Re: [PATCH net-next 2/2] tcp: put a TLV list of TCP stats in error queue

On Tue, Sep 6, 2016 at 9:32 PM, Francis Y. Yan [off-list ref] wrote:

To export useful TCP statistics along with timestamps, such as
rwnd-limited time and min RTT, we enqueue a TLV list in error queue
immediately when a timestamp is generated.

Specifically, if user space requests SOF_TIMESTAMPING_TX_* timestamps
and sets SOF_TIMESTAMPING_OPT_STATS, the kernel will create a list of
TLVs (struct nlattr) containing all the statistics and store the list
in payload of the skb that is going to be enqueued into error queue.
Notice that SOF_TIMESTAMPING_OPT_STATS can only be set together with
SOF_TIMESTAMPING_OPT_TSONLY.

In addition, if the application in user space also enables receiving
timestamp (e.g. by SOF_TIMESTAMPING_SOFTWARE), calling recvfrom() on
error queue will return one more control message with a cmsg_type of
SCM_OPT_STATS containing the list of TLVs in its cmsg_data.

Signed-off-by: Francis Y. Yan <redacted>
Signed-off-by: Yuchung Cheng <redacted>

Acked-by: Soheil Hassas Yeganeh <redacted>