Re: [virtio-comment] [PATCH 1/1] split-ring: clarify the field len in the used ring

[Stefan Hajnoczi <stefanha@redhat.com>]

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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