After a little digging it appears not to be a problem with linux per se but glibc 2. (Please correct me if I'm wrong) Fast stdio io in perl uses the hooks _ptr and _cnt specified in the normal stdio.h. Unfortunately _cnt is not visible in the glibc 2 version. I've seen mentions of a glue.c file in glibc source that may allow a work around.

If this is a glibc 2 then there may be future problems on other platforms, or do other platforms that use glibc 2 and have fast perl io, have a modified stdio.h?

Perhaps sfio allows such direct hooks, has anybody else made progress on this issue?

regards dino