получить тайм-аут, который будет использоваться при выполнении select () для записи в реальном времени (get a timeout to be used when doing select() for a live capture)
Имя (Name)
pcap_get_required_select_timeout - get a timeout to be used when
doing select() for a live capture
Синопсис (Synopsis)
#include <pcap/pcap.h>
const struct timeval *pcap_get_required_select_timeout(pcap_t *p);
Описание (Description)
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.
Возвращаемое значение (Return value)
A pointer to a struct timeval is returned if the timeout is
required; otherwise NULL is returned.
Обратная совместимость (Backward compatibility)
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.
Обратная совместимость (Backward compatibility)
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.
Смотри также (See also)
pcap(3PCAP), pcap_get_selectable_fd(3PCAP), select(2), poll(2),
epoll_wait(2), kqueue(2)
