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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 A932EC282CE for ; Wed, 10 Apr 2019 04:16:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76D452133D for ; Wed, 10 Apr 2019 04:16:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554869787; bh=6Tm/kYmmW/sLgnjhtsq5NqVafuKCWEF71UBQEpZeAxE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=wOXWRkCb2n4RJUjrH+6CXtXS4JY6BWXwvndh7wE5RY+GteKSsvHBjP/r+8mHB69BA gAaIJtXHur2+jV/BpFIWcseUBunJsQRrzGc4MdK5KiCtI83DA+PTfpCgZpphuRzgmW msf3BCg3Enhvzo2ZPM/RJsSgj6aWBwzL2eRRD5nU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727212AbfDJEQ0 (ORCPT ); Wed, 10 Apr 2019 00:16:26 -0400 Received: from mail.kernel.org ([198.145.29.99]:44514 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726026AbfDJEQ0 (ORCPT ); Wed, 10 Apr 2019 00:16:26 -0400 Received: from sol.localdomain (c-24-5-143-220.hsd1.ca.comcast.net [24.5.143.220]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 328EB2082E; Wed, 10 Apr 2019 04:16:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554869785; bh=6Tm/kYmmW/sLgnjhtsq5NqVafuKCWEF71UBQEpZeAxE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=G7cn+1cyy86BStCYV3WdPoQuvnWK1W7bmzPbBd41IoBWBpTlhqIm+S1LkVKhoPb5W AkLTHfLux2p0u7d1hRsm3S+yXWFmshgqw29obD7x1kAoPsoSQFu2pz/5whalqJZhZT zpl8WIo84MrqaC4qO/qfVqjWnMiE2MuG5kUXjlHg= Date: Tue, 9 Apr 2019 21:16:23 -0700 From: Eric Biggers To: Al Viro Cc: linux-fsdevel@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [PATCH] fscrypt: cache decrypted symlink target in ->i_link Message-ID: <20190410041623.GD7140@sol.localdomain> References: <20190409233544.156665-1-ebiggers@kernel.org> <20190410003346.GT2217@ZenIV.linux.org.uk> <20190410004553.GA2454@sol.localdomain> <20190410010425.GU2217@ZenIV.linux.org.uk> <20190410012247.GB2454@sol.localdomain> <20190410013934.GV2217@ZenIV.linux.org.uk> <20190410025808.GA7140@sol.localdomain> <20190410034414.GW2217@ZenIV.linux.org.uk> <20190410040413.GC7140@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190410040413.GC7140@sol.localdomain> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Apr 09, 2019 at 09:04:15PM -0700, Eric Biggers wrote: > On Wed, Apr 10, 2019 at 04:44:14AM +0100, Al Viro wrote: > > On Tue, Apr 09, 2019 at 07:58:08PM -0700, Eric Biggers wrote: > > > > > It could check a flag IOP_GET_LINK in ->i_opflags instead, so it would be the > > > same number of checks. See patch below. > > > > With that patch ->i_link is completely unused if ->get_link() is non-NULL, > > so you get a method call on each traversal... > > > > .get_link would be left NULL in all inode_operations that currently use > simple_get_link, then simple_get_link() would be removed. My example patch just > changed it in ext4 as an example. > > > > Benefits are that we get code that isn't actively misleading (via > > > simple_get_link() existing but actually never being called), and filesystems can > > > cache a symlink target in ->i_link if it becomes available later, i.e. if it's > > > not immediately available at iget() time. Otherwise a filesystem-private field > > > has to be used instead. (For fscrypt, I'd probably use fscrypt_info::ci_link.) > > > > What's to stop you from doing just that right now? You'd need to take > > care with barriers, but you'd need that anyway... As soon as ->i_link is set > > you'll get no more ->get_link() on that sucker, using the cached value > > from that point on. IDGI... > > 1.) The VFS won't know to drop of RCU-walk mode, so waiting an RCU grace period > before freeing the symlink target becomes mandatory. (Which I'd like to do > for fscrypt anyway, but doing it sanely appears to require implementing > .destroy_inode() for ext4, f2fs, and ubifs. I hoped I could do non-RCU mode > as a simpler first step.) > > 2.) The VFS won't know to use a read memory barrier when loading i_link. > The VFS could issue one unconditionally, but it would be unnecessary for > regular fast symlinks. > > - Eric Okay, actually all three filesystems have .destroy_inode() anyway. Not sure how I missed that. So it should be possible to free the decrypted symlink target from {ext4,f2fs,ubifs}_i_callback(). - Eric