Middleware / application testing - operating system, hypervisor and hardware

After the IBM statement of directions to support KVM on System z I've been asked many times for a criteria if a certain ISV software or customer solution needs to be retested or not. As in performance the answer is: it depends. Basically there are two / four different types of applications / products to consider

1. No retesting needed - certified and tested towards the operating system:
   Applications that use a standard API only, like Java or standard library functions that don't need and exploit the visibility of the underlying (virtualized) hardware.
2. Retesting recommended - certified and tested towards the operating system:
   Applications that do interact with virtualized hardware to a certain extend e.g. accessing raw devices.
3. Retesting and some coding needed - certified and tested towards the operating system and the virtualization layer:
   Applications that actively interact with the hypervisor, e.g. by vmcp commands under z/VM. They then needs an equivalent implementation of that kind of functionality for every type of virtualization. Other examles are the use of zLinux hypfs (hypervisor file system) or using the hypervisor details surfaced in /proc/sysinfo.
4. Retesting and additional code for the hypervisor needed - certified and tested towards the operating system and the virtualization layer:
   Applications that need hooks and special interfaces into the hypervisor e.g. for monitoring or systems management. Every new hypervisor will require new code as e.g. the reported performance metrics and systems management interfaces are different

For Linux on the mainframe today there is only z/VM and LPAR. And z/VM is really virtualizing the hardware in a 1:1 fashion as good as possible (with a lot of firmware and hardware support to keep the overhead to minimal levels).  For such a hardware virtualization the category #2 is nearly not existent. If there is no active interaction with hypervisor, no retesting is needed.
KVM has the concept of new virtual devices with new device names, so some products from #1 are going to slip into category #2.

(updated 4/15/2015)

Porting to Linux on System z

The recently released overview paper "Porting applications to Linux on IBM System z" prompted a few questions about porting in principal that I'll try to answer here in this blog entry.

• The developerWorks article "Porting applications to Linux for System z" provides more technical details, especially on the differences between 31bit and 64bit and of course the endianess problem. So before you start porting your C/C++ program take a look at this. The migration toolkit can be found here and here.
• Open Source packages not yet integrated in a distribution are usually pretty easy. Most of the time a simple ./configure, make, make install sequence does the job. You probably need to install a few development libraries before. Sometimes small changes to the make file are required to recognize s390x as a big-endian 64 bit architecture. Usually you can take a look at the ppc64 implementation.  
• Also for Open Source projects there is the possibility to get access to a System z using the  Community Development System for Linux on System z (CDSL). 
• Java workloads usually run just out of the box. 
• Don't forget to download and install the latest service pack though. 
• Due to the 31bit addressing the heap of the 31bit JVM on System z can't be as large as the heap on a 32bit JVM. So for e.g. a 3 GB heap you need to switch to the 64 bit JVM on zLinux. If you  then use the -Xcompressedrefs option you can keep the additional memory reasonable.
• For ISVs there is at IBM Partnerworld a special roadmap called "Porting your UNIX or Linux on x86 solution to Linux for IBM System z mainframe server platforms". 
• Also hosted on Partnerworld is the "IBM Systems Application Advantage for Linux (Chiphopper)". Which is an offering from IBM to help porting ISV applications.
• IBM als runs Porting Centers around the world for professional help. Also available is the IBM Migration Factory.
• For Open Source projects there is the Community Development System for Linux on System z (CDSL). Register there to get access to a System z. 

(updated 7/15/2014)

How to find software solutions for Linux on System z

There are multiple sources for finding middleware and solutions for Linux. As the web sites get updated this may change - let me know then I adapt the description.
Please note that none of those catalogs is complete, they are all snapshots. 

IBM Global Solution Directory (GSD)
Here you can create complex searches. To select Linux on System z select "IBM System z (Mainframe)" under platform configurations and then all the operating systems you are interested in. Finally click on "search" without entering anything else.
 
IBM Software (SWG) product compatibility
The most important reports are the operating system reports. When generating searches please be aware that their are two different entries for RHEL. The base one has RHEL2 - RHEL5 whereas the one titled RHEL server has RHEL6.
SUSE Enterprise Linux server is all under SLES.

IBM System z page (unfortunately discontinued by IBM end of 2013)
This page lists the ISV solutions updated in approximately the last year.

Red Hat Product Catalog
All the products registered with Red Hat. After you've searched for a specific product you can check the platform and see where it's running.
Note that Red Hat is still using the search term "zSeries" for referring to "System z". So you may want to try this search term as well.

SUSE Linux Enterprise Software Catalog
SUSE has a catalog that can be searched quite easily. Click on "advanced search" and select "IBM System z" as the platform and you get all the vendors offering products for the mainframe that registered with SUSE.