Linux: Fix builds on RHEL4
RHEL4 has a very old 2.6 kernel (2.6.9), which predates the start of
the Linux git tree. When I started using page_offset, I mistakenly assumed
that everything in the initial commit to that tree was available in all
2.6 versions we care about. That isn't the case, sadly.
Secondly, the new readpage code uses zero_user_segments, which has only
been available in the mainline kernel since 2.6.25 (RHEL5 appears to have
a backport)
Implement local wrappers for both of these functions when configure can't
find them in the kernel we're building for.
These functions have been created independently of the Linux tree.
page_offset is a copy of the code we used before we replaced it.
zero_user_segments() is a first-principles implementation
of the function (which zeros a pair of memory ranges within a single page)
FIXES 126678
Change-Id: I622aec4d653567d5234e7a127b981e97468bbe7c
Reviewed-on: http://gerrit.openafs.org/1525
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>