On Fri, Sep 18, 2009 at 12:47:57PM -0400, William A. (Andy) Adamson wrote: > On Mon, Sep 14, 2009 at 3:03 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > On Fri, Sep 11, 2009 at 06:52:55PM -0400, andros@xxxxxxxxxx wrote: > >> From: Andy Adamson <andros@xxxxxxxxxx> > >> > >> Both the max request and the max response size include the RPC header with > >> credential (request only) and verifier as well as the payload. > >> > >> The RPCSEC_GSS credential and verifier are the largest. Kerberos is the only > >> supported GSS security mechansim, so the Kerberos GSS credential and verifier > >> sizes are used. > > > > Rather than trying to estimate this is might be simplest just to use > > what the server's using to allocate memory: RPCSVC_MAXPAGES. No, that > > also takes into account space for the reply. You could do > > > > PAGE_SIZE * (1 + (RPCSVC_MAXPAYLOAD+PAGE_SIZE-1)/PAGE_SIZE) > > > > Actually, by design the server's real limit is actually on the sum of > > the request and the reply sizes. > > I think the actual limit is svc_max_payload rounded up to a multiple > of PAGE_SIZE plus PAGE_SIZE. which is a lot smaller than the sum of > the request and reply sizes. See below. Right. I think you're agreeing with me? > Note that svc_max_payload is what is returned in nfs4_encode_fattr for > MAXREAD and for MAXWRITE. These attributes use svc_max_payload in the > same way this patch does - the maximum data size not including rpc > headers. > > I don't think the server wants is to advertise a MAXREAD/WRITE that it > can't supply because the fore channel maxrequest/maxresponse is too > small, so some additional space needs to be added to svc_max_payload > for the fore channel. Yes. > > What happens if we get a request such that both the request and reply > > are under our advertised limits, but the sum is too much? Can we just > > declare that no client will be that weird and that we shouldn't have to > > worry about it? > > I think the server already has this problem. In svc_init_buffer which > sets up the pages for a server thread request/response handling, it > uses sv_max_mesg / PAGE_SIZE + 1 with the comment > > "extra page as we hold both request and reply. We assume one is at > most one page" > > where > sv_max_mesg = roundup(serv->sv_max_payload + PAGE_SIZE, PAGE_SIZE). Right. The difference is that now it looks to me like we're actually going to start promising that we support the large request + large response case, when actually we don't. I guess the problem's unlikely to arise, so maybe it's not worth fixing. But it's annoying to have yet another undocumented restriction on the compounds we'll accept. --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
