kcm: Convert kcm_sendpage() to use MSG_SPLICE_PAGES

Convert kcm_sendpage() to use sendmsg() with MSG_SPLICE_PAGES rather than
directly splicing in the pages itself.

This allows ->sendpage() to be replaced by something that can handle
multiple multipage folios in a single transaction.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Tom Herbert <tom@herbertland.com>
cc: Tom Herbert <tom@quantonium.net>
cc: Cong Wang <cong.wang@bytedance.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 8555ede..ba22af1 100644 (file)
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -761,149 +761,6 @@ static void kcm_push(struct kcm_sock *kcm)
                kcm_write_msgs(kcm);
 }
 
-static ssize_t kcm_sendpage(struct socket *sock, struct page *page,
-                           int offset, size_t size, int flags)
-
-{
-       struct sock *sk = sock->sk;
-       struct kcm_sock *kcm = kcm_sk(sk);
-       struct sk_buff *skb = NULL, *head = NULL;
-       long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
-       bool eor;
-       int err = 0;
-       int i;
-
-       if (flags & MSG_SENDPAGE_NOTLAST)
-               flags |= MSG_MORE;
-
-       /* No MSG_EOR from splice, only look at MSG_MORE */
-       eor = !(flags & MSG_MORE);
-
-       lock_sock(sk);
-
-       sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
-
-       err = -EPIPE;
-       if (sk->sk_err)
-               goto out_error;
-
-       if (kcm->seq_skb) {
-               /* Previously opened message */
-               head = kcm->seq_skb;
-               skb = kcm_tx_msg(head)->last_skb;
-               i = skb_shinfo(skb)->nr_frags;
-
-               if (skb_can_coalesce(skb, i, page, offset)) {
-                       skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
-                       skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;
-                       goto coalesced;
-               }
-
-               if (i >= MAX_SKB_FRAGS) {
-                       struct sk_buff *tskb;
-
-                       tskb = alloc_skb(0, sk->sk_allocation);
-                       while (!tskb) {
-                               kcm_push(kcm);
-                               err = sk_stream_wait_memory(sk, &timeo);
-                               if (err)
-                                       goto out_error;
-                       }
-
-                       if (head == skb)
-                               skb_shinfo(head)->frag_list = tskb;
-                       else
-                               skb->next = tskb;
-
-                       skb = tskb;
-                       skb->ip_summed = CHECKSUM_UNNECESSARY;
-                       i = 0;
-               }
-       } else {
-               /* Call the sk_stream functions to manage the sndbuf mem. */
-               if (!sk_stream_memory_free(sk)) {
-                       kcm_push(kcm);
-                       set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
-                       err = sk_stream_wait_memory(sk, &timeo);
-                       if (err)
-                               goto out_error;
-               }
-
-               head = alloc_skb(0, sk->sk_allocation);
-               while (!head) {
-                       kcm_push(kcm);
-                       err = sk_stream_wait_memory(sk, &timeo);
-                       if (err)
-                               goto out_error;
-               }
-
-               skb = head;
-               i = 0;
-       }
-
-       get_page(page);
-       skb_fill_page_desc_noacc(skb, i, page, offset, size);
-       skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;
-
-coalesced:
-       skb->len += size;
-       skb->data_len += size;
-       skb->truesize += size;
-       sk->sk_wmem_queued += size;
-       sk_mem_charge(sk, size);
-
-       if (head != skb) {
-               head->len += size;
-               head->data_len += size;
-               head->truesize += size;
-       }
-
-       if (eor) {
-               bool not_busy = skb_queue_empty(&sk->sk_write_queue);
-
-               /* Message complete, queue it on send buffer */
-               __skb_queue_tail(&sk->sk_write_queue, head);
-               kcm->seq_skb = NULL;
-               KCM_STATS_INCR(kcm->stats.tx_msgs);
-
-               if (flags & MSG_BATCH) {
-                       kcm->tx_wait_more = true;
-               } else if (kcm->tx_wait_more || not_busy) {
-                       err = kcm_write_msgs(kcm);
-                       if (err < 0) {
-                               /* We got a hard error in write_msgs but have
-                                * already queued this message. Report an error
-                                * in the socket, but don't affect return value
-                                * from sendmsg
-                                */
-                               pr_warn("KCM: Hard failure on kcm_write_msgs\n");
-                               report_csk_error(&kcm->sk, -err);
-                       }
-               }
-       } else {
-               /* Message not complete, save state */
-               kcm->seq_skb = head;
-               kcm_tx_msg(head)->last_skb = skb;
-       }
-
-       KCM_STATS_ADD(kcm->stats.tx_bytes, size);
-
-       release_sock(sk);
-       return size;
-
-out_error:
-       kcm_push(kcm);
-
-       err = sk_stream_error(sk, flags, err);
-
-       /* make sure we wake any epoll edge trigger waiter */
-       if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
-               sk->sk_write_space(sk);
-
-       release_sock(sk);
-       return err;
-}
-
 static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 {
        struct sock *sk = sock->sk;
@@ -1111,6 +968,24 @@ out_error:
        return err;
 }
 
+static ssize_t kcm_sendpage(struct socket *sock, struct page *page,
+                           int offset, size_t size, int flags)
+
+{
+       struct bio_vec bvec;
+       struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES, };
+
+       if (flags & MSG_SENDPAGE_NOTLAST)
+               msg.msg_flags |= MSG_MORE;
+
+       if (flags & MSG_OOB)
+               return -EOPNOTSUPP;
+
+       bvec_set_page(&bvec, page, size, offset);
+       iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
+       return kcm_sendmsg(sock, &msg, size);
+}
+
 static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
                       size_t len, int flags)
 {