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authorPatrick Ohly <patrick.ohly@intel.com>2009-02-12 05:03:37 +0000
committerDavid S. Miller <davem@davemloft.net>2009-02-15 22:43:34 -0800
commitac45f602ee3d1b6f326f68bc0c2591ceebf05ba4 (patch)
treec92c86bd0d89b844a3794c0e441aa2fccb36725f /include/net/scm.h
parentcb9eff097831007afb30d64373f29d99825d0068 (diff)
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>
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