Re: [Qemu-devel] [Qemu-block] [PATCH 03/20] qcow2: Extend spec for external data files

[Stefan Hajnoczi]

On Fri, Mar 01, 2019 at 10:32:27AM -0600, Eric Blake wrote:
> On 3/1/19 10:17 AM, Stefan Hajnoczi wrote:
> > On Wed, Feb 27, 2019 at 06:22:39PM +0100, Kevin Wolf wrote:
> >> @@ -148,6 +170,7 @@ be stored. Each extension has a structure like the 
> >> following:
> >>                          0x6803f857 - Feature name table
> >>                          0x23852875 - Bitmaps extension
> >>                          0x0537be77 - Full disk encryption header pointer
> >> +                        0x44415441 - External data file name
> > 
> > This new header extension isn't described in this patch?
> 
> I asked the same on v1, and the answer (which remains valid) is that
> neither is 0xe2792aca Backing file format name.  (In other words, both
> extensions are simple enough as a single file name to be implicitly
> described by the reference to the header in the earlier text).  Making
> both explicit wouldn't hurt my feelings, but I don't see it as a
> showstopper to the patch as-is.

The spec should make the representation clear.  Is it a NUL-terminated
string or is the length dictated by the header extension length field?

Otherwise implementors are forced to look at the QEMU source code or
guess based on hex dumping example files :(.

Stefan

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