#include <pcap/pcap.h> int pcap_set_immediate_mode(pcap_t *p, int immediate_mode);
pcap_set_immediate_mode() sets whether immediate mode should be set on a capture handle when the handle is activated. In immediate mode, packets are always delivered as soon as they arrive, with no buffering. If immediate_mode is non-zero, immediate mode will be set, otherwise it will not be set.
pcap_set_immediate_mode() returns 0 on success or PCAP_ERROR_ACTIVATED if called on a capture handle that has been activated.
This function became available in libpcap release 1.5.0. In previous releases, if immediate delivery of packets is required:
on FreeBSD, NetBSD, OpenBSD, DragonFly BSD, macOS, and Solaris 11, immediate mode must be turned on with a BIOCIMMEDIATE ioctl(2), as documented in bpf(4), on the descriptor returned by pcap_fileno(3PCAP), after pcap_activate(3PCAP) is called;
on Solaris 10 and earlier versions of Solaris, immediate mode must be turned on by using a read timeout of 0 when opening the device (this will not provide immediate delivery of packets on other platforms, so don't assume it's sufficient);
on Digital UNIX/Tru64 UNIX, immediate mode must be turned on by doing a BIOCMBIC ioctl, as documented in packetfilter(7), to clear the ENBATCH flag on the descriptor returned by pcap_fileno(3PCAP), after pcap_activate(3PCAP) is called;
on Windows, immediate mode must be turned on by calling pcap_setmintocopy() with a size of 0.
On Linux, with previous releases of libpcap, capture devices are always in immediate mode; however, in 1.5.0 and later, they are, by default, not in immediate mode, so if pcap_set_immediate_mode() is available, it should be used.
On other platforms, capture devices are always in immediate mode.
pcap(3PCAP), pcap_create(3PCAP), pcap_activate(3PCAP)