From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AACB9523A for ; Wed, 3 Jul 2024 01:03:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719968640; cv=none; b=e8Jq8qwgnWGnPVgGtV3L69hcIRma8AQRQHp7ySHPIZRPRiD5exgYSbQGq0UcO4QEVxf/j6DZz39Y8d01HsHOIVaM68gBE5Pr7rvOBF93fKn7lFUlUwhGU6I9/abuYOt+3Hpf8dCmdG763MTLwHfsnQ7vA9dD9hLJlrz6rANzVHU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719968640; c=relaxed/simple; bh=N5Ae9rGoE3GKngiy/Tj9+RKRVssoTFMAU66isGG61rg=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=IDttRSON4JMyH1SRLhRhH4OCUnFEl6zczdsju3OF5kyywep1QLBirMPbJIIz7rXC9uni6esSaFe+bbMYxiZw+zHLDVL6BMihte/Vv5v0oXWNPeUovckA2UcIApxZwkYeRW3aMV/vXrFWp7MUSHcob0xuZowRIM1cghnMVIOYPn0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--drosen.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=WwD6txZR; arc=none smtp.client-ip=209.85.128.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--drosen.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="WwD6txZR" Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-64b2a73ad0bso73564807b3.3 for ; Tue, 02 Jul 2024 18:03:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1719968638; x=1720573438; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=FyIaT//Jdg7f/8MKV1vKBRmhvJGqM0s2j18nW8bQEiY=; b=WwD6txZR1umu7OaMpP2iHFxLErv67xDOwVw4wkv7/N3RF+aXhGfYwCxgKpLxsu+vdf yDjWVsgJsEGaAphCy0FEzILvF23P2FN0yT5+tfCoAYLEtHx24XOnj6j80XpgToXYdmVo xLfmQXhYJK3SM/YhAoCs4slP8nMXyqWs8DKvKePUUJ8wjEtNHFXF1HzKWwZCivhxQW37 mU28kw1QQRzF8LyOS841o645rdVNv7rcMvg24fatFoFMRQhi1Al/s4gpLtHl31Giz6m5 8xsko30VSys6dYS3s7ncE5YX5/lH2rvZHbW61b5cQ93aF4ELhDtIEyF1LAi8Pn/E3YAV 9G/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1719968638; x=1720573438; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=FyIaT//Jdg7f/8MKV1vKBRmhvJGqM0s2j18nW8bQEiY=; b=WDaamXFbGwBUel8+JCWXROBdrBH6J1SKY9bzmpBs/S5p0gA7vLYjY4dyiZg/mxbhLK OzwHlGuF1WDOkVYZzMfl5XIB60vM6qfJtzykax+A2TTFPRumE0W/RrZgywNVDe1ZpDbI sweB3bCph8iknYiE4KW/GO2ZZ83LYVO6Vhqk3wQsXeRyuEswENUTVmZ0R5XGTARyheM3 xw04cbjPRlqBCxakyT/EeB6PDw4EGLAwrRt2pQ5NDsyJ31kAaUBylR2irw5Qgue6v36Y MVhUxT+mUAFt41H4GkZ9MOfMTEbbVhWWVcwnhxy75WqHoEB9FL7bIO2y8tZdtmdNrKUO Jniw== X-Gm-Message-State: AOJu0YzDH1SL8bFBsJuc9BWfyXFWIi7+3XgXTVyVW5GmQPXh77f+mhjb D2K0VK64mUARr9UwaMaXbzyty8kozVhyz4KJ1M9U9iVM7+DObtDsxpIEC7twKyn8g5oY0wpqR+P 23Q== X-Google-Smtp-Source: AGHT+IGV/NvoJUuArfID21GmDZBYGZ36B6phTaS0vo7MrU7Ut8oKdvUBr5uZ4z0FMUGS8o2DHX2qxiyBQyo= X-Received: from drosen.mtv.corp.google.com ([2620:15c:211:201:2ca5:53d1:2309:2615]) (user=drosen job=sendgmr) by 2002:a05:690c:480c:b0:62c:fb55:aeab with SMTP id 00721157ae682-6512ff21046mr20307b3.8.1719968637718; Tue, 02 Jul 2024 18:03:57 -0700 (PDT) Date: Tue, 2 Jul 2024 18:02:14 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.45.2.803.g4e1b14247a-goog Message-ID: <20240703010215.2013266-1-drosen@google.com> Subject: [PATCH 0/1] Fuse Passthrough cache issues From: Daniel Rosenberg To: Miklos Szeredi , Amir Goldstein Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, kernel-team@android.com, Daniel Rosenberg Content-Type: text/plain; charset="UTF-8" I've been attempting to recreate Android's usage of Fuse Passthrough with the version now merged in the kernel, and I've run into a couple issues. The first one was pretty straightforward, and I've included a patch, although I'm not convinced that it should be conditional, and it may need to do more to ensure that the cache is up to date. If your fuse daemon is running with writeback cache enabled, writes with passthrough files will cause problems. Fuse will invalidate attributes on write, but because it's in writeback cache mode, it will ignore the requested attributes when the daemon provides them. The kernel is the source of truth in this case, and should update the cached values during the passthrough write. The other issue I ran into is the restriction on opening a file in passthrough and non passthrough modes. In Android, one of our main usecases for passthrough is location metadata redaction. Apps without the location permission get back nulled out data when they read image metadata location. If an app has that permission, it can open the file in passthrough mode, but otherwise the daemon opens the file in normal fuse mode where it can do the redaction. Currently in passthrough, this behavior is explicitly blocked. What's needed to allow this? The page caches can contain different data, but in this case that's a feature, not a bug. They could theoretically be backed by entirely different things, although that would be fairly confusing. I would think the main thing we'd need would be to invalidate areas of the cache when writing in passthrough mode to give the daemon the opportunity to react to what's there now, and also something in the other direction. Might make more sense as something the daemon can opt into. Any thoughts on these issues? And does the proposed fix make sense to you? Daniel Rosenberg (1): fuse: Keep attributes consistent with Passthrough fs/fuse/passthrough.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) base-commit: 73e931504f8e0d42978bfcda37b323dbbd1afc08 -- 2.45.2.803.g4e1b14247a-goog