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Wong Cc: Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org Subject: Re: [RFC PATCH 0/10] ftrfs: Fault-Tolerant Radiation-Robust Filesystem In-Reply-To: <20260413181156.GY6202@frogsfrogsfrogs> References: <20260413142357.515792-1-aurelien@hackers.camp> <20260413181156.GY6202@frogsfrogsfrogs> Content-Type: text/plain; charset=UTF-8 Date: Tue, 14 Apr 2026 16:11:31 +0200 Message-Id: <1776175891.855383.12726.nullmailer@hackers.camp> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: On Mon, Apr 13, 2026 at 11:11:56AM -0700, Darrick J. Wong wrote: > Why not add FEC to btrfs instead? Then you can concentrate on getting > the IO paths correct, instead of burning time on ensuring that you've > implemented all the other posix filesystemisms correctly. Adding FEC to btrfs would produce a filesystem that cannot be certified under DO-178C, ECSS-E-ST-40C, or IEC 61508. btrfs at ~200k lines is not auditable under these frameworks regardless of what features are added or removed. The certification constraint is a hard requirement for the target environment (space, avionics, nuclear/industrial). It is not a preference. A smaller, purpose-built filesystem with RS FEC as a first-class design constraint is the only viable path to certification. btrfs also carries significant complexity in its COW B-tree allocator, extent maps, and RAID layer that would need to be analyzed and certified alongside the FEC addition. The audit surface would be orders of magnitude larger than a dedicated implementation. That said, the IO path concern is valid. v3 addresses this by migrating the data IO path to iomap as you and Matthew Wilcox requested. buffer_head is retained only for metadata IO (inode table, directory blocks) pending further review. Aurelien DESBRIERES