Re: [PATCH net-next v9 11/14] tcp: RX path for devmem TCP

On 2024-05-10 16:21, Mina Almasry wrote:

+/* On error, returns the -errno. On success, returns number of bytes sent to the

• • user. May not consume all of @remaining_len.
• */

+static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,

• 	      unsigned int offset, struct msghdr *msg,
  

• 	      int remaining_len)
  

+{

• struct dmabuf_cmsg dmabuf_cmsg = { 0 };
• struct tcp_xa_pool tcp_xa_pool;
• unsigned int start;
• int i, copy, n;
• int sent = 0;
• int err = 0;
• tcp_xa_pool.max = 0;
• tcp_xa_pool.idx = 0;
• do {

• start = skb_headlen(skb);
  

• if (skb_frags_readable(skb)) {
  

• 	err = -ENODEV;
  

• 	goto out;
  

• }
  

• /* Copy header. */
  

• copy = start - offset;
  

• if (copy > 0) {
  

• 	copy = min(copy, remaining_len);
  

• 	n = copy_to_iter(skb->data + offset, copy,
  

• 			 &msg->msg_iter);
  

• 	if (n != copy) {
  

• 		err = -EFAULT;
  

• 		goto out;
  

• 	}
  

• 	offset += copy;
  

• 	remaining_len -= copy;
  

• 	/* First a dmabuf_cmsg for # bytes copied to user
  

• 	 * buffer.
  

• 	 */
  

• 	memset(&dmabuf_cmsg, 0, sizeof(dmabuf_cmsg));
  

• 	dmabuf_cmsg.frag_size = copy;
  

• 	err = put_cmsg(msg, SOL_SOCKET, SO_DEVMEM_LINEAR,
  

• 		       sizeof(dmabuf_cmsg), &dmabuf_cmsg);
  

• 	if (err || msg->msg_flags & MSG_CTRUNC) {
  

• 		msg->msg_flags &= ~MSG_CTRUNC;
  

• 		if (!err)
  

• 			err = -ETOOSMALL;
  

• 		goto out;
  

• 	}
  

• 	sent += copy;
  

• 	if (remaining_len == 0)
  

• 		goto out;
  

• }
  

• /* after that, send information of dmabuf pages through a
  

•  * sequence of cmsg
  

•  */
  

• for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
  

• 	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
  

• 	struct net_iov *niov;
  

• 	u64 frag_offset;
  

• 	int end;
  

• 	/* !skb_frags_readable() should indicate that ALL the
  

• 	 * frags in this skb are dmabuf net_iovs. We're checking
  

• 	 * for that flag above, but also check individual frags
  

• 	 * here. If the tcp stack is not setting
  

• 	 * skb_frags_readable() correctly, we still don't want
  

• 	 * to crash here.
  

• 	 */
  

• 	if (!skb_frag_net_iov(frag)) {
  

• 		net_err_ratelimited("Found non-dmabuf skb with net_iov");
  

• 		err = -ENODEV;
  

• 		goto out;
  

• 	}
  

• 	niov = skb_frag_net_iov(frag);
  

Sorry if we've already discussed this.

We have this additional hunk:

+ if (niov->pp->mp_ops != &dmabuf_devmem_ops) { + err = -ENODEV; + goto out; + }

In case one of our skbs end up here, skb_frag_is_net_iov() and !skb_frags_readable(). Does this even matter? And if so then is there a better way to distinguish between our two types of net_iovs?