netdev - Re: Netperf UDP issue with connected sockets

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Message-Id: <20161130.131103.773051708416646032.davem@davemloft.net>
Date:   Wed, 30 Nov 2016 13:11:03 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     rick.jones2@....com
Cc:     brouer@...hat.com, eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: Netperf UDP issue with connected sockets

From: Rick Jones <rick.jones2@....com>
Date: Wed, 30 Nov 2016 09:42:40 -0800

> And indeed, based on a quick check, send() is what is being called,
> though it becomes it seems a sendto() system call - with the
> destination information NJULL:
> 
> write(1, "send\n", 5)                   = 5
> sendto(4, "netperf\0netperf\0netperf\0netperf\0"..., 1024, 0, NULL, 0)
> = 1024
> write(1, "send\n", 5)                   = 5
> sendto(4, "netperf\0netperf\0netperf\0netperf\0"..., 1024, 0, NULL, 0)
> = 1024
> 
> So I'm not sure what might be going-on there.

It's because of glibc's implementation of send() which is:

ssize_t
__libc_send (int sockfd, const void *buffer, size_t len, int flags)
{
  return SYSCALL_CANCEL (sendto, sockfd, buffer, len, flags, NULL, 0);
}
strong_alias (__libc_send, __send)
weak_alias (__libc_send, send)