Re: [PATCH v7 2/4] vdpa: Allow for printing negotiated features of a device

[David Ahern <dsahern@kernel.org>]

On 3/15/22 5:35 AM, Eli Cohen wrote:
>>> +};
>>> +
>>> +#define VIRTIO_F_IN_ORDER 35
>>> +#define VIRTIO_F_NOTIFICATION_DATA 38
>>> +#define VDPA_EXT_FEATURES_SZ (VIRTIO_TRANSPORT_F_END - \
>>> +			      VIRTIO_TRANSPORT_F_START + 1)
>>> +
>>> +static const char * const ext_feature_strs[VDPA_EXT_FEATURES_SZ] = {
>>> +	[VIRTIO_RING_F_INDIRECT_DESC - VIRTIO_TRANSPORT_F_START] = "RING_INDIRECT_DESC",
>>> +	[VIRTIO_RING_F_EVENT_IDX - VIRTIO_TRANSPORT_F_START] = "RING_EVENT_IDX",
>>> +	[VIRTIO_F_VERSION_1 - VIRTIO_TRANSPORT_F_START] = "VERSION_1",
>>> +	[VIRTIO_F_ACCESS_PLATFORM - VIRTIO_TRANSPORT_F_START] = "ACCESS_PLATFORM",
>>> +	[VIRTIO_F_RING_PACKED - VIRTIO_TRANSPORT_F_START] = "RING_PACKED",
>>> +	[VIRTIO_F_IN_ORDER - VIRTIO_TRANSPORT_F_START] = "IN_ORDER",
>>> +	[VIRTIO_F_ORDER_PLATFORM - VIRTIO_TRANSPORT_F_START] = "ORDER_PLATFORM",
>>> +	[VIRTIO_F_SR_IOV - VIRTIO_TRANSPORT_F_START] = "SR_IOV",
>>> +	[VIRTIO_F_NOTIFICATION_DATA - VIRTIO_TRANSPORT_F_START] = "NOTIFICATION_DATA",
>>
>> and the entries here should be a macro to handle the
>> VIRTIO_TRANSPORT_F_START  offset with column aligned strings.
>>
> 
> I guess I could define a macro here if all the flags would start with "VIRTIO_F_ =" but unfortunately,
> the first two flags don't follow this pattern.
> I could send kernel patches to replace VIRTIO_RING_F_INDIRECT_DESC and
> VIRTIO_RING_F_EVENT_IDX to VIRTIO_F_RING_INDIRECT_DESC and VIRTIO_F_RING_EVENT_IDX
> and then fix the format here.
> 
> If you meant something else, please be more specific.

It can still work with the existing naming - it's the redundant use of
VIRTIO_TRANSPORT_F_START as an offset that is hidden by the macro
allowing the feature to string conversion to be easier to read.