Dear Rick,
Thank you for your reply.
I am sorry that I don't quite understand your point. As far as I know, the
function call udp_flush_pending_frames() in net/ipv4/udp.c is invoked
regardless of whether the socket is set to either a blocking mode or a
non-blocking mode. Do you mean that the implementation in the function
sendto() handles the packet drop at the interface queue by caching data at
the socket level ? If so, could you please advise me the Linux Kernel source
file which contains the exact implementation of sendto() API function call
in Linux ? I tried to locate this souce file using a bottom-up approach
starting at the function call udp_sendmsg(), -> inet_sendmsg() in
net/ipv4/af_inet.c -> sock_sendmsg() in net/socket.c-> sys_sendto() in
net/socket.c ... but I finally got lost in sys_sendto().
Thank you for your help.
Regards,
Gary
----- Original Message -----
From: "Rick Jones" <[EMAIL PROTECTED]>
To: "Gary Chan" <[EMAIL PROTECTED]>
Sent: Friday, September 01, 2006 1:00 AM
Subject: Re: Linux UDP Implementation
Gary Chan wrote:
According to the function call udp_sendmsg() in the source file
net/ipv4/udp.c (Linux Kernel 2.6.17.11), when an error value is returned
from the function ip_append_data() due to local device congestion, say
interface queue overflow, pending packets in the queue
sk->sk_write_queue are simply flushed (udp_flush_pending_frames() is
invoked) without caching for future retransmission.
I called a network API function sendto() to transmit UDP packets in a
blocking I/O mode at a rate of 100Mbps over the 802.11b wireless ad hoc
network, the network was overloaded as the maximum transfer rate for
802.11b was just 11Mbps. Therefore, the outgoing interface queue must be
full and UDP packets will be dropped eventually. However, I checked that
there was no packet loss at the receiver side, i.e. the number of packets
sent from the sender is equal to that received.
It seems that the implementation (at code level) does not match with the
actual behaviour. I would like to seek expertise on clarifying my
understanding in UDP implementation so that this phenomenon can be
explained.
Perhaps you are seeing a difference in the behaviour of blocking vs
non-blocking sockets?
rick jones
--
VGER BF report: U 0.5
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