Linux compat 2.6.37, invalidate_inodes()

Linux compat 2.6.37, invalidate_inodes()

In the 2.6.37 kernel the function invalidate_inodes() is no longer
exported for use by modules.  This memory management functionality
is needed to invalidate the inodes attached to a super block without
unmounting the filesystem.

Because this function still exists in the kernel and the prototype
is available is a common header all we strictly need is the symbol
address.  The address is obtained using spl_kallsyms_lookup_name()
and assigned to the variable invalidate_inodes_fn.  Then a #define
is used to replace all instances of invalidate_inodes() with a
call to the acquired address.  All the complexity is hidden behind
HAVE_INVALIDATE_INODES and invalidate_inodes() can be used as usual.

Long term we should try to get this, or another, interface made
available to modules again.