On Mon, Aug 13, 2012 at 04:40:39PM +0000, Myklebust, Trond wrote: > On Mon, 2012-08-13 at 15:55 +0100, Jim Vanns wrote: > > Hello NFS hackers. First off, fear not - the attached patch is not > > something I wish to submit to the mainline kernel! However, it is > > important for me that you pass judgement or comment on it. It is small. > > > > Basically, I've written the patch solely to workaround a Bluearc bug > > where it duplicates fileids within an fsid and therefore we're not able > > to rely on the fsid+fileid to identify distinct files in an NFS > > filesystem. Some of our storage indexing and reporting software relies > > on this and works happily with other, more RFC-adherent > > implementations ;) > > > > The functional change is one that modified the received fileid to a hash > > of the file handle as that, thankfully, is still unique. As with a > > fileid I need this hash to remain consistent for the lifetime of a file. > > It is used as a unique identifier in a database. > > > > I'd really appreciate it if you could let me know of any problems you > > see with it - whether it'll break some client-side code, hash table use > > or worse still send back bad data to the server. > > > > I've modified what I can see as the least amount of code possible - and > > my test VM is working happily as a client with this patch. It is > > intended that the patch modifies only client-side code once the Bluearc > > RPCs are pulled off the wire. I never want to send back these modified > > fileids to the server. > > READDIR and READDIRPLUS will continue to return the fileid from the > server, so the getdents() and readdir() syscalls will be broken. Since > READDIRPLUS does return the filehandle, you might be able to fix that > up, but plain READDIR would appear to be unfixable. > > Otherwise, your strategy should in principle be OK, but with the caveat > that a hash does not suffice to completely prevent collisions even if it > is well chosen. > IOW: All you are doing is tweaking the probability of a collision. Also: the v4 rfc's allow two distinct filehandles to point to the same file, don't they? (See e.g. http://tools.ietf.org/html/rfc5661#section-10.3.4). --b. -- 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
