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 B0A77C7EE23 for ; Tue, 2 May 2023 07:13:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233252AbjEBHL5 (ORCPT ); Tue, 2 May 2023 03:11:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229449AbjEBHLr (ORCPT ); Tue, 2 May 2023 03:11:47 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 177A41FC2; Tue, 2 May 2023 00:11:46 -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 A6A8A61180; Tue, 2 May 2023 07:11:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C63C5C433D2; Tue, 2 May 2023 07:11:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1683011505; bh=iP0pkPRPF2yyWma5T57Jl+IkunllF4npRD1ZDpsaR2Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KJi7VM57+hCZiS5pBrGaI+NHHdNu1FIF4IW0ha2PSCAiIoxG6tmcNLAbkXg0MA75C +VDM+LebMyBRMM8yVmZr7EVissdk0UXryUkZdicKjBqiNXEWwoUQe846hstBOFfKX7 tzcIJoGi/7wv4eXxMhH96/1ekdQvRQphKUy3EE1UaruvbbDccOOIOHAwtTBA6jUU3v GiFL4mFRQqrMIxKAEix6xn+67N5dW1pa3lgg5wvQyPbINHPJ5WF6m0qpvfoO8WyRyf lNVLLGG0RL+qkhNkWlY/EZjM6hkeiQJ+pt+3qywul8y9ZcSzIp88HRGZfdbpMrl6ie Usm6IR1tKzdPA== Date: Tue, 2 May 2023 09:11:40 +0200 From: Christian Brauner To: Al Viro Cc: Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [GIT PULL] pidfd updates Message-ID: <20230502-wunsch-stinktier-46d58b6b57d6@brauner> References: <20230421-kurstadt-stempeln-3459a64aef0c@brauner> <20230425060427.GP3390869@ZenIV> <20230425-sturheit-jungautor-97d92d7861e2@brauner> <20230427010715.GX3390869@ZenIV> <20230427073908.GA3390869@ZenIV> <20230427170215.GC3390869@ZenIV> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230427170215.GC3390869@ZenIV> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 27, 2023 at 06:02:15PM +0100, Al Viro wrote: > On Thu, Apr 27, 2023 at 08:21:34AM -0700, Linus Torvalds wrote: > > On Thu, Apr 27, 2023 at 12:39 AM Al Viro wrote: > > > > > > int delayed_dup(struct file *file, unsigned flags) > > > > Ok, this is strange. Let me think about it. > > > > But even without thinking about it, this part I hate: > > > > > struct delayed_dup *p = kmalloc(sizeof(struct delayed_dup), GFP_KERNEL); > > > > Sure, if this is only used in unimportant code where performance > > doesn't matter, doing a kmalloc is fine. > > > > But if that is the only use, I think this is too subtle an interface. > > Still hadn't finished with the zoo... > > > Could we instead limit it to "we only have one pending delayed dup", > > and make this all be more like the restart-block thing, and be part of > > struct task_struct? > > Interesting... FWIW, *anything* that wants several descriptors has > special needs - there are some places like that (binder, for one) > and they have rather weird code implementing those. > > Just to restate the obvious: this is not applicable for the most frequent > caller - open(2). For the reasons that have nothing to do with performance. > If opening the file has hard-to-reverse side effects (like directory > modification due to O_CREAT), the things are very different. > > What I hope for is a small number of patterns, with clear rules for > choosing the one that is applicable and helpers for each that would > reduce the amount of headache when using it. And I've no problem > with "this particular pattern is not usable if you are adding more > than one descriptor" - that's not hard to understand and verify. > So I'm fine with doing that for one descriptor only and getting > rid of the allocation. > > BTW, another pattern is the same sans the "delayed" part. I.e. > "here's an opened file, get a descriptor and either attach the > file to it or fput() the damn thing; in any case, file reference > is consumed and descriptor-or-error is returned". That one is > definitely only for single descriptor case. > > In any case, I want to finish the survey of the callers first, just to > see what's there and whether anything is worth nicking. > > While we are at it, I want to make close_fd() use a very big red flag. > To the point of grepping for new callers in -next and asking the folks > who introduce those to explain WTF they are doing... Yeah, I'd fully support this and would be very nice to have.