Currently, any attempt to map a file shared writable gets ENOSYS. The function gfs_file_mmap() has a define
which is not on by default "GFS_SHARED_WRITEABLE_MMAP". We should fully support this capability.
Unfortunately, GFS does not do locking at the page level at this point. We either need to do that or for the time
being verify and enable the current code even if performance is poor. I don't know if the gfs_shared_mmap() code
For SSI we are using GFS as a shared root filesystem. The rpm command doesn't work until this is fixed.