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Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fix
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol |
Date: |
Tue, 17 May 2016 09:59:02 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 05/17/2016 09:52 AM, Eric Blake wrote:
>>> Perhaps nbdkit should implement NBD_OPT_LIST returning just "" (the
>>> default name) as its only list entry?
>>
>> Or "default".
>
> As I read the protocol, I don't see "default" as a permissible name of
> the default export, just "".
>
> Also, we currently state that NBD_OPT_LIST has zero or more
> NBD_REP_SERVER replies, which means that it is valid for the command to
> succeed with NBD_REP_ACK _without_ advertising any exports at all
> (rather annoying in that it tells you nothing about whether
> NBD_OPT_EXPORT_NAME/NBD_OPT_GO will succeed anyways). Should we reword
> that to require that if NBD_REP_ACK is sent, then at least one
> NBD_REP_SERVER reply was given (where "" is the obvious name, but at the
> same time where "" is not mandatory if some other name is given)?
Okay, I just downloaded nbdkit code and checked; nbdkit is sending 0
entries and NBD_REP_ACK (for success), and NOT an error code; so it is
implying that there are NO known export names but that the command was
recognized.
>>
>> My interpretation of NBD_OPT_LIST failing would be 'this server
>> doesn't have anything it can export'.
>
> Indeed, and that's why qemu as a client is currently dropping the
> connection with nbdkit.
Except that nbdkit is NOT failing NBD_OPT_LIST, just merely listing 0
replies.
> But I would also make that interpretation for
> NBD_OPT_LIST succeeding with NBD_REP_ACK with 0 NBD_REP_SERVER replies -
which is the nbdkit behavior
> so maybe it is worth a note in the protocol how to detect servers that
> are exporting exactly one volume and don't care what name you pass, then
> tweaking either nbdkit, qemu, or both to comply to that added protocol
> wording.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- Re: [Qemu-devel] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Alex Bligh, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Alex Bligh, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol,
Eric Blake <=
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Alex Bligh, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Alex Bligh, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Wouter Verhelst, 2016/05/21
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/22
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Richard W.M. Jones, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Alex Bligh, 2016/05/17
- Re: [Qemu-devel] [Nbd] [PULL 23/28] nbd: always query export list in fixed new style protocol, Eric Blake, 2016/05/17