[PATCH net-next 0/4] splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES), part 2

[PATCH net-next 0/4] splice, net: Replace sendpage with sendmsg(MSG_SPLICE_PAGES), part 2

[David Howells]

Here's the second tranche of patches towards providing a MSG_SPLICE_PAGES
internal sendmsg flag that is intended to replace the ->sendpage() op with
calls to sendmsg().  MSG_SPLICE_PAGES is a hint that tells the protocol
that it should splice the pages supplied if it can and copy them if not.

This set consists of the following parts:

 (1) Implement MSG_SPLICE_PAGES support in Chelsio TLS and make
     chtls_sendpage() just a wrapper around sendmsg().

 (2) Implement MSG_SPLICE_PAGES support in AF_KCM and make kcm_sendpage()
     just a wrapper around sendmsg().

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=sendpage-2

David

Link: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=51c78a4d532efe9543a4df019ff405f05c6157f6 # part 1

David Howells (4):
  chelsio: Support MSG_SPLICE_PAGES
  chelsio: Convert chtls_sendpage() to use MSG_SPLICE_PAGES
  kcm: Support MSG_SPLICE_PAGES
  kcm: Convert kcm_sendpage() to use MSG_SPLICE_PAGES

 .../chelsio/inline_crypto/chtls/chtls_io.c    | 121 ++--------
 net/kcm/kcmsock.c                             | 216 +++++-------------
 2 files changed, 74 insertions(+), 263 deletions(-)

[PATCH net-next 1/4] chelsio: Support MSG_SPLICE_PAGES

[David Howells]

Make Chelsio's TLS offload sendmsg() support MSG_SPLICE_PAGES, splicing in
pages from the source iterator if possible and copying the data in
otherwise.

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: Ayush Sawal <ayush.sawal@chelsio.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
 .../ethernet/chelsio/inline_crypto/chtls/chtls_io.c  | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
index ae6b17b96bf1..1d08386ac916 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
@@ -1092,7 +1092,17 @@ int chtls_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 		if (copy > size)
 			copy = size;
 
-		if (skb_tailroom(skb) > 0) {
+		if (msg->msg_flags & MSG_SPLICE_PAGES) {
+			err = skb_splice_from_iter(skb, &msg->msg_iter, copy,
+						   sk->sk_allocation);
+			if (err < 0) {
+				if (err == -EMSGSIZE)
+					goto new_buf;
+				goto do_fault;
+			}
+			copy = err;
+			sk_wmem_queued_add(sk, copy);
+		} else if (skb_tailroom(skb) > 0) {
 			copy = min(copy, skb_tailroom(skb));
 			if (is_tls_tx(csk))
 				copy = min_t(int, copy, csk->tlshws.txleft);

[PATCH net-next 2/4] chelsio: Convert chtls_sendpage() to use MSG_SPLICE_PAGES

[David Howells]

Convert chtls_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: Ayush Sawal <ayush.sawal@chelsio.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
 .../chelsio/inline_crypto/chtls/chtls_io.c    | 109 ++----------------
 1 file changed, 7 insertions(+), 102 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
index 1d08386ac916..65efd20ec796 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
@@ -1240,110 +1240,15 @@ int chtls_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 int chtls_sendpage(struct sock *sk, struct page *page,
 		   int offset, size_t size, int flags)
 {
-	struct chtls_sock *csk;
-	struct chtls_dev *cdev;
-	int mss, err, copied;
-	struct tcp_sock *tp;
-	long timeo;
-
-	tp = tcp_sk(sk);
-	copied = 0;
-	csk = rcu_dereference_sk_user_data(sk);
-	cdev = csk->cdev;
-	lock_sock(sk);
-	timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
+	struct bio_vec bvec;
+	struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES, };
 
