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 X-Spam-Level: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 81B36C433B4 for ; Wed, 7 Apr 2021 08:22:31 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 2B0F76139E for ; Wed, 7 Apr 2021 08:22:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2B0F76139E Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.106489.203637 (Exim 4.92) (envelope-from ) id 1lU3SA-0006Eh-60; Wed, 07 Apr 2021 08:22:22 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 106489.203637; Wed, 07 Apr 2021 08:22:22 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lU3SA-0006Ea-34; Wed, 07 Apr 2021 08:22:22 +0000 Received: by outflank-mailman (input) for mailman id 106489; Wed, 07 Apr 2021 08:22:20 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lU3S8-0006EV-HG for xen-devel@lists.xenproject.org; Wed, 07 Apr 2021 08:22:20 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id fe0acf2b-6174-45c6-b005-2b425ca1574f; Wed, 07 Apr 2021 08:22:19 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D3540B02A; Wed, 7 Apr 2021 08:22:18 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: fe0acf2b-6174-45c6-b005-2b425ca1574f X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617783739; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eLoWE++Hfb0OXAUTvq0iO3BKXC4CXas3soxCDljI5AY=; b=Kzp6j83t4Ebl64A+AVlG/QI0D0vnjibDBDgAVlTLCwvLYKqJqkd12hVIY8rveTOs6ASM2N /CGxiv4U+ygpTE/8nsM7R3RKTX9jIU3PfCuofzAEj5UCLTHN7XTG8fJ7xfneDqFyvYJllX CeWOCByYOU51S1eEYYIYD9ODPjM0JTE= Subject: Re: [PATCH 02/14] xen/sched: Constify name and opt_name in struct scheduler To: Julien Grall Cc: Julien Grall , George Dunlap , Dario Faggioli , xen-devel@lists.xenproject.org References: <20210405155713.29754-1-julien@xen.org> <20210405155713.29754-3-julien@xen.org> <5618bed6-a213-d2c9-4cbf-d95cb4dc02b4@suse.com> <00a75c04-fad1-7061-ac39-a811f442db05@xen.org> From: Jan Beulich Message-ID: Date: Wed, 7 Apr 2021 10:22:19 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <00a75c04-fad1-7061-ac39-a811f442db05@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 06.04.2021 20:24, Julien Grall wrote: > Hi Jan, > > On 06/04/2021 09:07, Jan Beulich wrote: >> On 05.04.2021 17:57, Julien Grall wrote: >>> From: Julien Grall >>> >>> Both name and opt_name are pointing to literal string. So mark both of >>> the fields as const. >>> >>> Signed-off-by: Julien Grall >> >> Reviewed-by: Jan Beulich >> albeit ... >> >>> --- a/xen/common/sched/private.h >>> +++ b/xen/common/sched/private.h >>> @@ -272,8 +272,8 @@ static inline spinlock_t *pcpu_schedule_trylock(unsigned int cpu) >>> } >>> >>> struct scheduler { >>> - char *name; /* full name for this scheduler */ >>> - char *opt_name; /* option name for this scheduler */ >>> + const char *name; /* full name for this scheduler */ >>> + const char *opt_name; /* option name for this scheduler */ >> >> ... I'd like to suggest considering at least the latter to become >> an array instead of a pointer - there's little point wasting 8 >> bytes of storage for the pointer when the strings pointed to are >> all at most 9 bytes long (right now; I don't expect much longer >> ones to appear). > > I have tried this simple/dumb change on top of my patch: > > diff --git a/xen/common/sched/private.h b/xen/common/sched/private.h > index a870320146ef..ab2236874217 100644 > --- a/xen/common/sched/private.h > +++ b/xen/common/sched/private.h > @@ -273,7 +273,7 @@ static inline spinlock_t > *pcpu_schedule_trylock(unsigned int cpu) > > struct scheduler { > const char *name; /* full name for this scheduler */ > - const char *opt_name; /* option name for this scheduler */ > + const char opt_name[9]; /* option name for this scheduler */ > unsigned int sched_id; /* ID for this scheduler */ > void *sched_data; /* global data pointer */ > struct cpupool *cpupool;/* points to this scheduler's pool */ > > GCC will throw an error: > > core.c: In function ‘scheduler_init’: > core.c:2987:17: error: assignment of read-only variable ‘ops’ > ops = *schedulers[i]; > ^ > core.c:2997:21: error: assignment of read-only variable ‘ops’ > ops = *schedulers[i]; > ^ > > I don't particularly want to drop the const. So the code would probably > need some rework. What's wrong with not having the const when the field is an array? The more that all original (build-time, i.e. contain in the binary) instances of the struct are already const as a whole? Jan