 #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */
 #define MSG_BATCH	0x40000 /* sendmmsg(): more messages coming */
 #define MSG_EOF         MSG_FIN
+#define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */
 
 #define MSG_ZEROCOPY	0x4000000	/* Use user data in kernel path */
 #define MSG_FASTOPEN	0x20000000	/* Send data in TCP SYN */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 7ac583a..56c6f49 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -995,7 +995,9 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
 			get_page(page);
 			skb_fill_page_desc(skb, i, page, offset, copy);
 		}
-		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
+
+		if (!(flags & MSG_NO_SHARED_FRAGS))
+			skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
 
 		skb->len += copy;
 		skb->data_len += copy;