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SubjectRe: [PATCH net-next 6/8] virtio: introduce packed ring defines
On Tue, Jul 03, 2018 at 01:38:02PM +0800, Jason Wang wrote:
> Signed-off-by: Jason Wang <jasowang@redhat.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.

> +
> /*
> * 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.

> +#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).

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;

> + /* 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

> +/* 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
>

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