From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 66F92CCA47A for ; Thu, 16 Jun 2022 10:23:34 +0000 (UTC) Received: from localhost ([::1]:39774 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o1mez-0001Sk-El for qemu-devel@archiver.kernel.org; Thu, 16 Jun 2022 06:23:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39016) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o1mZk-0005Qf-Q0 for qemu-devel@nongnu.org; Thu, 16 Jun 2022 06:18:10 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:57218) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o1mZg-0008TE-IP for qemu-devel@nongnu.org; Thu, 16 Jun 2022 06:18:06 -0400 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-448-38z1qM-ANI2pIvzrZmncTQ-1; Thu, 16 Jun 2022 06:18:00 -0400 X-MC-Unique: 38z1qM-ANI2pIvzrZmncTQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C388C1C14489; Thu, 16 Jun 2022 10:17:59 +0000 (UTC) Received: from bahia (unknown [10.39.193.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 47BF32166B26; Thu, 16 Jun 2022 10:17:59 +0000 (UTC) Date: Thu, 16 Jun 2022 12:17:57 +0200 From: Greg Kurz To: Christian Schoenebeck Cc: qemu-devel@nongnu.org Subject: Re: [PATCH v4 5/7] 9pfs: fix 'Twalk' to only send error if no component walked Message-ID: <20220616075217.087941be@bahia> In-Reply-To: <9146815.PM5Uiz2McI@silver> References: <20220615175249.21c497f3@bahia> <9146815.PM5Uiz2McI@silver> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Received-SPF: softfail client-ip=205.139.111.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 15 Jun 2022 18:36:46 +0200 Christian Schoenebeck wrote: > On Mittwoch, 15. Juni 2022 17:52:49 CEST Greg Kurz wrote: > > On Tue, 15 Mar 2022 11:08:39 +0100 > > > > Christian Schoenebeck wrote: > > > Current implementation of 'Twalk' request handling always sends an > > > 'Rerror' > > > > > > response if any error occured. The 9p2000 protocol spec says though: > > > " > > > If the first element cannot be walked for any reason, Rerror is > > > returned. > > > Otherwise, the walk will return an Rwalk message containing nwqid qids > > > corresponding, in order, to the files that are visited by the nwqid > > > successful elementwise walks; nwqid is therefore either nwname or the > > > index > > > of the first elementwise walk that failed. > > > " > > > > > > http://ericvh.github.io/9p-rfc/rfc9p2000.html#anchor33 > > > > > > For that reason we are no longer leaving from an error path in function > > > v9fs_walk(), unless really no path component could be walked successfully > > > or if the request has been interrupted. > > > > > > Local variable 'nwalked' counts and reflects the number of path components > > > successfully processed by background I/O thread, whereas local variable > > > 'name_idx' subsequently counts and reflects the number of path components > > > eventually accepted successfully by 9p server controller portion. > > > > > > New local variable 'any_err' is an aggregate variable reflecting whether > > > any error occurred at all, while already existing variable 'err' only > > > reflects the last error. > > > > > > Despite QIDs being delivered to client in a more relaxed way now, it is > > > important to note though that fid still must remain unaffected if any > > > error > > > occurred. > > > > > > Signed-off-by: Christian Schoenebeck > > > --- > > > > > > hw/9pfs/9p.c | 43 +++++++++++++++++++++++++++---------------- > > > 1 file changed, 27 insertions(+), 16 deletions(-) > > > > > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c > > > index 298f4e6548..e770972a71 100644 > > > --- a/hw/9pfs/9p.c > > > +++ b/hw/9pfs/9p.c > > > @@ -1766,7 +1766,7 @@ static void coroutine_fn v9fs_walk(void *opaque) > > > > > > { > > > > > > int name_idx, nwalked; > > > g_autofree V9fsQID *qids = NULL; > > > > > > - int i, err = 0; > > > + int i, err = 0, any_err = 0; > > > > > > V9fsPath dpath, path; > > > P9ARRAY_REF(V9fsPath) pathes = NULL; > > > uint16_t nwnames; > > > > > > @@ -1832,19 +1832,20 @@ static void coroutine_fn v9fs_walk(void *opaque) > > > > > > * driver code altogether inside the following block. > > > */ > > > > > > v9fs_co_run_in_worker({ > > > > > > + nwalked = 0; > > > > > > if (v9fs_request_cancelled(pdu)) { > > > > > > - err = -EINTR; > > > + any_err |= err = -EINTR; > > > > Not super fan of such constructs but I cannot think of anything > > better.. so be it ! :-) > > Mwa, :( and I thought this was a slick (though probably yet again unorthodox) > way to handle aggregate errors. > > [...] > > > @@ -1874,12 +1875,12 @@ static void coroutine_fn v9fs_walk(void *opaque) > > > > > > /* > > > > > > * Handle all the rest of this Twalk request on main thread ... > > > */ > > > > > > - if (err < 0) { > > > + if ((err < 0 && !nwalked) || err == -EINTR) { > > > > So this is making an exception to the spec excerpt you're mentioning > > in the changelog. > > > > EINTR can only come from the v9fs_request_cancelled(pdu) == true case, > > since QEMU doesn't have signal handlers AFAIK. This would be the result > > of a TFLUSH , likely to handle ^C from the client side. I guess that in > > that peculiar case, it quite makes sense to return RERROR/RLERROR instead > > of the "degraded" RWALK that the end user isn't waiting for. To sum up, > > TFLUSH behavior prevails on TWALK. Please add a comment though since > > this isn't super obvious in the spec. > > Yes, everything you said is depicting this exception here precisely, and I > agree that it deserves a comment for further clarification, which I'll simply > add on my end to avoid the noise. > > Does the following sound good to you? > > "NOTE: -EINTR is an exception where we deviate from the protocol spec and > simply send an (R)Lerror response instead of bothering to assemble a > (deducted) Rwalk response; because -EINTR is always the result of a Tflush > request, so client would no longer wait for a response in this case anyway." > LGTM > > Apart from that, LGTM. > > > > Reviewed-by: Greg Kurz > > Thanks for your reviews, much appreciated! > Sorry for the 3-month delay... Cheers, -- Greg > Best regards, > Christian Schoenebeck > >