The ldiskfs_dirhash() function is only used by the ldiskfs osd. Since this functionality was originally copied from ldiskfs it makes sense to remove it entirely and rely on the ldiskfs implementation.

Normally this symbol isn't exported but since we are already patching ldiskfs exporting it for use is trivial. This is currently done with the following ldiskfs patch for rhel6.

ldiskfs/kernel_patches/patches/ext4-osd-iam-exports-rhel6.patch