pcap_get_required_select_timeout(3pcap) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | BACKWARD COMPATIBILITY | SEE ALSO | COLOPHON

PCAP_GET_REQUIRED_SELECT_TIMEOUT(3PCAP)AP_GET_REQUIRED_SELECT_TIMEOUT(3PCAP)

NAME         top

       pcap_get_required_select_timeout  -  get  a  timeout  to be used when
       doing select() for a live capture

SYNOPSIS         top

       #include <pcap/pcap.h>

       const struct timeval *pcap_get_required_select_timeout(pcap_t *p);

DESCRIPTION         top

       pcap_get_required_select_timeout() returns, on UNIX, a pointer to a
       struct timeval containing a value that must be used as the minimum
       timeout in select(2), poll(2), epoll_wait(2), and kevent(2) calls, or
       NULL if there is no such timeout.  If a non-NULL value is returned,
       it must be used regardless of whether pcap_get_selectable_fd(3PCAP)
       returns -1 for any descriptor on which those calls are being done.
       pcap_get_required_select_timeout() should be called for all pcap_ts
       before a call to select(), poll(), epoll_wait(), or kevent(), and any
       timeouts used for those calls should be updated as appropriate given
       the new value of the timeout.

       For kevent(), one EVFILT_TIMER filter per selectable descriptor can
       be used, rather than using the timeout argument to kevent(); if the
       EVFILT_TIMER event for a particular selectable descriptor signals an
       event, pcap_dispatch(3PCAP) should be called for the corresponding
       pcap_t.

       On Linux systems with timerfd_create(2), one timer object created by
       timerfd_create() per selectable descriptor can be used, rather than
       using the timeout argument to epoll_wait(); if the timer object for a
       particular selectable descriptor signals an event,
       pcap_dispatch(3PCAP) should be called for the corresponding pcap_t.

       Otherwise, a timeout value no larger than the smallest of all
       timeouts returned by pcap_get_required_select_timeout() for devices
       from which packets will be captured and any other timeouts to be used
       in the call should be used as the timeout for the call, and, when the
       call returns, pcap_dispatch(3PCAP) should be called for all pcap_ts
       for which a non-NULL timeout was returned, regardless of whether it's
       indicated as having anything to read from it or not.

       All devices with a non-NULL timeout must be put in non-blocking mode
       with pcap_setnonblock(3PCAP).

       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 pcap_dispatch() or
       pcap_next_ex(3PCAP) will return 0 in this case, but will not block.

       pcap_get_required_select_timeout() is not available on Windows.

RETURN VALUE         top

       A pointer to a struct timeval is returned if the timeout is required;
       otherwise NULL is returned.

BACKWARD COMPATIBILITY         top

       This function became available in libpcap release 1.9.0.  In previous
       releases, select(), poll(), epoll_wait(), and kevent() cannot be used
       on any capture source for which pcap_get_selectable_fd() returns -1.

       In libpcap release 1.10.0 and later, the timeout value can change
       from call to call, so pcap_get_required_select_timeout() must be
       called before each call to select(), poll(), epoll_wait(), or
       kevent(), and the new value must be used to calculate timeouts for
       the call.  Code that does that will also work with libpcap 1.9.x
       releases, so code using pcap_get_required_select_timeout() should be
       changed to call it for each call to select(), poll(), epoll_wait(),
       or kevent() even if the code must also work with libpcap 1.9.x.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the libpcap (packet capture library) project.
       Information about the project can be found at 
       ⟨http://www.tcpdump.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://www.tcpdump.org/#patches⟩.  This page was obtained
       from the project's upstream Git repository
       ⟨https://github.com/the-tcpdump-group/libpcap.git⟩ on 2020-06-09.
       (At that time, the date of the most recent commit that was found in
       the repository was 2020-06-07.)  If you discover any rendering prob‐
       lems in this HTML version of the page, or you believe there is a bet‐
       ter or more up-to-date source for the page, or you have corrections
       or improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to man-pages@man7.org

                               29 JanuPaCrAyP_2G0E2T0_REQUIRED_SELECT_TIMEOUT(3PCAP)