linux-kernel - Re: [PATCH 2/2] virtio_scsi: Implement fc

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Date:   Tue, 17 Jan 2017 14:17:33 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Fam Zheng <famz@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        stefanha@...hat.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 2/2] virtio_scsi: Implement fc_host



On 16/01/2017 18:26, Fam Zheng wrote:
>> Is the endianness correct for big-endian host here?
>
> I think so. The fc_host sysfs uses u64 to represent port_name and node_name,
> this patch does the same, so using virtio_* helpers for these fields should
> handle the endianness correctly.

I was suspicious about it because they are defined as "u8 x[8]" in the
virtio_scsi_config struct.  So you would need to read with
virtio_cread_bytes and pass the result to wwn_to_u64.

For example, if you have 0x500123456789abcd this would be

	0x50 0x01 0x23 0x45 0x67 0x89 0xab 0cd

in virtio_scsi_config, and then virtio_cread64 would read it as a
little-endian u64, 0xcdab896745230150.  Maybe your QEMU patch is also
writing things as little-endian 64-bit integers, rather than 8-element
arrays of bytes?

Paolo

> Maybe we should use u64 in struct virtio_scsi_config as well?