Re: [Qemu-devel] [Qemu-block] storing machine data in qcow images?

[Dr. David Alan Gilbert]

* Michael S. Tsirkin (address@hidden) wrote:
> On Tue, Jun 05, 2018 at 03:09:17PM -0500, Eric Blake wrote:
> > On 06/05/2018 02:58 PM, Richard W.M. Jones wrote:
> > > > Binary blobs can always be base64 encoded for representation within
> > > > a valid JSON UTF-8 string (and we already have several QMP
> > > > interfaces that utilize base64 encoding to pass through what is
> > > > otherwise invalid UTF-8).  It does inflate things slightly compared
> > > > to a format that allows a raw length coupled with raw data, but that
> > > > is not necessarily a problem.
> > > 
> > > Of course how we represent them externally and/or while
> > > using QMP / qemu-img to store and retrieve them is up for grabs.
> > > Doesn't JSON allow binary to be encoded?  (Knowing how poorly
> > > done JSON is, I wouldn't be surprised if not)
> > 
> > JSON itself does not have a binary primitive; to pass arbitrary data through
> > JSON you have to first encode that data into something like base64 that can
> > then be represented as a UTF-8 string.  For reference, look at
> > qapi/crypto.json and the definition of QCryptoSecretFormat.
> 
> But there isn't a way to figure out that a string is base64, which
> means each application needs to know whether it's a string or
> a binary.
> 
> How about specifying the encoding in the value?
> 
> string value:
> [A-Za-z][^=\0]=S[^\0]*
> 
> base64 value:
> [A-Za-z][^=\0]=B[A-Za-z0-9+/]*
> 
> or the key:
> S[A-Za-z][^=\0]=[^\0]*
> 
> base64 value:
> B[A-Za-z][^=\0]=[A-Za-z0-9+/]*

Why reinvent the wheel yet again?
The world has enough encodings out there, and we're trying to add
something that's a trivial data store for a frankly trivial use.

While I hate json, it's at least standard.

Dave

> ?
> 
> -- 
> MST
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK