> On 03 Aug 2016, at 23:24, Jeff King <peff@xxxxxxxx> wrote: > > On Wed, Aug 03, 2016 at 06:42:20PM +0200, larsxschneider@xxxxxxxxx wrote: > >> From: Lars Schneider <larsxschneider@xxxxxxxxx> >> >> Some commands might need to perform cleanup tasks on exit. Let's give >> them an interface for doing this. >> >> Please note, that the cleanup callback is not executed if Git dies of a >> signal. The reason is that only "async-signal-safe" functions would be >> allowed to be call in that case. Since we cannot control what functions >> the callback will use, we will not support the case. See 507d7804 for >> more details. > > I'm not clear on why we want this cleanup filter. It looks like you use > it in the final patch to send an explicit shutdown to any filters we > start. But I see two issues with that: > > 1. This shutdown may come at any time, and you have no idea what state > the protocol conversation with the filter is in. You could be in > the middle of sending another pkt-line, or in a sequence of non-command > pkt-lines where "shutdown" is not recognized. Maybe I am missing something, but I don't think that can happen because the cleanup callback is *only* executed if Git exits normally without error. In that case we would be in a sane protocol state, no? > 2. If your protocol does bad things when it is cut off in the middle > without an explicit shutdown, then it's a bad protocol. As you > note, this patch doesn't cover signal death, nor could it ever > cover something like "kill -9", or a bug which prevented git from > saying "shutdown". > > You're much better off to design the protocol so that a premature > EOF is detected as an error. For example, if we're feeding file > data to the filter, and we're worried it might be writing it to > a data store (like LFS), we would not want it to see EOF and say > "well, I guess I got all the data; time to store this!". Instead, > it should know how many bytes are coming, or should have some kind > of framing so that the sender says "and now you have seen all the > bytes" (like a pkt-line flush). > > AFAIK, your protocol _does_ do those things sensibly, so this > explicit shutdown isn't really accomplishing anything. Thanks. The shutdown command is not intended to be a mechanism to tell the filter that everything went well. At this point - as you mentioned - the filter already received all data in the right way. The shutdown command is intended to give the filter some time to perform some post processing before Git returns. See here for some brainstorming how this feature could be useful in filters similar to Git LFS: https://github.com/github/git-lfs/issues/1401#issuecomment-236133991 - Lars -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html