Re: [PATCH 3/7] oxenstored: refactor request processing

[David Scott <dave@recoil.org>]

> On 29 Mar 2016, at 17:38, Wei Liu <wei.liu2@citrix.com> wrote:
> 
> On Tue, Mar 29, 2016 at 10:08:30AM +0100, Jonathan Davies wrote:
>> On Thu, Mar 24, 2016 at 07:57:30PM -0400, Boris Ostrovsky wrote:
>>> On 03/24/2016 06:49 PM, Andrew Cooper wrote:
>>>> On 24/03/2016 22:22, Boris Ostrovsky wrote:
>>>>> On 03/17/2016 01:51 PM, Jonathan Davies wrote:
>>>>>> Encapsulate the request in a record that is passed from do_input to
>>>>>> process_packet and input_handle_error.
>>>>>> 
>>>>>> This will be helpful when keeping track of the requests made as part
>>>>>> of a
>>>>>> transaction.
>>>>>> 
>>>>>> Signed-off-by: Jonathan Davies <jonathan.davies@citrix.com>
>>>>>> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>>>> Reviewed-by: Jon Ludlam <jonathan.ludlam@citrix.com>
>>>>>> Reviewed-by: Euan Harris <euan.harris@citrix.com>
>>>>>> ---
>>>>>>  tools/ocaml/xenstored/process.ml |   15 ++++++++++-----
>>>>>>  1 file changed, 10 insertions(+), 5 deletions(-)
>>>>>> 
>>>>>> diff --git a/tools/ocaml/xenstored/process.ml
>>>>>> b/tools/ocaml/xenstored/process.ml
>>>>>> index 7a73669..c92bec7 100644
>>>>>> --- a/tools/ocaml/xenstored/process.ml
>>>>>> +++ b/tools/ocaml/xenstored/process.ml
>>>>>> @@ -344,11 +344,11 @@ let function_of_type ty =
>>>>>>      | Xenbus.Xb.Op.Invalid           -> reply_ack do_error
>>>>>>      | _                              -> reply_ack do_error
>>>>>>  -let input_handle_error ~cons ~doms ~fct ~ty ~con ~t ~rid ~data =
>>>>>> +let input_handle_error ~cons ~doms ~fct ~con ~t ~req =
>>>>>>      let reply_error e =
>>>>>>          Packet.Error e in
>>>>>>      try
>>>>>> -        fct con t doms cons data
>>>>>> +        fct con t doms cons req.Packet.data
>>>>>>      with
>>>>>>      | Define.Invalid_path          -> reply_error "EINVAL"
>>>>>>      | Define.Already_exist         -> reply_error "EEXIST"
>>>>>> @@ -370,7 +370,10 @@ let input_handle_error ~cons ~doms ~fct ~ty ~con
>>>>>> ~t ~rid ~data =
>>>>>>  (**
>>>>>>   * Nothrow guarantee.
>>>>>>   *)
>>>>>> -let process_packet ~store ~cons ~doms ~con ~tid ~rid ~ty ~data =
>>>>>> +let process_packet ~store ~cons ~doms ~con ~req =
>>>>>> +    let ty = req.Packet.ty in
>>>>>> +    let tid = req.Packet.tid in
>>>>>> +    let rid = req.Packet.rid in
>>>>>>      try
>>>>>>          let fct = function_of_type ty in
>>>>>>          let t =
>>>>>> @@ -379,7 +382,7 @@ let process_packet ~store ~cons ~doms ~con ~tid
>>>>>> ~rid ~ty ~data =
>>>>>>              else
>>>>>>                  Connection.get_transaction con tid
>>>>>>              in
>>>>>> -        let response = input_handle_error ~cons ~doms ~fct ~ty ~con
>>>>>> ~t ~rid ~data in
>>>>>> +        let response = input_handle_error ~cons ~doms ~fct ~con ~t
>>>>>> ~req in
>>>>>>            (* Put the response on the wire *)
>>>>>>          send_response ty con t rid response
>>>>>> @@ -412,11 +415,13 @@ let do_input store cons doms con =
>>>>>>      if newpacket then (
>>>>>>          let packet = Connection.pop_in con in
>>>>>>          let tid, rid, ty, data = Xenbus.Xb.Packet.unpack packet in
>>>>>> +        let req = {Packet.tid; Packet.rid; Packet.ty; Packet.data} in
>>>>>> +
>>>>> I think this change breaks the build with older ocaml versions:
>>>>> 
>>>>> root@haswell> ocamlopt -v
>>>>> The OCaml native-code compiler, version 4.00.1
>>>>> Standard library directory: /usr/lib64/ocaml
>>>>> root@haswell> ocamlopt -g -ccopt "    " -dtypes -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/xb -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/mmap -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/xc -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/eventchn -cc gcc -w F
>>>>> -warn-error F -c -o process.cmx process.ml
>>>>> root@haswell>
>>>>> 
>>>>> 
>>>>> root@ovs104> ocamlopt -v
>>>>> The Objective Caml native-code compiler, version 3.11.2
>>>>> Standard library directory: /usr/lib64/ocaml
>>>>> root@ovs104> ocamlopt -g -ccopt "    " -dtypes -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/xb -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/mmap -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/xc -I
>>>>> /root/tmp/xen/tools/ocaml/xenstored/../libs/eventchn -cc gcc -w F
>>>>> -warn-error F -c -o process.cmx process.ml
>>>>> File "process.ml", line 487, characters 23-24:
>>>>> Error: Syntax error
>>>>> root@ovs104>
>>>>> 
>>>>> I don't know much about ocaml (OK, I know *nothing* about ocaml) so I
>>>>> can't say what exactly might be wrong.
>>>> Could you perhaps try this instead?
>>>> 
>>>> let req = {tid = Packet.tid; rid = Packet.rid; ty = Packet.ty; data =
>>>> Packet.data} in
>>>> 
>>>> It is most likely that the older version of Ocaml can't infer the order
>>>> of fields.
>>>> 
>>>> ~Andrew
>>> 
>>> 
>>> No, it now gives me "Error: Unbound record field label tid"
>>> 
>>> -boris
>> 
>> Andrew's guess was close, but the wrong way around -- please could you try the
>> following with the older compiler?
>> 
>> let req = {Packet.tid=tid; Packet.rid=rid; Packet.ty=ty; Packet.data=data} in
>> 
>> I was using a syntactic feature of OCaml called 'field punning' which is
>> generally considered good practice and makes for more readable code. It looks
>> like this feature was introduced in OCaml 3.12.0 (dating from 2010), which is
>> consistent with Boris' findings.
>> 
>> What's the policy here -- is there a defined version of the OCaml compiler which
>> tools/ocaml needs to be able to compile with?
> 
> It is not explicitly listed in README or INSTALL. The ocaml tools
> maintainer (Dave in this case) is welcome to provide the minimum version
> required.
> 
> Meanwhile, I don't think we should break existing build without pinning
> down the minimum required version first, so we should fix Boris's
> breakage.  The fix seems simple enough anyway.

It looks like the fix is small and easy — I think this is good for now.

Let’s postpone requiring a later OCaml version until we really need a feature only present in a later version. I suspect this will happen eventually, probably when we try to add a dependency (e.g. from the Mirage world) which requires 4.02+.

Cheers,
Dave

> 
> Wei.
> 
>> 
>> Thanks,
>> Jonathan
>> 
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel


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