Re: Offloading checksums to H/W

• Subject: Re: Offloading checksums to H/W
• From: Platon Fomichev <email@hidden>
• Date: Sat, 25 Aug 2007 00:24:13 +0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Let's say .8 is my Mac:

Thus in order to use the h/w for checksum calc one should:

Have fun,
        Stauff

On Aug 24, 2007, at 9:40 PM, mm w wrote:

Hi platon,

as far i know, it isn't implemented
i understand well your problem, the problem is, the check-sum
is applied to the whole of packet, if you change the size, you change it

struct packet {
	struct  mbuf *buf;
	struct  iphdr header;
	int 	sum;
	tcp_seq seq;
	int     size;
... /* what you want */
};

@+

On 8/24/07, Platon Fomichev <email@hidden> wrote:

Hey mm

Yup exactly, that's what is written in Apple's docs but as we all
have access to the kernel and overall - why on earth we should need
to do this? Of course there are cases - when I change destination,
metric, etc, etc. But if f.ex. I just changed packet length? Imho
it's not the case for re-injection. And it actually works as expected
on my test-cases - I can do whatever I want as long as I keep its
destination, etc. But my case is simple I need to increase data size
for say 20 bytes.

I actually managed to get some weird checksum (wrong) from H/w - I
will keep you informed about my progress..

Best regards,
             Platon

On Aug 24, 2007, at 7:54 PM, mm w wrote:

Hi Platon,

If your modifications involve changes to packet header information you
must swallow the packet entirely and reinject it.

Cheers

On 8/24/07, Platon Fomichev <email@hidden> wrote:

Hi Everybody

It seems I can't figure how to correctly offload my TCP/UDP packet to
the H/W network checksumming routines. It seems rather inconvenient
that I have to add all typical checksumming code into the driver -
because neither of mbuf API can actually re-checksum the packet. As
for H/W support - I can see from the flags that my H/W supports TCP
offload but if I set tcp checksum f.ex. to zero in my Interface
filter the packet will not be checksummed later in the hardware.

Thus some questions:

1) Seems that there is no kernel API to do IP checksumming in Mac -
is it true, if not how to do it? mbuf finalize func does not do it.
2) Seems that hardware TCP/UDP checksum offload is actually missing
from Mac at all? At least it is not present on MacBook/MacBook pro.
If yes why does it advertise itself using ifnet API as capable to do
it? If I am wrong how can I check that my network adapter is actually
doing its work and how can I benefit from this in my code (I am
actively changing the packet)

Best regards,
             Platon.

On Aug 23, 2007, at 9:05 AM, JanakiRam wrote:

email@hidden

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