netdev - Re: [PATCH net-next v3 01/13] virtio: add packed ring types and macros

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Date:   Fri, 30 Nov 2018 07:47:48 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Tiwei Bie <tiwei.bie@...el.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        virtio-dev@...ts.oasis-open.org, wexu@...hat.com,
        jfreimann@...hat.com, maxime.coquelin@...hat.com
Subject: Re: [PATCH net-next v3 01/13] virtio: add packed ring types and
 macros

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@...el.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.


> > 
> > 
> > > + */
> > > +#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 */