On Mon, 21 Jun 2010, Chuck Lever wrote: > > /* > > + * FIXME: currently, the RPC layer will allocate the maximum buffer size > > + * here for each call (which can be ~ 64k). The Labeled NFS prototype code > > + * uses 4k, although we should not impose limits for NFS which don't exist > > + * in the OS unless absolutely necsssary. We likely need a dynamic scheme > > + * here, possibly using pages. > > + */ > > Encoding directly into RPC buffers is usually only for small objects, a few > hundred bytes at most. What are the challenges to using the page cache for > these right now? We already do that for symlinks and ACLs, right? There's nothing stopping it -- the code just needs to be written that way. > Is there a way the server can advertise a size limit for these objects, > similar to rsize and wsize? I guess we could add this, although most xattrs are quite small anyway, with upper limits defined by the OS (and then likely the same defined in the protocol). > > +/* > > + * Special case of xdr_encode_opaque, where the xattr helpers hand us > > + * separate namespace and name buffers, which we encode as a single XDR > > + * string over the wire. Neither namespace nor name may be empty or null. > > + */ > > +static __be32 *xattr_encode_name(__be32 *p, const char *namespace, const > > char *name) > > By convention this function would be called "xdr_encode_xattr_name()". Ok. > > Are these names going to be UTF-8 strings? I believe so. > > +#define NFS_XATTR_PROGRAM 391063 /* TODO: find another value */ > > RFC 5531, appendix B proscribes the appropriate method for requesting an RPC > program number assignment. > > Even though the NFSACL protocol doesn't have one, I have to agree with Deniel > that we should have the RPCL definition of the on-the-wire protocol first, so > we can review it and ensure our user space and kernel XDR functions remain > consistent and correct over time. Indeed, this is something I'm hoping to do soon. > Is there an RFC? No, there have been several implementations, but never an RFC for xattrs. I'm using the XFS implementation as a starting point, and following the ACL model of implementing a side-protocol. > Especially if we expect non-Linux implementations, I would think an > IANA-assigned program number and a proper RPCL definition would be apriori > requirements. It's possible the FreeBSD folk may want to interop with this, as they have similar name/value xattrs. (Btw, slides from a presentation I did on this last year at LinuxCon are at http://namei.org/presentations/linuxcon09_nfsv3xattrs.pdf) Thanks for reviewing the code! -- James Morris <jmorris@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
