net: cleanup and document skb fclone layout

Lets use a proper structure to clearly document and implement
skb fast clones.

Then, we might experiment more easily alternative layouts.

This patch adds a new skb_fclone_busy() helper, used by tcp and xfrm,
to stop leaking of implementation details.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 4 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ee567e9e98c3..8d4eac793700 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2110,10 +2110,7 @@ bool tcp_schedule_loss_probe(struct sock *sk)
 static bool skb_still_in_host_queue(const struct sock *sk,
                                     const struct sk_buff *skb)
 {
-        const struct sk_buff *fclone = skb + 1;
-
-        if (unlikely(skb->fclone == SKB_FCLONE_ORIG &&
-                     fclone->fclone == SKB_FCLONE_CLONE)) {
+        if (unlikely(skb_fclone_busy(skb))) {
                 NET_INC_STATS_BH(sock_net(sk),
                                  LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
                 return true;