Re: libpcap pcap_sendpacket support across plaatforms.

[Guy Harris <guy () alum mit edu>]

On Mar 12, 2004, at 2:03 AM, Mark Pizzolato wrote:

> I've been working on a system simulator (simh 
> http://simh.trailing-edge.com)
> which provides ethernet device emulation for the systems which 
> originally
> had ethernet devices (i.e. vax, pdp11 and pdp10).
>
> The ethernet support for this package was originally implemented on 
> Windows
> with Winpcap, and then ported back to other platforms leveraging the 
> generic
> libpcap capabilities.  The only lacking piece here, from an API poinit 
> of
> view, has been pcap_sendpacket.  Just to get by, we've had platform 
> specific
> network code in the layer which uses libpcap to provide a 
> pcap_sendpacket
> for the non Windows platforms.  This only solves part of the problem 
> since
> several platforms use pcap-bpf.c or pcap-pf.c or pcap-snit.c which 
> open the
> network device O_RDONLY.  To get useful functionality on these 
> platforms,
> we've needed to hack pcap-bpf.c, or pcap-pf.c or pcap-snit.c and change
> O_RDONLY to O_RDWR.  If would seem that the right thing to do is to
> generically include pcap_sendpacket and the related open requirements 
> in the
> base pcap library.

Well, the right thing to do is not necessarily to change O_RDONLY to 
O_RDWR, as that would mean you can't give people "capture but not send" 
privileges on BPF platforms by giving them read but not write access to 
the BPF devices.

The best thing to do probably is to add a new API for opening captures 
that lets you specify whether you're opening for capturing, sending, or 
both; the new API can also fix a number of other problems (setting the 
internal capture buffer size - which, on BPF devices, must be done 
before the BPF device is bound to an interface; allowing things such as 
monitor mode to be specified at open time; supporting remote capture, 
as per WinPcap's "pcap_open_ex()"; etc.).

> In pcap.h, I've messed with PCA_MINOR_VERSION in  an attempt to have 
> the
> code which uses pcap.h to have a compile time means of determinig if
> pcap_sendpacket is available:
>
> #if (_WIN32) || (PCAP_MAJOR_VERSION > 2) || ((PCAP_MAJOR_VERSION == 2) 
> &&
> (PCAP_MINOR_VERSION > 4))
> #define HAS_PCAP_SENDPACKET 1
> #endif
>
> Is there a better way to do this at compile time?

autoconf.

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