-	err = sk_stream_wait_connect(sk, &timeo);
-	if (!sk_in_state(sk, TCPF_ESTABLISHED | TCPF_CLOSE_WAIT) &&
-	    err != 0)
-		goto out_err;
-
-	mss = csk->mss;
-	csk_set_flag(csk, CSK_TX_MORE_DATA);
-
-	while (size > 0) {
-		struct sk_buff *skb = skb_peek_tail(&csk->txq);
-		int copy, i;
-
-		if (!skb || (ULP_SKB_CB(skb)->flags & ULPCB_FLAG_NO_APPEND) ||
-		    (copy = mss - skb->len) <= 0) {
-new_buf:
-			if (!csk_mem_free(cdev, sk))
-				goto wait_for_sndbuf;
+	if (flags & MSG_SENDPAGE_NOTLAST)
+		msg.msg_flags |= MSG_MORE;
 
-			if (is_tls_tx(csk)) {
-				skb = get_record_skb(sk,
-						     select_size(sk, size,
-								 flags,
-								 TX_TLSHDR_LEN),
-						     true);
-			} else {
-				skb = get_tx_skb(sk, 0);
-			}
-			if (!skb)
-				goto wait_for_memory;
-			copy = mss;
-		}
-		if (copy > size)
-			copy = size;
-
-		i = skb_shinfo(skb)->nr_frags;
-		if (skb_can_coalesce(skb, i, page, offset)) {
-			skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
-		} else if (i < MAX_SKB_FRAGS) {
-			get_page(page);
-			skb_fill_page_desc(skb, i, page, offset, copy);
-		} else {
-			tx_skb_finalize(skb);
-			push_frames_if_head(sk);
-			goto new_buf;
-		}
-
-		skb->len += copy;
-		if (skb->len == mss)
-			tx_skb_finalize(skb);
-		skb->data_len += copy;
-		skb->truesize += copy;
-		sk->sk_wmem_queued += copy;
-		tp->write_seq += copy;
-		copied += copy;
-		offset += copy;
-		size -= copy;
-
-		if (corked(tp, flags) &&
-		    (sk_stream_wspace(sk) < sk_stream_min_wspace(sk)))
-			ULP_SKB_CB(skb)->flags |= ULPCB_FLAG_NO_APPEND;
-
-		if (!size)
-			break;
-
-		if (unlikely(ULP_SKB_CB(skb)->flags & ULPCB_FLAG_NO_APPEND))
-			push_frames_if_head(sk);
-		continue;
-wait_for_sndbuf:
-		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
-wait_for_memory:
-		err = csk_wait_memory(cdev, sk, &timeo);
-		if (err)
-			goto do_error;
-	}
-out:
-	csk_reset_flag(csk, CSK_TX_MORE_DATA);
-	if (copied)
-		chtls_tcp_push(sk, flags);
-done:
-	release_sock(sk);
-	return copied;
-
-do_error:
-	if (copied)
-		goto out;
-
-out_err:
-	if (csk_conn_inline(csk))
-		csk_reset_flag(csk, CSK_TX_MORE_DATA);
-	copied = sk_stream_error(sk, flags, err);
-	goto done;
+	bvec_set_page(&bvec, page, size, offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
+	return chtls_sendmsg(sk, &msg, size);
 }
 
 static void chtls_select_window(struct sock *sk)

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

[David Howells]

Make AF_KCM sendmsg() support MSG_SPLICE_PAGES.  This causes pages to be
spliced from the source iterator if possible.

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 | 55 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 38 insertions(+), 17 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index cfe828bd7fc6..411726d830c0 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -989,29 +989,50 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 			merge = false;
 		}
 
-		copy = min_t(int, msg_data_left(msg),
-			     pfrag->size - pfrag->offset);
+		if (msg->msg_flags & MSG_SPLICE_PAGES) {
+			copy = msg_data_left(msg);
+			if (!sk_wmem_schedule(sk, copy))
+				goto wait_for_memory;
 
-		if (!sk_wmem_schedule(sk, copy))
-			goto wait_for_memory;
+			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;
+			}
 
-		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;
+			sk_wmem_queued_add(sk, copy);
+			sk_mem_charge(sk, copy);
 
