Add documentation for indirect descriptors Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> --- virtio-spec.lyx | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 files changed, 114 insertions(+), 4 deletions(-) diff --git a/virtio-spec.lyx b/virtio-spec.lyx index 8062e11..b5a8fbd 100644 --- a/virtio-spec.lyx +++ b/virtio-spec.lyx @@ -1,4 +1,4 @@ -#LyX 1.6.4 created this file. For more info see http://www.lyx.org/ +#LyX 1.6.5 created this file. For more info see http://www.lyx.org/ \lyxformat 345 \begin_document \begin_header @@ -36,8 +36,7 @@ \paperpagestyle default \tracking_changes true \output_changes true -\author "" -\author "" +\author "Michael S. Tsirkin" \author "" \end_header @@ -1441,7 +1440,28 @@ struct vring_desc { \begin_layout Plain Layout -#define VRING_DESC_F_WRITE 2 +#define VRING_DESC_F_WRITE 2 +\change_deleted 0 1265802057 + +\change_inserted 0 1265802048 + +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1265802054 + +/* This means the buffer contains a list of buffer descriptors. + */ +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1265802049 + +#define VRING_DESC_F_INDIRECT 4 +\change_unchanged + \end_layout \begin_layout Plain Layout @@ -1478,6 +1498,96 @@ struct vring_desc { \begin_layout Standard The number of descriptors in the table is specified by the Queue Size field for this virtqueue. +\change_deleted 0 1265801065 + +\end_layout + +\begin_layout Subsubsection + +\change_inserted 0 1265801341 +Indirect Descriptors +\end_layout + +\begin_layout Standard + +\change_inserted 0 1265805736 +Some devices benefit by concurrently dispatching a large number of large + requests. + To increase ring capacity it is possible to store a table of +\emph on +indirect descriptors +\emph default + anywhere in memory, and insert a descriptor in main virtqueue (with flags&INDIRECT on) that refers to memory buffer containing this +\emph on +indirect descriptor table +\emph default +; fields +\emph on +addr +\emph default + and +\emph on +len +\emph default + refer to the indirect table address and length in bytes, respectively. + The indirect table layout structure looks like this (len is the length + of the descriptor that refers to this table, which is a variable, so this + code won't compile): +\end_layout + +\begin_layout Standard + +\change_inserted 0 1265804397 +\begin_inset listings +inline false +status open + +\begin_layout Plain Layout + +\change_inserted 0 1265804526 + +struct indirect_descriptor_table { +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1265804397 + + /* The actual descriptors (16 bytes each) */ +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1265804473 + + struct vring_desc desc[len / 16]; +\end_layout + +\begin_layout Plain Layout + +\change_inserted 0 1265804397 + +}; +\end_layout + +\end_inset + + +\end_layout + +\begin_layout Standard + +\change_inserted 0 1265805219 +The first indirect descriptor is located at start of the indirect descriptor + table (index 0), additional indirect descriptors are chained by next field. + An indirect descriptor without next field (with flags&NEXT off) signals + the end of the indirect descriptor table, and transfers control back to + the main virtqueue. + An indirect descriptor can not refer to another indirect descriptor table + (flags&INDIRECT must be off). + A single indirect descriptor table can include both read-only and write-only + descriptors; write-only flag (flags&WRITE) in the descriptor that refers + to it is ignored. \end_layout \begin_layout Subsection -- 1.6.6.144.g5c3af -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
