Re: [PATCH 3/4] tools/libxc: Avoid generating inappropriate zero-length records

[David Vrabel <david.vrabel@citrix.com>]

On 21/07/16 18:17, Andrew Cooper wrote:
> It was never intended for records such as these to be sent with zero content.

As the original author of the specification I'm perhaps best placed to
say what the original intention is.

For records such as HVM_PARAMS which consist of a set of N items, the
intention was to most definitely send a record with 0 items.

For records that fetch an opaque blob from the hypervisor, again the
intention was to sent this blob as-is with no sort of processing or
other checking. i.e., if the hypervisor gives us a zero-length blob we
sent that as-is.

This makes all the streams look the same with all the same records,
regardless of what hardware platform it was run on.  Including
zero-length/count records also makes diagnosing problems easier -- the
empty record is visible in the stream instead of having to remember that
sometimes these records are deliberately omitted.

As such, this series should be limited to making the restore side handle
the zero count sets or zero length blobs if it does not do so already.

The specification should be clarified to note that some records may have
zero-length blobs or contain zero items.

David


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