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Rewrapped and rephrased comments.

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This commit is contained in:
henri
2013-07-31 19:11:09 +00:00
parent 23a58a1bc8
commit 8352b28e55
1 changed files with 42 additions and 35 deletions
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77
nsock/src/nsock_pcap.h
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@@ -56,7 +56,7 @@
/* $Id$ */
#ifndef NSOCK_PCAP_H
#ifndef NSOCK_PCAP_H
#define NSOCK_PCAP_H
#include "nsock_internal.h"
@@ -69,18 +69,22 @@
/*
* There are three possible ways of reading packets from pcap descriptor:
* do select() on descriptor -> this one is of course the best, but
* there are systems that don't support this like WIN32
* This works perfectly for Linux.
* do select() but with some hacks -> this one is hack for older bsd
* systems, Descriptor *must* be set in nonblocking mode.
* never do select() -> this one is for WIN32 and other systems that
* return descriptor -1 from pcap_get_selectable_fd()
* In this case descriptor *must* be set in nonblocking mode.
* If that fails than we can't do any sniffing from that box.
*
* In all cases we try to set descriptor to non-blocking mode.
* There are three possible ways to read packets from pcap descriptor:
* - select() on descriptor:
* this one is of course the best, but there are systems that
* don't support this like WIN32. This works perfectly for Linux.
*
* - select() + some hacks:
* this one is hack for older bsd systems,
* Descriptor *must* be set in nonblocking mode.
*
* - never do select():
* this one is for WIN32 and other systems that return descriptor -1
* from pcap_get_selectable_fd().
* In this case descriptor *must* be set in nonblocking mode.
* If that fails than we can't do any sniffing from that box.
*
* In any case we try to set descriptor to non-blocking mode.
*/
/* Returns whether the system supports pcap_get_selectable_fd() properly */
@@ -88,32 +92,35 @@
#define PCAP_CAN_DO_SELECT 1
#endif
/*
* In some systems (like Windows), the pcap descriptor is not selectable. Therefore,
* we cannot just select() on it and expect it to wake us up and deliver a packet,
* but we need to poll it continuously. This define sets the frequency, in milliseconds,
* at which the pcap handle is polled to determine if there are any captured packets.
* Note that this is only used when PCAP_CAN_DO_SELECT is not defined and therefore it
* has no effect on systems like Linux.
/* In some systems (like Windows), the pcap descriptor is not selectable.
* Therefore, we cannot just select() on it and expect it to wake us up and
* deliver a packet, but we need to poll it continuously. This define sets the
* frequency, in milliseconds, at which the pcap handle is polled to determine
* if there are any captured packets. Note that this is only used when
* PCAP_CAN_DO_SELECT is not defined and therefore it has no effect on systems
* like Linux.
*/
#define PCAP_POLL_INTERVAL 2
/*
* Note that on most versions of most BSDs (including Mac OS X) select() and poll() do not work
* correctly on BPF devices; pcap_get_selectable_fd() will return a file descriptor on most of those
* versions (the exceptions being FreeBSD 4.3 and 4.4), a simple select() or poll() will
* not return even after a timeout specified in pcap_open_live() expires. To work around
* this, an application that uses select() or poll() to wait for packets to arrive must put
* the pcap_t in non-blocking mode, and must arrange that the select() or poll() have a timeout
* less than or equal to the timeout specified in pcap_open_live(), and must try to read packets
* after that timeout expires, regardless of whether select() or poll() indicated that the file
* descriptor for the pcap_t is ready to be read or not. (That workaround will not work in
* FreeBSD 4.3 and later; however, in FreeBSD 4.6 and later, select() and poll() work correctly
* on BPF devices, so the workaround isn't necessary, although it does no harm.)
/* Note that on most versions of most BSDs (including Mac OS X) select() and
* poll() do not work correctly on BPF devices; pcap_get_selectable_fd() will
* return a file descriptor on most of those versions (the exceptions being
* FreeBSD 4.3 and 4.4), a simple select() or poll() will not return even after
* a timeout specified in pcap_open_live() expires. To work around this, an
* application that uses select() or poll() to wait for packets to arrive must
* put the pcap_t in non-blocking mode, and must arrange that the select() or
* poll() have a timeout less than or equal to the timeout specified in
* pcap_open_live(), and must try to read packets after that timeout expires,
* regardless of whether select() or poll() indicated that the file descriptor
* for the pcap_t is ready to be read or not. (That workaround will not work in
* FreeBSD 4.3 and later; however, in FreeBSD 4.6 and later, select() and poll()
* work correctly on BPF devices, so the workaround isn't necessary, although it
* does no harm.)
*/
#if defined(MACOSX) || defined(FREEBSD) || defined(OPENBSD)
/* Well, now select() is not receiving any pcap events on MACOSX, but maybe it will someday :)
* in both cases. It never hurts to enable this feature. It just has performance penalty. */
/* Well, now select() is not receiving any pcap events on MACOSX, but maybe it
* will someday :) in both cases. It never hurts to enable this feature. It just
* has performance penalty. */
#define PCAP_BSD_SELECT_HACK 1
#endif
@@ -121,7 +128,7 @@
* (and thus by readip_pcap()) should be considered valid. When
* invalid (Windows and Amiga), readip_pcap returns the time you called it. */
#if !defined(WIN32) && !defined(__amigaos__)
#define PCAP_RECV_TIMEVAL_VALID 1
#define PCAP_RECV_TIMEVAL_VALID 1
#endif