osd_io code seems to be using struct fiemap_extent's fi_extents_start field directly even though it has __user qualifier.
We then pass this buffer straight into inode's fiemap method that does assume the pointer is userspace which is boind to break on some conigurations.

We need to at least set ds to kernel_ds to have it working,
or find some other wayst to call into fiemap code with kernelspace buffers.

Offending functions are osd_fiemap_get() and osd_is_mapped()