[bpf-next PATCH 03/16] net: do_tcp_sendpages flag to avoid SKBTX_SHARED_FRAG

[John Fastabend]

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.

The flag is not exposed to userspace because the sendpage call from
the splice logic masks out all bits except MSG_MORE.

Signed-off-by: John Fastabend <john.fastab...@gmail.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 1ce1f76..60e0148 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 a335397..ff8a8d3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -994,7 +994,9 @@ 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;