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Date: Fri, 11 Dec 2015 13:19:24 -0800 (PST)
From: Don Lewis <truckman@FreeBSD.org>
Subject: Re: XOR pt. 2
To: mmcco@mykolab.com
cc: freebsd-current@freebsd.org
In-Reply-To: <20151211194204.GA26628@thinkpad.swarthmore.edu>
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On 11 Dec, Michael McConville wrote:
> Note that IFCAP_HWCSUM has two bits set. Because of this, it doesn't XOR
> cleanly in the current if-else condition, but I'm not sure whether that
> was intended. I just wanted to pass this by people in case it was a
> logical bug.

Yeah, the original code looks incorrect.   If HWCSUM is totally disabled
and the user requests RXCSUM, then the current code will enable both
RXCSUM and TXCSUM.

> --- dev/ixgb/if_ixgb.c.orig
> +++ dev/ixgb/if_ixgb.c
> @@ -599,10 +599,7 @@ ixgb_ioctl(struct ifnet * ifp, IOCTL_CMD
>  		}
>  #endif /* DEVICE_POLLING */
>  		if (mask & IFCAP_HWCSUM) {
> -			if (IFCAP_HWCSUM & ifp->if_capenable)
> -				ifp->if_capenable &= ~IFCAP_HWCSUM;
> -			else
> -				ifp->if_capenable |= IFCAP_HWCSUM;
> +			ifp->if_capenable ^= IFCAP_HWCSUM;

I think that would need to be:
			ifp->if_capenable ^= (mask & IFCAP_HWCSUM);

>  			if (ifp->if_drv_flags & IFF_DRV_RUNNING)
>  				ixgb_init(adapter);
>  		}
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