On Tue, Aug 01, 2017 at 08:54:27PM -0700, Steven Luong wrote:
> * Descriptor ring:
>
> Guest adds descriptors with unique index values and DESC_HW set in flags.
> Host overwrites used descriptors with correct len, index, and DESC_HW
> clear. Flags are always set/cleared last.
>
> #define DESC_HW 0x0080
>
> struct desc {
> __le64 addr;
> __le32 len;
> __le16 index;
> __le16 flags;
> };
>
> When DESC_HW is set, descriptor belongs to device. When it is clear,
> it belongs to the driver.
>
> We can use 1 bit to set direction
> /* This marks a buffer as write-only (otherwise read-only). */
> #define VRING_DESC_F_WRITE 2
>
> * Scatter/gather support
>
> We can use 1 bit to chain s/g entries in a request, same as virtio 1.0:
>
> /* This marks a buffer as continuing via the next field. */
>
>
> This comment here is confusing to me. In 1.0, virtq_desc has the next field.
> When the flag VRING_DESC_F_NEXT is set, the next entry to continue is
> specified
> in the next field.
>
> Here in 1.1, struct desc does not have the next field, only addr, len, index,
> and flags. So when VRING_DESC_F_NEXT is set in struct desc's flags field,
> where
> is the next entry to continue the current descriptor, the entry immediately
> following the current entry? ie, if the current entry is at index 10 in the
> descriptor table and its flags is set for VRING_DESC_F_NEXT, is the entry
> continuing the current entry in index 11?
>
> Steven
Exactly, you got it right.
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