On Thu, Feb 3, 2011 at 9:52 AM, Tommi Virtanen
<tommi.virtanen@xxxxxxxxxxxxx> wrote:
> On Thu, Feb 03, 2011 at 09:29:32AM -0800, Sage Weil wrote:
>> Which leaves us with a final problem: what if the fh is generated for
>> /foo/bar, but bar is renamed to /baz/bar, bar drops out of all caches, and
>> the client tries to use the fh. We're still stuck with ESTALE in that
>> case. The only real solution there is to include a backpointer on the
>> file's data object. This is doable, but comes at a cost. We could make
>> it optional, and/or mitigate it somewhat (backpointer is only created once
>> a file is renamed, or something like that).
>>
>> I'm not really sure to what lengths a server is supposed to go to avoid
>> ESTALE. I seem to remember that NFSv4 has a different class of fh's that
>> are allowed to expire. I'm not sure how that helps, though; it seems
>> likeif a client has a file open that is renamed by another node and then
>> idle for long enough and then tries to read it'll still be screwed,
>> regardless of what the server does/does not promise the client.
>
> NFSv4 volatile filehandles move away from the whole "stale"
> terminology into "expiring" filehandles, which a client SHOULD recover
> from, and that's said with fairly strong language in RFC3530. The
> volatile filehandles may go away at any moment (for FH4_VOLATILE_ANY).
>
> The RFC suggests clients remember the full path of every volatile
> filehandle, and points out that doesn't let you recover if someone
> else renamed the file.. which means your "final problem" above is
> still a problem, and smells unavoidable. But at least shifting
> responsibility for remembering the path to the client makes recovery
> easy in the typical case.
>
> If the real-world support is there, I'd say NFSv4 is the way to go,
> for future Ceph re-exporting.
I was playing around with implementing this. I was trying to get the
ceph client's export functions to return NFS4ERR_FHEXPIRED instead of
ESTALE (hoping that my nfs4 clients would then attempt the full lookup
again). I noticed also that the mds itself can also return an ESTALE
to the ceph kernel client, which seems to be getting propagated back
to the NFS client. I'm wondering where I could intercept that and
send back an expiry notice?
-Brian
>
> --
> :(){ :|:&};:
>
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