[OpenAFS] On desupporting Linux 2.4

[Benjamin Kaduk]

Hi all,

Linux 2.4 is getting long in the tooth, and it is becoming clear that
attempting to continue to support it is a drain on the scarce OpenAFS
development resources which could be better used to modernize the
codebase and implement security and performance improvements such as rxgk
and fine-grained pthreaded locking.

In particular, the threading library used by Linux 2.4, LinuxThreads, is
not compliant to the POSIX (pthread) standard, and the non-standard
behaviors are preventing improvements to OpenAFS such as
http://gerrit.openafs.org/#change,6947 .  Even attempting to retain the
old OpenAFS behavior on systems with LinuxThreads and provide improved
functionality for other systems seems to be beyond the available developer
resources.

When discussion on http://gerrit.openafs.org/#change,6947 began in 2012,
it was claimed that dropping support for Linux 2.4 was premature at that
time.  It is now nearly three years later, and no progress has been made
on that change in gerrit, because of the difficulty of dealing with
LinuxThreads and Linux 2.4.

As such, I propose that OpenAFS drop support for Linux 2.4 (and thus
LinuxThreads) starting with the forthcoming 1.8 release.  Because this is
a substantial change, I invite comments from the community as to whether
it is appropriate and acceptable to desupport Linux 2.4, and what the
scope of the impact of such a change would be.

Thank you,

Ben Kaduk