tcpdump mailing list archives
Re: Monotonic clock timestamp on packets
From: Guy Harris <guy () alum mit edu>
Date: Tue, 4 May 2010 00:46:33 -0700
On May 3, 2010, at 11:29 PM, Thomas Habets wrote:
Has anyone looked into timestamping the captured packets using clock_gettime(CLOCK_MONOTONIC, ...)? I'm thinking adding a struct timespec to struct pcap_pkthdr
pcap_pkthdr is in a file. You cannot add *ANYTHING* to it without breaking compatibility; you'd have to introduce a new magic number. BTW, note that if you call clock_gettime(), there is *NO* guarantee that the time it returns has anything to do with the time the packe arrived; it tells you the time when it's called, not the time when the packet arrived.
and filling that in addition to the struct timeval. For a request-reply situation a monotonic clock is much more reliable than gettimeofday().
The only platforms on which libpcap uses gettimeofday() are: DLPI platforms where the DLPI module doesn't supply the time stamp (e.g., HP-UX); DOS; Septel devices; USB capturing on Linux if you're not using the memory-mapped interface. On all other platforms - i.e., on most of the platforms where libpcap is used - the time stamps are supplied to userland by the kernel, so if you want to use a different timer, you'll have to modify the kernel. (*BSD, Mac OS X, Linux, Solaris, etc.)
take a look at the code.
I did. See above. - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
Current thread:
- Monotonic clock timestamp on packets Thomas Habets (May 04)
- Re: Monotonic clock timestamp on packets Guy Harris (May 04)
- Re: Monotonic clock timestamp on packets Thomas Habets (May 04)
- Re: Monotonic clock timestamp on packets Prasanna Kumar Nelam (May 04)
- Re: Monotonic clock timestamp on packets Thomas Habets (May 04)
- Re: Monotonic clock timestamp on packets Thomas Habets (May 04)
- Re: Monotonic clock timestamp on packets Guy Harris (May 04)