I will need to disagree with the assertion regarding XDR and the packed struct. XDR can handle a versioned struct very neatly. It can do so just as easily as text string parsing and with greatly reduced overhead. Ps -----Original Message----- From: Jeff Layton [mailto:jlayton@xxxxxxxxxx] Sent: Wednesday, December 21, 2011 5:28 PM To: Peter Staubach Cc: Chuck Lever; bfields@xxxxxxxxxxxx; steved@xxxxxxxxxx; linux-nfs@xxxxxxxxxxxxxxx Subject: Re: [PATCH v3 4/5] nfsd: add a header describing upcall to nfsdcld On Wed, 21 Dec 2011 17:04:02 -0500 Peter Staubach <pstaubach@xxxxxxxxxxx> wrote: > By text based, you don't really mean encoding the binary structure as a string of ascii hex bytes, right? Bleah. > > I would suggest that XDR encoding seems quite natural to use when passing binary structs around. > No, I was thinking along the lines of encoding the struct fields as key/value pairs in a string: "ver=1,cmd=create,clname=0x1a012bd..." ...binary stuff like the nfs_client_id4 would be hex encoded. Integers would be converted to text representations, etc. I think if we're going to go to the trouble of encoding this stuff at all, it makes sense to do it in as flexible a manner as possible. Now that I think about it, using XDR has little benefit over the current packed binary struct. If we ever need to rev the format, it'll be just as much of a pain. With key/value pairs, we should be able to ensure that a mismatch between kernel and userspace versions is more easily dealt with. > > -----Original Message----- > From: linux-nfs-owner@xxxxxxxxxxxxxxx > [mailto:linux-nfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Jeff Layton > Sent: Wednesday, December 21, 2011 4:59 PM > To: Jeff Layton > Cc: Chuck Lever; bfields@xxxxxxxxxxxx; steved@xxxxxxxxxx; > linux-nfs@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v3 4/5] nfsd: add a header describing upcall to > nfsdcld > > On Wed, 21 Dec 2011 16:48:10 -0500 > Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > On Wed, 21 Dec 2011 16:37:30 -0500 > > Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > > > > > > > On Dec 21, 2011, at 4:33 PM, Jeff Layton wrote: > > > > > > > On Wed, 21 Dec 2011 15:45:01 -0500 Chuck Lever > > > > <chuck.lever@xxxxxxxxxx> wrote: > > > > > > > >> > > > >> On Dec 21, 2011, at 3:34 PM, Jeff Layton wrote: > > > >> > > > >>> The daemon takes a versioned binary struct. Hopefully this > > > >>> should allow us to revise the struct later if it becomes necessary. > > > >> > > > >> This breaks the pattern of using text-based up- and downcalls in NFSD. I assume this is binary because nfs_client_id4 is a string of opaque bytes? > > > >> > > > > > > > > That's the main reason. We could, of course encode that string > > > > in hex or something, and decode it on the other end. No one has > > > > presented a strong argument for doing it that way as of yet though. > > > > > > > > If anyone feels strongly about that, then it would be helpful to > > > > have them pipe up now and state why they do... > > > > > > <pipe>Because binary data structures are difficult to work with > > > over time, which is why other NFSD user space interfaces are > > > text-based.</pipe> > > > > > > ;-) > > > > > > > *sigh* that was the sort of comments I was hoping to get out of the > > RFC postings. But ok... > > > > I'll see about respinning the whole thing with either a text-based > > or XDR-based upcall/downcall format. That'll take a while, but I'll > > see if I can get it in shape in time for 3.3. > > > > ...and while we're discussing it. Does anyone have thoughts on which would be better? I'd probably prefer a text-based format. That's more flexible but is also going to be more verbose. I think we're still well under a page with these requests even in text however so I don't really see that as a problem. > -- Jeff Layton <jlayton@xxxxxxxxxx> -- 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
