Date: Wed, 5 Sep 2001 15:32:40 -0500 From: "Ramasubramanian Ramamoorthy (EXT-NRC/Boston)" <EXT-Ramamoorthy.Ramasubramanian@nokia.com> To: "'ext Julian Elischer'" <julian@elischer.org> Cc: <freebsd-net@freebsd.org> Subject: RE: Reg. mbuf structure Message-ID: <B9CFA6CE8FFDD211A1FB0008C7894E4604559012@bseis01nok>
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Yes, I used this copydata function, to extract some data to calculate my
checksum. But, how do I send the same extracted data which is contained
in skbuff structure in the linux machine?
I need to check that the packet what I am sending from the Linux machine
to the BSD machine using the checksum that I am generating.=20
I am able to extract data using m_copydata() in BSD. But, I need the
same data in Linux for calculating the same checksum, as the algorithms
are same at both ends.
Thanks,
Ram.
-----Original Message-----
From: ext Julian Elischer [mailto:julian@elischer.org]
Sent: Wednesday, September 05, 2001 5:00 PM
To: Ramasubramanian Ramamoorthy (EXT-NRC/Boston)
Cc: freebsd-net@freebsd.org
Subject: RE: Reg. mbuf structure
On Wed, 5 Sep 2001, Ramasubramanian Ramamoorthy (EXT-NRC/Boston) wrote:
> Hi,
> I had mailed regarding extracting the same data from the skbuff
> structure in Linux and the mbuf structure in BSD. I am calculating the
> checksum in two machines, one running BSD and the other running Red
Hat.
> I need to calculate the checksum at both the machines, for which I
> should be extracting the same data from these structures and send that
> to the algorithm, which calculates the checksum.
>=20
> Can you tell me how we can confirm that we are extracting the same
data
> from both these structures. It would be of great help, if anybody
could
> help me in this regard soon.
>=20
Do you know how much data you are supposed to be extracting?
Do you have an IP header or something on the front you want to=20
ignore?
I assume this is a kernel module.
Here is a data extraction function from kern/uipc_mbuf.c
You can modify this function to checksum intead of copying..
or since this is always in the kernel, you could just call it.
/*
* Copy data from an mbuf chain starting "off" bytes from the beginning,
* continuing for "len" bytes, into the indicated buffer.
*/
void
m_copydata(m, off, len, cp)
register struct mbuf *m;
register int off;
register int len;
caddr_t cp;
{
register unsigned count;
while (off > 0) {
if (off < m->m_len)
break;
off -=3D m->m_len;
m =3D m->m_next;
}
while (len > 0) {
count =3D min(m->m_len - off, len);
bcopy(mtod(m, caddr_t) + off, cp, count);
len -=3D count;
cp +=3D count;
off =3D 0;
m =3D m->m_next;
}
}
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