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Date: Wed, 06 Jun 2007 13:53:55 +0930
From: Anton <Anton.Uzunov@...o.defence.gov.au>
To: netdev@...r.kernel.org
Subject: sending IPv6 packets via kern_sendmsg
Hi,
Following on from a previous (now lost :-)) posting, I have been trying
to send out IPv6 packets from a kernel module using the kern_sendmsg()
function. Since in theory I need this function to be started in
interrupt context (actually, softirq context), but since this is
impossible because kern_sendmsg() needs to sleep, I have created a work
queue which calls the kern_sendmsg() function separately. The work queue
is scheduled from the softirq context (actually, at the moment this
happens from a Netfilter hook). The work queue function creates a msghdr
structure, fills in a sin6_addr structure, calls sock_create_kern() and
then uses this socket to send an IPv6 packet, which consists of a header
(struct ipv6hdr *iphdr) and some data following on from this. The above
packet is placed in the msghdr structure by setting (after the
appropriate initializations):
msg.msg_iov->iov_base = (char *) ip6hdr;
msg.msg_iov->iov_len = sizeof( struct ipv6hdr + ntohs(
ip6hdr->payload_len ) );
msg.msg_iovlen = 1;
msg.msg_name = &sin6addr;
msg.msg_namelen = sizeof( struct sin6_addr );
However, when trying to send this using kern_sendmsg() (or even
sock_sendmsg()) to perform the send operation, I get an error (-22 -
EINVAL), which, according to the user-space sendmsg(), corresponds to:
"The sum of the iov_len values overflows an ssize_t. "
Certainly this is not the case, since the packet in question is an
ICMPv6 ping packet whose header size and data would rarely exceed 100
bytes.
The test is being run on kernel 2.6.18.
From what I have read on the internet, in books and in a previous
suggestion from the netdev mailing-list, the use of kern_sendmsg() seems
to be the appropriate way of sending packets from a kernel module. Am I
doing something incorrectly above, or should I be using some other
function instead of kern_sendmsg() (or sock_sendmsg())?
I would appreciate any ideas.
Regards,
Anton
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