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SubjectRe: [PATCH net-next v3 01/13] virtio: add packed ring types and macros
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On 11/30/18 1:47 PM, Michael S. Tsirkin wrote:
> On Fri, Nov 30, 2018 at 05:53:40PM +0800, Tiwei Bie wrote:
>> On Fri, Nov 30, 2018 at 04:10:55PM +0800, Jason Wang wrote:
>>>
>>> On 2018/11/21 下午6:03, Tiwei Bie wrote:
>>>> Add types and macros for packed ring.
>>>>
>>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>>> ---
>>>> include/uapi/linux/virtio_config.h | 3 +++
>>>> include/uapi/linux/virtio_ring.h | 52 ++++++++++++++++++++++++++++++++++++++
>>>> 2 files changed, 55 insertions(+)
>>>>
>>>> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
>>>> index 449132c76b1c..1196e1c1d4f6 100644
>>>> --- a/include/uapi/linux/virtio_config.h
>>>> +++ b/include/uapi/linux/virtio_config.h
>>>> @@ -75,6 +75,9 @@
>>>> */
>>>> #define VIRTIO_F_IOMMU_PLATFORM 33
>>>> +/* This feature indicates support for the packed virtqueue layout. */
>>>> +#define VIRTIO_F_RING_PACKED 34
>>>> +
>>>> /*
>>>> * Does the device support Single Root I/O Virtualization?
>>>> */
>>>> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
>>>> index 6d5d5faa989b..2414f8af26b3 100644
>>>> --- a/include/uapi/linux/virtio_ring.h
>>>> +++ b/include/uapi/linux/virtio_ring.h
>>>> @@ -44,6 +44,13 @@
>>>> /* This means the buffer contains a list of buffer descriptors. */
>>>> #define VRING_DESC_F_INDIRECT 4
>>>> +/*
>>>> + * Mark a descriptor as available or used in packed ring.
>>>> + * Notice: they are defined as shifts instead of shifted values.
>>>
>>>
>>> This looks inconsistent to previous flags, any reason for using shifts?
>>
>> Yeah, it was suggested to use shifts, as _F_ should be a bit
>> number, not a shifted value:
>>
>> https://patchwork.ozlabs.org/patch/942296/#1989390
>
> But let's add a _SPLIT_ variant that uses shifts consistently.

Maybe we could avoid adding SPLIT and PACKED, but define as follow:

#define VRING_DESC_F_INDIRECT_SHIFT 2
#define VRING_DESC_F_INDIRECT (1ull << VRING_DESC_F_INDIRECT_SHIFT)

#define VRING_DESC_F_AVAIL_SHIFT 7
#define VRING_DESC_F_AVAIL (1ull << VRING_DESC_F_AVAIL_SHIFT)

I think it would be better for consistency.
>
>
>>>
>>>
>>>> + */
>>>> +#define VRING_PACKED_DESC_F_AVAIL 7
>>>> +#define VRING_PACKED_DESC_F_USED 15
>>>> +
>>>> /* The Host uses this in used->flags to advise the Guest: don't kick me when
>>>> * you add a buffer. It's unreliable, so it's simply an optimization. Guest
>>>> * will still kick if it's out of buffers. */
>>>> @@ -53,6 +60,23 @@
>>>> * optimization. */
>>>> #define VRING_AVAIL_F_NO_INTERRUPT 1
>>>> +/* Enable events in packed ring. */
>>>> +#define VRING_PACKED_EVENT_FLAG_ENABLE 0x0
>>>> +/* Disable events in packed ring. */
>>>> +#define VRING_PACKED_EVENT_FLAG_DISABLE 0x1
>>>> +/*
>>>> + * Enable events for a specific descriptor in packed ring.
>>>> + * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
>>>> + * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
>>>> + */
>>>> +#define VRING_PACKED_EVENT_FLAG_DESC 0x2
>>>
>>>
>>> Any reason for using _FLAG_ instead of _F_?
>>
>> Yeah, it was suggested to not use _F_, as these are values,
>> should not have _F_:
>>
>> https://patchwork.ozlabs.org/patch/942296/#1989390
>>
>> Regards,
>> Tiwei
>>
>>>
>>> Thanks
>>>
>>>
>>>> +
>>>> +/*
>>>> + * Wrap counter bit shift in event suppression structure
>>>> + * of packed ring.
>>>> + */
>>>> +#define VRING_PACKED_EVENT_F_WRAP_CTR 15
>>>> +
>>>> /* We support indirect buffer descriptors */
>>>> #define VIRTIO_RING_F_INDIRECT_DESC 28
>>>> @@ -171,4 +195,32 @@ static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
>>>> return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
>>>> }
>>>> +struct vring_packed_desc_event {
>>>> + /* Descriptor Ring Change Event Offset/Wrap Counter. */
>>>> + __le16 off_wrap;
>>>> + /* Descriptor Ring Change Event Flags. */
>>>> + __le16 flags;
>>>> +};
>>>> +
>>>> +struct vring_packed_desc {
>>>> + /* Buffer Address. */
>>>> + __le64 addr;
>>>> + /* Buffer Length. */
>>>> + __le32 len;
>>>> + /* Buffer ID. */
>>>> + __le16 id;
>>>> + /* The flags depending on descriptor type. */
>>>> + __le16 flags;
>>>> +};
>>>> +
>>>> +struct vring_packed {
>>>> + unsigned int num;
>>>> +
>>>> + struct vring_packed_desc *desc;
>>>> +
>>>> + struct vring_packed_desc_event *driver;
>>>> +
>>>> + struct vring_packed_desc_event *device;
>>>> +};
>>>> +
>>>> #endif /* _UAPI_LINUX_VIRTIO_RING_H */

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