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 AABB830E85D; Fri, 20 Mar 2026 20:31:43 +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=1774038703; cv=none; b=fBmj40A4oyTbzj+86CRBTXRjJkfJ5ZV4PCsFf6cq1rZ5ZDHLyfHvs6Rpovi5+YDWktF33OTXXCB46Px3+TUzbNpATni8dzFCP8aidmKsMzLk6gEBFHwJAVMMxeUtL7yhxaW0OPbkkuMPHapecykS70Zcd9fWepOW77DHNPblJ1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774038703; c=relaxed/simple; bh=i0s+LzSLkC8i53m2t8mMgkVZFd3f8MqMpwRKN4kXtQI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=e+jqLOfkwAFx0hrHW0OmhORUuMpoi9AESzr/it3hBQybU4uWPLNL5mvF3vOtVOETTgHf+8LtIIJFZ8tkf7UGupUTas6NZ4UgnRAeUakQT2bRlZwT0qfG2esnaJzi++pLvVSlzQr+L2hJcGDDt/jtsIuVHrAuGMfJoPTuwO5AhZQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WZMh6tEV; 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="WZMh6tEV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 43027C4CEF7; Fri, 20 Mar 2026 20:31:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774038703; bh=i0s+LzSLkC8i53m2t8mMgkVZFd3f8MqMpwRKN4kXtQI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WZMh6tEV4IKEd/VfHWbN0d5M8/HTySYyMtAlrBM034uuy50zGzyr0QSg8TyBvGNQs iqyi0/Z5nt1Q4KjytGu+u9M2zJ1S1d8owDDchFDCc8G1Fi3Zgh1nUpKh9s9blc7lAO 5eF+d00phhvQ6B9RJkRm5F4frQt1YDm+kTE0uyCpdbJbyJC1jcZiDKYCYNbn3Ce3eJ WsqyOvJdmPHGhKF+z4TlZNV5zEJESLFOf69j4uI3fYQg+6WqyEmz3sywSqcuIj3iVY jaOds8pTK8YRLsWrmy8gHzheEfq3I3WLjS1QZZxGOnukppKCWnNOXXCw6fmz0xG4Al L+/g+yLitGiRw== Date: Fri, 20 Mar 2026 13:31:42 -0700 From: "Darrick J. Wong" To: Joanne Koong Cc: Demi Marie Obenour , linux-fsdevel , bpf@vger.kernel.org, linux-ext4 , Miklos Szeredi , Bernd Schubert , Theodore Ts'o , Neal Gompa , Amir Goldstein , Christian Brauner , Jeff Layton , John@groves.net Subject: Re: [PATCHBLIZZARD v7] fuse/libfuse/e2fsprogs: containerize ext4 for safer operation Message-ID: <20260320203142.GB6254@frogsfrogsfrogs> References: <20260223224617.GA2390314@frogsfrogsfrogs> <20260316180408.GN6069@frogsfrogsfrogs> <20260316234137.GJ1742010@frogsfrogsfrogs> <208bfbd2-d671-462c-925f-4d51b7df1f18@gmail.com> <20260318213129.GB6004@frogsfrogsfrogs> <20260319160836.GC6004@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Mar 20, 2026 at 10:04:29AM -0700, Joanne Koong wrote: > > > >>>> - easier to maintain vs. having to maintain each filesystem's > > > >>>> userspace server implementation > > > >>> > > > >>> Yeah. > > > >>> > > > >>>> lklfuse cons: > > > >>>> - worse (not sure by how much) performance > > > >>> > > > >>> Probably a lot, because now you have to run a full IO stack all the way > > > >>> through lklfuse. > > > >> > > > >> How much is "a lot"? Is it "this is only useful for non-interactive > > > >> overnight backups", "you will notice this in benchmarks but it's okay > > > >> for normal use", or somewhere in between? > > > > > > > > Startup is painfully slow. Normal operation isn't noticeably bad, but I > > > > didn't bother doing any performance comparisons. > > For the CI/filesystem testing use case, could fork() help amortize > lklfuse's slow startup time? eg start lklfuse + pay LKL initialization > cost once, fork for each test, and each child mounts its own test > image? I suppose you could prefork like that (with some difficulty) if you had a means to convey the device, fstype, and mount options to each new child as a mount request comes in. Though if you had a way to do that, then you might be better off shipping a canned kernel + hibernate image which would "unhibernate" quickly, discover the fs parameters, and immediately engage the fuse server. > > > > > > > >> Could lklfuse and iomap be combined? > > > > > > > > Probably, though you'd have to find a way to route the FUSE_IOMAP_* > > > > requests to a filesystem driver. That's upside-down of the current > > > > iomap model where filesystems have to opt into using iomap on a > > > > per-IO-path basis, and then iomap calls the filesystem to find mappings. > > > > > > If it does get done it would be awesome. I don't think I'll be able to > > > contribute, though. > > > > I wonder if one could export a (pnfs) layout from the lklfuse kernel to > > the real one, that's where struct iomap came from. A huge > > downside to that solution is that layouts don't support out of place > > writes because pnfs doesn't support out of place writes. > > > > > >>>> - once it's merged into the kernel, we can't choose to not > > > >>>> maintain/support it in the future > > > >>> > > > >>> Correct. > > > >>> > > > >>>> Am I understanding this correctly? > > > >>>> > > > >>>> In my opinion, if near-native performance is not a hard requirement, > > > >>>> it seems like less pain overall to go with lklfuse. lklfuse seems a > > > >>>> lot easier to maintain and I'm not sure if some complexities like > > > >>>> btrfs's copy-on-write could be handled properly with fuse-iomap. > > > >>> > > > >>> btrfs cow can be done with iomap, at least on the directio end. It's > > > >>> the other features like fsverity/fscrypt/data checksumming that aren't > > > >>> currently supported by iomap. > > > >> > > > >> Pretty much everyone on btrfs uses data checksumming. > > > >> > > > >>>> What are your thoughts on this? > > > >>> > > > >>> "Gee, what if I could simplify most of my own work out of existence?" > > > >> > > > >> What is that work? > > > > > > > > Everything I've put out since the end of online fsck for xfs. > > > > > > Is pretty much all of that work either on better FUSE performance or > > > fixes for problems found by fuzzers? > > > > Mostly the iomap parts of fuse-iomap. It's a huge complication to add > > to the already confusing fuse codebase. > > imo if you did end up going the lklfuse route, I think it'd still be > useful to have the generic iomap infrastructure pieces of your > fuse-iomap patchblizzard added, for future new filesystem > implementations that can provide extent mappings to get near-native IO > performance. But, uh, are those patches going to be reviewed? --D