netdev - Re: [PATCH v5 net-next 01/36] net: Introduce direct data placement tcp offload

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Date:   Thu, 22 Jul 2021 17:02:58 +0300
From:   Boris Pismenny <borispismenny@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Boris Pismenny <borisp@...dia.com>,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...dia.com>,
        Christoph Hellwig <hch@....de>, sagi@...mberg.me, axboe@...com,
        kbusch@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
        smalin@...vell.com, boris.pismenny@...il.com,
        linux-nvme@...ts.infradead.org, netdev <netdev@...r.kernel.org>,
        benishay@...dia.com, ogerlitz@...dia.com, yorayz@...dia.com,
        Boris Pismenny <borisp@...lanox.com>,
        Ben Ben-Ishay <benishay@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Yoray Zack <yorayz@...lanox.com>
Subject: Re: [PATCH v5 net-next 01/36] net: Introduce direct data placement
 tcp offload

On 22/07/2021 16:39, Eric Dumazet wrote:
> On Thu, Jul 22, 2021 at 3:33 PM Boris Pismenny <borispismenny@...il.com> wrote:
> 
>> Sorry. My response above was about skb_condense which I've confused with
>> tcp_collapse.
>>
>> In tcp_collapse, we could allow the copy, but the problem is CRC, which
>> like TLS's skb->decrypted marks that the data passed the digest
>> validation in the NIC. If we allow collapsing SKBs with mixed marks, we
>> will need to force software copy+crc verification. As TCP collapse is
>> indeed rare and the offload is opportunistic in nature, we can make this
>> change and submit another version, but I'm confused; why was it OK for
>> TLS, while it is not OK for DDP+CRC?
>>
> 
> Ah.... I guess I was focused on the DDP part, while all your changes
> are really about the CRC part.
> 
> Perhaps having an accessor to express the CRC status (and not be
> confused by the DDP part)
>  could help the intent of the code.
> 

An accessor function sounds like a great idea for readability, thanks Eric!

We will re-spin the series and add it to v6.