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.
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.
-Peff
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