Protocol version of Attach API

[臧琳]

Hi David, Yasumasa, Thomas,
    Thanks for point out this issue. it is introduced by enlarged the arg_count_max for 8215622.
    I have reproduced it on my side, and I will handle the fix.
    would you like to help create a JBS for this issue?


Cheers,
Lin
________________________________________
From: serviceability-dev <serviceability-dev-bounces at openjdk.java.net> on behalf of Yasumasa Suenaga <yasuenag at gmail.com>
Sent: Tuesday, February 26, 2019 3:25:15 PM
To: David Holmes
Cc: serviceability-dev at openjdk.java.net serviceability-dev at openjdk.java.net
Subject: Re: Protocol version of Attach API

2019年2月26日(火) 16:11 David Holmes <david.holmes at oracle.com>:
>
> On 26/02/2019 5:01 pm, Yasumasa Suenaga wrote:
> > 2019年2月26日(火) 15:47 Thomas Stüfe <thomas.stuefe at gmail.com>:
> >>
> >> Hi David, Yasumasa,
> >>
> >>>
> >>>
> >>>> Do we support connection to later VMs from earlier JDK tools?
> >>>
> >>> I could not find the spec about this.
> >>> So I asked to serviceability folks before filing this to JBS :-)
> >>>
> >>
> >> Just to chime in on that, I do not know if it is specified but it is certainly very handy in daily use. I often use old jcmd tools to connect to newer VMs. I always thought that was a neat design.
> >
> > I agree with Thomas,
> > but I think we can update protocol version and reject request(s) from
> > jcmd and other tools on earlier release.
>
> That is not a decision to be taken lightly and one that requires a CSR
> request. Simply allowing for an extra arg on the jmap histo subcommand
> should not break all backward compatability.
>
> I think this is a "simple" bug in the Linux (and possibly other) attach
> listener logic. It should be reading a protocol "packet" with up to 4
> arguments, but it should be perfectly fine to get a packet with fewer
> than 4. The current code doesn't do that, but assumes the "packet" is
> always the maximum size.

Ok,
but I can create a patch for Linux only.

AFAICS this issue seems to be in AttachListener for Linux, AIX, OS X.
(Solaris and Windows are ok)

Can you handle this issue?
Of course I can take this if it allows for Linux only :-)


Thanks,

Yasumasa


> David
> -----
>
> >
> > I guess serviceability tools like a jhsdb are recommended in use with
> > same version.
> >
> >
> > Thanks,
> >
> > Yasumasa
> >
> >
> >> ..Thomas
> >>