Linux Birds of Feathers

Rational staff:

• Will Taber: author of the port of mvfs.o to GNU Linux
• Rich Rakich: interface to support (coordinator) for Linux issues
• John Kohl
• Terry Durkin: product manager for Unix ClearCase.

Comments heard:

• Linux is not Unix. It is significantly different. Linux developers are proud of the fact it is a rewrite.
• Linus Torvalds doesn't believe (even) in source control.
• The file system interface has been and is still unstable. This is especially true in the area of locking. Note that symmetrical multiprocessing is currently not supported yet.
• There is name caching in the kernel.
• The timing of the introduction of ClearCase on Linux was bad. It had in fact to be done twice.
• Kernel versions are expensive.
• Linux is a moving target. By the time you release support for one configuration, there are already several newer versions.
• Some of the so-called security fixes contain other stuff (blaster? I don't remember what that meant... Support for sound blasters in a recent patch?!). An other example was protection against DOS (Denial of Service). The Rational guys thought this shouldn't concern host running ClearCase, which should be behind a firewall anyway.
• Linux doesn't panic. It tries hard to stay alive (ksumoops) with the risk of degrading performance or slowly locking the system (no nice release of resources, etc...), ending up in hangs.
• NFS appears slower to update caches: try again

Most problems are with mvfs, and should show up at load time. There are wrappers to most functions which check for assumptions and on failure, typically issue messages such as:

 structure size mismatch - expected ...

Rational is very aware that their traditional support model doesn't work with Linux. The issue is not so much to make Linux a 1st-tier platform, as to react faster to changes (patches).

They need our (their customers') help to spot the critical patches, and to test valuable configurations. They would value to identify a team of technical people with whom to communicate more tightly. I promised to send them such a list.

As a summary, their message was for now: Call support fast.