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 95C8CC19F2D for ; Tue, 9 Aug 2022 18:12:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344920AbiHISM2 (ORCPT ); Tue, 9 Aug 2022 14:12:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345956AbiHISME (ORCPT ); Tue, 9 Aug 2022 14:12:04 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 145482B61F; Tue, 9 Aug 2022 11:05:05 -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 ams.source.kernel.org (Postfix) with ESMTPS id C7205B817B7; Tue, 9 Aug 2022 18:04:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2D54BC433C1; Tue, 9 Aug 2022 18:04:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660068289; bh=s+ZsIaocJsUaJFjFm4CBKMF8tunKkWAAOKS5RQlQwic=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=nUtiLryrFDHCGTbuhYMq7e+oqxYoa8dwzvsYvhsuYsL7/jaJztUW38wLJE+8fehPD DfG2BGs+GV4Jak5BEfWKyYgmknU+3htBLVvKLgFwnI0C/u7/CRfxUHDLYU3aj7MDwm f1NpFcohTqKBTOVebCfZspgpXk67zCszY+G/FQlawU0NpHi4mzN7ewwhIQc+JYzkZ1 61vDF7FqmgZuR7fk7R6ESzHmrX5xRjhYaNHkOD0MgnnNz3dLjC9wOMmGE9JfhKIOaL EdEdiQ80kX6q8IBOswLXfXYZv+tHG13kLNYUEZ7xLxPaBF8t8kNPedubVsK1AdtCB7 8U4+TqVppAHPQ== Message-ID: <52c6fb93a0dff332dbc81c4a7d5d9f8ad11e09dc.camel@kernel.org> Subject: Re: [RFC PATCH 1/4] vfs: report change attribute in statx for IS_I_VERSION inodes From: Jeff Layton To: "Darrick J. Wong" Cc: Dave Chinner , linux-fsdevel@vger.kernel.org, dhowells@redhat.com, lczerner@redhat.com, bxue@redhat.com, ceph-devel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-afs@lists.infradead.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, fstests Date: Tue, 09 Aug 2022 14:04:46 -0400 In-Reply-To: References: <20220805183543.274352-1-jlayton@kernel.org> <20220805183543.274352-2-jlayton@kernel.org> <20220805220136.GG3600936@dread.disaster.area> <33176ee0f896aef889ad1930fb1e008323135a2e.camel@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.44.4 (3.44.4-1.fc36) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, 2022-08-09 at 08:33 -0700, Darrick J. Wong wrote: > On Mon, Aug 08, 2022 at 09:19:05AM -0400, Jeff Layton wrote: > > On Fri, 2022-08-05 at 18:06 -0400, Jeff Layton wrote: > > > On Sat, 2022-08-06 at 08:01 +1000, Dave Chinner wrote: > > > > On Fri, Aug 05, 2022 at 02:35:40PM -0400, Jeff Layton wrote: > > > > > From: Jeff Layton > > > > >=20 > > > > > Claim one of the spare fields in struct statx to hold a 64-bit ch= ange > > > > > attribute. When statx requests this attribute, do an > > > > > inode_query_iversion and fill the result in the field. > > > > >=20 > > > > > Also update the test-statx.c program to fetch the change attribut= e as > > > > > well. > > > > >=20 > > > > > Signed-off-by: Jeff Layton > > > > > --- > > > > > fs/stat.c | 7 +++++++ > > > > > include/linux/stat.h | 1 + > > > > > include/uapi/linux/stat.h | 3 ++- > > > > > samples/vfs/test-statx.c | 4 +++- > > > > > 4 files changed, 13 insertions(+), 2 deletions(-) > > > > >=20 > > > > > diff --git a/fs/stat.c b/fs/stat.c > > > > > index 9ced8860e0f3..976e0a59ab23 100644 > > > > > --- a/fs/stat.c > > > > > +++ b/fs/stat.c > > > > > @@ -17,6 +17,7 @@ > > > > > #include > > > > > #include > > > > > #include > > > > > +#include > > > > > =20 > > > > > #include > > > > > #include > > > > > @@ -118,6 +119,11 @@ int vfs_getattr_nosec(const struct path *pat= h, struct kstat *stat, > > > > > stat->attributes_mask |=3D (STATX_ATTR_AUTOMOUNT | > > > > > STATX_ATTR_DAX); > > > > > =20 > > > > > + if ((request_mask & STATX_CHGATTR) && IS_I_VERSION(inode)) { > > > > > + stat->result_mask |=3D STATX_CHGATTR; > > > > > + stat->chgattr =3D inode_query_iversion(inode); > > > > > + } > > > >=20 > > > > If you're going to add generic support for it, shouldn't there be a > > > > generic test in fstests that ensures that filesystems that advertis= e > > > > STATX_CHGATTR support actually behave correctly? Including across > > > > mounts, and most importantly, that it is made properly stable by > > > > fsync? > > > >=20 > > > > i.e. what good is this if different filesystems have random quirks > > > > that mean it can't be relied on by userspace to tell