-		/* Update the skb. */
-		if (merge) {
-			skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
+			if (head != skb)
+				head->truesize += copy;
 		} else {
-			skb_fill_page_desc(skb, i, pfrag->page,
-					   pfrag->offset, copy);
-			get_page(pfrag->page);
+			copy = min_t(int, msg_data_left(msg),
+				     pfrag->size - pfrag->offset);
+			if (!sk_wmem_schedule(sk, copy))
+				goto wait_for_memory;
+
+			err = skb_copy_to_page_nocache(sk, &msg->msg_iter, skb,
+						       pfrag->page,
+						       pfrag->offset,
+						       copy);
+			if (err)
+				goto out_error;
+
+			/* Update the skb. */
+			if (merge) {
+				skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
+			} else {
+				skb_fill_page_desc(skb, i, pfrag->page,
+						   pfrag->offset, copy);
+				get_page(pfrag->page);
+			}
+
+			pfrag->offset += copy;
 		}
 
-		pfrag->offset += copy;
 		copied += copy;
 		if (head != skb) {
 			head->len += copy;

[PATCH net-next 4/4] kcm: Convert kcm_sendpage() to use MSG_SPLICE_PAGES

[David Howells]

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 411726d830c0..f6e0e017e3cc 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;
@@ -1109,6 +966,24 @@ 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, 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)
 {

Re: [PATCH net-next 2/4] chelsio: Convert chtls_sendpage() to use MSG_SPLICE_PAGES

[Simon Horman]

On Wed, May 24, 2023 at 03:49:21PM +0100, David Howells wrote:
> Convert chtls_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: Ayush Sawal <ayush.sawal@chelsio.com>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Eric Dumazet <edumazet@google.com>
> cc: Jakub Kicinski <kuba@kernel.org>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: netdev@vger.kernel.org
> ---
>  .../chelsio/inline_crypto/chtls/chtls_io.c    | 109 ++----------------
>  1 file changed, 7 insertions(+), 102 deletions(-)
> 
> diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
> index 1d08386ac916..65efd20ec796 100644
> --- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
> +++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_io.c
> @@ -1240,110 +1240,15 @@ int chtls_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>  int chtls_sendpage(struct sock *sk, struct page *page,
>  		   int offset, size_t size, int flags)
>  {
> -	struct chtls_sock *csk;
> -	struct chtls_dev *cdev;
> -	int mss, err, copied;
> -	struct tcp_sock *tp;
> -	long timeo;
> -
> -	tp = tcp_sk(sk);
> -	copied = 0;
> -	csk = rcu_dereference_sk_user_data(sk);
> -	cdev = csk->cdev;
> -	lock_sock(sk);
> -	timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
> +	struct bio_vec bvec;
> +	struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES, };
>  

Hi David,

a minor nit, in case you need to repost this series for some other reason.

Please use reverse Xmas tree - longest line to shortest - order for
Networking code. I understand this file doesn't adhere to that, and
we probably don't want churn due to addressing it throughout this file.
But my preference is to move towards this standard, or at least not away
from it.

So in this case:

	struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES, };
	struct bio_vec bvec;

This tool can be useful:

	https://github.com/ecree-solarflare/xmastree

Re: [PATCH net-next 2/4] chelsio: Convert chtls_sendpage() to use MSG_SPLICE_PAGES

[David Howells]

Simon Horman <simon.horman@corigine.com> wrote:

> a minor nit, in case you need to repost this series for some other reason.

Note that the aim is to delete chtls_sendpage() entirely at some point soon.

David

Re: [PATCH net-next 2/4] chelsio: Convert chtls_sendpage() to use MSG_SPLICE_PAGES

[Simon Horman]

On Thu, May 25, 2023 at 09:41:46AM +0100, David Howells wrote:
> Simon Horman <simon.horman@corigine.com> wrote:
> 
> > a minor nit, in case you need to repost this series for some other reason.
> 
> Note that the aim is to delete chtls_sendpage() entirely at some point soon.

Excellent.

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

[Jakub Kicinski]

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;

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

[David Howells]

Jakub Kicinski <kuba@kernel.org> wrote:

> 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? 

Yeah.  Good point.  I didn't add one because the normal operation code doesn't
do that - but I guess that's all-or-nothing.

David