Re: [Qemu-devel] vNVRAM / blobstore design

[Stefan Berger]

On 03/27/2013 01:14 PM, Anthony Liguori wrote:
> Stefan Berger <address@hidden> writes:
>
> >
> What I struggle with is that we're calling this a "blobstore".  Using
> BER to store "blobs" seems kind of pointless especially when we're
> talking about exactly three blobs.
>
> I suspect real hardware does something like, flash is N bytes, blob 1 is
> a max of X bytes, blob 2 is a max of Y bytes, and blob 3 is (N - X - Y)
> bytes.
>
> Do we really need to do anything more than that?

I typically call it NVRAM, but earlier discussions seemed to prefer 
'blobstore'.

Using BER is the 2nd design of the NVRAM/blobstore. The 1st one didn't 
use any visitors but used a directory in the first sector pointing to 
the actual blobs in other sectors of the block device. The organization 
of the directory and assignment of the blobs to their sectors, aka 'the 
layout of the data' in the disk image, was handled by the 
NVRAM/blobstore implementation.

I think the least one needs is to make the NVRAM/blobstore a bit more 
generic than making it too TPM-specific is to provide a layer that 
organizes the blobs the device may produce and provides functions to 
register those blobs, have them read or written to without the device 
knowing where exactly the data are located on the storage device. A 
nugget of the 1st implementation was that we could encrypt the blobs 
themselves easily which made it also easier to support encrypted blobs 
on non-QCOW2 devices (modulo the loss of snapshotting then).

   Stefan