RE: mbuf from scratch
RE: mbuf from scratch
- Subject: RE: mbuf from scratch
- From: "Carl Smith" <email@hidden>
- Date: Tue, 28 Jun 2005 18:28:39 -0400
- Thread-topic: mbuf from scratch
Great news Josh, this solves a few headaches for me.
I appreciate your come back.
Carl
-----Original Message-----
From: darwin-kernel-bounces+csmith=email@hidden
[mailto:darwin-kernel-bounces+csmith=email@hidden]
On Behalf Of Josh Graessley
Sent: Tuesday, June 28, 2005 6:08 PM
To: Darwin Kernel
Subject: Re: mbuf from scratch
On Jun 28, 2005, at 2:37 PM, Justin C. Walker wrote:
> Thanks for enlarging on that idea.
>
> It's been a while since I looked deeply at the output path, but
> there are a few things to consider here. Perhaps Josh can comment.
>
> I believe that, unless the destination is the loopback adapter
> ("lo0"), rcvif on outbound packets is NULL; it is mostly used on
> the input path.
>
> If it is used in a serious way on the outbound path, you should be
> really careful about doing what you are doing. If there is an
> "ifp" associated to the mbuf, and it is somehow pointing to the
> outbound interface, a change in routing information that occurs
> between the time you snag the original and the time that you inject
> the munged mbuf might affect the proper value for that ifp. I
> don't think this is the case, but you should try to verify it
> (i.e., try to follow the ip_output code, as well as that for the
> transport protocols :-}).
>
> This is just a note of caution; as I said, I don't think it's an
> issue. Josh?
As Justin noted, the rcvif is ignored for the outbound path, hence
the name receive if. This will usually be NULL on the outbound path.
If you go to inject a packet inbound, you will need to set the rcvif
to something as well as fiddle with the packet to get it in the right
state.
-josh
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