[Gluster-devel] Need for -o remount support for FUSE mount

[Deepak Shetty]

Hi List,
   As i understand, currently we don't support -o remount for glusterfs
FUSE mounts.
It would be good to add this support and I wanted to describe an openstack
cinder usecase that will benefit from it. I am sure in general having -o
remount (with whatever options we can support) is beneficial. NFS supports
it (in a limited way)

Usecase:

     Today cinder uses gluster fuse mount and if someone changes some -o
option in the conf file (after cinder service was started) there is no way
to do -o remount (for the -o options to take effect) as gluster doesnt
support it.  Here we are not even looking at supporting addnl -o options,
we just need to do -o remount on whatever was present on the existing mount
point.

        Ideally when cinder service is restarted the gluster mount shud be
taken down and remounted but that doesn't happen today as cidner doesn't
yet have a gracefull framework to do cleanups for the backend drivers

       Even if it comes in future.. unmounting and remounting would break
the in-flight I/O so if we support -o remount (with whatever options we
can.. even NFS supports it case by case basis) we can do a remount on the
fly w/o the need to do cinder service restart which means no breaks for
inflght I/O. Breaks in inflight I/O also means nova instance will
epxerience timeouts and in extreme case will error out.

Thoughts ?

thanx,
deepak
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