Re: [Qemu-block] BLOCK_STATUS extension

[Eric Blake]

[using the updated nbd list email]

On 02/14/2018 08:35 AM, Vladimir Sementsov-Ogievskiy wrote:
> Hi all.
>
> Just note: looks like we allow zero-sized metadata context name. Is it ok?
>
>   *
>
>     |NBD_REP_META_CONTEXT| (4)
>
>     A description of a metadata context. Data:
>
>       o 32 bits, NBD metadata context ID.
>       o String, name of the metadata context. This is not required to be
>         a human-readable string, but it MUST be valid UTF-8 data.

No; elsewhere we state:

> Metadata contexts are identified by their names. The name MUST consist of a 
> namespace, followed by a colon, followed by a leaf-name. The namespace must 
> consist entirely of printable non-whitespace UTF-8 characters other than 
> colons, and be non-empty. The entire name (namespace, colon, and leaf-name) 
> MUST follow the restrictions for strings as laid out earlier in this document.
>
> Namespaces MUST be consist of one of the following:
>
>     base, for metadata contexts defined by this document;
>     nbd-server, for metadata contexts defined by the implementation that 
> accompanies this document (none currently);
>     x-*, where * can be replaced by an arbitrary string not containing colons, 
> for local experiments. This SHOULD NOT be used by metadata contexts that are 
> expected to be widely used.
>     A third-party namespace from the list below.

So a name must be at least 2 bytes (for a one-byte namespace, if someone 
ever registers one - and supposing that namespace has zero-byte leaf 
names), but will more commonly be even longer.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org