On Wed, 23 Mar 2011 17:36:38 -0400 <Daniel.Muntz@xxxxxxx> wrote: > > > > -----Original Message----- > > From: linux-nfs-owner@xxxxxxxxxxxxxxx > > [mailto:linux-nfs-owner@xxxxxxxxxxxxxxx] On Behalf Of NeilBrown > > Sent: Wednesday, March 23, 2011 2:28 PM > > To: Trond Myklebust > > Cc: Staubach, Peter; bfields@xxxxxxxxxxxx; > > bjschuma@xxxxxxxxxx; linux-nfs@xxxxxxxxxxxxxxx > > Subject: Re: [PATCH 3/3] NFS: Detect loops in a readdir due > > to bad cookies > > > > On Wed, 23 Mar 2011 14:48:35 -0400 Trond Myklebust > > <Trond.Myklebust@xxxxxxxxxx> wrote: > > > > > On Wed, 2011-03-23 at 14:42 -0400, peter.staubach@xxxxxxx wrote: > > > > Although I think that it is a good thing to protect the > > client against broken servers, it does seem like the right > > solution is to get the server fixed... > > > > > > Don't get me wrong: I fully agree with that! > > > > Ack. > > > > As I understand it, ext4 (and ext3) use the hash of the > > basename as the > > cookie. This hash has a per-directory random seed which is > > hidden so it is > > not possible to deliberately create files with the same hash, > > but thanks to > > the birthday paradox it isn't too hard to get collisions in a > > suitably large > > directory. > > > > For 'readdir' ext4 keeps extra state in the 'struct file' so > > that it knows > > where it was up to in a list of names with the same hash and > > so won't return > > duplicates. > > Would it be possible to use this "extra state" to uniqify the cookie used by NFS? Having no idea what this extra state is, I'm just wildly speculating. > No, it is all hidden inside filp->private_data. It is just a linked-list of file names (see 'extra_fname' in fs/ext4/dir.c). The best you could do would be to shift the cookie up a few bits (ext4 cookies are 62 bit already!) and add a sequence counter. But I don't think that approach will really give more reliability than just trying to hide cookie-runs by making sure they don't cross from one packet to the next. NeilBrown -- 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
