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

[Michael Tuexen]

On Dec 5, 2013, at 7:29 PM, Adrian Chadd <adrian at freebsd.org> wrote:

> Hi,
> 
> 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?
Sure. I'll report the result.

Best regards
Michael
> 
> Thanks!
> 
> 
> 
> 
> -adrian
>