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, 90 insertions, 1 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 924700844580..f96bc91bf0a3 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -132,6 +132,57 @@ struct skb_frag_struct {
         __u32 size;
 };
 
+#define HAVE_HW_TIME_STAMP
+
+/**
+ * skb_shared_hwtstamps - hardware time stamps
+ *
+ * @hwtstamp:   hardware time stamp transformed into duration
+ *              since arbitrary point in time
+ * @syststamp:  hwtstamp transformed to system time base
+ *
+ * Software time stamps generated by ktime_get_real() are stored in
+ * skb->tstamp. The relation between the different kinds of time
+ * stamps is as follows:
+ *
+ * syststamp and tstamp can be compared against each other in
+ * arbitrary combinations.  The accuracy of a
+ * syststamp/tstamp/"syststamp from other device" comparison is
+ * limited by the accuracy of the transformation into system time
+ * base. This depends on the device driver and its underlying
+ * hardware.
+ *
+ * hwtstamps can only be compared against other hwtstamps from
+ * the same device.
+ *
+ * This structure is attached to packets as part of the
+ * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
+ */
+struct skb_shared_hwtstamps {
+        ktime_t hwtstamp;
+        ktime_t syststamp;
+};
+
+/**
+ * skb_shared_tx - instructions for time stamping of outgoing packets
+ *
+ * @hardware:           generate hardware time stamp
+ * @software:           generate software time stamp
+ * @in_progress:        device driver is going to provide
+ *                      hardware time stamp
+ *
+ * These flags are attached to packets as part of the
+ * &skb_shared_info. Use skb_tx() to get a pointer.
+ */
+union skb_shared_tx {
+        struct {
+                __u8    hardware:1,
+                        software:1,
+                        in_progress:1;
+        };
+        __u8 flags;
+};
+
 /* This data is invariant across clones and lives at
  * the end of the header data, ie. at skb->end.
  */
@@ -143,10 +194,12 @@ struct skb_shared_info {
         unsigned short  gso_segs;
         unsigned short  gso_type;
         __be32          ip6_frag_id;
+        union skb_shared_tx tx_flags;
 #ifdef CONFIG_HAS_DMA
         unsigned int    num_dma_maps;
 #endif
         struct sk_buff  *frag_list;
+        struct skb_shared_hwtstamps hwtstamps;
         skb_frag_t      frags[MAX_SKB_FRAGS];
 #ifdef CONFIG_HAS_DMA
         dma_addr_t      dma_maps[MAX_SKB_FRAGS + 1];
@@ -465,6 +518,16 @@ static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 /* Internal */
 #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
 
+static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
+{
+        return &skb_shinfo(skb)->hwtstamps;
+}
+
+static inline union skb_shared_tx *skb_tx(struct sk_buff *skb)
+{
+        return &skb_shinfo(skb)->tx_flags;
+}
+
 /**
  *      skb_queue_empty - check if a queue is empty
  *      @list: queue head
@@ -1730,6 +1793,11 @@ static inline void skb_copy_to_linear_data_offset(struct sk_buff *skb,
 
 extern void skb_init(void);
 
+static inline ktime_t skb_get_ktime(const struct sk_buff *skb)
+{
+        return skb->tstamp;
+}
+
 /**
  *      skb_get_timestamp - get timestamp from a skb
  *      @skb: skb to get stamp from
@@ -1739,11 +1807,18 @@ extern void skb_init(void);
  *      This function converts the offset back to a struct timeval and stores
  *      it in stamp.
  */
-static inline void skb_get_timestamp(const struct sk_buff *skb, struct timeval *stamp)
+static inline void skb_get_timestamp(const struct sk_buff *skb,
+                                     struct timeval *stamp)
 {
         *stamp = ktime_to_timeval(skb->tstamp);
 }
 
+static inline void skb_get_timestampns(const struct sk_buff *skb,
+                                       struct timespec *stamp)
+{
+        *stamp = ktime_to_timespec(skb->tstamp);
+}
+
 static inline void __net_timestamp(struct sk_buff *skb)
 {
         skb->tstamp = ktime_get_real();
@@ -1759,6 +1834,20 @@ static inline ktime_t net_invalid_timestamp(void)
         return ktime_set(0, 0);
 }
 
+/**
+ * skb_tstamp_tx - queue clone of skb with send time stamps
+ * @orig_skb:   the original outgoing packet
+ * @hwtstamps:  hardware time stamps, may be NULL if not available
+ *
+ * If the skb has a socket associated, then this function clones the
+ * skb (thus sharing the actual data and optional structures), stores
+ * the optional hardware time stamping information (if non NULL) or
+ * generates a software time stamp (otherwise), then queues the clone
+ * to the error queue of the socket.  Errors are silently ignored.
+ */
+extern void skb_tstamp_tx(struct sk_buff *orig_skb,
+                        struct skb_shared_hwtstamps *hwtstamps);
+
 extern __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len);
 extern __sum16 __skb_checksum_complete(struct sk_buff *skb);