[PATCH][WIP] Make vfs_acl_xattr use hash of the posix ACL

[Volker Lendecke]

On Sat, Oct 13, 2012 at 04:27:10PM -0400, simo wrote:
> On Sat, 2012-10-13 at 15:09 +1100, Andrew Bartlett wrote:
> > On Fri, 2012-10-12 at 17:53 -0400, simo wrote:
> > 
> > > Sorry I am afraid you didn't explain why it is ok to keep mappings on
> > > disk that do not match anymore.
> > 
> > Thinking about this some more, we can now do that.  We can confirm if
> > the mapping NT -> posix has changed (because we have stored the result
> > of that), as well as tell if the posix ACL itself has changed, or
> > (because I store both hashes) the posix ACL is unchanged but the posix
> > -> NT mapping has changed.
> > 
> > We couldn't do that before, all we would know is that *either* the posix
> > -> NT mapping (which is the mapping this module is specifically trying
> > to avoid returning to the client) has changed, or the the posix ACL has
> > changed. 

I haven't fully followed this discussion, so excuse me if
I'm talking rubbish here and just ignore me...

To be really correct, I think we need to properly version
the NT SD in the acl_xattr module and provide upgrade
routines. Whenever we change the mapping code, a new version
is created. I know upgrade routines are really a pain, but
if we want data on disk to remain valid across versions, I
think this is the only way to avoid horrible confusion with
multiple hashes and their different meanings.

Volker

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