Re: Wishlist: credential file update/access collision avoidance?

On Sun, Oct 02, 2011 at 01:21:58PM +0200, [email protected] wrote:
>

> [*] well, for completeness, there are scenarios (probably not of a real
> practical value for this group but anyway...) when even on Unix you do
> not have atomicity guarantees with a rename, while e.g. an "open, write,
> close" sequence is atomic for a concurrent open(). This depends on the
> file system, not all of them are posix. Of course such file systems are
> rarely used for ccaches but you never know. (Note that nothing actually
> prevents a ccache from being shared between computers.)

Well, I would say that it is completely reasonable to say that
ccaches will not correctly operate on file systems that do not
conform to the POSIX specifications because ccaches are local
credentials which should not be stored on distributed file systems.

Also, if compatibility with non-POSIX file systems is desired, then
specific implementations will have to be named such that they can
be tested against.  After all, saying ``a filesystem that does not
conform with POSIX'' without naming a specific implementation is
more or less meaningless.  What exactly does it mean for a file
system to break a few rules?  Which rules?

Generally, in these sorts of discussions, the examples would be
distributed file systems such as NFS, AFS, etc.  But, these file
systems pose different problems and frequently code will have to
have specific work-arounds for them.  And, in the case of ccaches
and keytabs, distributed file systems probably should not be used.

Replay caches, OTOH, may benefit from either being placed on
distributed filesystems.

--
    Roland Dowdeswell                      http://Imrryr.ORG/~elric/