On Fri, Mar 25 2022, Jeff Hostetler wrote: > On 3/25/22 3:02 PM, rsbecker@xxxxxxxxxxxxx wrote: >> On March 25, 2022 2:03 PM, Jeff Hostetler wrote: > [...] >> So that we can plan for next time, would you mind giving some >> thought to what would be required for Linux and whether it makes >> sense to extend this. No urgency, but I would not mind participating >> - assuming my $DAYJOB lets me. I have a backlog for git that I need >> to get done first anyway. >> Kind Regards, >> Randall >> > > A Linux backend would need to: > > (1) stub in compat/fsmonitor/fsm-listen-linux.c (see commits > 8/30 and 9/30 in this series). That gives you enough for > the builtin/fsmonitor--daemon.c to link with your new > backend. > > (2) populate those 4 routines. > > (2a) __ctor() and __dtor() will be called from the main thread > before and after the listener thread is created. You can > do anything you need there to register/deregister a watch > on the FS. > > See inotify() and/or fanotify(). I haven't looked at those > routines for a while, so all I can say is google it. > > (2b) __stop_async() will be called by "some" thread to request > that the listener thread stop listening. This is an async > request, so just notify the listener thread and return. > (There is an example of this for Unix in > compat/simple-ipc/ipc-unix-sockets.c) > > (2c) __loop() will be called (once) by the "listener" thread-proc > to process/service events from the FS until a shutdown event > is received. This runs in the body of the "listener" thread. > It should probably use poll()/select()/whatever on fd's from > inotify()/fsnotify() *and* whatever you set up in (2b) to > wait for a shutdown event. > > (There are examples of this wait-loop in the Windows and Mac > backends, but they have *very* different FS event and wait > models, so they might not be very helpful here.) > > When you get a "batch" of one or more paths from the FS, > use the fsmonitor_classify_*() routines to classify or > discard them and then use fsmonitor_publish() to publish > newly changed paths to the other threads. > > The core code will handle path de-dup and all locking so > you don't have to. > > It is important that you figure out how to get recursive data > from the FS. We want to watch the complete worktree. Windows > and Mac let you register the root directory of the watch and > automatically give me events for anything under it. IIRC, > inotify() only gave you a single directory and you had to > readdir() and recurse to get fd's to the subdirs. I haven't > looked to see if fanotify() solves that or not. So there may > be some fd juggling and tree walking required. That could/should > all be hidden inside the __ctor() and/or __loop() routines. > > (3) stub in compat/fsmonitor/fsm-settings-linux.c (see the > peers. This is needed to link. > > (4) fill in any platform-specific reasons why you might want > to reject a worktree. for example, when they are remote > (NFS/SMB might support it, but do you trust it....) > > (5) stub in compat/fsmonitor/fsm-health-linux.c (see > fsm-health-*.c in part 3). That will give you enough > to link the health thread. > > (6) this part is probably optional (at least for now). we > can use this if we want to add platform-specific things > like auto-shutdown after idle. The mac version is currently > empty, but the Windows version needs to watch the worktree > root separately (because the FS watch is limited to what > is *within* watched directory root). > > That should help get you get started. > Let me know if you have questions. Wouldn't it be much simpler POC in this case to write "watchman backend"? Then we'd both get a Linux backend, and an alternate backend for the other platforms to validate their implementation. Some past references to that: https://lore.kernel.org/git/871r8c73ej.fsf@xxxxxxxxxxxxxxxxxxx/ & https://lore.kernel.org/git/87h7lgfchm.fsf@xxxxxxxxxxxxxxxxxxx/
