[PATCH v3 34/55] kcm: Convert kcm_sendpage() to use MSG_SPLICE_PAGES

David Howells
2023-03-31T16:17:16Z

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: Jakub Kicinski <kuba@kernel.org>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
net/kcm/kcmsock.c | 161 ++++++----------------------------------------
1 file changed, 18 insertions(+), 143 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 0a3f79d81595..d77d28fbf389 100644
--- 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;
@@ -1143,6 +1000,24 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
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, offset, size);
+ 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)
{