linux-kernel - Re: [PATCH net-next 6/8] virtio: introduce packed ring defines

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Date:   Wed, 4 Jul 2018 13:26:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, wexu@...hat.com,
        maxime.coquelin@...hat.com, jfreimann@...hat.com
Subject: Re: [PATCH net-next 6/8] virtio: introduce packed ring defines



On 2018年07月04日 12:48, Tiwei Bie wrote:
> On Tue, Jul 03, 2018 at 01:38:02PM +0800, Jason Wang wrote:
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>   include/uapi/linux/virtio_config.h |  2 ++
>>   include/uapi/linux/virtio_ring.h   | 32 ++++++++++++++++++++++++++++++++
>>   2 files changed, 34 insertions(+)
>>
>> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
>> index 449132c..947f6a3 100644
>> --- a/include/uapi/linux/virtio_config.h
>> +++ b/include/uapi/linux/virtio_config.h
>> @@ -75,6 +75,8 @@
>>    */
>>   #define VIRTIO_F_IOMMU_PLATFORM		33
>>   
>> +#define VIRTIO_F_RING_PACKED		34
> It's better to add some comments for this macro.

Ok.

>
>> +
>>   /*
>>    * 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 6d5d5fa..71c7a46 100644
>> --- a/include/uapi/linux/virtio_ring.h
>> +++ b/include/uapi/linux/virtio_ring.h
>> @@ -43,6 +43,8 @@
>>   #define VRING_DESC_F_WRITE	2
>>   /* This means the buffer contains a list of buffer descriptors. */
>>   #define VRING_DESC_F_INDIRECT	4
>> +#define VRING_DESC_F_AVAIL      7
> It's better to use tab between VRING_DESC_F_AVAIL and 7.

Let me fix.

>
>> +#define VRING_DESC_F_USED	15
> Maybe it's better to define VRING_DESC_F_AVAIL and
> VRING_DESC_F_USED as (1 << 7) and (1 << 15) or something
> similar to make them consistent with VRING_DESC_F_NEXT
> (1 << 0), VRING_DESC_F_WRITE (1 << 1) and
> VRING_DESC_F_INDIRECT (1 << 2).

Ok.

>
> I plan to define below macros in virtio_ring.c:
>
> #define _VRING_DESC_F_AVAIL(b)  ((__u16)(b) << 7)
> #define _VRING_DESC_F_USED(b)   ((__u16)(b) << 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
>> @@ -62,6 +64,36 @@
>>    * at the end of the used ring. Guest should ignore the used->flags field. */
>>   #define VIRTIO_RING_F_EVENT_IDX		29
>>   
>> +struct vring_desc_packed {
> We may have other related types named as:
>
> struct vring_packed;
> struct vring_packed_desc_event;
>
> So maybe it's better to name this type as:
>
> struct vring_packed_desc;

Yes.

>
>> +	/* Buffer Address. */
>> +	__virtio64 addr;
>> +	/* Buffer Length. */
>> +	__virtio32 len;
>> +	/* Buffer ID. */
>> +	__virtio16 id;
>> +	/* The flags depending on descriptor type. */
>> +	__virtio16 flags;
>> +};
>> +
>> +/* Enable events */
>> +#define RING_EVENT_FLAGS_ENABLE 0x0
>> +/* Disable events */
>> +#define RING_EVENT_FLAGS_DISABLE 0x1
>> +/*
>> + * Enable events for a specific descriptor
>> + * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
>> + * Only valid if VIRTIO_F_RING_EVENT_IDX has been negotiated.
>> + */
>> +#define RING_EVENT_FLAGS_DESC 0x2
> For above three macros, maybe it's better to name
> them as:
>
> VRING_EVENT_FLAGS_ENABLE
> VRING_EVENT_FLAGS_DISABLE
> VRING_EVENT_FLAGS_DESC
>
> or
>
> VRING_EVENT_F_ENABLE
> VRING_EVENT_F_DISABLE
> VRING_EVENT_F_DESC
>
> VRING_EVENT_F_* will be more consistent with
> VIRTIO_F_*, VRING_DESC_F_*, etc

True. Let me fix above in next version.

Thanks

>> +/* The value 0x3 is reserved */
>> +
>> +struct vring_packed_desc_event {
>> +	/* Descriptor Ring Change Event Offset and Wrap Counter */
>> +	__virtio16 off_wrap;
>> +	/* Descriptor Ring Change Event Flags */
>> +	__virtio16 flags;
>> +};
>> +
>>   /* Virtio ring descriptors: 16 bytes.  These can chain together via "next". */
>>   struct vring_desc {
>>   	/* Address (guest-physical). */
>> -- 
>> 2.7.4
>>