On Tue, Sep 21, 2021 at 02:39:39PM +0000, Chuck Lever III wrote: > > On Sep 21, 2021, at 10:32 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > +It is possible to reexport an NFS filesystem over NFS. However, this > > +feature comes with a number of limitations. Before trying it, we > > +recommend some careful research to determine wether it will work for > > +your purposes. > > ^wether^whether Fixed. > > + > > +A discussion of current known limitations follows. > > + > > +"fsid=" required, crossmnt broken > > +--------------------------------- > > + > > +We require the "fsid=" export option on any reexport of an NFS > > +filesystem. > > Recommended approach? I would just say use 'uuidgen -r' Looking at the manual.... I'd somehow missed that fsid= would take a uuid (and not just a small integer) now. So, sure, I'll add that as a suggestion. Longer term I wonder if it would work to do this automatically for new nfs reexports. The annoying part is you'd have to keep the fsid= argument on disk somehow, either by modifying the export configuration in /etc or by keeping them on the side somewhere. That'd fix crossmnt too. > > +The "crossmnt" export option does not work in the reexport case. > > Can you expand on this a little? Consequences? Risks? crossmnt doesn't propagate fsid= (for obvious reasons), so if you cross into another nfs filesystem then it'll fail. Actually if you just had disk filesystems mounted underneath it'd probably work. > > +Reboot recovery > > +--------------- > > + > > +The NFS protocol's normal reboot recovery mechanisms don't work for the > > +case when the reexport server reboots. Clients will lose any locks > > +they held before the reboot, and further IO will result in errors. > > +Closing and reopening files should clear the errors. > > Any recommended workarounds? Or does this simply mean that > administrators need to notify client users to unmount (or > at least stop their workloads) before rebooting the proxy? I think so. If you don't use any file locking or delegations I suppose you're also OK. Delegations might be useful, though. I'd expect reexport to be useful mainly for data that changes very rarely, if that helps. --b. diff --git a/Documentation/filesystems/nfs/reexport.rst b/Documentation/filesystems/nfs/reexport.rst index 892cb1e9c45c..ff9ae4a46530 100644 --- a/Documentation/filesystems/nfs/reexport.rst +++ b/Documentation/filesystems/nfs/reexport.rst @@ -6,7 +6,7 @@ Overview It is possible to reexport an NFS filesystem over NFS. However, this feature comes with a number of limitations. Before trying it, we -recommend some careful research to determine wether it will work for +recommend some careful research to determine whether it will work for your purposes. A discussion of current known limitations follows. @@ -15,9 +15,12 @@ A discussion of current known limitations follows. --------------------------------- We require the "fsid=" export option on any reexport of an NFS -filesystem. +filesystem. You can use "uuidgen -r" to generate a unique argument. -The "crossmnt" export option does not work in the reexport case. +The "crossmnt" export does not propagate "fsid=", so it will not allow +traversing into further nfs filesystems; if you wish to export nfs +filesystems mounted under the exported filesystem, you'll need to export +them explicitly, assigning each its own unique "fsid= option. Reboot recovery ---------------
