[RFC] Improve libnl non-blocking behaviour

[Holger Eitzenberger]

Hi Thomas,

I noticed that nl_recvmsgs_default() does return 0 instead of
-NLE_AGAIN when looping on a non-blocking file descriptor.  And in
nl_recv() I see this:

	if (errno == EAGAIN || errno == EWOULDBLOCK) {                           
		NL_DBG(3, "recvmsg() returned EAGAIN||EWOULDBLOCK,
					aborting\n");     
		retval = 0;                                                          
		goto abort;                                                          
	}                                                                        

Is this intended?

I'm asking because with non-blocking programs you often have read-like
loops from the file descriptor until EGAIN is returned.

The patchlet attached changes retval to -NLE_AGAIN in this case.
And I have a test program which then works as intended.  Does this
make sense?  I haven't tested for the actual performance improvement
though, but I can if need be.

When doing so it could also make sense to remove the debug message in
this case, because by returning -NLE_AGAIN to the program the NL_DBG()
is somewhat duplicate information.

Any comments appreciated.

 /Holger

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