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 8980A374739; Fri, 15 May 2026 13:23:11 +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=1778851397; cv=none; b=YGwwg9LPHBY4A7xpI0LxB3JunRP33YTOBu8ppDPlLbYpkvIyyqhpKd23dqdYZr+QaABUDeX0uK+kXBf3ntgBDe47x4XmXJQOsWyydrrgALJo0na9sZ40aEgrKoMzMyla47pwjp1+1Qwjwe8zMg4SS8BV3pxudvwxK3hIwfz/vu8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778851397; c=relaxed/simple; bh=OUAeRmGFrKAqbEYEjKvXJL44Nuyi/LEDMyEDp0FfMaA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=JotOCs9pWMU4XiR7L+6MKwbLBCufDHDeawplnHM4LeMa1ycz3xDOMdGv9Z2gJfM5xoOKGIGGqlyTWBwFQ5GfX5+hFRrp6JipCQtNsEBkmsq4azDloEG10PbVsQHeh29mowSMJ+vToNL3Do20xw9Jb+NGaNw4taJfQYAhwPNeRcI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (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=tiJ39MvV; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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="tiJ39MvV" 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=clJs/M02D+bpYA4hUyzi57jr0yjvLDgea9w+FNfRfKU=; b=tiJ39MvVhLAZdQ5j27zAQ5DMcT RShTWjEanrg80OEmROi8UfaDW3sCxIWRgBa7Wj2i/acxpbXiTczr62knQK1e3weVYNN+FMc9ywXzq Ok6uylH3sYhFcNZbq8c4yY2cpjD5ozZyeyDdWWc55ir5Gggi9ZCZS5vvgsMBYL84Dc/BoFW/kqbP6 YdgCjDsE1Iz10yJRTEkqx0oWzdzXVQq7XraIj57n/x8/96S1Ko1yzR2VTiSyD/g4vA0pAu3/H0G9w 72GNA+toFOqeC/XgeaFtS7rsN2P6FIfoNvA2L2oE5t2WtKIrni7/Zi/eNARAu91pFSL0MVzPvgbXz HjuzvMtA==; Received: from hch by bombadil.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNsVS-00000008R2w-0O8z; Fri, 15 May 2026 13:23:10 +0000 Date: Fri, 15 May 2026 06:23:10 -0700 From: Christoph Hellwig To: Arun Rao Cc: hch@infradead.org, Arun , lenb@kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, pavel@kernel.org, rafael@kernel.org Subject: Re: [PATCH] docs/power: note Btrfs limitation with FIBMAP for swap file offset Message-ID: References: Precedence: bulk X-Mailing-List: linux-pm@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: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Tue, May 12, 2026 at 03:12:44PM +0530, Arun Rao wrote: > Understood. My intent was mainly to document the current behaviour > observed by users on Btrfs systems where filefrag/FIBMAP-based > guidance fails, and to point users toward the existing btrfs-progs > tooling. > > That said, I understand the concern about encouraging users to rely on > resume_offset-based workflows in general given the underlying > fragility of file block mappings on moving or CoW filesystems. Yes. Can you maybe extend the text a bit to generally warn about this? I also realized that filefrag uses FIEMAP by default these days and not just FIBMAP, which is what makes it so dangerous on btrfs. btrfs smartly does not implement ->bmap, but it does implement FIEMAP in this weird way mapping to the logical address space.