sock: enable timestamping using control messages

Currently, SOL_TIMESTAMPING can only be enabled using setsockopt.
This is very costly when users want to sample writes to gather
tx timestamps.

Add support for enabling SO_TIMESTAMPING via control messages by
using tsflags added in `struct sockcm_cookie` (added in the previous
patches in this series) to set the tx_flags of the last skb created in
a sendmsg. With this patch, the timestamp recording bits in tx_flags
of the skbuff is overridden if SO_TIMESTAMPING is passed in a cmsg.

Please note that this is only effective for overriding the recording
timestamps flags. Users should enable timestamp reporting (e.g.,
SOF_TIMESTAMPING_SOFTWARE | SOF_TIMESTAMPING_OPT_ID) using
socket options and then should ask for SOF_TIMESTAMPING_TX_*
using control messages per sendmsg to sample timestamps for each
write.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 5 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1ecfa710ca98..0007e23202e4 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1837,6 +1837,7 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg,
         DECLARE_SOCKADDR(struct sockaddr_pkt *, saddr, msg->msg_name);
         struct sk_buff *skb = NULL;
         struct net_device *dev;
+        struct sockcm_cookie sockc;
         __be16 proto = 0;
         int err;
         int extra_len = 0;
@@ -1925,12 +1926,21 @@ retry:
                 goto out_unlock;
         }
 
+        sockc.tsflags = 0;
+        if (msg->msg_controllen) {
+                err = sock_cmsg_send(sk, msg, &sockc);
+                if (unlikely(err)) {
+                        err = -EINVAL;
+                        goto out_unlock;
+                }
+        }
+
         skb->protocol = proto;
         skb->dev = dev;
         skb->priority = sk->sk_priority;
         skb->mark = sk->sk_mark;
 
-        sock_tx_timestamp(sk, &skb_shinfo(skb)->tx_flags);
+        sock_tx_timestamp(sk, sockc.tsflags, &skb_shinfo(skb)->tx_flags);
 
         if (unlikely(extra_len == 4))
                 skb->no_fcs = 1;
@@ -2486,7 +2496,8 @@ static int packet_snd_vnet_gso(struct sk_buff *skb,
 
 static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
                 void *frame, struct net_device *dev, void *data, int tp_len,
-                __be16 proto, unsigned char *addr, int hlen, int copylen)
+                __be16 proto, unsigned char *addr, int hlen, int copylen,
+                const struct sockcm_cookie *sockc)
 {
         union tpacket_uhdr ph;
         int to_write, offset, len, nr_frags, len_max;
@@ -2500,7 +2511,7 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
         skb->dev = dev;
         skb->priority = po->sk.sk_priority;
         skb->mark = po->sk.sk_mark;
-        sock_tx_timestamp(&po->sk, &skb_shinfo(skb)->tx_flags);
+        sock_tx_timestamp(&po->sk, sockc->tsflags, &skb_shinfo(skb)->tx_flags);
         skb_shinfo(skb)->destructor_arg = ph.raw;
 
         skb_reserve(skb, hlen);
@@ -2624,6 +2635,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
         struct sk_buff *skb;
         struct net_device *dev;
         struct virtio_net_hdr *vnet_hdr = NULL;
+        struct sockcm_cookie sockc;
         __be16 proto;
         int err, reserve = 0;
         void *ph;
@@ -2655,6 +2667,13 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
                 dev = dev_get_by_index(sock_net(&po->sk), saddr->sll_ifindex);
         }
 
+        sockc.tsflags = 0;
+        if (msg->msg_controllen) {
+                err = sock_cmsg_send(&po->sk, msg, &sockc);
+                if (unlikely(err))
+                        goto out;
+        }
+
         err = -ENXIO;
         if (unlikely(dev == NULL))
                 goto out;
@@ -2712,7 +2731,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
                         goto out_status;
                 }
                 tp_len = tpacket_fill_skb(po, skb, ph, dev, data, tp_len, proto,
-                                          addr, hlen, copylen);
+                                          addr, hlen, copylen, &sockc);
                 if (likely(tp_len >= 0) &&
                     tp_len > dev->mtu + reserve &&
                     !po->has_vnet_hdr &&
@@ -2851,6 +2870,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
         if (unlikely(!(dev->flags & IFF_UP)))
                 goto out_unlock;
 
+        sockc.tsflags = 0;
         sockc.mark = sk->sk_mark;
         if (msg->msg_controllen) {
                 err = sock_cmsg_send(sk, msg, &sockc);
@@ -2908,7 +2928,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
                 goto out_free;
         }
 
-        sock_tx_timestamp(sk, &skb_shinfo(skb)->tx_flags);
+        sock_tx_timestamp(sk, sockc.tsflags, &skb_shinfo(skb)->tx_flags);
 
         if (!vnet_hdr.gso_type && (len > dev->mtu + reserve + extra_len) &&
             !packet_extra_vlan_len_allowed(dev, skb)) {