diff options
Diffstat (limited to 'Documentation/networking/packet_mmap.txt')
| -rw-r--r-- | Documentation/networking/packet_mmap.txt | 18 |
1 files changed, 6 insertions, 12 deletions
diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt index 38112d5..a6d7cb9 100644 --- a/Documentation/networking/packet_mmap.txt +++ b/Documentation/networking/packet_mmap.txt @@ -1008,14 +1008,9 @@ hardware timestamps to be used. Note: you may need to enable the generation of hardware timestamps with SIOCSHWTSTAMP (see related information from Documentation/networking/timestamping.txt). -PACKET_TIMESTAMP accepts the same integer bit field as -SO_TIMESTAMPING. However, only the SOF_TIMESTAMPING_SYS_HARDWARE -and SOF_TIMESTAMPING_RAW_HARDWARE values are recognized by -PACKET_TIMESTAMP. SOF_TIMESTAMPING_SYS_HARDWARE takes precedence over -SOF_TIMESTAMPING_RAW_HARDWARE if both bits are set. - - int req = 0; - req |= SOF_TIMESTAMPING_SYS_HARDWARE; +PACKET_TIMESTAMP accepts the same integer bit field as SO_TIMESTAMPING: + + int req = SOF_TIMESTAMPING_RAW_HARDWARE; setsockopt(fd, SOL_PACKET, PACKET_TIMESTAMP, (void *) &req, sizeof(req)) For the mmap(2)ed ring buffers, such timestamps are stored in the @@ -1023,14 +1018,13 @@ tpacket{,2,3}_hdr structure's tp_sec and tp_{n,u}sec members. To determine what kind of timestamp has been reported, the tp_status field is binary |'ed with the following possible bits ... - TP_STATUS_TS_SYS_HARDWARE TP_STATUS_TS_RAW_HARDWARE TP_STATUS_TS_SOFTWARE ... that are equivalent to its SOF_TIMESTAMPING_* counterparts. For the -RX_RING, if none of those 3 are set (i.e. PACKET_TIMESTAMP is not set), -then this means that a software fallback was invoked *within* PF_PACKET's -processing code (less precise). +RX_RING, if neither is set (i.e. PACKET_TIMESTAMP is not set), then a +software fallback was invoked *within* PF_PACKET's processing code (less +precise). Getting timestamps for the TX_RING works as follows: i) fill the ring frames, ii) call sendto() e.g. in blocking mode, iii) wait for status of relevant |
