From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from libero.it (smtp-18.italiaonline.it [213.209.10.18]) (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 9C52D3BF672 for ; Thu, 14 May 2026 19:54:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.209.10.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778788487; cv=none; b=oyGUDkVPjgrD3LrkKfSXswjx0S6pCFzg6zyjuqiDbOnBBk9edC3bB6bWCP4x0x9fvsPRJy5jlCwrCgMI4doN33uAEEwLWZKJgIQ8meLcfEa/BAAssDlqekOiLV+U4jG2eEFEHuOAdtjRuZxeal08xgALSYSlvtOAU9/MDJOYUMQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778788487; c=relaxed/simple; bh=bxZEKtTP0qO2jIGzW7Kwa31tfboGR2aCepPMKsO9DGg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pDdWIWzHt44l85xzSBWyQ+A3PPeRoEA2c8NdN/NYG4y9Gz7GRHFuDHlfrztCEk1Yo4UfNQi7ihXDguN7nGTkGDXAtSfm4KHdQTUx1UOALYBGi2n/vpWqNbs5nqfwhnwTOC1C2diG9BQYhoNTiYJ8sGDXtrtqLspSiCEUgCImIxw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=libero.it; spf=pass smtp.mailfrom=libero.it; dkim=pass (2048-bit key) header.d=libero.it header.i=@libero.it header.b=WjBd6m5G; arc=none smtp.client-ip=213.209.10.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=libero.it Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=libero.it Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=libero.it header.i=@libero.it header.b="WjBd6m5G" Received: from [192.168.1.27] ([84.220.171.3]) by smtp-18.iol.local with ESMTPA id Nc6CwXG9svXD3Nc6CwmS65; Thu, 14 May 2026 21:52:07 +0200 x-libjamoibt: 1601 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=libero.it; s=s2021; t=1778788327; bh=bD3QJ+lr63//8NcpvDCT9tKc3YLZWQgdbpAaQhjYRpQ=; h=From; b=WjBd6m5GeZLiEpJDmyyT/8VPp5EOXd4PhZx9kHUiOpqfvSBe7IFbl7krzNd92M9Ij h6EhL6qXXq9UaNsQfdJ5a66jWHPe3D2L7Nu/xrybOS+yOAwV6LdAjAl7orTfUz4kwH 3auL6iqBbyl11V0qHQa1mg54QFrGy31tudePZPxfmDSHUVOc9cV7FN4yHppkUtjtZO 1eNNuq7/0Y74HmPuEqWqRhs3SrQQlZ7arXDilEcB+jEsAp8ofe+4bD0Y0I0ZeAg86U 3nuNpLvyVhMptjCg9r0R4NKBj3/xghtHqCInpSBZcxe6j2wOauOLHj8pRwkeniaUAa v7xxVDpm6+b5w== X-CNFS-Analysis: v=2.4 cv=KNpaDEFo c=1 sm=1 tr=0 ts=6a0627e7 cx=a_exe a=hciw9o01/L1eIHAASTHaSw==:117 a=hciw9o01/L1eIHAASTHaSw==:17 a=IkcTkHD0fZMA:10 a=gdOXTq2rPY5K92qxl70A:9 a=QEXdDO2ut3YA:10 Message-ID: <0a8d1ff4-f5a2-49e9-aa45-d25dbe4ded40@libero.it> Date: Thu, 14 May 2026 21:51:59 +0200 Precedence: bulk X-Mailing-List: linux-raid@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: kreijack@inwind.it Subject: Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6 To: Christoph Hellwig , David Sterba Cc: Andrew Morton , Catalin Marinas , Will Deacon , Ard Biesheuvel , Huacai Chen , WANG Xuerui , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Herbert Xu , Dan Williams , Chris Mason , David Sterba , Arnd Bergmann , Song Liu , Yu Kuai , Li Nan , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org, linux-raid@vger.kernel.org References: <20260512052230.2947683-1-hch@lst.de> <20260512052230.2947683-2-hch@lst.de> <20260512114231.GG2558453@suse.cz> <20260513054742.GA1018@lst.de> Content-Language: en-US From: Goffredo Baroncelli In-Reply-To: <20260513054742.GA1018@lst.