Hello!
Right now NFSD depends on FS_REQUIRES_DEV to be set in sb->s_type->fs_flags
or manually set fsid= in /etc/exports in order to export filesystem.
But there are non-device based filesystems (Lustre for example ;) ) that
would like to be exported via NFS without guiding users through this
fsid= business. Of course it is easy to cheat through by setting
FS_REQUIRES_DEV, but this does not solve entire problem. While allowing
for single-node export of filesystem to work ok, more generic problem of
exporting same filesystem from several NFS servers in clustered manner
won't work because sb->s_dev might be different on different nodes.
This is not only Lustre problem, I believe same problem will happen
with GFS or OCFS2 or whatever other SAN-based fs if different nodes
have different device names (/dev/sda | /dev/sdb) for same SAN device,
in such a case fsid calculated would be different on different nodes too.
I wonder if e.g. another export op could be introduced to ask filesystem
for its unique id (if supported) and use that instead of sb->s_dev in
fsid calculations. Does this look sane?
I hope I am not missing anything?
Or are there better ideas?
Thanks.
Bye,
Oleg
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