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

David Howells
2023-05-24T14:50:45Z

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;