Re: libpcap & poll()

["Gianluca Varenni" <gianluca.varenni () cacetech com>]

----- Original Message ----- 
From: "Eloy Paris" <peloy () chapus net>
To: <tcpdump-workers () lists tcpdump org>
Sent: Thursday, November 13, 2008 3:24 PM
Subject: Re: [tcpdump-workers] libpcap & poll()


> Hi Ben,
>
> On Thu, Nov 13, 2008 at 03:13:05PM -0800, Ben Greear wrote:
>
> [...]
>
> > The code above works on Solaris, but does not work on Windows since
> > there is nothing to poll() on windows.
>
> Windows has select() but it is my understanding that you can't use it on
> a packet capture descriptor. At least pcap_get_selectable_fd() is not
> available on Windows, according to the pcap man page.

True, select() on windows basically works on sockets only. The reason is 
that while on the various unix flavors select is a system call, on Windows 
it's a shim over the native WaitForSingleObject/WaitForMultipleObjects (as 
much as file descriptors are a shim over the native HANDLEs). The Windows 
folks decided to create this select shim over sockets, only.

On Windows, you cannot get a selectable file descriptor to make a select() 
on, but you can call pcap_gethandle() and use 
WaitForSingleObject/WaitForMultipleObjects on it. In particular you can wait 
on multiple pcap_t handles by getting a waitable handle on each of them and 
then calling "WaitForMultipleObjects" on them.

Hope it helps
GV

> This is a major bummer for my application and is the only reason I
> haven't tried to attempt a port of my application to Windows. I'd love
> to know how to efficiently read from multiple packet capture descriptors
> on Linux...
>
> > On Linux, I just use raw sockets, which are faster and easier to deal
> > with than pcap..but my app is probabl different in nature from yours.
>
> If portability is not needed raw sockets are nice. The nice thing about
> PCAP is that it's portable.
>
> Cheers,
>
> Eloy Paris.-
> netexpect.org
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