[OpenAFS] best practice for salvage

[Jeffrey Altman]

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John Hascall wrote:
>>>> Since the file server has no way of knowing if the file is still in
>>>> use it can't delete it.
> 
>>>    Why not?  Is there no way for the file server to query the
>>>    cache manager and ask?
> 
>> The fact that the file is considered temporary is only known to the
>> client.
> 
>      And to salvager :)

No, the salvager does not know it is temporary.  The salvager simply
deletes any files that begin with .__afs which means that if I have
to be using trading software from the American Foundry Society or 
Associated Food Stores and the application happens to use hidden 
configuration files called .__afsConfig you are erasing the 
configuration file each time you run salvager.

>      So, the client has opened the file.  Doesn't this mean the
>      the fileserver has a callback for this file/client?  Then
>      the fileserver sees a RENAME op to the magic .__afsNNNN
>      name.  Seems to me like it might be possible to pervert
>      the callback to check up on the client/file.

All it means is that at one point the client registered a callback.
It does not mean that there always will be a callback.   Callbacks
are flushed by the file server when the callback table runs out of
room.  The status cache objects might be flushed by the cache manager
even if the file is still open according to the operating system
because it hasn't been written to in a while.

>      Your idea seems less icky. Besides typically the client
>      just wrote the file, so it probably has most or all of it
>      in it's cache anyway.  BUT, what do you do when it is
>      too big to be entirely cached by the client?

don't cache it.  leave it on the file server.

The point is that only the client knows what is safe to delete.
It would be exactly the same if an application left temporary files
behind on the local disk if it crashed before they were deleted.

Only someone with knowledge of the application and the context
in which the files were left behind could 100% know that it was
safe to delete them.




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