From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51150) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zc7y1-0000WY-OS for qemu-devel@nongnu.org; Wed, 16 Sep 2015 04:21:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zc7y0-0001zf-Ek for qemu-devel@nongnu.org; Wed, 16 Sep 2015 04:21:25 -0400 From: Markus Armbruster References: <1441878905-5272-1-git-send-email-wency@cn.fujitsu.com> <1441878905-5272-2-git-send-email-wency@cn.fujitsu.com> <87r3m1krdl.fsf@blackfin.pond.sub.org> <55F6EBF5.2090101@redhat.com> <55F776CC.3050601@cn.fujitsu.com> <87fv2g876a.fsf@blackfin.pond.sub.org> <55F7D06D.1080205@cn.fujitsu.com> <87mvwo3phm.fsf@blackfin.pond.sub.org> <55F9054F.1000001@cn.fujitsu.com> Date: Wed, 16 Sep 2015 10:21:12 +0200 In-Reply-To: <55F9054F.1000001@cn.fujitsu.com> (Wen Congyang's message of "Wed, 16 Sep 2015 13:59:43 +0800") Message-ID: <87r3lyzsef.fsf@blackfin.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v3 1/5] support nbd driver in blockdev-add List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wen Congyang Cc: Kevin Wolf , Alberto Garcia , zhanghailiang , qemu block , Jiang Yunhong , Dong Eddie , qemu devel , "Dr. David Alan Gilbert" , Gonglei , Stefan Hajnoczi , Yang Hongyang Wen Congyang writes: > On 09/15/2015 07:12 PM, Markus Armbruster wrote: >> Wen Congyang writes: >> >>> On 09/15/2015 03:37 PM, Markus Armbruster wrote: >>>> Wen Congyang writes: >>>> >>>>> On 09/14/2015 11:47 PM, Eric Blake wrote: >>>>>> On 09/14/2015 08:27 AM, Markus Armbruster wrote: >>>>>>> Wen Congyang 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 >>>>>>>> Signed-off-by: zhanghailiang >>>>>>>> Signed-off-by: Gonglei >>>>>>>> --- >>>>>>>> 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? Question still open. >>> 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". > > Yes, we need "host" in nbd_config(), but we pass "addr.data.host" to it. > > How to avoid this problem? Where is the code constructing the QDict?