netdev - RE: [PATCH v2 1/2] udp: UDP socket send queue repair

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Message-ID: <29dc7ac9781344f1a57e16c14900a7da@AcuMS.aculab.com>
Date:   Fri, 13 Aug 2021 13:00:12 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Bui Quang Minh' <minhquangbui99@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
        "dsahern@...nel.org" <dsahern@...nel.org>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "avagin@...il.com" <avagin@...il.com>,
        "alexander@...alicyn.com" <alexander@...alicyn.com>,
        "lesedorucalin01@...il.com" <lesedorucalin01@...il.com>
Subject: RE: [PATCH v2 1/2] udp: UDP socket send queue repair

From: Bui Quang Minh
> Sent: 13 August 2021 12:08
...
> The reason we want to dump the packet in send queue is to make to state of the
> application consistent. The scenario is that when an application sends UDP
> packets via UDP_CORK socket or with MSG_MORE, CRIU comes and checkpoints the
> application. If we drop the data in send queue, when application restores, it
> sends some more data then turns off the cork and actually sends a packet. The
> receiving side may get that packet but it's unusual that the first part of that
> packet is missing because we drop it. So we try to solve this problem with some
> help from the Linux kernel.

Patient: It hurts if I do xxx.
Doctor: Don't do xxx then.

It has to be more efficient to buffer partial UDP packets
in userspace and only send when all the packet is available.

	David

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