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Re: [Qemu-devel] vde-inject 0.0.1

From: Jim C. Brown
Subject: Re: [Qemu-devel] vde-inject 0.0.1
Date: Fri, 10 Feb 2006 12:09:32 -0500
User-agent: Mutt/

On Fri, Feb 10, 2006 at 12:34:10PM +0700, Mulyadi Santosa wrote:
> Hi Jim
> It's me again. here I send you another patch for the vde_pcap_inject.c. 
> Nothing fancy here, I only did:

> -  move out "open" and "close" from relay() and put them on main() 
> before entering for() loop. IMHO, this will make file operation a bit 
> faster

This one I've thought about myself.

Your way makes vde_pcap_inject more efficient. My way makes it usable if
vde_pcap_inject is run before the kernel module is loaded.

The idea is that vde_pcap_inject can be used everywhere vde_pcap can be, but
in addition if you have vde-inject then it can and will make use of that as

> - I use __builtin_expect magic to optimize the "if" condition before 
> writing to /proc/vdeinject. here, inside relay() we assume that 
> vdeinject is likely exist.

What is __buiultin_expect() ? I've never seen it before.

Your tests to make sure the fd is valid are unnecessary. perror() causes
vde_pcap_inject to abort with an error, so any code called later on is
guarranteed that fd is valid.

Of course this means that vde_pcap_inject can only be used in combo with
vde-inject, which I'm not sure is a good thing. E.g. a freeBSD host lacks
vde-inject, so this would make vde_pcap_inject linux-specific.

> PS: I can't check it thoroughly since my libpcap version (0.7.2, default 
> on Redhat 9. Yes I know it is old) doesn't have 
> pcap_get_selectable_fd(), so I can't compile it.

Change it to pcap_fileno(), and it should compile and work identically.
(The difference is that pcap_get_selectable_fd() adds some basic sanity checks
to make sure the fd is selectable before returning it. See
http://www.tcpdump.org/lists/workers/2004/06/msg00093.html for more 

I'll probably add an #ifdef for this.

> regards
> Mulyadi

Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.

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