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 9A8A4C77B7E for ; Thu, 27 Apr 2023 16:36:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243894AbjD0Qgg (ORCPT ); Thu, 27 Apr 2023 12:36:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33294 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243284AbjD0Qgf (ORCPT ); Thu, 27 Apr 2023 12:36:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 221244C03; Thu, 27 Apr 2023 09:36:34 -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 A162B60C11; Thu, 27 Apr 2023 16:36:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52C78C433EF; Thu, 27 Apr 2023 16:36:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1682613393; bh=NK9ShzjIwWFJFvl4S+tgaxQhD/QPtKHv3Jo+GnfBb+U=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=UjDFpJZoT48prhNYEjw5dEOwMhWF7S44SIUuN4OmLrtQ0Wp4Xo+JCZwTZjytFWli+ xOcJUGLITZqsrbXF1DpI+rhTDKL7eZke9o6MfdOlrkI1bG+T1fW/gU9/iK/wFK5500 mhMimazuDWJ4QFkg7Ru7ITEtrOtL9lQ5Zj6koermvzLx4TgaAbbNuXcShfskfaIq05 k8NmaaZs/G7mHADteyOhZNvfVBx9x0Glp4/Ti3KZBBazdjyrvoWO1b7B4uxKe8Hoe5 18AcDllwtR61V01N1DaY1eCWcN8SzAZ4vt2Q8hkwHe0nxlu4KryIPcgr8qPAe5iIo2 63vdsPh6KReaw== Message-ID: Subject: Re: [RFC][PATCH 0/4] Prepare for supporting more filesystems with fanotify From: Jeff Layton To: Amir Goldstein Cc: Jan Kara , Christian Brauner , Miklos Szeredi , linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org Date: Thu, 27 Apr 2023 12:36:30 -0400 In-Reply-To: References: <20230425130105.2606684-1-amir73il@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.48.1 (3.48.1-1.fc38) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, 2023-04-27 at 18:52 +0300, Amir Goldstein wrote: > On Thu, Apr 27, 2023 at 6:13=E2=80=AFPM Jeff Layton = wrote: > >=20 > > On Tue, 2023-04-25 at 16:01 +0300, Amir Goldstein wrote: > > > Jan, > > >=20 > > > Following up on the FAN_REPORT_ANY_FID proposal [1], here is a shot a= t an > > > alternative proposal to seamlessly support more filesystems. > > >=20 > > > While fanotify relaxes the requirements for filesystems to support > > > reporting fid to require only the ->encode_fh() operation, there are > > > currently no new filesystems that meet the relaxed requirements. > > >=20 > > > I will shortly post patches that allow overlayfs to meet the new > > > requirements with default overlay configurations. > > >=20 > > > The overlay and vfs/fanotify patch sets are completely independent. > > > The are both available on my github branch [2] and there is a simple > > > LTP test variant that tests reporting fid from overlayfs [3], which > > > also demonstrates the minor UAPI change of name_to_handle_at(2) for > > > requesting a non-decodeable file handle by userspace. > > >=20 > > > Thanks, > > > Amir. > > >=20 > > > [1] https://lore.kernel.org/linux-fsdevel/20230417162721.ouzs33oh6mb7= vtft@quack3/ > > > [2] https://github.com/amir73il/linux/commits/exportfs_encode_fid > > > [3] https://github.com/amir73il/ltp/commits/exportfs_encode_fid > > >=20 > > > Amir Goldstein (4): > > > exportfs: change connectable argument to bit flags > > > exportfs: add explicit flag to request non-decodeable file handles > > > exportfs: allow exporting non-decodeable file handles to userspace > > > fanotify: support reporting non-decodeable file handles > > >=20 > > > Documentation/filesystems/nfs/exporting.rst | 4 +-- > > > fs/exportfs/expfs.c | 29 ++++++++++++++++++-= -- > > > fs/fhandle.c | 20 ++++++++------ > > > fs/nfsd/nfsfh.c | 5 ++-- > > > fs/notify/fanotify/fanotify.c | 4 +-- > > > fs/notify/fanotify/fanotify_user.c | 6 ++--- > > > fs/notify/fdinfo.c | 2 +- > > > include/linux/exportfs.h | 18 ++++++++++--- > > > include/uapi/linux/fcntl.h | 5 ++++ > > > 9 files changed, 67 insertions(+), 26 deletions(-) > > >=20 > >=20 > > This set looks fairly benign to me, so ACK on the general concept. >=20 > Thanks! >=20 > >=20 > > I am starting to dislike how the AT_* flags are turning into a bunch of > > flags that only have meanings on certain syscalls. I don't see a cleane= r > > way to handle it though. >=20 > Yeh, it's not great. >=20 > There is also a way to extend the existing API with: >=20 > Perhstruct file_handle { > unsigned int handle_bytes:8; > unsigned int handle_flags:24; > int handle_type; > unsigned char f_handle[]; > }; >=20 > AFAICT, this is guaranteed to be backward compat > with old kernels and old applications. >=20 That could work. It would probably look cleaner as a union though. Something like this maybe? union { unsigned int legacy_handle_bytes; struct { u8 handle_bytes; u8 __reserved; u16 handle_flags; }; } __reserved must be zeroed (for now). You could consider using it for some other purpose later. It's a little ugly as an API but it would be backward compatible, given that we never use the high bits today anyway. Callers might need to deal with an -EINVAL when they try to pass non- zero handle_flags to existing kernels, since you'd trip the MAX_HANDLE_SZ check that's there today. > It also may not be a bad idea that the handle_flags could > be used to request specific fh properties (FID) and can also > describe the properties of the returned fh (i.e. non-decodeable) > that could also be respected by open_by_handle_at(). >=20 > For backward compact, kernel will only set handle_flags in > response if new flags were set in the request. >=20 > Do you consider this extension better than AT_HANDLE_FID > or worse? At least it is an API change that is contained within the > exportfs subsystem, without polluting the AT_ flags global namespace. >=20 Personally, yes. I think adding a struct file_handle_v2 would be cleaner and allows for expanding the API later through new flags. --=20 Jeff Layton