linux-kernel - Re: [PATCH net-next 3/4] kcm: Support MSG_SPLICE

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Date:   Wed, 31 May 2023 09:51:53 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     dhowells@...hat.com, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Tom Herbert <tom@...bertland.com>,
        Tom Herbert <tom@...ntonium.net>
Subject: Re: [PATCH net-next 3/4] kcm: Support MSG_SPLICE_PAGES

Jakub Kicinski <kuba@...nel.org> wrote:

> On Wed, 24 May 2023 15:49:22 +0100 David Howells wrote:
> > +			err = skb_splice_from_iter(skb, &msg->msg_iter, copy,
> > +						   sk->sk_allocation);
> > +			if (err < 0) {
> > +				if (err == -EMSGSIZE)
> > +					goto wait_for_memory;
> > +				goto out_error;
> > +			}
> >  
> 
> should there be a:
> 
> 		copy = err;
> or:
> 		copy -= msg_data_left(msg);
> 
> or some such here? Can we safely assume that skb_splice_from_iter() will
> copy all or nothing? 

Yeah.  Good point.  I didn't add one because the normal operation code doesn't
do that - but I guess that's all-or-nothing.

David