Buyer Beware: A Major Change in NFS is about to happen

[Howard Wilkinson]

Steve,

just for clarity what you are actually saying is that.
On Tue, 2009-09-29 at 22:45 -0400, Steve Dickson wrote:
> On 09/29/2009 09:42 PM, Chris Adams wrote:
> > Once upon a time, Steve Dickson <SteveD at redhat.com> said:
> >> On the server (Which is suggested):
> >>    * Add the following entry to the /etc/exports file:
> >>      / *(ro,fsid=0) Note: 'fsid=0' is explained in the exports(5) man pages.
> > 
> > The "suggested solution" is to change your NFS servers (that work just
> > fine with other clients today) to export the root filesystem to
> > everybody?
> > 
> Unfortunately the answer to your question yes... 
> 
> With version 4 there is this concept of a pseudo root. Which meanings
> one can define, through exports, what the root of an export
> can be. Which is a good idea because you can define /export as
> the root, and nothing above /export can be accessed... 
But if there is a /data *(ro,fsid=0) export then that will do, but it
becomes the root of the export tree against which mounts are made?
> 
> So the idea was to use 'fsid=0' to define the V4 root of the
> exports. Which, in theory is a good idea because you can define
> the namespace the client have access to. A feature, I believe,
> is not available in any other NFS implementation... But...  
> 
> The problem is the V4 protocol requires a pseudo root to exist. 
> So with Linux servers, if the fsid=0 export does not exist, the
> mount will die with ENOENT (or 'No such file or directory').
> 
> Other NFS implementation decided not to support a definable pseudo
> roots and they just made, under the covers, their '/' as the pseudo 
> root, along with the appropriate protections.
So putting the / *(ro,fsid=0) is only adding an export of that part of
the name space into the tree to make it compatible with pre-V4 name
spaces.
> 
> With F-12, I have added code to both the kernel and nfs-utils that will 
> do both. Allow the 'fsid=0' export to define the pseudo root and 
> make '/' the pseudo root (with the appropriate protections) when
> there is not an fsid=0 entry.
> 
> So Yes, one work around to make F-12 mounts work with Linux servers is 
> to define a pseudo root on the server with a fsid=0 export. But if
> that is not an option, you can make the F12 clients only use V3 mount
> (which would avoid the problem, but not take advantage of the
> V4 protocol) by set either setting the '-o v3' mount option or 
> set the Nfsvers=3 in the new /etc/nfsmount.conf file (which would make
> all mounts from that machine v3 mounts).
> 
But the downside of the / *(ro,fsid=0) approach is we now have all of
the root files (but not any other filing systems visible.

So perhaps a better approach would be to specify a /V4root *(ro,fsid=0)
directory being created and a bind mount for each export from the pre-V3
name space being made into that tree. Or have I missed something
entirely?

> I hope this helped...
It did!
> 
> steved.
> 
> 
-- 
Howard Wilkinson <howard at cohtech.com>
Coherent Technology Limited