Libpcap reentrancy and PF_RING patch

[Luca Deri <deri () ntop org>]

Dear all,
please find enclosed a patch (against the code that's in CVS) that  
adds reentrancy in pcap.

IMHO libpcap has been designed for single-threaded applications, so  
when using threads it is necessary to add a mutex around pcap_next/ 
pcap_next_ex calls. According to some tests I have performed, the  
mutex (even when using spinlocks) is a real performance killer. In my  
patch I have added a new function called pcap_next_pkt defined as  
follows

const u_char *  pcap_next_pkt(pcap_t *p, struct pcap_pkthdr *h, u_char  
*buf, u_short bufsize);

This function is the same as pcap_next with the difference that a  
buffer + buffersize is added. This allows libpcap not to use the  
shared buffer (e.g. allocated in pcap_open_xxx) so that replacing in  
applications calls of pcap_next with calls to pcap_next_pkt adds  
reentrancy without the need to use a mutex. Although this change is  
pretty simple, many files have been affected due to the way the  
library works and to the many different platforms that are supported.  
I have tested the code on Linux and OSX but patched all the supported  
platforms. I have decided not to change the behavior of other pcap  
functions (e.g. pcap_next, pcap_loop..) this to avoid compatibility  
issues with existing applications.

My patch also adds support for  PF_RING (http://www.ntop.org/PF_RING.html 
) that is a Linux packet acceleration technique that uses a shared  
ring buffer between the kernel and user-space. In addition to packet  
acceleration, it features also packet filtering and classification. As  
PF_RING code has been around for some years now and used by many  
users, if you include this patch into the mainstream code you will  
allow me to stop keeping a patched version of the library. As PF_RING  
is a kernel module, if the module is not present, the library will  
fallback to standard libpcap.

If you think my work is valuable, I would appreciate if you could  
include my contribution to the pcap library.

Thanks in advance, Luca

Attachment: libpcap_reentrancy_pfring.diff.gz
Description:

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