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That worked; move it after the warning-disabling-and-reenabling.
[libpcap] / pcap_setnonblock.3pcap
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20 .TH PCAP_SETNONBLOCK 3PCAP "25 July 2018"
21 .SH NAME
22 pcap_setnonblock, pcap_getnonblock \- set or get the state of
23 non-blocking mode on a capture device
24 .SH SYNOPSIS
25 .nf
26 .ft B
27 #include <pcap/pcap.h>
28 .ft
29 .LP
30 .nf
31 .ft B
32 char errbuf[PCAP_ERRBUF_SIZE];
33 .ft
34 .LP
35 .ft B
36 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
37 int pcap_getnonblock(pcap_t *p, char *errbuf);
38 .ft
39 .fi
40 .SH DESCRIPTION
41 .BR pcap_setnonblock ()
42 puts a capture handle into ``non-blocking'' mode, or takes it out
43 of ``non-blocking'' mode, depending on whether the
44 .I nonblock
45 argument is non-zero or zero. It has no effect on ``savefiles''.
46 If there is an error,
47 .B PCAP_ERROR
48 is returned and
49 .I errbuf
50 is filled in with an appropriate error message; otherwise, 0 is
51 returned.
52 .PP
53 In
54 ``non-blocking'' mode, an attempt to read from the capture descriptor
55 with
56 .BR pcap_dispatch (3PCAP)
57 and
58 .BR pcap_next_ex (3PCAP)
59 will, if no packets are currently available to be read, return 0
60 immediately rather than blocking waiting for packets to arrive.
61 .PP
62 .BR pcap_loop (3PCAP)
63 will loop forever, consuming CPU time when no packets are currently
64 available;
65 .BR pacp_dispatch ()
66 should be used instead.
67 .BR pcap_next (3PCAP)
68 will return NULL if there are no packets currently available to read;
69 this is indistinguishable from an error, so
70 .BR pcap_next_ex ()
71 should be used instead.
72 .PP
73 When first activated with
74 .BR pcap_activate (3PCAP)
75 or opened with
76 .BR pcap_open_live (3PCAP) ,
77 a capture handle is not in ``non-blocking mode''; a call to
78 .BR pcap_setnonblock ()
79 is required in order to put it into ``non-blocking'' mode.
80 .SH RETURN VALUE
81 .BR pcap_getnonblock ()
82 returns the current ``non-blocking'' state of the capture descriptor; it
83 always returns 0 on ``savefiles''.
84 If there is an error,
85 .B PCAP_ERROR
86 is returned and
87 .I errbuf
88 is filled in with an appropriate error message.
89 .PP
90 .I errbuf
91 is assumed to be able to hold at least
92 .B PCAP_ERRBUF_SIZE
93 chars.
94 .SH SEE ALSO
95 .BR pcap (3PCAP),
96 .BR pcap_next_ex (3PCAP),
97 .BR pcap_geterr (3PCAP)