Fwd: VDSM API schema inconsistencies

10 Oct 2018

      Adding devel.

---------- Forwarded message ---------
From: Nir Soffer <nsoffer@redhat.com>
Date: Wed, 10 Oct 2018, 11:07
Subject: Re: VDSM API schema inconsistencies
To: Piotr Kliczewski <pkliczew@redhat.com>
Cc: Dan Kenigsberg <danken@redhat.com>, Edward Haas <ehaas@redhat.com>,
Milan Zamazal <mzamazal@redhat.com>, Tomasz Baranski <tbaransk@redhat.com>,
Francesco Romani <fromani@redhat.com>, Irit Goihman <igoihman@redhat.com>,
Marcin Sobczyk <msobczyk@redhat.com>

On Wed, 10 Oct 2018, 10:21 Piotr Kliczewski, <pkliczew@redhat.com> wrote:
...
+Nir
On Wed, Oct 10, 2018 at 8:39 AM Marcin Sobczyk <msobczyk@redhat.com>
wrote:
...
Hi,
I would love to get some feedback from you about it on the VDSM call
today so if you have a moment, please take a look.
Marcin
---------- Forwarded message ---------
From: Marcin Sobczyk <msobczyk@redhat.com>
Date: Mon, Oct 8, 2018 at 2:40 PM
Subject: VDSM API schema inconsistencies
To: devel <devel@ovirt.org>
Hi,
when I was working on BZ#1624306 it turned out, that even if I'd fix the
help-printing code in vdsm-client, there's still a lot of inconsistencies
in API's schema files.
After some investigation, I found that there's a code for reporting
schema inconsistencies, but it's turned off because it bloats the logs.
Right, an it should remain like this. In runtime
we never want these warnings.
There's also a "strict" mode that raises an exception each time an
...
...
inconsistency is found, but it's also off because there's so many of them.
Same.

Both are debugging aids for developers, to
make it easy to check the schema.
...
I think that no one wants to maintain both: the actual code and schema
...
files.
This is not a big issue. We rarely add or
change APIs. But it is nice if we don't need to
manualy make the schema correct.
...
My idea would be to make the schema derived from the code at build time as
...
a long-term effort.
...
...
https://gerrit.ovirt.org/#/q/status:open+project:vdsm+branch:master+topic:vd...
This is a series of patches that helps fixing schema issues. What it
does, is it adds a bunch of information from stack to vastly ease the
process of fixing them. The logging level is also changed from 'WARNING' to
'DEBUG'. Here's an example of a logged entry:
Host.setKsmTune
With message: Required property pages_to_scan is not provided when
calling Host.setKsmTune
With backtrace: [
        [
                "_verify_object_type",
                {
                        "call_arg_keys":[
                                "merge_across_nodes",
                                "run"
                        ],
                        "schema_type_name":"KsmTuneParams"
                }
        ],
        [
                "_verify_complex_type",
                {
                        "schema_type_type":"object"
                }
        ]
]
To make it work, a patch for OST's 'basic-master-suite' is on the way
that switches 'schema.inconsistency' logger's logging level do 'DEBUG'.
That way, we can find all reported errors in 'vdsm-schema-error.log' files.
An initial report that groups reported errors by namespaces/methods has
also been made. Please note, that an implementation that completely avoids
error duplicates is really hard and IMHO not worth the effort. You can find
the results here:
- Host: https://pastebin.com/YM2XnvTV
   - Image: https://pastebin.com/GRc1yErL
   - LVMVolumeGroup: https://pastebin.com/R1276gTu
   - SDM: https://pastebin.com/P3tfYEDD
   - StorageDomain: https://pastebin.com/Q0DxKgF5
   - StoragePool: https://pastebin.com/VXFWpfRC
   - VM: https://pastebin.com/tDC60c29
   - Volume: https://pastebin.com/TYkr9Zsd
   - |jobs|: https://pastebin.com/jeXpYyz9
   - |virt|: https://pastebin.com/nRREuEub
File a bug per vertical (infra, storage, virt) for
This cannot work, since clients depend on the schema, it should not change
if when someone
makes uintended change in the code.

It should work in the opposite way, you change the schema, and generate new
code frome schema.

Threre are existing tools like grpc and thrift that
work in this way. For long term we should drop
our jsonrpc/stomp stack and move to grpc.

For short term we can just fix the schema to
reflect actual engine interaction. when engine
and schema do not match, engine is usualy
right. For responses, if engine can handle the
response the code is right.

Please do not make RPC code more complex
and inefficient for improving schema issues
detection. I would rather remove this code
instead.

Before we can do that though, we need to address the inconsistencies first.
these issues. Since we don't know about real user issues with these apis
this must be incorrect schema.

Nir

Nir Soffer

Marcin Sobczyk

Nir Soffer

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