netdev - Re: [PATCH net-next v2 2/3] net: dev: Makes sure netif

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Message-ID: <20220207084717.5b7126e7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 7 Feb 2022 08:47:17 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Toke Høiland-Jørgensen 
        <toke@...e.dk>
Subject: Re: [PATCH net-next v2 2/3] net: dev: Makes sure netif_rx() can be
 invoked in any context.

On Sat, 5 Feb 2022 21:36:05 +0100 Sebastian Andrzej Siewior wrote:
> On 2022-02-04 20:17:15 [-0800], Jakub Kicinski wrote:
> > On Fri,  4 Feb 2022 21:12:58 +0100 Sebastian Andrzej Siewior wrote:  
> > > +int __netif_rx(struct sk_buff *skb)
> > > +{
> > > +	int ret;
> > > +
> > > +	trace_netif_rx_entry(skb);
> > > +	ret = netif_rx_internal(skb);
> > > +	trace_netif_rx_exit(ret);
> > > +	return ret;
> > > +}  
> > 
> > Any reason this is not exported? I don't think there's anything wrong
> > with drivers calling this function, especially SW drivers which already
> > know to be in BH. I'd vote for roughly all of $(ls drivers/net/*.c) to
> > get the same treatment as loopback.  
> 
> Don't we end up in the same situation as netif_rx() vs netix_rx_ni()?

Sort of. TBH my understanding of the motivation is a bit vague.
IIUC you want to reduce the API duplication so drivers know what to
do[1]. I believe the quote from Eric you put in the commit message
pertains to HW devices, where using netif_rx() is quite anachronistic. 
But software devices like loopback, veth or tunnels may want to go via
backlog for good reasons. Would it make it better if we called
netif_rx() netif_rx_backlog() instead? Or am I missing the point?