Subject: Re: [Patch bpf-next v4 03/11] skmsg: introduce skb_send_sock() for sock_map

From: Jakub Sitnicki <[email-masked]>
Date: Thu, 11 Mar 2021 12:42:16 +0100

On Wed, Mar 10, 2021 at 06:32 AM CET, Cong Wang wrote:
> From: Cong Wang <[email-masked]>
>
> We only have skb_send_sock_locked() which requires callers
> to use lock_sock(). Introduce a variant skb_send_sock()
> which locks on its own, callers do not need to lock it
> any more. This will save us from adding a ->sendmsg_locked
> for each protocol.
>
> To reuse the code, pass function pointers to __skb_send_sock()
> and build skb_send_sock() and skb_send_sock_locked() on top.
>
> Cc: John Fastabend <[email-masked]>
> Cc: Daniel Borkmann <[email-masked]>
> Cc: Jakub Sitnicki <[email-masked]>
> Cc: Lorenz Bauer <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> ---
>  include/linux/skbuff.h |  1 +
>  net/core/skbuff.c      | 52 ++++++++++++++++++++++++++++++++++++------
>  2 files changed, 46 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 0503c917d773..2fc8c3657c53 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -3626,6 +3626,7 @@ int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
>  		    unsigned int flags);
>  int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
>  			 int len);
> +int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len);
>  void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
>  unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
>  int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 545a472273a5..396586bd6ae3 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -2500,9 +2500,12 @@ int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
>  }
>  EXPORT_SYMBOL_GPL(skb_splice_bits);
>
> -/* Send skb data on a socket. Socket must be locked. */
> -int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
> -			 int len)
> +typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg,
> +			    struct kvec *vec, size_t num, size_t size);
> +typedef int (*sendpage_func)(struct sock *sk, struct page *page, int offset,
> +			   size_t size, int flags);
> +static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
> +			   int len, sendmsg_func sendmsg, sendpage_func sendpage)
>  {
>  	unsigned int orig_len = len;
>  	struct sk_buff *head = skb;
> @@ -2522,7 +2525,7 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
>  		memset(&msg, 0, sizeof(msg));
>  		msg.msg_flags = MSG_DONTWAIT;
>
> -		ret = kernel_sendmsg_locked(sk, &msg, &kv, 1, slen);
> +		ret = sendmsg(sk, &msg, &kv, 1, slen);

Maybe use INDIRECT_CALLABLE_DECLARE() and INDIRECT_CALL_2() since there
are just two possibilities? Same for sendpage below.

>  		if (ret <= 0)
>  			goto error;
>
> @@ -2553,9 +2556,9 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
>  		slen = min_t(size_t, len, skb_frag_size(frag) - offset);
>
>  		while (slen) {
> -			ret = kernel_sendpage_locked(sk, skb_frag_page(frag),
> -						     skb_frag_off(frag) + offset,
> -						     slen, MSG_DONTWAIT);
> +			ret = sendpage(sk, skb_frag_page(frag),
> +				       skb_frag_off(frag) + offset,
> +				       slen, MSG_DONTWAIT);
>  			if (ret <= 0)
>  				goto error;
>

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