Christopher J. Morrone (morrone2@llnl.gov) uploaded a new patch: http://review.whamcloud.com/19248
Subject: LU-7961 build: Fix ldiskfs source autodetect for CentOS 6
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: ebeeaef314283ee06c13f761384cd6920e5f3df3
Hi Bob,
Can you please have a look at the patch?
Thanks.
Joe
Joe,
I can't tell if this patch makes any sense or not. All the build environments I'm aware of or have access to find the ext4 sources under $linux_src/fs/ext4. Where alternate source might live under /usr/src/debug/* is a don't care.
If Chris M. insists this patch is needed I see no harm in it, but can't reproduce or test needing it at all.
There are build environments outside of the HPDD bubble. 
Yes, you will often find contents under /usr/src/kernel on a CentOS or RHEL system. But where do those files usually come from? The come from the "kernel-devel-*" package. The kernel-devel package contains header files, Makefiles, and smattering of other files.
What should be noticeably absent are the the .c files. What does Lustre need .c file for? To copy ext4's source code so that it can patch it and build ldiskfs.
So how then does a person easily obtain .c files for a CentOS kernel? That person runs "yum install kernel-debuginfo".
Great! Now we've got everything we need to build lustre, including ldiskfs.
Some of us have been building Lustre this way, or something similar, for many years.
Pretty soon we're hoping to go full patchless kernel for servers (see LU-20), and this kind of build pattern will become more of the norm rather than the exception.
Christopher,
Most of the build methods and environments i know of get additional needed sources by installing and expanding the kernel .src rpm, not by installing kernel-debuginfo. Not claiming that what you say is invalid, just saying that I haven't run into it.
Bob, actually, no normal kernel modules should ever need to install the kernel .src rpm. The vast majority of modules are going require the kernel-devel and be perfectly happy with just that. Lustre is almost entirely happy (or should be) with kernel-devel as well. The only problem is ldiskfs.
ldiskfs is, of course, very unusual. It isn't a complete kernel module on its own. The lustre tree needs to go make a copy of the ext4 source and then apply a bunch of patches to turn it into the ldiskfs source code. Then it can actually do the build.
This is problematic because with rpms there is no way (to the best of my knowledge) to express a dependency on a .src.rpm package!
So how, on an rpm-based system would you make the lustre .src.rpm express this odd dependency on the kernel .src.rpm? You pretty much can't.
So while it is kind of dirty in its own right, the best that we have come up with at LLNL is to make the lustre .src.rpm BuildRequires the kernel-debuginfo package.
Oleg Drokin (oleg.drokin@intel.com) merged in patch http://review.whamcloud.com/19248/
Subject: LU-7961 build: Fix ldiskfs source autodetect for CentOS 6
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 2ad5491d6822bd2e813c4e428aee987e71781713
Patch has landed to master for 2.9.0