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Subject: Re: [virtio-dev] [PATCH v6 4/5] packed virtqueues: more efficient virtqueue layout
On Wed, Jan 10, 2018 at 02:49:42PM +0100, Jens Freimann wrote: > On Wed, Jan 10, 2018 at 11:47:58AM +0200, Michael S. Tsirkin wrote: > [...] > > +\subsection{Supplying Buffers to The Device}\label{sec:Basic Facilities of a Virtio Device / Packed Virtqueues / Supplying Buffers to The Device} > > + > > +The driver offers buffers to one of the device's virtqueues as follows: > > + > > +\begin{enumerate} > > +\item The driver places the buffer into free descriptor in the Descriptor Ring. > > + > > +\item The driver performs a suitable memory barrier to ensure that it updates > > + the descriptor(s) before checking for notification suppression. > > + > > +\item If notifications are not suppressed, the driver notifies the device > > + of the new available buffers. > > +\end{enumerate} > > + > > +What follows is the requirements of each stage in more detail. > > + > > +\subsubsection{Placing Available Buffers Into The Descriptor Ring}\label{sec:Basic Facilities of a Virtio Device / Virtqueues / Supplying Buffers to The Device / Placing Available Buffers Into The Descriptor Ring} > > + > > +For each buffer element, b: > > + > > +\begin{enumerate} > > +\item Get the next descriptor table entry, d > > +\item Get the next free buffer id value > > +\item Set \field{d.addr} to the physical address of the start of b > > +\item Set \field{d.len} to the length of b. > > +\item Set \field{d.id} to the buffer id > > +\item Calculate the flags as follows: > > +\begin{enumerate} > > +\item If b is device-writable, set the VIRTQ_DESC_F_WRITE bit to 1, otherwise 0 > > +\item Set VIRTQ_DESC_F_AVAIL bit to the current value of the Available Ring Wrap Counter > > +\item Set VIRTQ_DESC_F_AVAIL bit to inverse value > > This should be "Set VIRTQ_DESC_F_USED bit to inverse value, no? > > regards, > Jens Right.
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