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SubjectRe: How to manage shared persistent local caching (FS-Cache) with NFS?
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On Wed, 2007-12-05 at 17:11 +0000, David Howells wrote:
> The downside of this is that each shared superblock only has one NFS connection
> to the server, and so only one set of connection parameters can be used.
> However, since persistent local caching is novel to Linux, I think that it is
> entirely reasonable to overrule the attempts to make mounts with different
> parameters if they are to be shared and cached.

I think the shared superblock approach is the right one, but I'm a
little concerned that there would now be different behavior for fscache
and non-cached setups. Not sure of any better idea though.

> The R/O mount flag can be dealt with by moving readonlyness into the vfsmount
> rather than having it a property of the superblock. The superblock would then
> be read-only only if all its vfsmounts are also read-only.

Given that, how many connection parameters are there that are likely to
actually differ on the same client, talking to the same server? Really?

> Would it be reasonable to have an outside way of setting directory options?
> For instance, if there was a table like this:
>
> FS SERVER VOLUME DIR OPTIONS
> ======= ======= ======= =============== =========================
> nfs home0 - /home/* fscache
> afs redhat data /data/* fscache
>
> This could then be loaded into the kernel as a set of rules which directory
> lookup by the filesystem involved could attempt to match and apply.

You could store the table in a NIS map, for example, and a udev rule or
similar could trigger to load it later.

Jon.




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