Re: NFSv4 pseudo filesystem

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <Pine.SOL.4.44.0205101340370.27306-100000@mspacman.gpcc.itd.umich.edu>
By author:    "Kendrick M. Smith" <kmsmith@umich.edu>
In newsgroup: linux.dev.fs.devel
> 
> Background: In NFSv2/v3, the server's exports are more or less independent
> of each other, and must be mounted seperately by the client.  NFSv4
> introduced the requirement that the server must export a 'root filehandle'
> (which must be a directory), and that all the exports be obtainable by
> browsing the subtree rooted at the root filehandle.  In other words, the
> server must present the client with ficticious directories, which live
> above the exports and serve to tie them all together into one tree.  (The
> term "pseudo filesystem" is used to refer to this collection of ficticious
> directories.)
> 
>   Proposal 1: Have the server export a pseudofs which "mirrors" the actual
>   namespace on the server, or at least enough of it to cover all the
>   exports.  In other words, if the server's exports are named
>   /home/kmsmith and /usr/local/src, then the server will present the
>   client with the following pseudo filesystem:
> 
>                              /
>        /home                                 /usr
>        /home/kmsmith                         /usr/local
>           ...                                /usr/local/src
>                                                   ...
> 
> 
> This is the approach suggested by RFC3010 for Unix servers, but it
> seems like a nice feature to relax the requirement that pathnames in
> the pseduofs be the same as pathnames in the server's filesystem.
> The next 2 proposals allow the possibility of setting up an
> arbitarily-named tree of ficticious directories, for the server
> to export as the pseudofs.  (This would require changing the
> /etc/exports file format, presumably in a backward-compatible way,
> such as adding an export option pseudo_pathname=...)
> 

I would really like to suggest making it possible to map these
arbitrarily, although the default should presumably be the "real"
path.

This, in fact, applies to NFSv2/v3 as well: the path that you want to
mount a client with shouldn't need to be so closely tied to the path
on the physical filesystem.

For example, I should be able to specify something like:

/exports/clients/dorkface/ready \
	somehost.bigcorp.com(ro,path=/clients/bigcorp) \
	*.mycorp.com(rw)

... and have somehost.bigcorp.com mount this filesystem as
myhost.mycorp.com:/clients/bigcorp whereas my own local hosts would
see it as /export/clients/dorkface/ready.

	-hpa

-- 
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"Unix gives you enough rope to shoot yourself in the foot."
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