Re: [Qemu-devel] [Qemu-block] [PATCH] nbd/server: fix NBD_CMD_CACHE

[Eric Blake <eblake@redhat.com>]

On 10/4/18 8:02 AM, Kevin Wolf wrote:
> Am 03.10.2018 um 17:10 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> 03.10.2018 17:57, Eric Blake wrote:
>>> On 10/3/18 9:47 AM, Vladimir Sementsov-Ogievskiy wrote:
>>>> We should not go to structured-read branch on CACHE command, fix that.
>>>>
>>>> Bug intoroduced in bc37b06a5cde24 "nbd/server: introduce NBD_CMD_CACHE"
>>>
>>> s/intoroduced/introduced/
>>>
>>>> with the whole feature and affects 3.0.0 release.
>>>
>>> Ouch. It's because I don't have an NBD client that can issue the
>>> command, so the server side got released without sufficient testing.
>>> Is there some way we could enhance qemu-io as NBD client to issue such
>>> a command?
>>
>> may be, just add qemu-io command, like x-debug-nbd-cmd, which will just
>> send any nbd command? and prints all server replies? Then we'll be able
>> to write any unit tests on nbd-server. It's not the first time the
>> problem arise..
> 
> Shouldn't it be easy to write a simple NBD client in Python and then use
> that for test cases? I don't see why this needs to be in qemu-io, and
> testing illegal requests is certainly easier with a custom client.

Indeed, and we already have tests/qemu-iotests/nbd-fault-injector.py 
which implements a custom server (unfortunately, it has not been updated 
to use newstyle yet!), as a reference for implementing a similar custom 
client.

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