Comment 2 for bug 1761534

The following patch fixes the bug :

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commit bda7fab54828bbef2164bb23c0f6b1a7d05cc718
Author: Jay Vosburgh <email address hidden>
Date: Thu Mar 22 14:42:41 2018 +0000

    virtio-net: Fix operstate for virtio when no VIRTIO_NET_F_STATUS

    The operstate update logic will leave an interface in the
    default UNKNOWN operstate if the interface carrier state never changes
    from the default carrier up state set at creation. This includes the
    case of an explicit call to netif_carrier_on, as the carrier on to on
    transition has no effect on operstate.

            This affects virtio-net for the case that the virtio peer does
    not support VIRTIO_NET_F_STATUS (the feature that provides carrier state
    updates). Without this feature, the virtio specification states that
    "the link should be assumed active," so, logically, the operstate should
    be UP instead of UNKNOWN. This has impact on user space applications
    that use the operstate to make availability decisions for the interface.

            Resolve this by changing the virtio probe logic slightly to call
    netif_carrier_off for both the "with" and "without" VIRTIO_NET_F_STATUS
    cases, and then the existing call to netif_carrier_on for the "without"
    case will cause an operstate transition.

    Cc: "Michael S. Tsirkin" <email address hidden>
    Cc: Jason Wang <email address hidden>
    Cc: Ben Hutchings <email address hidden>
    Signed-off-by: Jay Vosburgh <email address hidden>
    Acked-by: Michael S. Tsirkin <email address hidden>
    Signed-off-by: David S. Miller <email address hidden>
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