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[100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 4EE4E60166; Mon, 19 Jan 2026 12:30:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CDFBBC116C6; Mon, 19 Jan 2026 12:30:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768825811; bh=RtY/9HsvsbQ43gxyokWK1eA4XLPwg28gpyJ6yeklrHA=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=pp+0oHTy4cEhiZOObpsf2aYf1ExFvc8XLitDob6luVYaxmtTLIkENwaClVxplN4qA yh8iZqlkWyxe5krLs80mgdeLygmdXRb4e4p0sdPzzthaPgVukqNHkIIumJhMsZ0JNU VrluA2lM6pwVcquf6xKUFaaTp9RiTax+p82P9xJXDSychteaqHvvoSIfbIhkE+FCHG oj70jwgAubWNpL0YmUijpecHU0kuqRhBxYP87tWrTzg9hJ83T4B+Wblk0Usht1yD8T ZJXtsK8R3lHJSXlrbZQlUzIth36pN+jQcyTm/koQCbCCC53raFMHDKC/EoJNBCHIh5 SNIGKhT/ql1Kw== Message-ID: <9fdf7a8c04861306b453a78233f4bd6004c465f4.camel@kernel.org> Subject: Re: [PATCH 00/29] fs: require filesystems to explicitly opt-in to nfsd export support From: Jeff Layton To: NeilBrown , Christoph Hellwig Cc: Amir Goldstein , Christian Brauner , Alexander Viro , Chuck Lever , Olga Kornievskaia , Dai Ngo , Tom Talpey , Hugh Dickins , Baolin Wang , Andrew Morton , Theodore Ts'o , Andreas Dilger , Jan Kara , Gao Xiang , Chao Yu , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo , Carlos Maiolino , Ilya Dryomov , Alex Markuze , Viacheslav Dubeyko , Chris Mason , David Sterba , Luis de Bethencourt , Salah Triki , Phillip Lougher , Steve French , Paulo Alcantara , Ronnie Sahlberg , Shyam Prasad N , Bharath SM , Miklos Szeredi , Mike Marshall , Martin Brandenburg , Mark Fasheh , Joel Becker , Joseph Qi , Konstantin Komarov , Ryusuke Konishi , Trond Myklebust , Anna Schumaker , Dave Kleikamp , David Woodhouse , Richard Weinberger , Jan Kara , Andreas Gruenbacher , OGAWA Hirofumi , Jaegeuk Kim , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-xfs@vger.kernel.org, ceph-devel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-cifs@vger.kernel.org, linux-unionfs@vger.kernel.org, devel@lists.orangefs.org, ocfs2-devel@lists.linux.dev, ntfs3@lists.linux.dev, linux-nilfs@vger.kernel.org, jfs-discussion@lists.sourceforge.net, linux-mtd@lists.infradead.org, gfs2@lists.linux.dev, linux-f2fs-devel@lists.sourceforge.net Date: Mon, 19 Jan 2026 07:30:03 -0500 In-Reply-To: <176880736225.16766.4203157325432990313@noble.neil.brown.name> References: <20260115-exportfs-nfsd-v1-0-8e80160e3c0c@kernel.org> , , <9c99197dde2eafa55a1b55dce2f0d4d02c77340a.camel@kernel.org> , <176877859306.16766.15009835437490907207@noble.neil.brown.name> , <176880736225.16766.4203157325432990313@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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 FRe3gO8N zMZQT5oAGCeQ6WPja/Dw5nJ3MTHDJxlCfrl6uwcdKMpnzenqDt/oW9t2hXKDAPJ2b+LbtyMRo8p0ihw2gFZ509fj7hHpJevQVBaBionJlLcPMcleVoOBOh+WLVOOTKKPlqJ2hZfhz2N1usbJho3HkXqxi6J9Ofh0blXJsDzcMG7y/VDSI7ZwrGTMmGqNbYYnVMEqWLIFI5OWuNwKY0A2Cfd8JEwCSi6lfcuFDpSqA+pcggixhQvM0iIw/WsFeblEkKYFSm/YOFpWSv1L7zsIUzB8TbAWsHEzgo/F4C4ffLr0zDlv7aICzoXnalA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 2026-01-19 at 18:22 +1100, NeilBrown wrote: > On Mon, 19 Jan 2026, Christoph Hellwig wrote: > > On Mon, Jan 19, 2026 at 10:23:13AM +1100, NeilBrown wrote: > > > > This was Chuck's suggested name. His point was that STABLE means th= at > > > > the FH's don't change during the lifetime of the file. > > > >=20 > > > > I don't much care about the flag name, so if everyone likes PERSIST= ENT > > > > better I'll roll with that. > > >=20 > > > I don't like PERSISTENT. > > > I'd rather call a spade a spade. > > >=20 > > > EXPORT_OP_SUPPORTS_NFS_EXPORT > > > or > > > EXPORT_OP_NOT_NFS_COMPATIBLE > > >=20 > > > The issue here is NFS export and indirection doesn't bring any benefi= ts. > >=20 > > No, it absolutely is not. And the whole concept of calling something > > after the initial or main use is a recipe for a mess. >=20 > We are calling it for it's only use. If there was ever another use, we > could change the name if that made sense. It is not a public name, it > is easy to change. >=20 > >=20 > > Pick a name that conveys what the flag is about, and document those > > semantics well. This flag is about the fact that for a given file, > > as long as that file exists in the file system the handle is stable. > > Both stable and persistent are suitable for that, nfs is everything > > but. >=20 > My understanding is that kernfs would not get the flag. > kernfs filehandles do not change as long as the file exist. > But this is not sufficient for the files to be usefully exported. >=20 > I suspect kernfs does re-use filehandles relatively soon after the > file/object has been destroyed. Maybe that is the real problem here: > filehandle reuse, not filehandle stability. >=20 > Jeff: could you please give details (and preserve them in future cover > letters) of which filesystems are known to have problems and what > exactly those problems are? >=20 The only one I'm aware of at the moment is cgroupfs. sb->s_export_op gets populated on that fs, so it's exportable via nfsd. Its fs does not show up under the v4 pseudoroot, but you can mount /sys/fs/cgroup with v3 if it's specifically exported. Directories seem to work properly (I can ls and cd around in there), but the files all come back empty when read. I didn't play around with trying to write to any of them. I didn't do a lot of investigation here, since I didn't actually expect it to work properly. > >=20 > > Remember nfs also support volatile file handles, and other applications > > might rely on this (I know of quite a few user space applications that > > do, but they are kinda hardwired to xfs anyway). >=20 > The NFS protocol supports volatile file handles. knfsd does not. > So maybe > EXPORT_OP_NOT_NFSD_COMPATIBLE > might be better. or EXPORT_OP_NOT_LINUX_NFSD_COMPATIBLE. > (I prefer opt-out rather than opt-in because nfsd export was the > original purpose of export_operations, but it isn't something > I would fight for) >=20 The whole point of this is to make nfsd export an opt-in in. Exporting via NFS is something that filesystem developers need to consider carefully. cgroupfs is not that big a worry. My bigger concern is new filesystems being added that do add this for local access and become exportable without vetting that they will actually work correctly (well, that and FUSE exportability, which is a bigger can of worms). There is another approach we could consider: We could move the export_operations that are needed for local filehandle access into a new struct filehandle_operations or something. It does mean adding an extra pointer to the super_block for the new operations vector, but it might be more intuitive. --=20 Jeff Layton