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Subject: Re: [virtio-comment] [PATCH 1/1] split-ring: clarify the field len in the used ring
On Fri, Nov 26, 2021 at 06:12:33PM +0100, Halil Pasic wrote: > The current descriptor is misleading: "the descriptor chain which was s/current descriptor/current description/? > used" generally includes both the descriptors that map the device read > only, and descriptors that map the device write only portions of the > buffer described by the descriptor chain. The argument that "used" means > "written to" does not stand because one has to "use" the descriptor > chain even when the whole buffer is device read only. > > One can argue, that the most straightforward way to interpret the phrase > "total length of that descriptor chain" (without context) like the > length of the list is usually defined: i.e. like the number of > descriptors that constitute the chain. This is clearly not what we want > here. Another intuitive way to interpret "total length of that > descriptor chain" is size of the buffer mapped by the descriptor chain. > This is not what we want either. In fact such wrongful interpretations > have caused bugs in the wild. > > On the other hand, the text below the listing that gets modified here > clearly describes the semantics of \field{len}. So let us replace > the ambiguous explanation in the listing, with a hopefully non-ambiguous > one. > > Signed-off-by: Halil Pasic <pasic@linux.ibm.com> > --- > split-ring.tex | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/split-ring.tex b/split-ring.tex > index bfef62d..68dca07 100644 > --- a/split-ring.tex > +++ b/split-ring.tex > @@ -402,7 +402,10 @@ \subsection{The Virtqueue Used Ring}\label{sec:Basic Facilities of a Virtio Devi > struct virtq_used_elem { > /* Index of start of used descriptor chain. */ > le32 id; > - /* Total length of the descriptor chain which was used (written to) */ > + /* > + * The number of bytes written into the device writable portion of > + * the buffer described by the descriptor chain. > + */ Spaces vs tabs. It looks like 8 spaces should be used here. Otherwise: Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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