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 BD786C6FD1D for ; Fri, 17 Mar 2023 20:30:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229816AbjCQUaI (ORCPT ); Fri, 17 Mar 2023 16:30:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229581AbjCQUaG (ORCPT ); Fri, 17 Mar 2023 16:30:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7E84A279 for ; Fri, 17 Mar 2023 13:29:34 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8FD1261731 for ; Fri, 17 Mar 2023 20:29:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFD5FC433D2; Fri, 17 Mar 2023 20:29:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1679084960; bh=VTalCe5hTRChUfz9djok16NsRktOIeNIyiq4jDsse+E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=s77YRYxFtz+RLzkryj8+fE5RAIbSOkKsep+Ll9h0FnERkqwJ3shQ7i9R+e4oArFoh af/NzW7l+bRgaQYOIMDnJZmah1mIa0DHHpZslg6QH3i2NjeKFp2Qan0saaVy3fwGpc JPdmSePqD3J5fFJXhL9HHbvBTKYY8v+uKvIogdAdQ02Ayq7GQtnqqXNTN2zhwq7m6B E1KiM4SbVzcO3vfM3ElJnehKD4HytmZW+wZ/fcN7byPOqTzxY/HzjhghvfCoGXlEnh 2Fx5/ILZue9J9gP7NAisWpWcahkBOT/RhqUjbzgHkPrYAz5ieC9Niz0bLYPjS8R8Ip q27FcWKzixGeQ== Date: Fri, 17 Mar 2023 13:29:20 -0700 From: "Darrick J. Wong" To: Alan Huang Cc: Carlos Maiolino , linux-xfs@vger.kernel.org Subject: Re: [PATCH] xfs_db: fix complaints about unsigned char casting Message-ID: <20230317202920.GJ11394@frogsfrogsfrogs> References: <20230315010110.GD11376@frogsfrogsfrogs> <20230317102559.agpsaa2fmgd32mc6@andromeda> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, Mar 17, 2023 at 06:43:40PM +0800, Alan Huang wrote: > Is there any reason keep these definition with different types? Question from a newbie... Probably not, but char* handling in C is a mess if you don't specify signedness -- on some arches gcc interprets "char" as "signed char", and on others it uses "unsigned char". The C library string functions all operate on "char *", so if you start changing types you quickly end up in compiler warning hell over that. libxfs seems to use "unsigned char*" and "uint8_t *". I don't know if that was just an SGI thing, or merely a quirk of the codebase? The Linux VFS code all take "char *", though as of 6.2 the makefiles force those to unsigned everywhere. As far as directory entry and extended attribute names go, all eight bits are allowed. UTF8 encoding uses the upper bit of a char, which means that we really want unsigned to avoid problems with sign extension when computing hashes and things like that, because emoji and kanji characters are in use around the world. IOWS: it's a giant auditing headache to research what parts use the type declarations they do, figure out what subtleties go with them, and decide on appropriate fixes. And in the end... the system still behaves the same way it did. --D > Thanks, > Alan > > > 2023年3月17日 下午6:25，Carlos Maiolino 写道： > > > > On Tue, Mar 14, 2023 at 06:01:10PM -0700, Darrick J. Wong wrote: > >> From: Darrick J. Wong > >> > >> Make the warnings about signed/unsigned char pointer casting go away. > >> For printing dirent names it doesn't matter at all. > >> > >> Signed-off-by: Darrick J. Wong > > > > Looks good, will test. > > > > Reviewed-by: Carlos Maiolino > > > >> --- > >> db/namei.c | 4 ++-- > >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> > >> diff --git a/db/namei.c b/db/namei.c > >> index 00e8c8dc6d5..063721ca98f 100644 > >> --- a/db/namei.c > >> +++ b/db/namei.c > >> @@ -98,7 +98,7 @@ path_navigate( > >> > >> for (i = 0; i < dirpath->depth; i++) { > >> struct xfs_name xname = { > >> - .name = dirpath->path[i], > >> + .name = (unsigned char *)dirpath->path[i], > >> .len = strlen(dirpath->path[i]), > >> }; > >> > >> @@ -250,7 +250,7 @@ dir_emit( > >> uint8_t dtype) > >> { > >> char *display_name; > >> - struct xfs_name xname = { .name = name }; > >> + struct xfs_name xname = { .name = (unsigned char *)name }; > >> const char *dstr = get_dstr(mp, dtype); > >> xfs_dahash_t hash; > >> bool good; > > > > -- > > Carlos Maiolino >