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

[Jonathan Davies <jonathan.davies@xxxxxxxxxx>]

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@xxxxxxxxxx>
> >>>Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >>>Reviewed-by: Jon Ludlam <jonathan.ludlam@xxxxxxxxxx>
> >>>Reviewed-by: Euan Harris <euan.harris@xxxxxxxxxx>
> >>>---
> >>>   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?

Thanks,
Jonathan

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