diff options
Diffstat (limited to 'Documentation/networking/timestamping.txt')
| -rw-r--r-- | Documentation/networking/timestamping.txt | 23 |
1 files changed, 15 insertions, 8 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt index b08e27261ff9..a5c784c89312 100644 --- a/Documentation/networking/timestamping.txt +++ b/Documentation/networking/timestamping.txt @@ -130,19 +130,26 @@ SOF_TIMESTAMPING_OPT_ID: have multiple concurrent timestamping requests outstanding. Packets can be reordered in the transmit path, for instance in the packet scheduler. In that case timestamps will be queued onto the error - queue out of order from the original send() calls. This option - embeds a counter that is incremented at send() time, to order - timestamps within a flow. + queue out of order from the original send() calls. It is not always + possible to uniquely match timestamps to the original send() calls + based on timestamp order or payload inspection alone, then. + + This option associates each packet at send() with a unique + identifier and returns that along with the timestamp. The identifier + is derived from a per-socket u32 counter (that wraps). For datagram + sockets, the counter increments with each sent packet. For stream + sockets, it increments with every byte. + + The counter starts at zero. It is initialized the first time that + the socket option is enabled. It is reset each time the option is + enabled after having been disabled. Resetting the counter does not + change the identifiers of existing packets in the system. This option is implemented only for transmit timestamps. There, the timestamp is always looped along with a struct sock_extended_err. The option modifies field ee_data to pass an id that is unique among all possibly concurrently outstanding timestamp requests for - that socket. In practice, it is a monotonically increasing u32 - (that wraps). - - In datagram sockets, the counter increments on each send call. In - stream sockets, it increments with every byte. + that socket. SOF_TIMESTAMPING_OPT_CMSG: |