From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9A0802F0C63 for ; Tue, 27 Jan 2026 16:04:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769529854; cv=none; b=IfzsZnTDpvxeJN73/HMJtSkdbwS9qt5dVVH601rXwf/KpDw/hZuBqhKA8YczSSLvOH7MgWDQdVNVPwr4U3vIRlqR06jH33Lm4DdGdUDd3OUaJWMPGRNg5nUF12pSayXxaC4YQv/+iEVXg0EzULu031yXANFkslHvIkCVKtYnxBQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769529854; c=relaxed/simple; bh=D40ph4TOaFFWGbtIdNMHA0r8oT8LFVd/WsRmyAiB/8w=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=hkpv29nK9XPzHke6osYlL5gFW/O2jBDqSvXJbGlh0NBIXZPhbqYl53/Dvr192Z8fTc9dmAa494aOPcAYe1EUM+F5+/+oHpRR8AtPhc0X/BxDVP5mXIrH9OYJD6IQEWeMQuxJkRlBwGkt8eOeI3JhN89tPRqtBR5WArk5cOiMFbU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZFwXzXu4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZFwXzXu4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9771C116C6; Tue, 27 Jan 2026 16:04:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769529854; bh=D40ph4TOaFFWGbtIdNMHA0r8oT8LFVd/WsRmyAiB/8w=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ZFwXzXu4Ze1PST9XCVJ43Xm95/b7+wdxH/v6EVVhOucdy/f8miby7ofnMi3ZZGB9Z 8/P351YWNiOrO5N3DBGkLoJDweBfxj32EoHjuCrtpOekucS/CZShNHhTBL4VbWhDTM yvJvIoyUXjnOsd8YFIkbz3CJcwSLS9upiesBNd9AB3WZF0nt5myQFzMPMC6V/9V0vl 8Hnqpd9x1N1ldDEce2FWw0qEHMP0b/50zFKHIXrGpcOASKQX9QR9R8LLN74t0sU5Vd 9VXsk4tRHVRWf/b0Jn4lPtlXINkDkDICZl3cAKmpp8zUsdT/lLtxLAPjDMaruDIbzh r12oKICtJYLHg== Message-ID: <96c77cc077fb3b8ec6c00dd0a712508af8323014.camel@kernel.org> Subject: Re: [PATCH RFC] NFS: Add some knobs for disabling delegations in sysfs From: Jeff Layton To: Trond Myklebust , Olga Kornievskaia Cc: Scott Mayhew , anna@kernel.org, linux-nfs@vger.kernel.org Date: Tue, 27 Jan 2026 11:04:12 -0500 In-Reply-To: References: <20251125001544.18584-1-smayhew@redhat.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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8:01=E2=80=AFPM Trond Myklebust > > wrote: > > >=20 > > > Hi Scott, > > >=20 > > > On Mon, 2025-11-24 at 19:15 -0500, Scott Mayhew wrote: > > > > There's occasionally a need to disable delegations, whether it be > > > > due > > > > to > > > > known bugs or simply to give support staff some breathing room to > > > > troubleshoot issues.=C2=A0 Currently the only real method for > > > > disabling > > > > delegations in Linux NFS is via /proc/sys/fs/leases-enable, which > > > > has > > > > some major drawbacks in that 1) it's only applicable to knfsd, > > > > and 2) > > > > it > > > > affects all clients using that server. > > > >=20 > > > > Technically it's not really possible to disable delegations from > > > > the > > > > client side since it's ultimately up to the server whether grants > > > > a > > > > delegation or not, but we can achieve a similar affect in > > > > NFSv4.1+ by > > > > manipulating the OPEN4_SHARE_ACCESS_WANT* flags. > > > >=20 > > > > Rather than proliferating a bunch of new mount options, add some > > > > sysfs > > > > knobs to allow some of the nfs_server->caps flags related to > > > > delegations > > > > to be adjusted. > > > >=20 > > >=20 > > > Shouldn't we rather be allowing the application to select whether > > > it > > > wants to request a delegation or not? > > >=20 > > > IOW: while there may or may not be a place for a 'big hammer' > > > solution > > > like you propose, should we not rather first try to enable a > > > solution > > > in which someone could add a O_DELEGATION or O_NODELEGATION flag to > > > open() in order to specify what they want. > >=20 > > Hi Trond, > >=20 > > Shouldn't open flags be something that's a generic concept for all > > filesystems? O_DELEGATION seems to be NFS specific (or at most > > network > > filesystem specific). > >=20 > > > That might also allow someone to add an LD_PRELOAD library to add > > > or > > > remove these flags from an existing application's open() calls. > > >=20 > > > It might also be useful for the directory delegation functionality > > > that > > > Anna and Jeff have been working on... > >=20 > > Being able to control directory delegations feature (might be) useful > > too? We used to be able to toggle features via mount options, > > wouldn't > > it be nice if we could again.... Toggling features via sysfs is > > useful > > for when mount is already in place though. > > >=20 >=20 > Isn't Jeff Layton in the process of exporting the NFSv4 delegation > functionality to userspace through the lease mechanisms? It's not quite the same thing, as they aren't acquired at open time. Similar to leases, you have to call fcntl(..., F_SETDELEG, ...) to get one. It doesn't seem like it really meshes with the idea of an O_NODELEGATION flag. Being able to disable delegations on a per-mount basis seems like it could be useful though. --=20 Jeff Layton