net: infrastructure for hardware time stamping

The additional per-packet information (16 bytes for time stamps, 1
byte for flags) is stored for all packets in the skb_shared_info
struct. This implementation detail is hidden from users of that
information via skb_* accessor functions. A separate struct resp.
union is used for the additional information so that it can be
stored/copied easily outside of skb_shared_info.

Compared to previous implementations (reusing the tstamp field
depending on the context, optional additional structures) this
is the simplest solution. It does not extend sk_buff itself.

TX time stamping is implemented in software if the device driver
doesn't support hardware time stamping.

The new semantic for hardware/software time stamping around
ndo_start_xmit() is based on two assumptions about existing
network device drivers which don't support hardware time
stamping and know nothing about it:
 - they leave the new skb_shared_tx unmodified
 - the keep the connection to the originating socket in skb->sk
   alive, i.e., don't call skb_orphan()

Given that skb_shared_tx is new, the first assumption is safe.
The second is only true for some drivers. As a result, software
TX time stamping currently works with the bnx2 driver, but not
with the unmodified igb driver (the two drivers this patch series
was tested with).

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 41 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ab7d2e9f02fa..e5a8351ff12d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -55,6 +55,7 @@
 #include <linux/rtnetlink.h>
 #include <linux/init.h>
 #include <linux/scatterlist.h>
+#include <linux/errqueue.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
@@ -215,7 +216,9 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
         shinfo->gso_segs = 0;
         shinfo->gso_type = 0;
         shinfo->ip6_frag_id = 0;
+        shinfo->tx_flags.flags = 0;
         shinfo->frag_list = NULL;
+        memset(&shinfo->hwtstamps, 0, sizeof(shinfo->hwtstamps));
 
         if (fclone) {
                 struct sk_buff *child = skb + 1;
@@ -2945,6 +2948,44 @@ int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer)
 }
 EXPORT_SYMBOL_GPL(skb_cow_data);
 
+void skb_tstamp_tx(struct sk_buff *orig_skb,
+                struct skb_shared_hwtstamps *hwtstamps)
+{
+        struct sock *sk = orig_skb->sk;
+        struct sock_exterr_skb *serr;
+        struct sk_buff *skb;
+        int err;
+
+        if (!sk)
+                return;
+
+        skb = skb_clone(orig_skb, GFP_ATOMIC);
+        if (!skb)
+                return;
+
+        if (hwtstamps) {
+                *skb_hwtstamps(skb) =
+                        *hwtstamps;
+        } else {
+                /*
+                 * no hardware time stamps available,
+                 * so keep the skb_shared_tx and only
+                 * store software time stamp
+                 */
+                skb->tstamp = ktime_get_real();
+        }
+
+        serr = SKB_EXT_ERR(skb);
+        memset(serr, 0, sizeof(*serr));
+        serr->ee.ee_errno = ENOMSG;
+        serr->ee.ee_origin = SO_EE_ORIGIN_TIMESTAMPING;
+        err = sock_queue_err_skb(sk, skb);
+        if (err)
+                kfree_skb(skb);
+}
+EXPORT_SYMBOL_GPL(skb_tstamp_tx);
+
+
 /**
  * skb_partial_csum_set - set up and verify partial csum values for packet
  * @skb: the skb to set