[Qemu-devel] Re: RFC: blockdev_add & friends, brief rationale, QMP docs

[Markus Armbruster]

Avi Kivity <address@hidden> writes:

> On 06/04/2010 05:16 PM, Markus Armbruster wrote:
>> - "protocol": json-array of json-object
>>    Each element object has a member "name"
>>      - Possible values: "file", "nbd", ...
>>    Additional members depend on the value of "name".
>>    For "name" = "file":
>>      - "file": file name (json-string)
>>    For "name" = "nbd":
>>      - "domain": address family (json-string, optional)
>>          - Possible values: "inet" (default), "unix"
>>      - "file": file name (json-string), only with "domain" = "unix"
>>      - "host": host name (json-string), only with "domain" = "inet"
>>      - "port": port (json-int), only with "domain" = "inet"
>>    ...
>>
>>    
>
> This loses the nesting that protocols have.  I'd like to see the each
> nested protocol as member of the parent protocol.  Besides the lovely
> } } }s in the json representation, this allows us to have more
> complicated protocols, for example a mirror protocol that has two
> child protocol each specifying a different backing store.

Even though we don't have such a protocol yet, not even plans to get it,
your argument tips the balance towards nesting.

Revised sketch: instead of

- "file": the disk image file to use (json-string, optional)
- "format": disk format (json-string, optional)
    - Possible values: "raw", "qcow2", ...

have

- "format": image format (json-string, optional)
    - Possible values: "raw", "qcow2", [...]
- "protocol": image access protocol (json-object)
    - It has a member "name" (json-string), and depending on its value
      additional members.
    - For "name" = "auto", "file", [...]
      - "file": name of image file (json-string)
    - For "name" = "nbd":
      - "domain": address family (json-string, optional)
          - Possible values: "inet" (default), "unix"
      - "file": name of socket file (json-string), only with "domain" =
        "unix"
      - "host": host name (json-string), only with "domain" = "inet"
      - "port": port (json-int), only with "domain" = "inet"
    - For "name" = "blkdebug":
      - "config": name of config file (json-string)
      - "protocol": image access protocol (json-object), as above
    [...]

Examples:

* Format "qcow2", protocol "auto" with argument filename "foo.img"

    "format": "qcow2",
    "protocol": { "name": "auto", "file": "foo.qcow2" }

* Format "raw", protocol "nbd" with arguments domain "unix", filename
  "/tmp/my_socket"

    "format": "raw"
    "protocol": { "name": "nbd", "domain": "unix", "file": "/tmp/my_socket" }

* Format not specified (system guesses one), protocol "blkdebug" with
  argument filename "/tmp/blkdebug.cfg" stacked onto protocol "fat" with
  arguments floppy true, dirname "/tmp/dir"

    "protocol": { "name": "blkdebug", "file": "/tmp/blkdebug.cfg",
        "protocol": { "name": "fat", "floppy": true, "dir": "/tmp/dir" }
    }

This nesting business is easy enough for QMP, but it'll be awkward on
the command line.  Ideas on how to do it cleanly with -blockdev?