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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | BACKWARD COMPATIBILITY | SEE ALSO | COLOPHON |
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PCAP_GET_REQ...LECT_TIMEOUT(3PCAP) PCAP_GET_REQ...LECT_TIMEOUT(3PCAP)
pcap_get_required_select_timeout - get a timeout to be used when
doing select() for a live capture
#include <pcap/pcap.h>
const struct timeval *pcap_get_required_select_timeout(pcap_t *p);
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.
A pointer to a struct timeval is returned if the timeout is
required; otherwise NULL is returned.
This function became available in libpcap release 1.9.0. In
previous releases, select(), poll(), epoll_wait(), and kevent()
could not be used for devices that don't provide a selectable
file descriptor (in other words, on any capture source for that
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.
pcap(3PCAP), pcap_get_selectable_fd(3PCAP), select(2), poll(2),
epoll_wait(2), kqueue(2)
This page is part of the libpcap (packet capture library)
project. Information about the project can be found at
⟨http:https://www.tcpdump.org/⟩. If you have a bug report for this
manual page, see ⟨http:https://www.tcpdump.org/#patches⟩. This page
was obtained from the project's upstream Git repository
⟨https://github.com/the-tcpdump-group/libpcap.git⟩ on 2023-12-22.
(At that time, the date of the most recent commit that was found
in the repository was 2023-12-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better 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
[email protected]
29 JanuaryPC2A0P2_0GET_REQ...LECT_TIMEOUT(3PCAP)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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