From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="P4WwO+D7" Received: from mail-lf1-x130.google.com (mail-lf1-x130.google.com [IPv6:2a00:1450:4864:20::130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23D492128 for ; Fri, 24 Nov 2023 10:40:11 -0800 (PST) Received: by mail-lf1-x130.google.com with SMTP id 2adb3069b0e04-50aabfa1b75so3019734e87.3 for ; Fri, 24 Nov 2023 10:40:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; t=1700851209; x=1701456009; darn=vger.kernel.org; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=n6dMaBnN8wPxxEjM8N0CTPmBnvpOexlwMzfQXUjTE8U=; b=P4WwO+D7apZBePL1C5YgXrneQu5IVGUSqxZLcXpMu+huujzgzVvDCLmxVJHSPHamga G9zvX/p+6n4NB8ZtJwoesfdplhfIPT0roKRnDxxA1dahtXIoYtnq8qlEZ6yvvbam3dKg HsMchHogW7CobpjAI7pBLMxQjqjo3s618Nwo8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1700851209; x=1701456009; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=n6dMaBnN8wPxxEjM8N0CTPmBnvpOexlwMzfQXUjTE8U=; b=tUS6yZc1q3ehvRschmVlD3cy8IpshAM6xFwm/OAndVuKqeEDAYcz4BibtufJ+bhl3b LczEIdv/kvHxEK4xLMnu7YmDvzIaDxIrFc5RSVT1ZXHIUwx+wSrTZ5hPbdHbANdYCDjp rhNLZMl0AyX0+U1Adyz2l8+u+3ixq8SDVXPZcYkmvnmMqWeAx8Sjjnm4Q74Vgcv8uHMu ATMkiODTRKWNivFfawGlbKsnykHlt+R6Ikf1BQ2Ioh+E3bBRA+kSR6areqH85vnZKRVC vfxmKLO/daptpbL1agYdhvym8w3p2MzbyCy2lQeqZLcwUFxuABrevvkTcxeUswie5S7d 5LHw== X-Gm-Message-State: AOJu0YxehwJ2asa/KjrYQhlAti0+nlB8jxOZezjyCqE08qRMb9ow8ber XasTL+GzUs1UFIlvRLJPmgM+3ooReuz1fneA74I7og== X-Google-Smtp-Source: AGHT+IEhnoN1YQK6aIjZ8+PTtOIBiL+yaiNG+vLOM/RTjsS0BeSNNHJQB3/lZfASLQrCCjO3fSMo3Q== X-Received: by 2002:a05:6512:3f0a:b0:507:b1f8:7895 with SMTP id y10-20020a0565123f0a00b00507b1f87895mr3209781lfa.38.1700851209252; Fri, 24 Nov 2023 10:40:09 -0800 (PST) Received: from mail-lf1-f44.google.com (mail-lf1-f44.google.com. [209.85.167.44]) by smtp.gmail.com with ESMTPSA id j3-20020a19f503000000b0050aaaaf82f7sm569447lfb.260.2023.11.24.10.40.08 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Nov 2023 10:40:08 -0800 (PST) Received: by mail-lf1-f44.google.com with SMTP id 2adb3069b0e04-50797cf5b69so3015689e87.2 for ; Fri, 24 Nov 2023 10:40:08 -0800 (PST) X-Received: by 2002:a05:651c:1208:b0:2bc:c771:5498 with SMTP id i8-20020a05651c120800b002bcc7715498mr3557404lja.18.1700851207707; Fri, 24 Nov 2023 10:40:07 -0800 (PST) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <1205248.1700841140@warthog.procyon.org.uk> In-Reply-To: <1205248.1700841140@warthog.procyon.org.uk> From: Linus Torvalds Date: Fri, 24 Nov 2023 10:39:51 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT PULL] afs: Miscellaneous fixes To: David Howells Cc: Marc Dionne , linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" On Fri, 24 Nov 2023 at 07:52, David Howells wrote: > Btw, I did want to ask about (5): Does a superblock being marked SB_RDONLY > imply immutability to the application? Obviously not - any network filesystem can and will change from under you, even if the local copy is read-only. So SB_RDONLY can only mean that writes to that instance of the filesystem will fail. It's a bit stronger than MNT_READONLY, in that for a *local* filesystem, SB_RDONLY tends to mean that it's truly immutable (while MNT_READONLY is obviously per mount) but even then some sub-mount thing (and I guess the AFS snapshot is a good example of that) might expose the same filesystem through multiple superblocks. Exactly like a network filesystem inevitably will. In any case, any user space that thinks SB_RDONLY is some kind of immutability signal is clearly buggy. At a minimum, such user space would have to limit itself to particular filesystem types and say "I know _this_ filesystem can have only one superblock"). And I'd argue that while that might work in practice, it's insane. Linus