netdev - Re: [PATCH v2 2/5] VSOCK: support fill data to mergeable rx buffer in host

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Message-Id: <20181212.215905.1657023590815103551.davem@davemloft.net>
Date:   Wed, 12 Dec 2018 21:59:05 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     jiangyiwen@...wei.com
Cc:     stefanha@...hat.com, mst@...hat.com, jasowang@...hat.com,
        netdev@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 2/5] VSOCK: support fill data to mergeable rx buffer
 in host

From: jiangyiwen <jiangyiwen@...wei.com>
Date: Thu, 13 Dec 2018 11:11:48 +0800

> I hope Host can fill fewer bytes into rx virtqueue, so
> I keep structure virtio_vsock_mrg_rxbuf_hdr one byte
> alignment.

The question is if this actully matters.

Do you know?

If the obejct this is embeeded inside of is at least 2 byte aligned,
you are marking it packed for nothing.

There are only %100 downsides to using the packed attribute.

Simply define your datastructures properly, with fixed sized types,
and all padding defined explicitly.