A small fix for if_em.c, if_igb.c, if_ixgbe.c

[John-Mark Gurney]

Michael Tuexen wrote this message on Fri, Dec 06, 2013 at 21:08 +0100:
> On Dec 5, 2013, at 7:29 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> 
> > Yes. Looking at the ixgbe code, ixgbe_mq_start_locked() returns an
> > error from ixgbe_xmit() but if it fails, it puts the buffer back. But
> > it's already successfully queued a frame to the driver, so in this
> > instance it shouldn't return the error from ixgbe_mq_start_locked().
> > 
> > The same deal in if_em.c and igb.c
> > 
> > Now, drbr_putback() used to fail and now it doesn't, as you've said.
> > So we should change the xxx_mq_start_locked() to set err=0 if we go
> > via the drbr_putback() routine, as it hasn't actually failed to
> > transmit.
> > 
> > Now the very dirty thing is this - the error from xxx_transmit() is
> > for the mbuf being queued at the end; but xxx_mq_start_locked()
> > failures are for transmitting from the front. If there's only packet
> > in the queue and that fails then they're the same thing and returning
> > the error from xxx_mq_start_locked() matches the current mbuf being
> > queued. But otherwise, they're referring to totally different packets.
> > For TCP this may hurt; the TCP stack treats ENOBUFS a certain way and
> > kicks off a timer to schedule a retransmit. I don't think we can fix
> > _this_ right now.
> > 
> > So Michael - can you redo your patch to set err=0 if drbr_putback() is
> > called, and retest?
> Hi Adrian,
> 
> I guess you are talking about a patch like:
> 
> [bsd5:~/head/sys/dev] tuexen% svn diff -x -p
> Index: e1000/if_em.c
> ===================================================================
> --- e1000/if_em.c	(revision 259039)
> +++ e1000/if_em.c	(working copy)
> @@ -935,6 +935,7 @@ em_mq_start_locked(struct ifnet *ifp, struct tx_ri
>  				drbr_advance(ifp, txr->br);
>  			else 
>  				drbr_putback(ifp, txr->br, next);
> +				err = 0;

You probably want curly braces around this...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."