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(softbank126013051224.bbtec.net. [126.13.51.224]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-83f196660f9sm10289117b3a.10.2026.05.16.00.16.49 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 16 May 2026 00:16:56 -0700 (PDT) Message-ID: Date: Sat, 16 May 2026 15:16:43 +0800 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: "linux-btrfs@vger.kernel.org" From: Sun YangKai Subject: Opt-in non-fatal data csum mismatch handling? Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hi btrfs developers and maintainers, Many btrfs deployments run on consumer hardware — desktop PCs, home NAS boxes, laptops with no ECC RAM, USB-attached drives, consumer SSDs — environments where occasional data corruption are not rare. For many of these users, the data that fills most of the volume is also the data they care least about per-byte: BitTorrent downloads, build caches, browser caches, transcoded media, and so on. They would prefer "warn me and give me the data" over "fail the read with -EIO". Today btrfs offers two ways out: `nodatasum` (and the `chattr +C` linkage) and `rescue=ignoredatacsums`. Both disable detection entirely, losing the diagnostic signal users might still want. The middle option — keep verifying, keep logging, but let the read succeed on mismatch — isn't available short of patching the kernel. A possible interface: a mount option (e.g. `datacsum_action=warn`) that preserves the existing diagnostics — `btrfs_print_data_csum_error()` and the `BTRFS_DEV_STAT_CORRUPTION_ERRS` counter — but, after all mirror-repair attempts have failed, returns the corrupted data to the caller instead of `-EIO`. Disk-layer EIO from below the csum check would continue to propagate unchanged. Before sketching a patch I wanted to ask: 1. Is the concept acceptable in principle, or is "never silently return corrupt data" a hard line for btrfs? 2. If acceptable, is "suppress csum-fail only, never disk EIO" the right boundary? 3. Are the existing diagnostic anchors (dev_stat counter + ratelimited dmesg) sufficient for the "warn" half, or would you want a statx/xattr surface as well? Happy to send an RFC patch if the direction sounds reasonable. Thanks, Sun YangKai