[Bug 205264] XOR logic error in ixgb(4)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=205264

Don Lewis <truckman at FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |truckman at FreeBSD.org

--- Comment #1 from Don Lewis <truckman at FreeBSD.org> ---
IFCAP_HWCSUM is defined as (IFCAP_RXCSUM | IFCAP_TXCSUM), so this code:

    case SIOCSIFCAP:
        IOCTL_DEBUGOUT("ioctl rcv'd: SIOCSIFCAP (Set Capabilities)");
        mask = ifr->ifr_reqcap ^ ifp->if_capenable;
        [snip]
        if (mask & IFCAP_HWCSUM) {
            if (IFCAP_HWCSUM & ifp->if_capenable)
                ifp->if_capenable &= ~IFCAP_HWCSUM;
            else
                ifp->if_capenable |= IFCAP_HWCSUM;
            if (ifp->if_drv_flags & IFF_DRV_RUNNING)
                ixgb_init(adapter);
        }

will set both bits even if the request only specifies one bit, and it
will clear both bits even if the request only wants to clear one bit.

Replacing the inner if/else block with this should fix the problem:

            ifp->if_capenable ^= (mask & IFCAP_HWCSUM);

or alternatively:

            ifp->if_capenable = (ifr->ifr_reqcap & IFCAP_HWCSUM) |
                (ifp->if_capenable & ~IFCAP_HWCSUM);

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