[OpenAFS-devel] question: binary interface to kernel module (RHEL6.2/6.3, openafs 1.6.1)?

[Stephan Wiesand]

Hi All,

this is just a question. I'm not asserting an openafs bug.

Since SL6, we have we have been using "kABI tracking kmods" for =
installing the OpenAFS kernel module on clients. For full information on =
this mechanism, see =
http://people.redhat.com/jcm/el6/dup/docs/dup_book.pdf . In short, you =
only have to compile and install the module once, and it will be used =
with future kernels as long as it doesn't use parts of the ABI that =
changed.

Trying this may have been stupid in the first place. If so, happy =
bashing :-)

But in practice, it has worked perfectly for a long time. The modules =
built against the EL6 GA kernel (2.6.32-71.el6) work fine with every =
released kernel up to the latest EL6.2 kernels (2.6.32-220.23.1.el6), on =
both 32-bit and 64-bit systems.

But with the EL6.3 update (2.6.32-279.el5), something changed that broke =
at least the interface to the 32-bit module. The symptoms are reads =
getting stuck at the very beginning, except for very small files. The =
reads can be interrupted, but the client can no longer be stopped =
cleanly.

Using a module built against the 6.3 kernel with pre-6.3 ones has worse =
effects. BUGs, panics, spontaneous reboots.

All this was only observed on 32-bit systems, and only if the cache is =
on ext4. I have a suspicion that it might be related to a change =
described here: =
http://joejulian.name/blog/glusterfs-bit-by-ext4-structure-change/ . =
Quote: << a patch against ext4 to "return 32/64-bit dir name hash =
according to usage type". Prior to that, ext2/3/4 would return a 32-bit =
hash value from telldir()/seekdir() [. . .] That patch was for kernel =
v3.3-rc2. To make things more fun, [. . .] merged in that patch in =
2.6.32-268.el6 >>

The direct link to the patch is =
http://git.kernel.org/?p=3Dlinux/kernel/git/stable/linux-stable.git;a=3Dco=
mmit;h=3Dd1f5273e9adb40724a85272f248f210dc4ce919a .

Does anyone familiar withe the openafs module's inner workings see =
whether that patch would have the effects described above, on 32-bit =
systems only?

Thanks a lot in advance for any insights.

	Stephan


--=20
Stephan Wiesand
DESY - DV -
Platanenallee 6
15732 Zeuthen, Germany