Re: [virtio] [OASIS Issue Tracker] Created: (VIRTIO-7) Reserve device ID 0 (zero) as invalid

[Rusty Russell <rusty@au1.ibm.com>]

Pawel Moll <pawel.moll@arm.com> writes:
> On Tue, 2013-08-20 at 07:44 +0100, Rusty Russell wrote:
>> diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
>> index 8fc96b2..f989630 100644
>> --- a/virtio-v1.0-wd01-part1-specification.txt
>> +++ b/virtio-v1.0-wd01-part1-specification.txt
>> @@ -1069,6 +1069,8 @@ Discovering what devices are available and their type is bus-dependent.
>>  | Device ID  |   Virtio Device    |
>>  +------------+--------------------+
>>  +------------+--------------------+
>> +| 0          |   none (ignore)    |
>> ++------------+--------------------+
>>  | 1          |   network card     |
>>  +------------+--------------------+
>>  | 2          |   block device     |
>> @@ -1094,6 +1096,8 @@ Discovering what devices are available and their type is bus-dependent.
>>  | 12         |   virtio CAIF      |
>>  +------------+--------------------+
>>  
>> +When a device is discovered with a device ID of 0, it should be ignored.
>
> How about:
>
> 0 reserved (invalid)
>
> No device will ever have an ID of 0 (zero). Transports may choose to
> ignore such devices.

Mark it as reserved (invalid), then put a section under MMIO explicitly
stating that such devices are possible but must be ignored?

Cheers,
Rusty.