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.TH PCAP_GET_REQUIRED_SELECT_TIMEOUT 3PCAP "25 July 2018"

.SH NAME

pcap_get_required_select_timeout \- get a file descriptor on which a

select() can be done for a live capture

.SH SYNOPSIS

.nf

.ft B

#include <pcap/pcap.h>

.ft

.LP

.ft B

struct timeval *pcap_get_required_select_timeout(pcap_t *p);

.ft

.fi

.SH DESCRIPTION

.B pcap_get_required_select_timeout()

returns, on UNIX, a pointer to a

.B struct timeval

containing a value that must be used as the minimum timeout in

.BR select(2) ,

.BR poll(2) ,

.BR epoll_wait(2) ,

and

.B kevent()

calls if

.B pcap_get_selectable_fd(3PCAP)

returns

.BR PCAP_ERROR .

.PP

The timeout that should be used in those calls must be no larger than

the smallest of all timeouts returned by

.B \%pcap_get_required_select_timeout()

for devices from which packets will be captured.

.PP

The device for which

.B pcap_get_selectable_fd()

returned

.B PCAP_ERROR

must be put in non-blocking mode with

.BR pcap_setnonblock(3PCAP) ,

and an attempt must always be made to read packets from the device

when the

.BR select() ,

.BR poll() ,

.BR epoll_wait() ,

or

.B kevent()

call returns.

.PP

Note that a device on which a read can be done without blocking may,

on some platforms, not have any packets to read if the packet buffer

timeout has expired.  A call to

.B pcap_dispatch(3PCAP)

or

.B pcap_next_ex(3PCAP)

will return 0 in this case, but will not block.

.PP

.B pcap_get_required_select_timeout()

is not available on Windows.

.SH RETURN VALUE

A pointer to a

.B struct timeval

is returned if the timeout is required; otherwise

.B NULL

is returned.

.SH BACKWARD COMPATIBILITY

This function became available in libpcap release 1.9.0.  In previous

releases,

.BR select() ,

.BR poll() ,

.BR epoll_wait() ,

and

.B kevent()

cannot be used on any capture source for which

.B pcap_get_selectable_fd

returns \-1.

.SH SEE ALSO

pcap(3PCAP), pcap_get_selectable_fd(3PCAP), select(2), poll(2),

epoll_wait(2), kqueue(2)