Re: [Qemu-block] [Qemu-devel] [PATCH v3 1/5] support nbd driver in blockdev-add

[Markus Armbruster]

Wen Congyang <address@hidden> writes:

> On 09/15/2015 03:37 PM, Markus Armbruster wrote:
>> Wen Congyang <address@hidden> writes:
>> 
>>> On 09/14/2015 11:47 PM, Eric Blake wrote:
>>>> On 09/14/2015 08:27 AM, Markus Armbruster wrote:
>>>>> Wen Congyang <address@hidden> writes:
>>>>>
>>>>>> The NBD driver needs: filename, path or (host, port, exportname).
>>>>>> It checks which key exists and decides use unix or inet socket.
>>>>>> It doesn't recognize the key type, so we can't use union, and
>>>>>> can't reuse InetSocketAddress.
>>>>>>
>>>>>> Signed-off-by: Wen Congyang <address@hidden>
>>>>>> Signed-off-by: zhanghailiang <address@hidden>
>>>>>> Signed-off-by: Gonglei <address@hidden>
>>>>>> ---
>>>>>>  qapi/block-core.json | 42 ++++++++++++++++++++++++++++++++++++++++--
>>>>>>  1 file changed, 40 insertions(+), 2 deletions(-)
>>>>>>
>>>>
>>>>>>  ##
>>>>>> +# @BlockdevOptionsNBD
>>>>>> +#
>>>>>> +# Driver specific block device options for NBD
>>>>>> +#
>>>>>> +# @filename: #optional unix or inet path. The format is:
>>>>>> +#            unix: nbd+unix:///export?socket=path or
>>>>>> +#                  nbd:unix:path:exportname=export
>>>>>> +#            inet: nbd[+tcp]://host[:port]/export or
>>>>>> +#                  nbd:host[:port]:exportname=export
>>>>
>>>> Yuck. You are passing structured data through a single 'str', when you
>>>> SHOULD be passing it through structured JSON.  Just because we have a
>>>> filename shorthand for convenience does NOT mean that we want to expose
>>>> that convenience in QMP.  Instead, we really want the breakdown of the
>>>> pieces (here, using abbreviated syntax of an inline base, since there
>>>> are pending qapi patches that will allow it):
>>>
>>> Do you mean that: there is no need to support filename?
>> 
>> Rule of thumb: if the QMP command handler needs to parse a string
>> argument, that argument should be a complex QAPI type instead.
>> 
>> Example: @filename needs to be parsed into its components, either
>> 
>>     * protocol unix, socket path, export name, or
>>     * protocol tcp, host, port, export name
>> 
>> Since there's an either/or, the complex QAPI type should be a union.
>> 
>>>> { 'enum': 'NBDTransport', 'data': ['unix', 'tcp', 'udp'] }
>>>
>>> NBD only uses tcp, it doesn't support udp.
>>>
>>>> { 'union': 'BlockdevOptionsNBD',
>>>>   'base': { 'transport': 'NBDTransport', 'export': 'str' },
>>>>   'discriminator': 'transport',
>>>>   'data': { 'unix': 'NBDUnix', 'tcp': 'NBDInet', 'udp': 'NBDInet' } }
>>>> { 'struct': 'NBDUnix', 'data': { 'socket': 'str' } }
>>>
>>> unix socket needs a path, and I think we can use UnixSocketAddress here.
>> 
>> Yes, we should try to reuse common types like SocketAddress,
>> InetSocketAddress, UnixSocketAddress.
>> 
>> Perhaps it could be as simple as
>> 
>>     { 'struct': 'BlockdevOptionsNBD',
>>       'data': { 'addr: 'SocketAddress', 'export': 'str' } }
>
> The problem is that: NBD doesn't use the fd.

Is that fundamental, or just a matter of implementation?

> Another question is: what key will we see in nbd_open()? "addr.host"
> or "host"?

As long as nbd_config() looks for "host" in the options QDict, we need
to put "host".

> Thanks
> Wen Congyang
>
>> 
>> Eric, what do you think?
>> 
>>>> { 'struct': 'NBDInet', 'data': { 'host': 'str', '*port': 'int',
>>>>      '*ipv4': 'bool', '*ipv6': 'bool' } }
>>>
>>> Thanks for the above, and I will try it.
>> 
>> [...]
>> .
>>