Proposal for new lock ownership scheme to support NFS over distributed filesystems

[Juan Gomez <juang@us.ibm.com>]

Hello all,

As a prelude to adding support in kNFS(lockd) to pass lock information via
the VFS interface I want to firsr propose some minor changes that will
enable us to have a single lock ownership space that is shared and enforced
at all nodes.

Currently lockd identified range locks with two fields fl_owner and fl_pid.
NFS code places a memory pointer (pointer to host structure representing
NFS client holding the lock) in fl_owner which works great in single node
NFS but breaks when we attempt to pass lock requests to an the underlying
distributed filesystem in the context of a clustered NAS head. This can be
easily fixed by filling fl_owner field with the IP address of the NFS
client requesting the lock, which is just a minor patch.

The patch above, however, does not fix all our problems as locks acquired
locally in the NFS server nodes could collide with NFS locks. Currently,
the fl_owner field for locks acquired via the local file system is filled
with another memory pointer (i.e. current->files). This also breaks appart
when using a distributed file system. My proposal for this would be use a
local IP address to put in the fl_owner field of locks acquired locally in
a node.

These two patches cause no problem for current single node NFS servers and
enable Linux as a platform to support distributed filesystems and NFS
serving simultaneously and correctly.

I would like to get your feedback on this proposal and if accepted as it is
I will later follow with patches for current versions of the kernel NFS.


Regards, Juan