Manpage of PCAP_SET_IMMEDIATE_MODE

Section: Misc. Reference Manual Pages (3PCAP)
Updated: 22 August 2018
Return to Main Contents

NAME

pcap_set_immediate_mode - set immediate mode for a not-yet-activated capture handle

SYNOPSIS

#include <pcap/pcap.h>

int pcap_set_immediate_mode(pcap_t *p, int immediate_mode);

DESCRIPTION

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.

RETURN VALUE

pcap_set_immediate_mode() returns 0 on success or PCAP_ERROR_ACTIVATED if called on a capture handle that has been activated.

BACKWARD COMPATIBILITY

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.