From ac45f602ee3d1b6f326f68bc0c2591ceebf05ba4 Mon Sep 17 00:00:00 2001 From: Patrick Ohly Date: Thu, 12 Feb 2009 05:03:37 +0000 Subject: 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 Signed-off-by: David S. Miller --- net/core/dev.c | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) (limited to 'net/core/dev.c') diff --git a/net/core/dev.c b/net/core/dev.c index 1e27a67df24..d20c28e839d 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -1672,10 +1672,21 @@ static int dev_gso_segment(struct sk_buff *skb) return 0; } +static void tstamp_tx(struct sk_buff *skb) +{ + union skb_shared_tx *shtx = + skb_tx(skb); + if (unlikely(shtx->software && + !shtx->in_progress)) { + skb_tstamp_tx(skb, NULL); + } +} + int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, struct netdev_queue *txq) { const struct net_device_ops *ops = dev->netdev_ops; + int rc; prefetch(&dev->netdev_ops->ndo_start_xmit); if (likely(!skb->next)) { @@ -1689,13 +1700,29 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, goto gso; } - return ops->ndo_start_xmit(skb, dev); + rc = ops->ndo_start_xmit(skb, dev); + /* + * TODO: if skb_orphan() was called by + * dev->hard_start_xmit() (for example, the unmodified + * igb driver does that; bnx2 doesn't), then + * skb_tx_software_timestamp() will be unable to send + * back the time stamp. + * + * How can this be prevented? Always create another + * reference to the socket before calling + * dev->hard_start_xmit()? Prevent that skb_orphan() + * does anything in dev->hard_start_xmit() by clearing + * the skb destructor before the call and restoring it + * afterwards, then doing the skb_orphan() ourselves? + */ + if (likely(!rc)) + tstamp_tx(skb); + return rc; } gso: do { struct sk_buff *nskb = skb->next; - int rc; skb->next = nskb->next; nskb->next = NULL; @@ -1705,6 +1732,7 @@ gso: skb->next = nskb; return rc; } + tstamp_tx(skb); if (unlikely(netif_tx_queue_stopped(txq) && skb->next)) return NETDEV_TX_BUSY; } while (skb->next); -- cgit v1.2.3