From: "J. Bruce Fields" Subject: Re: [RFC] Reinstate NFS exportability for JFFS2. Date: Sat, 2 Aug 2008 17:33:38 -0400 Message-ID: <20080802213337.GA2833@fieldses.org> References: <76bd70e30807311753m2785c6d3kd82edd1fe8b5f8b7@mail.gmail.com> <1217552437.3719.30.camel@shinybook.infradead.org> <76bd70e30807311831p771d0f1eia3e303bd84919422@mail.gmail.com> <1217597759.3454.356.camel@pmac.infradead.org> <1217598976.3454.359.camel@pmac.infradead.org> <76bd70e30808010905j3010a6bfy534c068a662d348d@mail.gmail.com> <1217607571.3454.417.camel@pmac.infradead.org> <76bd70e30808011047u3cd0a56cg3b2d62e01afed014@mail.gmail.com> <20080802182644.GE30454@fieldses.org> <1217709752.2500.5.camel@shinybook.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: chucklever@gmail.com, viro@zeniv.linux.org.uk, Neil Brown , Christoph Hellwig , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-mtd@lists.infradead.org To: David Woodhouse Return-path: In-Reply-To: <1217709752.2500.5.camel@shinybook.infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Sat, Aug 02, 2008 at 09:42:32PM +0100, David Woodhouse wrote: > On Sat, 2008-08-02 at 14:26 -0400, J. Bruce Fields wrote: > > Could you add a readdirplus vfs operation which took a flag indicating > > how much extra information you're going to need? > > Actually, if we're screwing with readdir then xfs would like to know how > much it's going to be asked to read, rather than just have the filldir > callback return zero when it's done. OK. > > The three cases where readdir can be called are: > > - ordinary readdir, for which the existing filldir_t provides > > all the information needed. > > - nfsv3 readdirplus, where the only additional information > > needed is whether there's a mountpoint. > > It also wants a file handle. Oops, right. > For which I think it just needs > i_generation in addition to the information it already has. Typically, right, though the filesystem's allowed some choice about what exactly it wants to use in the filehandle. I don't know how the various filesystems are actually using that in practice. > > - nfsv4 readdir, where we may need all the stat info, acls, > > etc., etc. > > We _might_, but most of the time we won't. It might be OK to fall back > to the existing double-buffer hack for the cases where we _do_ need that > extra information. How bad is the "double-buffer hack" anyway? Rather than have this as a fallback case that's rarely used (hence rarely tested), it might be simpler just to use it for everything if we're going to use it at all. --b. > I think a ->lookup_fh() method (which _expects_ to be called from within > filldir, and hence does its locking automatically) is the way to go. > > One alternative might just be a full lookup method with the same locking > rules: ->lookup_locked(). That might be easier to implement, and would > solve the problem even for the corner cases of NFSv4. Although I still > think we'd do best to avoid populating the inode cache with _all_ > children when we do a readdirplus. > > -- > David Woodhouse Open Source Technology Centre > David.Woodhouse@intel.com Intel Corporation >