Re: [PATCH net-next 3/4] kcm: Support MSG_SPLICE_PAGES

From: Jakub Kicinski <kuba@kernel.org>
To: David Howells <dhowells@redhat.com>
Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	David Ahern <dsahern@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Jens Axboe <axboe@kernel.dk>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Tom Herbert <tom@herbertland.com>,
	Tom Herbert <tom@quantonium.net>
Subject: Re: [PATCH net-next 3/4] kcm: Support MSG_SPLICE_PAGES
Date: Fri, 26 May 2023 20:12:02 -0700	[thread overview]
Message-ID: <20230526201202.1cd35fe9@kernel.org> (raw)
In-Reply-To: <20230524144923.3623536-4-dhowells@redhat.com>

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? 

> -		err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,
> -					       pfrag->page,
> -					       pfrag->offset,
> -					       copy);
> -		if (err)
> -			goto out_error;
> +			skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;