linux-kernel - Re: [PATCH v2 2/2] nvme-tcp: support specifying the congestion-control

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Date:   Wed, 9 Mar 2022 15:32:33 +0800
From:   Mingbao Sun <sunmingbao@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Chaitanya Kulkarni <kch@...dia.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        tyler.sun@...l.com, ping.gan@...l.com, yanxiu.cai@...l.com,
        libin.zhang@...l.com, ao.sun@...l.com
Subject: Re: [PATCH v2 2/2] nvme-tcp: support specifying the
 congestion-control

> > @@ -1447,6 +1449,21 @@ static int nvme_tcp_alloc_queue(struct nvme_ctrl *nctrl,
> >  	if (nctrl->opts->tos >= 0)
> >  		ip_sock_set_tos(queue->sock->sk, nctrl->opts->tos);
> >  
> > +	if (nctrl->opts->mask & NVMF_OPT_TCP_CONGESTION) {
> > +		strncpy(ca_name, nctrl->opts->tcp_congestion,
> > +			TCP_CA_NAME_MAX-1);
> > +		optval = KERNEL_SOCKPTR(ca_name);
> > +		ret = sock_common_setsockopt(queue->sock, IPPROTO_TCP,
> > +					     TCP_CONGESTION, optval,
> > +					     strlen(ca_name));  
> 
> This needs to use kernel_setsockopt.  I also can see absolutely no
> need for the optval local variable, and I also don't really see why
> we need ca_name either - if we need to limit the length and terminate
> it (but why?) that can be done during option parsing.

Well, actually at the beginning I did use kernel_setsockopt.
But the compilation failed.

Then I found the API kernel_setsockopt disappeared from kernel v5.8.
So I use sock_common_setsockopt instead.
The birth of variable ca_name and optval is just because of the
the relevant definitions related to the prototype of
sock_common_setsockopt.

But now through thinking your comments and investigating the story of
the disappearance of kernel_setsockopt, I feel I should use
tcp_set_congestion_control instead of sock_common_setsockopt.
Just as target/tcp.c replaced kernel_setsockopt with ip_sock_set_tos.

As for the length limitation of the ca name, I will (if required) move
them into the phase of option parsing in the next version.