Messages in this thread | | | Date | Sat, 5 Oct 2002 00:16:21 -0700 (PDT) | From | devnetfs <> | Subject | questions regarding sending/recving udp packets in kernel |
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Hello,
I am trying to write a kernel module, to send and receive udp packets. I have the following questions/problems:
[1] I wish to receive packets asynchronously (thru a callback), rather than polling [i.e calling udp_recvmsg() periodically to check for packtets].
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?
[2] 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.
[3] 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,
Regards, Abhi.
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