netdev - Re: [net-next PATCH v4 1/6] net: virtio dynamically disable/enable LRO

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Message-Id: <20161203.230103.2147950370567010856.davem@davemloft.net>
Date:   Sat, 03 Dec 2016 23:01:03 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     john.fastabend@...il.com
Cc:     daniel@...earbox.net, mst@...hat.com, shm@...ulusnetworks.com,
        tgraf@...g.ch, alexei.starovoitov@...il.com,
        john.r.fastabend@...el.com, netdev@...r.kernel.org,
        bblanco@...mgrid.com, brouer@...hat.com
Subject: Re: [net-next PATCH v4 1/6] net: virtio dynamically disable/enable
 LRO

From: John Fastabend <john.fastabend@...il.com>
Date: Fri, 02 Dec 2016 12:49:45 -0800

> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) {
> +		sg_init_one(&sg, &offloads, sizeof(uint64_t));
> +		if (!virtnet_send_command(vi,
> +					  VIRTIO_NET_CTRL_GUEST_OFFLOADS,
> +					  VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET,
> +					  &sg)) {
> +			dev_warn(&netdev->dev,
> +				 "Failed to set guest offloads by virtnet command.\n");
> +			return -EINVAL;
> +		}
> +	} else if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS) &&
> +		   !virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {

Hmmm, to me this reads as:

	if (X) {
	 ...
	else if (X && ...) {

I don't see how the second basic block can ever execute.  If the virtio
has the VIRTIO_NET_F_CTRL_GUEST_OFFLOADS feature, we will execute only
the first basic block.

Maybe I misunderstand the logic for whatever reason.