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20 .TH PCAP_GET_SELECTABLE_FD 3PCAP "22 July 2011"
22 pcap_get_selectable_fd \- get a file descriptor on which a select() can
23 be done for a live capture
27 #include <pcap/pcap.h>
31 int pcap_get_selectable_fd(pcap_t *p);
35 .B pcap_get_selectable_fd()
36 returns, on UNIX, a file descriptor number for a file descriptor on
42 to wait for it to be possible to read packets without blocking, if such
43 a descriptor exists, or \-1, if no such descriptor exists. Some network
49 .BR pcap_open_live() ,
54 (for example, regular network devices on FreeBSD 4.3 and 4.4, and Endace
55 DAG devices), so \-1 is returned for those devices.
59 FreeBSD prior to FreeBSD 4.6;
61 NetBSD prior to NetBSD 3.0;
63 OpenBSD prior to OpenBSD 2.4;
65 Mac OS X prior to Mac OS X 10.7;
70 do not work correctly on BPF devices;
71 .B pcap_get_selectable_fd()
72 will return a file descriptor on most of those versions (the exceptions
73 being FreeBSD 4.3 and 4.4), but a simple
77 will not indicate that the descriptor is readable until a full buffer's
78 worth of packets is received, even if the read timeout expires before
79 then. To work around this, an application that uses
83 to wait for packets to arrive must put the
85 in non-blocking mode, and must arrange that the
89 have a timeout less than or equal to the read timeout,
90 and must try to read packets after that timeout expires, regardless of
95 indicated that the file descriptor for the
97 is ready to be read or not. (That workaround will not work in FreeBSD
98 4.3 and later; however, in FreeBSD 4.6 and later,
102 work correctly on BPF devices, so the workaround isn't necessary,
103 although it does no harm.)
107 doesn't work on character special files, including BPF devices, in Mac
108 OS X 10.4 and 10.5, so, while
110 can be used on the descriptor returned by
111 .BR pcap_get_selectable_fd() ,
113 cannot be used on it those versions of Mac OS X. Kqueues also don't
114 work on that descriptor.
116 but not kqueues, work on that descriptor in Mac OS X releases prior to
119 and kqueues work on that descriptor in Mac OS X 10.6 and later.
121 .B pcap_get_selectable_fd()
122 is not available on Windows.
124 A selectable file descriptor is returned if one exists; otherwise, \-1
127 pcap(3PCAP), select(2), poll(2)