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From: Jeff King <peff@peff.net>
To: Denton Liu <liu.denton@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
	Eric Sunshine <sunshine@sunshineco.com>
Subject: Re: [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects
Date: Mon, 18 May 2020 12:50:56 -0400
Message-ID: <20200518165056.GD42240@coredump.intra.peff.net> (raw)
In-Reply-To: <cover.1589816718.git.liu.denton@gmail.com>

On Mon, May 18, 2020 at 11:47:17AM -0400, Denton Liu wrote:

> Changes since v1:
> 
> * Remove fallthrough in switch in favour of just extracting the common
>   call out of the switch in patch 3
> 
> * Add more detail in function comment and use `const char linelen[4]` in
>   patch 4
> 
> * Implement most of Peff's suggestions[0] in patch 5
> 
> * Only operate on stateless_connect() in patch 5
> 
> * Add tests in patch 5
> 
> * Drop "remote-curl: ensure last packet is a flush" in favour of
>   "stateless-connect: send response end packet"

Overall this looks pretty cleanly done. I left a few minor comments
throughout, but the real question is whether we prefer the "0002" packet
in the last one, or if we instead insist that the response end in a
flush.

At first glance, the "0002" seems like it's more flexible, because we're
making fewer assumptions about what's being transferred over the
stateless-connect channel. But in reality it still has to be pktlines
(because we're checking them for incomplete or invalid packets already).
So all it really buys us is that the server response doesn't have to end
with a flush packet.

So I dunno. The "0002" solution is slightly more flexible, but I'm not
sure it helps in practice. And it does eat up one of our two remaining
special packet markers.

There is another solution, which would allow arbitrary data over
stateless-connect: adding an extra level of pktline framing between the
helper and the parent process. But that's rather ugly (inner pktlines
may be split across outer ones, so you have to do a bunch of buffer
reassembly). I think that's actually how v0 http works, IIRC.
IMHO it probably isn't worth pursuing. That extra layer wrecks the
elegance to the v2 stateless-connect approach, and we really do expect
only pktlines to go over it.

So I think either of your solutions (enforcing a final flush, or the
0002 packet) is preferable. I'm on the fence between them.

-Peff

  parent reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13 18:04 [PATCH 0/6] remote-curl: partial fix for a deadlock with stateless rpc Denton Liu
2020-05-13 18:04 ` [PATCH 1/6] remote-curl: fix typo Denton Liu
2020-05-13 18:04 ` [PATCH 2/6] remote-curl: remove label indentation Denton Liu
2020-05-13 18:04 ` [PATCH 3/6] transport: combine common cases with a fallthrough Denton Liu
2020-05-13 23:14   ` Eric Sunshine
2020-05-18  9:18     ` Denton Liu
2020-05-18 17:43       ` Eric Sunshine
2020-05-13 18:04 ` [PATCH 4/6] pkt-line: extern packet_length() Denton Liu
2020-05-13 23:23   ` Eric Sunshine
2020-05-15 20:56   ` Jeff King
2020-05-15 20:57     ` Jeff King
2020-05-13 18:04 ` [PATCH 5/6] remote-curl: error on incomplete packet Denton Liu
2020-05-15 21:38   ` Jeff King
2020-05-18  9:08     ` Denton Liu
2020-05-18 15:49       ` Jeff King
2020-05-13 18:04 ` [PATCH 6/6] remote-curl: ensure last packet is a flush Denton Liu
2020-05-15 21:02   ` Denton Liu
2020-05-15 21:41     ` Jeff King
2020-05-18 16:34       ` Junio C Hamano
2020-05-18 16:52         ` Jeff King
2020-05-18 21:00           ` Jeff King
2020-05-18 15:47 ` [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects Denton Liu
2020-05-18 15:47   ` [PATCH v2 1/7] remote-curl: fix typo Denton Liu
2020-05-18 15:47   ` [PATCH v2 2/7] remote-curl: remove label indentation Denton Liu
2020-05-18 18:37     ` Junio C Hamano
2020-05-18 15:47   ` [PATCH v2 3/7] transport: extract common fetch_pack() call Denton Liu
2020-05-18 18:40     ` Junio C Hamano
2020-05-18 15:47   ` [PATCH v2 4/7] pkt-line: extern packet_length() Denton Liu
2020-05-18 16:04     ` Jeff King
2020-05-18 17:50       ` Eric Sunshine
2020-05-18 20:08         ` Jeff King
2020-05-18 18:44       ` Junio C Hamano
2020-05-18 15:47   ` [PATCH v2 5/7] remote-curl: error on incomplete packet Denton Liu
2020-05-18 16:22     ` Jeff King
2020-05-18 16:51       ` Denton Liu
2020-05-18 15:47   ` [PATCH v2 6/7] pkt-line: PACKET_READ_RESPONSE_END Denton Liu
2020-05-18 15:47   ` [PATCH v2 7/7] stateless-connect: send response end packet Denton Liu
2020-05-18 16:43     ` Jeff King
2020-05-18 17:12       ` Denton Liu
2020-05-18 17:26         ` Jeff King
2020-05-18 16:50   ` Jeff King [this message]
2020-05-18 17:36     ` [PATCH v2 0/7] remote-curl: fix deadlocks when remote server disconnects Denton Liu
2020-05-18 20:58       ` Jeff King
2020-05-18 22:52         ` Junio C Hamano
2020-05-19  2:38           ` Jeff King
2020-05-18 19:36     ` Junio C Hamano
2020-05-19 10:53   ` [PATCH v3 " Denton Liu
2020-05-19 10:53     ` [PATCH v3 1/7] remote-curl: fix typo Denton Liu
2020-05-19 10:53     ` [PATCH v3 2/7] remote-curl: remove label indentation Denton Liu
2020-05-19 10:53     ` [PATCH v3 3/7] transport: extract common fetch_pack() call Denton Liu
2020-05-19 10:53     ` [PATCH v3 4/7] pkt-line: extern packet_length() Denton Liu
2020-05-19 16:23       ` Eric Sunshine
2020-05-19 10:53     ` [PATCH v3 5/7] remote-curl: error on incomplete packet Denton Liu
2020-05-19 10:53     ` [PATCH v3 6/7] pkt-line: define PACKET_READ_RESPONSE_END Denton Liu
2020-05-19 10:54     ` [PATCH v3 7/7] stateless-connect: send response end packet Denton Liu
2020-05-19 18:40     ` [PATCH v3 0/7] remote-curl: fix deadlocks when remote server disconnects Jeff King
2020-05-19 21:14       ` Denton Liu
2020-05-19 20:51     ` [PATCH v3 8/7] fixup! pkt-line: extern packet_length() Denton Liu
2020-05-22 13:33     ` [PATCH v3 9/9] fixup! remote-curl: error on incomplete packet Denton Liu
2020-05-22 15:54       ` Jeff King
2020-05-22 16:05         ` Denton Liu
2020-05-22 16:31           ` Jeff King

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