site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=m1FTIZZGWE1cpj7kSPgIkmFO0w9SfBgDduDmOtcQPTgYO60KTebrcV6+RklsjVz4ZTqA9Uj1fEzSVnqKnnEDa7UlONmdo7vgmWx63ivalD1R0zmurWc3oGfq27thX5xo/8HDITpyb73WfBdX6MmLAiLXDQOO3bEhmYD61WobNCQ= Hi Terry, That's exactly what I ended up implementing. I haven't read RFC 1624, but I will. Related question: if ever csum_flags has both CSUM_IP and CSUM_TCP | CSUM_UDP set, then what is csum_data going to point to? Thanks! - Bhavesh Are you changing the length of the packet, or only the contents? If you are only changing the contents, then I suggest an mbuf-chain aware incremental checksum update as an alternative to copying it to a contiguous buffer, operating on it, converting it to mbufs, then doing a full software checksum of the whole packet. See RFC 1624. -- Terry On Dec 22, 2006, at 10:12 AM, Adi Masputra wrote:

On Dec 22, 2006, at 9:58 AM, Bhavesh Davda wrote:

...

I compare the result of mbuf_pkthdr_len agains the network-byte-order value of IP length on purpose, to know whether indeed the value of IP length in the packet is *not* in host-byte-order, as I thought you said mbuf_outbound_finalize() expects.

Since your module is an interface filter, the field(s) in the header(s) will be in network byte-order. All you need to do is to byte-swap the length at all times assuming it is an IPv4 packet.

...

Oh boy. This is going to get quite expensive to do on a per packet basis. I thought I could simply get a pointer into the packet payload to the IP length field in the IP header, and do a memory read/write, rather than going through so many function calls and memcpy's, albeit small (2 byte) ones.

Well, you are already requesting the stack to perform software checksum calculation on the packet which includes the transport payload; in terms of per-byte cost that is much more significant than traversing the mbuf chain to safely obtain the 2-octets IP length in the header. :)

...

Is there any other way to do it more optimally? I understand your concern about non-linear mbufs, and not assuming that the IP header is in the pkthdr mbuf. But realistically, is that ever going to be the case?

There's no guarantee that the headers will be in contiguous span although for the majority of cases they would. Sorry, but as I said the fix is already in order.

Adi

...

Thanks!

-- Bhavesh P. Davda

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-- Bhavesh P. Davda _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... On 12/28/06, Terry Lambert <tlambert@apple.com> wrote: This email sent to site_archiver@lists.apple.com