it changes hav= e > > > > occurred? > > >=20 > > > Absolutely. Being able to better test the i_version field for consist= ent > > > behavior is a primary goal. I haven't yet written any yet, but we'd > > > definitely want something in xfstests if we decide this is worthwhile= . > >=20 > > I started writing some tests for this today, and hit a bit of a chicken= - > > and-egg problem: > >=20 > > I'd prefer to use xfs_io for easier maintainability, but the STATX_* > > constants are defined via UAPI header. Older kernels don't have them an= d > > old xfs_io programs don't understand or report this value. > >=20 > > Should I just write a one-off binary program for xfstests to fetch this > > value for now, or are we better off merging the patchset first, and the= n > > fix xfs_io and then write the tests using the updated xfs_io program? >=20 > What we've done in the past to support new APIs until they land in > kernel headers is: >=20 > Add an autoconf macro to decide if the system header files are recent > enough to support whatever functionality is needed by xfs_io; >=20 > Modify the build system to #define OVERRIDE_FUBAR if the system headers > aren't new enough to have FUBAR; and >=20 > Modify (or create) the relevant header file to override the system > header definitions as needed to support building the relevant pieces of > code. A year or so after the functionality lands, we can then remove > the overrides, or just leave them in place until the next time we need > it. >=20 > For example, Eric Biggers wanted to teach the fscrypt commands to use a > new feature he was adding to an existing API, so he AC_DEFUN'd a macro > that checks to see if the system linux/fs.h *does not* define a > structure containing the desired field. If this is the case, it sets > need_internal_fscrypt_add_key_arg=3Dyes. >=20 > AC_DEFUN([AC_NEED_INTERNAL_FSCRYPT_ADD_KEY_ARG], > [ > AC_CHECK_TYPE(struct fscrypt_add_key_arg, > [ > AC_CHECK_MEMBER(struct fscrypt_add_key_arg.key_id, > , > need_internal_fscrypt_add_key_arg=3Dyes, > [#include ] > ) > ],, > [#include ] > ) > AC_SUBST(need_internal_fscrypt_add_key_arg) > ]) >=20 > This macro is called from configure.ac. >=20 > Next, include/builddefs.in was modified to include the selected value in > the make variables: >=20 > NEED_INTERNAL_FSCRYPT_ADD_KEY_ARG =3D @need_internal_fscrypt_add_key_arg@ >=20 > And then the shouty variable is used in the same file to set a compiler > define: >=20 > ifeq ($(NEED_INTERNAL_FSCRYPT_ADD_KEY_ARG),yes) > PCFLAGS+=3D -DOVERRIDE_SYSTEM_FSCRYPT_ADD_KEY_ARG > endif >=20 > Then io/encrypt.c does the following to move the system's definition of > struct fscrypt_add_key_arg out of the way... >=20 > #ifdef OVERRIDE_SYSTEM_FSCRYPT_ADD_KEY_ARG > # define fscrypt_add_key_arg sys_fscrypt_add_key_arg > #endif > #include /* via io.h -> xfs.h -> xfs/linux.h */ >=20 > ...so that the file can provide its own definition further down: >=20 > /* > * Since the key_id field was added later than struct > * fscrypt_add_key_arg itself, we may need to override the system > * definition to get that field. > */ > #if !defined(FS_IOC_ADD_ENCRYPTION_KEY) || \ > defined(OVERRIDE_SYSTEM_FSCRYPT_ADD_KEY_ARG) > #undef fscrypt_add_key_arg > struct fscrypt_add_key_arg { > struct fscrypt_key_specifier key_spec; > __u32 raw_size; > __u32 key_id; > __u32 __reserved[8]; > __u8 raw[]; > }; > #endif >=20 Darrick, thanks for the detailed instructions. They've been very helpful! My approach is slightly different since xfsprogs already has a statx.h. I'm just updating that to allow for overriding. I think I have the autoconf part worked out. I'm having a problem with the above though. I have this in statx.h: #undef statx_timestamp struct statx_timestamp { __s64 tv_sec; __s32 tv_nsec; __s32 __reserved; }; ...but when I go to build, I get this: In file included from stat.c:11: statx.h:60:8: error: redefinition of =E2=80=98struct statx_timestamp=E2=80= =99 60 | struct statx_timestamp { | ^~~~~~~~~~~~~~~ ...it seems like the "#undef statx_timestamp" isn't doing the right thing. Is my syntax wrong? --=20 Jeff Layton