On Thu, 2011-08-04 at 13:30 -0400, J. Bruce Fields wrote: > On Thu, Aug 04, 2011 at 01:21:32PM -0400, Trond Myklebust wrote: > > On Thu, 2011-08-04 at 13:03 -0400, J. Bruce Fields wrote: > > > On Thu, Aug 04, 2011 at 09:48:32AM -0700, Myklebust, Trond wrote: > > > > > -----Original Message----- > > > > > From: J. Bruce Fields [mailto:bfields@xxxxxxxxxxxx] > > > > > Oh, neat, I'd forgotten that; you're thinking of STATUS4_FIXED? But > > > > > I'm > > > > > not sure it does the job: > > > > > > > > > > STATUS4_FIXED, which indicates a read-only image in the sense > > > > > that it will never change. The possibility is allowed that, as > > > > > a result of migration or switch to a different image, changed > > > > > data can be accessed, but within the confines of this instance, > > > > > no change is allowed. The client can use this fact to cache > > > > > aggressively. > > > > > > > > > > OK, so permission to set your attribute cache timeout very high, > > > > > perhaps, but I don't see why "changed data" couldn't mean changed > > > > > paths.... > > > > > > > > No, but you can presumably use the FSLI4BX_CLSIMUL flag from > > > > fs_locations_info in order to find an equivalent replica. > > > > > > I lost you. > > > > > > Actually my real problem is that I don't understand the description of > > > STATUS4_FIXED. What does "or switch to a different image" mean? Not > > > "migration", or the sentence would have ended before the "or". > > > > > > I read it as allowing a server admin to replace the filesystem image in > > > place, in which case from the client's point of view this allows the > > > filesystem to change at any time. Which makes the whole thing not > > > terribly useful, except (as the last sentence says) as a caching hint. > > > > If the server admin replaces one filesystem, with a different > > filesystem, then nothing is going to work anyway. I don't see how that > > is relevant. That's a case of 'doctor it hurts...' > > > > The bit that _is_ relevant is the 'migration' part, but since the > > fs_locations_info FSLI4BX_CLSIMUL flag allows you to conclude that > > replica is an exact replica at all times (i.e. contents are guaranteed > > to be the same even if filehandles, directory cookies, etc are not) then > > the STATUS4_FIXED flag does allow you to assume that paths have not > > changed. > > So you're position is that "or switch to a different image" in the above > is redundant, or just a mistake? It's redundant: STATUS4_VERSIONED, STATUS4_UPDATED, STATUS4_WRITABLE, and STATUS4_REFERRAL are also subject to the 'or switch to a different image' caveat. -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
