From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 848202773FD for ; Mon, 29 Sep 2025 08:50:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759135849; cv=none; b=A+QO6pEfZkyaC85O8TMaGund6HAGCP1zlRTZ9hztAPqGNb0yiPwzU6Pv2EDwHymrPKFMrb1fS4xE+7CLSjAqxlaDnpy76qDkuxdEFbmqZGRscIuWzSxTWSjkAPCRpIHi9mCdPDhMk6Z3+0rI6/LpVzYSHtJhz2iHzMHW+w7DMc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759135849; c=relaxed/simple; bh=1e3OXyqYVtTOrH4/RKLiNO/x1SmRRQX28kSMnCTUu0U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WILBndgs0mM2xIiYC0Nj6VgkX9cMrmDl9gutFxmuWM2IcPbtal/qWcdkhSxEZWdkITvTSmELKIO0syhlDCAztu9/OmkGHUrN6QK7r2RB8Yu7vTDbmwIy9BmvQ5X6yUT0DWKBajn3A9OOY0RDdGsuEd01CizYWc3CshsCe4cL7tA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=PuL/togi; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="PuL/togi" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=dZ45+WyHj8eXGCdFjwCn6mLQX15JZ+wkjQPct1edF0Y=; b=PuL/togieHe62l25RDwugdWUeK g2rj+Th1ELmtCqePUMJ5mbrhG3WpkDZ0Vyl6yf8BXZmdDa/eg7JFuZFEtktPFNoEZsC1YBckDP0N7 gXCgz/VzEH2ZIuD/rsanZ0WIwAj8PA8Dayd24VsYu68KsxdifcUFD+mnyqGRelK/yY+l6eUOFKzG6 UYVd0ip8gARAaBDpHTqKMOILG0m13hsrSFTe3+7FZ8B13BOMrkFv1MbEauus4UKTmtv2msyBBWVz+ 6HQGjGvpdvOWBsXOne6Wb5tObs/EcTxRY7CZYRqIXFKvY4dCl4GqpmTibgVAF16Xp0FPfwZmwyd/J j15WBAzQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1v39ap-00000001pez-0lPt; Mon, 29 Sep 2025 08:50:47 +0000 Date: Mon, 29 Sep 2025 01:50:47 -0700 From: Christoph Hellwig To: Demi Marie Obenour Cc: Christoph Hellwig , linux-btrfs@vger.kernel.org Subject: Re: Can the output of FIEMAP on BTRFS be used to check if a file and its reflink copy might have diverged? Message-ID: References: <38f350b0-9a71-4627-9d36-57bf2f85e67a@gmail.com> <7b756bc3-fae4-4cbb-99a1-117880269269@gmail.com> <0b428deb-3711-4671-96dd-69c149fd8ccb@gmail.com> Precedence: bulk X-Mailing-List: linux-btrfs@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: <0b428deb-3711-4671-96dd-69c149fd8ccb@gmail.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Mon, Sep 22, 2025 at 01:54:56PM -0400, Demi Marie Obenour wrote: > This leaves the question of whether the needed information is in the > filesystem metadata. If so, xfsprogs and/or btrfsprogs could obtain > it from a block-layer snapshot offline without needing kernel changes. > Otherwise, kernel changes will be needed. I don't know if the changes > to the userspace tools will be accepted, though. Until then, btrfs > send/receive will be the only way to efficiently back up a BTRFS > filesystem, and XFS will only be able to be efficiently backed up > at the block level. Using userspace tools that poke at the block-level mapping is fundamentally unsafe because it is not synchronized with the file system.