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CMAE-Envelope: MS4xfIDtr7UvibXhotDq/eGXiDloNUqbPDkdUcxlgBaAHHbQvsiYahHpeNORunqIajszasgr8c3B8z/XyVOyAuN5hf4175nD+vlvtMC0bIY9QJZp6woWJNrG aQk3PfyHHPYy0hAJeCmEsrwL+sXrn8raXvwSVFwja+mNIGcKFygU4bdVw8v1VKDOhOcKheYp3BbVwQqMojH7Fl3INb7gtuRV2KJmyAjSGXNJhncVaQGAWAXT oo9oBSC2F1t8jl/GotUy7wzpLHDbKBEqbAMmtYHdik+INpHro8RYa5E9Xq6OjONzHdXTvo9rbFmCDPwVpbwYHwCe0MqnMSDrNEtco2tbBGAHXZQltPV0OL6m Xs4XHyVNJychZ3wNHl+FP7VInrjAJxVyZarLA6h1GLmH6C7bo7xh7AiFVhmS448mJ7oddw2E4GcHCQLw5nc+mncOBuUBdW8FPmgVqBmLYRW/E1uHf5H7ymxf 7+M72Ab7Lfz5l1ZroO9USEopaT2TBjueXvWWFJeuh+TSc+GQh5CVcLujqqlEOSlSp1R8OM48gPzAiNRzuVncRPYO912eFvGsZNofHbnJZ9P4JQlVvIPXrGUB k7Rksq1+0+/sGJ2glUPm+veTLd0hOFrGOX4ZELZW5Img1Rjh7oT/YM8G+lXjJbJOhlr6dtYSc1AC8AObXM80AsLIGbqAOpJVhPL0SZOZ5g6Eu3Cfm1/Q33as QHSlwOGbMr3uM6BXBwCA/iRSLcteO0RORQvEAQO/e8MiSvc/dUNZzTez6wHixpEXWQgZ9Z2NCRxukJhNoR1Rx4h+eGB19h2fhW2x2HiNZrbKd9S9OcLI88MY VUksbcbJ5ZMjktY8kGFSnH8Sl2ShB0yrH/NgA0RY1roEXSzCGqsE7TP3RQARPk+NJazqFOqfqBBqnZtd5+mQ4UNQ7vAQ8hGUUzJa0YumkRS4nD9X559FZfXe 3QOgg2TlhwAwcQGvb+Ss+4k9h9DXM6VcEJLsA1QfBnYHYKfliz3h16SIG6W9Iv+uyDk540G1k9dytoNAOXtfwInzV/kvD8Gdkx/D5xTLs2Sy2Vsz+fiNYheM RnLdoR588cGVPiQvhFzHmun/E7dTIUBeFfbij8HjYQhlm3iRhm0aHJPBV9Vy9cCHzTY2Xgl9a5O9fV2pbB+fheegaejlj1NEvwMJXnqpW4b7V72sTbFeBBpq sV7UY0G4iFsh4psQSpK2n56bqWeEew5AkQ99Y/kUreS7WeUBfBiERWWaetQDZDCQNQA8U71Vc5hY0RLOFV2Aw7GFB7tuY8UWgz+lrNAODlW3lBkv98wvQAM2 elm5SufYC+WToRDZbALHIfeKQaWetyvkUyIdnsY+d8sgX9LlFz8i7BQ2NdF+Kx5bVl5SHJ+7SVGlrENFPkZmuc9c76uB16GUvPNEKCGDocJxGmG4zCOAHF2C /C9IjdfcMCOt4BPR2AQ5I7a7UIHbl/0cLeCT3ndssV7yObVQj8fyrC9JvV103G4ONfKQAFRlbxqOghcPn/SVhhkuA7CbWDbiGwsvIIr4aWyBADP7w9O7YYob oxPW28FwtEbUoi7iCAVuNr75ZuhwG4v9wrI1nPiKemFdJA== On 13/05/2026 07.47, Christoph Hellwig wrote: > On Tue, May 12, 2026 at 01:42:31PM +0200, David Sterba wrote: > >> The degenerate modes of >> raid0, 5, or 6 are explicit as a possible middle step when converting >> profiles. We can use a fallback implementation for this case if the >> accelerated implementations cannot do it. > > This is not about a degenerated mode. For a degenerated RAID 6, parity > generation uses the RAID 5 XOR routines as the second parity will be > missing. This is about generating two parities for a single data disk, > which must be explicitly selected. > I think that the David concern is : "what happens for an already existing btrfs raid6 3 disks filesystem when the user upgrade the kernel ?" (I am thinking when a new BG needs to be allocated)... BR GB -- gpg @keyserver.linux.it: Goffredo Baroncelli Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5