Re: [RFC PATCH 0/3] Use DIAG318 to set Control Program Name & Version Codes

Re: [RFC PATCH 0/3] Use DIAG318 to set Control Program Name & Version Codes

[Collin Walling]

On 08/31/2018 12:51 PM, Collin Walling wrote:
> A new diagnose instruction, 318, allows the kernel to set an 8-byte "Control 
> Program Code" (CPC) that is composed of:
> 
>     1-byte Control Program Name Code (CPNC)
>     7-byte Control Program Version Code (CPVC) composed of:
>         3-bytes for Linux Kernel version (determined at build-time)
>         3-bytes for Distribution Identifier (referred to as distro_id; set by Kconfig option)
>         1-byte trailing NULL
> 
> Note about distro_id:
> [
> The initial idea for the 3-byte distro_id is for each distribution to set 
> three characters that correspond to their distribution name (for a theoretical 
> distributor "ACME," they could set "ACM" as the distro_id). A registry file 
> could be included in the s390 kernel documentation to avoid name collisions.
> ]

Another (likely better) idea is to use 1-byte for the distribution, followed
by 2-bytes for major.minor release.




-- 
Respectfully,
- Collin Walling

Re: [RFC PATCH 0/3] Use DIAG318 to set Control Program Name & Version Codes

[Cornelia Huck]

On Wed, 19 Sep 2018 13:09:34 -0400
Collin Walling <walling@linux.ibm.com> wrote:

> On 09/19/2018 05:30 AM, Cornelia Huck wrote:
> > On Fri, 31 Aug 2018 12:51:16 -0400
> > Collin Walling <walling@linux.ibm.com> wrote:

> >> The CPC and HPID are used for problem diagnosis and allows IBM to identify 
> >> control program information by answering the following questions:
> >>
> >>     "What environment is this guest running in?" (CPNC)
> >>     "What distribution is this guest running?" (CPVC)
> >>     "What underlying host environment is this guest running on?" (HPID)  
> > 
> > Is there also a way for people-who-are-not-IBM to find out what these
> > values have been set to? :) (IOW, is that write-only from a Linux
> > perspective?)
> > 
> > I see that for the emulated instruction the values are logged into the
> > debug feature, which seems useful.
> >   
> 
> Maybe it would help to include a toString-esque macro for these values. Then
> when the HPID and CPNC get logged we will have something us humans can read? :)
> 
> The distro_id will have to be deciphered via the registry file. Thoughts?

It's probably fine if this has to be decoded outside of the kernel.

One thing that came to my mind: Would it be useful to be able to
introspect a live guest from the hypervisor? For example, being able to
get the CPNC/CPVC from a QEMU monitor command? (The debug feature may
wrap around so that the info can get lost, I guess?)