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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9289C433EF for ; Wed, 8 Dec 2021 23:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241252AbhLHXsQ (ORCPT ); Wed, 8 Dec 2021 18:48:16 -0500 Received: from ams.source.kernel.org ([145.40.68.75]:45636 "EHLO ams.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238277AbhLHXsP (ORCPT ); Wed, 8 Dec 2021 18:48:15 -0500 Received: from mail.kernel.org (unknown [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id EA711B82312; Wed, 8 Dec 2021 23:44:41 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id CF5CE603E4; Wed, 8 Dec 2021 23:44:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1639007080; bh=UkQani6FEO+P7NP71yI3ezLyKvLVm8th0l7ERr+VtXM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=EUwAtzZ4il4NboJbOfflvB9STYCCGKnPsyM1Kx+UZicRJY2jIlEX+pWzbzZKA7rJg 5mXivCSeUyD9QvoEO6vhhT9wtSX3TvfYHC7X1hg6aO5TIsoZ7QMOgG+bNdm1NckAN/ xJBrUVFEic3wFBBoBYWBQkLpBP+Y7AUWHE3mhLm4= Date: Wed, 8 Dec 2021 15:44:37 -0800 From: Andrew Morton To: xiujianfeng Cc: , , , , , , , , , , , , , , , , , Subject: Re: [PATCH -next 1/2] string.h: Introduce memset_range() for wiping members Message-Id: <20211208154437.01441d2dcf4cd812a9c58a7d@linux-foundation.org> In-Reply-To: References: <20211208030451.219751-1-xiujianfeng@huawei.com> <20211208030451.219751-2-xiujianfeng@huawei.com> <20211207202829.48d15f0ffa006e3656811784@linux-foundation.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, 8 Dec 2021 18:30:26 +0800 xiujianfeng wrote: > > 在 2021/12/8 12:28, Andrew Morton 写道: > > On Wed, 8 Dec 2021 11:04:50 +0800 Xiu Jianfeng wrote: > > > >> Motivated by memset_after() and memset_startat(), introduce a new helper, > >> memset_range() that takes the target struct instance, the byte to write, > >> and two member names where zeroing should start and end. > > Is this likely to have more than a single call site? > There maybe more call site for this function, but I just use bpf as an > example. > > > >> ... > >> > >> --- a/include/linux/string.h > >> +++ b/include/linux/string.h > >> @@ -291,6 +291,26 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count, > >> sizeof(*(obj)) - offsetof(typeof(*(obj)), member)); \ > >> }) > >> > >> +/** > >> + * memset_range - Set a value ranging from member1 to member2, boundary included. > > I'm not sure what "boundary included" means. > I mean zeroing from member1 to member2(including position indicated by > member1 and member2) > > > >> + * > >> + * @obj: Address of target struct instance > >> + * @v: Byte value to repeatedly write > >> + * @member1: struct member to start writing at > >> + * @member2: struct member where writing should stop > > Perhaps "struct member before which writing should stop"? > memset_range should include position indicated by member2 as well In that case we could say "struct member where writing should stop (inclusive)", to make it very clear. > > > >> + * > >> + */ > >> +#define memset_range(obj, v, member_1, member_2) \ > >> +({ \ > >> + u8 *__ptr = (u8 *)(obj); \ > >> + typeof(v) __val = (v); \ > >> + BUILD_BUG_ON(offsetof(typeof(*(obj)), member_1) > \ > >> + offsetof(typeof(*(obj)), member_2)); \ > >> + memset(__ptr + offsetof(typeof(*(obj)), member_1), __val, \ > >> + offsetofend(typeof(*(obj)), member_2) - \ > >> + offsetof(typeof(*(obj)), member_1)); \ > >> +}) > > struct a { > > int b; > > int c; > > int d; > > }; > > > > How do I zero out `c' and `d'? > if you want to zero out 'c' and 'd', you can use it like > memset_range(a_ptr, c, d); But I don't think that's what the code does! it expands to memset(__ptr + offsetof(typeof(*(a)), c), __val, offsetofend(typeof(*(a)), d) - offsetof(typeof(*(a)), c)); which expands to memset(__ptr + 4, __val, 8 - 4); and `d' will not be written to.