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 DE4AA1EB1AF; Sun, 8 Jun 2025 10:19:31 +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=1749377972; cv=none; b=qRRVC5Lb6X3rNpjnqgFNGpDsecIduLVxuFHWLbeyv+SqFmNCjht5/AQwtwCEuutG1jJ1ptqDlldVHMUBAiJvnCXLyg+PkbLf813bOrDVoSOJ00eYdNTpLw9nOxybkpvmRy6k26G2tTr6UB6MVJDL+GipgD79VOTtoFxTxucVr6A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749377972; c=relaxed/simple; bh=8fPYTbO3TYcPGIC9ne6WHJXSW/FawlGBC3YokhHoaXI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=CC9jRoGtUGaOld4HTkEiOqbfjakF7K/584UBgK2Khg6Zyg+V5Q9s8qiW2bWfb0zZXWCNN7Ga5OsE2Wq5u/vdMt6JV3ZWRWdXp2NafF/DArQvzvU5Stg4liKimRM+5HzNcYWlJ3cxsnnWJ2LnhFpGZl9U6wGsqkXUINZqTbDScD4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eVIQTRfi; 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="eVIQTRfi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C05A3C4CEEE; Sun, 8 Jun 2025 10:19:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749377971; bh=8fPYTbO3TYcPGIC9ne6WHJXSW/FawlGBC3YokhHoaXI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=eVIQTRfiHCvxnPT5SbMsyYPA9mtl+KyksBJe8oPjTIVqG8u+jJfgwjeupLsBqooC3 oFlPySaW+9bCJ1LVkU8NXagl4FqWeg6hwt0MQYp+qta35kjVSUbSYYs4IvIkUo6Tbw GEGx72dbhqR04jMlBWsYRzNw8KW1ZwsAv7yyaJHidGBcQnFuNkVjg7UQDKLyMFwsT/ ndYYlO1257TXjrDlzscGBUZoLtxoBZ1A3R6lrLUDKqb6+CAoJJg1TWMLlawdhPvwj4 5kfH24DIN9reWMhs38Kyc7//Q5yI1Qo2Sak+RvBgqxQHeugcsnYlhCjALMZNyUiZq2 A7nv8lz7RfBdw== Message-ID: <59fb3f42954e9817a878b3d700b8e427c5888d6e.camel@kernel.org> Subject: Re: LInux NFSv4.1 client and server- case insensitive filesystems supported? From: Jeff Layton To: Theodore Ts'o , Chuck Lever Cc: Cedric Blancher , Linux NFS Mailing List , linux-fsdevel Date: Sun, 08 Jun 2025 06:19:29 -0400 In-Reply-To: <20250607223951.GB784455@mit.edu> References: <44250631-2b70-4ce8-b513-a632e70704ed@oracle.com> <20250607223951.GB784455@mit.edu> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf 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Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-06-07 at 22:39 +0000, Theodore Ts'o wrote: > On Sat, Jun 07, 2025 at 02:30:37PM -0400, Chuck Lever wrote: > >=20 > > My impression is that real case-insensitivity has been added to the > > dentry cache in support of FAT on Android devices (or something like > > that). That clears the path a bit for NFSD, but it needs to be > > researched to see if that new support is adequate for NFS to use. >=20 > Case insensitivty was added in Linux in 2019, with the primary coding > work being done by Gabriel Krisman Bertazi of Collabora, and design > work being done being done by Gabriel, Michael Halcrow, and myself. > (Michael Halcrow in particular was responsible for devising how to > make case-insensitivity work with filename encryption and indexed > directories.) >=20 > The initial file systems that had case-insensitivty implemented was > ext4 and f2fs. The initial use cases was Android devices (which had > used this horible wrapfs stacking file system thing which was trivial > to deadlock under stress, and its original reason for existing was > bug-for-bug compatibility with FAT), and for Steam so that Windows > games could have their expected case insensitivity. (Collabora's work > was underwritten by Steam.) >=20 > There is an interesting write-up about NFS and case-insensitivity in a > relatively recent Internet-Draft[1], dated 2025-May-16. In this I-D, > it points out that one of the primary concerns is that if the client > caches negative lookups under one case (say, MaDNeSS), and then the > file is created using a different case (say "madness"), then the > negative dentry cache indicating that MaDNeSS does not exist needs to > be removed when "madness" is created. I'm not sure how Linux's NFS > client handles negative dentries, since even without > case-insensitivity, a file name that previously didn't exist could > have subsequently been created by another client on a different host. > So does Linux's NFS client simply does not use negative dentries, or > does it have some kind of cache invalidation scheme when the directory > has a new mtime, or some such? >=20 It's a little more complicated than that, but that's basically right: When the attrs on the parent directory indicate that there has been a change to it since a dentry was last revalidated, the client will return <=3D0 to d_revalidate attempts on the dentry. That will make the VFS re-drive a lookup instead of trusting the cache. > [1] https://www.ietf.org/id/draft-ietf-nfsv4-internationalization-12.html= #name-handling-of-string-equivale >=20 > Anyway, case sensitivity is one of those "interesting" problems which > has caused many headaches, including a potential security issue, and a > botched attempt to fix that security issue interacting poorly with > some of the more subtle design requirements so that file systems can > use tree-indexed directory lookups, even with case-insensitivty file > names and encrypted directory entries. So in general, unless you have > strong financial backing where someone is willing to pay $$$ to > address a business-critical use case, my personal advice is to stay > far, far, away. And I say this as a someone (with apologies to Linus) > who was partially responsible for Linux having case insensitivty > lookups in the first place. :-) --=20 Jeff Layton