2002-10-06 10:25:14

by devnetfs

[permalink] [raw]
Subject: [RESEND-2: Pl. Help] questions regarding sending/receiving udp packets in kernel

Resending it again to the Gurus. Can somebody *please* help me with
these networking+kernel issues?

thanks once again,


I am trying to write a kernel module, to send and receive udp packets.
I have the following questions/problems:

I wish to receive packets asynchronously (thru a callback), rather
than polling [i.e calling udp_recvmsg() periodically to check for

To get this done, presently after creating a socket (sock_create), I
replace sk->data_ready with my own function, which when called (by the
kernel) wakes up a kernel thread that does skb_recv_datagram() to get a
udp sk_buff.

Is this the correct approach? or is there a better way to register a
callback with the core-networking subsystem, which will get called and
deliver the pkt, when a udp pkt arrives on an ip/port?

The memory allocted for the sk_buff (which i get thru
skb_recv_datagram() is charged to the socket (i created). But I wish to
use this sk_buff in my module (for processing etc.) so i dont call
kfree_skb for a long time (hence the rmem_alloc does not get
decremented). I tried to unlink the sk_buff from the socket list by
calling skb_unlink() but that does NOT decrease 'rmem_alloc'.

How do I cleanly (and truly) unlink a sk_buff from a socket list and
decrease equivalent memory charged to this socket? I would be calling
kfree_skb() later though which will eventually decrease rmem_alloc, but
I wish to do it as part of skb_unlink(). Please advice.

My kernel module sends/recvs UDP pkts process and store these packets
internally sk_buffs only. But udp_sendmsg() requires an iovec.
I can construct an iovec from an sk_buff and give it to udp_sendmsg()
but that will involve an additional COPYING from one kernel memory
space (sk_buff data buffer) to another new buffer (for iovec). I want
to avoid this xtra copying.

Am I missing something?
And if above approach does involve extra copying is there a way to
transmit a udp packet if one has the data in form of sk_buff (assuming
there is head space for ether+ip+udp header)?

Thanks in advance,


I am not subscribed to this list. Please Cc: me the replies. -- thanks.

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