doc/README.linux

Currently, libpcap supports packet capturing on Linux 2.6.27 and later;
earlier versions are not supported.

You must configure 2.6.x kernels with the CONFIG_PACKET_MMAP option for
this protocol.  3.x and later kernels do not require that.

Note that, by default, libpcap will, if libnl is present, build with it;
it uses libnl to support monitor mode on mac80211 devices.  There is a
configuration option to disable building with libnl, but, if that option
is chosen, the monitor-mode APIs (as used by tcpdump's "-I" flag, and as
will probably be used by other applications in the future) won't work
properly on mac80211 devices.

Linux's run-time linker allows shared libraries to be linked with other
shared libraries, which means that if an older version of a shared
library doesn't require routines from some other shared library, and a
later version of the shared library does require those routines, the
later version of the shared library can be linked with that other shared
library and, if it's otherwise binary-compatible with the older version,
can replace that older version without breaking applications built with
the older version, and without breaking configure scripts or the build
procedure for applications whose configure script doesn't use the
pcap-config script if they build with the shared library.  (The build
procedure for applications whose configure scripts use the pcap-config
script if present will not break even if they build with the static
library.)

Statistics:
Statistics reported by pcap are platform specific.  The statistics
reported by pcap_stats on Linux are as follows:

ps_recv   Number of packets that were accepted by the pcap filter
ps_drop   Number of packets that had passed filtering but were not
          passed on to pcap due to things like buffer shortage, etc.
          This is useful because these are packets you are interested in
          but won't be reported by, for example, tcpdump output.