virtio — archive

[Cornelia Huck <mst@redhat.com>]

On Tue, 11 Aug 2020 04:23:13 -0400 "Michael S. Tsirkin" <mst@redhat.com> wrote: > On Mon, Aug 10, 2020 at 06:59:28PM +0200, Cornelia Huck wrote: > > On Mon, 10 Aug 2020 12:15:15 -0400 > > "Michael S. Tsirkin" <mst@redhat.com> wrote: > > > diff --git a/split-ring.tex b/split-ring.tex > > > index 123ac9f..cf197f8 100644 > > > --- a/split-ring.tex > > > +++ b/split-ring.tex > > > @@ -398,10 +398,11 @@ \subsection{The Virtqueue Used Ring}\label{sec:Basic Facilities of a Virtio Devi > > > le16 avail_event; /* Only if VIRTIO_F_EVENT_IDX */ > > > }; > > > > > > -/* le32 is used here for ids for padding reasons. */ > > > struct virtq_used_elem { > > > /* Index of start of used descriptor chain. */ > > > - le32 id; > > > + le16 id; > > > +#define VIRTQ_USED_ELEM_F_FLUSH 0x8000 > > > + le16 flags; > > > > This is a bit confusing for legacy, as this will only work for > > little-endian. The flags field will only be used for non-legacy, but I > > think the id field should still be treated as 32 bit for legacy. > > (We have a wholesale "it's guest endian when legacy" further up.) > > True. How do you suggest handling this? Just say that id is > OR with VIRTQ_USED_ELEM_F_FLUSH ? Or maybe just add > struct virtq_used_elem_legacy? I think introducing a legacy struct is the least confusing option. > > > > > /* Total length of the descriptor chain which was used (written to) */ > > > le32 len; > > > };