[RFC PATCH v2 16/48] ip, udp: Support MSG_SPLICE_PAGES

David Howells
2023-03-29T14:18:28Z

Make IP/UDP sendmsg() support MSG_SPLICE_PAGES. This causes pages to be
spliced from the source iterator if possible (the iterator must be
ITER_BVEC and the pages must be spliceable).

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: Willem de Bruijn <willemdebruijn.kernel@gmail.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
---
net/ipv4/ip_output.c | 85 +++++++++++++++++++++++++++++++++++++++++---
1 file changed, 81 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 4e4e308c3230..07736da70eab 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -973,11 +973,11 @@ static int __ip_append_data(struct sock *sk,
int hh_len;
int exthdrlen;
int mtu;
- int copy;
+ ssize_t copy;
int err;
int offset = 0;
bool zc = false;
- unsigned int maxfraglen, fragheaderlen, maxnonfragsize;
+ unsigned int maxfraglen, fragheaderlen, maxnonfragsize, xlength;
int csummode = CHECKSUM_NONE;
struct rtable *rt = (struct rtable *)cork->dst;
unsigned int wmem_alloc_delta = 0;
@@ -1017,6 +1017,7 @@ static int __ip_append_data(struct sock *sk,
(!exthdrlen || (rt->dst.dev->features & NETIF_F_HW_ESP_TX_CSUM)))
csummode = CHECKSUM_PARTIAL;

+ xlength = length;
if ((flags & MSG_ZEROCOPY) && length) {
struct msghdr *msg = from;

@@ -1047,6 +1048,14 @@ static int __ip_append_data(struct sock *sk,
skb_zcopy_set(skb, uarg, &extra_uref);
}
}
+ } else if ((flags & MSG_SPLICE_PAGES) && length) {
+ struct msghdr *msg = from;
+
+ if (inet->hdrincl)
+ return -EPERM;
+ if (!(rt->dst.dev->features & NETIF_F_SG))
+ return -EOPNOTSUPP;
+ xlength = transhdrlen; /* We need an empty buffer to attach stuff to */
}

cork->length += length;
@@ -1074,6 +1083,50 @@ static int __ip_append_data(struct sock *sk,
unsigned int alloclen, alloc_extra;
unsigned int pagedlen;
struct sk_buff *skb_prev;
+
+ if (unlikely(flags & MSG_SPLICE_PAGES)) {
+ skb_prev = skb;
+ fraggap = skb_prev->len - maxfraglen;
+
+ alloclen = fragheaderlen + hh_len + fraggap + 15;
+ skb = sock_wmalloc(sk, alloclen, 1, sk->sk_allocation);
+ if (unlikely(!skb)) {
+ err = -ENOBUFS;
+ goto error;
+ }
+
+ /*
+ * Fill in the control structures
+ */
+ skb->ip_summed = CHECKSUM_NONE;
+ skb->csum = 0;
+ skb_reserve(skb, hh_len);
+
+ /*
+ * Find where to start putting bytes.
+ */
+ skb_put(skb, fragheaderlen + fraggap);
+ skb_reset_network_header(skb);
+ skb->transport_header = (skb->network_header +
+ fragheaderlen);
+ if (fraggap) {
+ skb->csum = skb_copy_and_csum_bits(
+ skb_prev, maxfraglen,
+ skb_transport_header(skb),
+ fraggap);
+ skb_prev->csum = csum_sub(skb_prev->csum,
+ skb->csum);
+ pskb_trim_unique(skb_prev, maxfraglen);
+ }
+
+ /*
+ * Put the packet on the pending queue.
+ */
+ __skb_queue_tail(&sk->sk_write_queue, skb);
+ continue;
+ }
+ xlength = length;
+
alloc_new_skb:
skb_prev = skb;
if (skb_prev)
@@ -1085,7 +1138,7 @@ static int __ip_append_data(struct sock *sk,
* If remaining data exceeds the mtu,
* we know we need more fragment(s).
*/
- datalen = length + fraggap;
+ datalen = xlength + fraggap;
if (datalen > mtu - fragheaderlen)
datalen = maxfraglen - fragheaderlen;
fraglen = datalen + fragheaderlen;
@@ -1099,7 +1152,7 @@ static int __ip_append_data(struct sock *sk,
* because we have no idea what fragment will be
* the last.
*/
- if (datalen == length + fraggap)
+ if (datalen == xlength + fraggap)
alloc_extra += rt->dst.trailer_len;

if ((flags & MSG_MORE) &&
@@ -1206,6 +1259,30 @@ static int __ip_append_data(struct sock *sk,
err = -EFAULT;
goto error;
}
+ } else if (flags & MSG_SPLICE_PAGES) {
+ struct msghdr *msg = from;
+ struct page *page = NULL, **pages = &page;
+ size_t off;
+
+ copy = iov_iter_extract_pages(&msg->msg_iter, &pages,
+ copy, 1, 0, &off);
+ if (copy <= 0) {
+ err = copy ?: -EIO;
+ goto error;
+ }
+
+ err = skb_append_pagefrags(skb, page, off, copy);
+ if (err < 0)
+ goto error;
+
+ if (skb->ip_summed == CHECKSUM_NONE) {
+ __wsum csum;
+ csum = csum_page(page, off, copy);
+ skb->csum = csum_block_add(skb->csum, csum, skb->len);
+ }
+
+ skb_len_add(skb, copy);
+ refcount_add(copy, &sk->sk_wmem_alloc);
} else if (!zc) {
int i = skb_shinfo(skb)->nr_frags;