From patchwork Thu Jun 7 02:45:40 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 926098 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=suse.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 411VKT3z53z9s01 for ; Thu, 7 Jun 2018 12:46:05 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753348AbeFGCpw (ORCPT ); Wed, 6 Jun 2018 22:45:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:50777 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752973AbeFGCpv (ORCPT ); Wed, 6 Jun 2018 22:45:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id A6562AD0B; Thu, 7 Jun 2018 02:45:49 +0000 (UTC) From: NeilBrown To: Tom Herbert Date: Thu, 07 Jun 2018 12:45:40 +1000 Cc: Herbert Xu , Thomas Graf , Linux Kernel Network Developers , LKML , Tom Herbert Subject: [PATCH - RFC] rhashtable: add rhashtable_walk_last_seen() In-Reply-To: <87in6wo636.fsf@notabene.neil.brown.name> References: <152782754287.30340.4395718227884933670.stgit@noble> <152782824964.30340.6329146982899668633.stgit@noble> <20180602154851.pfy4wryezuhxp76v@gondor.apana.org.au> <87y3fvpf40.fsf@notabene.neil.brown.name> <87sh63pakb.fsf@notabene.neil.brown.name> <87r2lmnj2c.fsf@notabene.neil.brown.name> <87in6wo636.fsf@notabene.neil.brown.name> Message-ID: <871sdjnwkr.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org rhashtable_walk_last_seen() returns the object returned by the previous rhashtable_walk_next(), providing it is still in the table (or was during this grace period). This works even if rhashtable_walk_stop() and rhashtable_talk_start() have been called since the last rhashtable_walk_next(). If there have been no calls to rhashtable_walk_next(), or if the object is gone from the table, then NULL is returned. This can usefully be used in a seq_file ->start() function. If the pos is the same as was returned by the last ->next() call, then rhashtable_walk_last_seen() can be used to re-establish the current location in the table. If it returns NULL, then rhashtable_walk_next() should be used. Signed-off-by: NeilBrown --- include/linux/rhashtable.h | 1 + lib/rhashtable.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h index 657e37ae314c..d63b472e9d50 100644 --- a/include/linux/rhashtable.h +++ b/include/linux/rhashtable.h @@ -248,6 +248,7 @@ static inline void rhashtable_walk_start(struct rhashtable_iter *iter) void *rhashtable_walk_next(struct rhashtable_iter *iter); void *rhashtable_walk_peek(struct rhashtable_iter *iter); +void *rhashtable_walk_last_seen(struct rhashtable_iter *iter); void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU); void rhashtable_free_and_destroy(struct rhashtable *ht, diff --git a/lib/rhashtable.c b/lib/rhashtable.c index e0060cb264e9..45f2554399a5 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -949,6 +949,36 @@ void *rhashtable_walk_peek(struct rhashtable_iter *iter) } EXPORT_SYMBOL_GPL(rhashtable_walk_peek); +/** + * rhashtable_walk_last_seen - Return the previously returned object, if available + * @iter: Hash table iterator + * + * If rhashtable_walk_next() has previously been called and the object + * it returned is still in the hash table, that object is returned again, + * otherwise %NULL is returned. + * + * If the recent rhashtable_walk_next() call was since the most recent + * rhashtable_walk_start() call then the returned object may not, strictly + * speaking, still be in the table. It will be safe to dereference. + * + * Note that the iterator is not changed. + */ +void *rhashtable_walk_last_seen(struct rhashtable_iter *iter) +{ + struct rhashtable *ht = iter->ht; + struct rhash_head *p = iter->p; + + if (!p) + return NULL; + if (!iter->p_is_unsafe || ht->rhlist) + return p; + rht_for_each_rcu(p, iter->walker.tbl, iter->slot) + if (p == iter->p) + return p; + return NULL; +} +EXPORT_SYMBOL_GPL(rhashtable_walk_last_seen); + /** * rhashtable_walk_stop - Finish a hash table walk * @iter: Hash table iterator