From: Paul Tarjan Date: Wed, 04 Mar 2026 18:17:52 GMT Subject: Re: [PATCH v7 08/10] fsmonitor: add tests for Linux Message-ID: <20260304181752.25768-1-github@paulisageek.com> In-Reply-To: On Tue, Mar 4, 2026, Patrick Steinhardt wrote: > Hm. So the fsmonitor listener for Linux is not reliable? Wouldn't the > end user see the same issue then? I'm not sure whether just ignoring > that issue and adding a timeout to our tests is the proper way to fix > it. > > Before we jump to such solutions I'd rather want to know what the root > cause of this. We had similar issues in the past on macOS, where we > eventually figured out that we were missing events due to the buffers > not being big enough. So did you investigate what the conditions are to > trigger this? This isn't a buffer issue or a bug in our code, it's a kernel limitation in overlayfs. On older kernels, overlayfs doesn't implement the fsnotify hooks that inotify depends on, so inotify_add_watch succeeds but events are silently never delivered. Newer kernels have partially fixed this but it still affects some configurations. An end user on overlayfs would hit the same thing: the cookie wait times out and they get a full-scan fallback. Correct results, just no incremental speedup. The smoke test catches this early so we can skip instead of timing out on every subsequent test.