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.

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.fastabend@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 1ce1f768a58c..60e01482a9c4 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 fb350f740f69..f90ec24c2cc8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -994,7 +994,9 @@ new_segment:
                         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;