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

David Howells
2023-03-30T15:14:28Z

Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:

> > + unsigned int maxfraglen, fragheaderlen, maxnonfragsize, xlength;
>
> Does x here stand for anything?

Yeah... "bad naming". How about if I call it initial_length? I'm trying to
avoid allocating bufferage for the data.

> This does add a lot of code to two functions that are already
> unwieldy. It may be unavoidable, but it if can use helpers, that would
> be preferable.

Something like the attached? (This is on top of patches 16-17, but I would
need to fold it in)

David
---
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index b38dbb2f9c3f..019ed9bb6745 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -956,6 +956,96 @@ csum_page(struct page *page, int offset, int copy)
return csum;
}

+/*
+ * Allocate a packet for MSG_SPLICE_PAGES.
+ */
+static int __ip_splice_alloc(struct sock *sk, struct sk_buff **pskb,
+ unsigned int fragheaderlen, unsigned int maxfraglen,
+ unsigned int hh_len)
+{
+ struct sk_buff *skb_prev = *pskb, *skb;
+ unsigned int fraggap = skb_prev->len - maxfraglen;
+ unsigned int alloclen = fragheaderlen + hh_len + fraggap + 15;
+
+ skb = sock_wmalloc(sk, alloclen, 1, sk->sk_allocation);
+ if (unlikely(!skb))
+ return -ENOBUFS;
+
+ /* 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);
+ *pskb = skb;
+ return 0;
+}
+
+/*
+ * Add (or copy) data pages for MSG_SPLICE_PAGES.
+ */
+static int __ip_splice_pages(struct sock *sk, struct sk_buff *skb,
+ void *from, size_t *pcopy)
+{
+ struct msghdr *msg = from;
+ struct page *page = NULL, **pages = &page;
+ ssize_t copy = *pcopy;
+ size_t off;
+ bool put = false;
+ int err;
+
+ copy = iov_iter_extract_pages(&msg->msg_iter, &pages, copy, 1, 0, &off);
+ if (copy <= 0)
+ return copy ?: -EIO;
+
+ if (!sendpage_ok(page)) {
+ const void *p = kmap_local_page(page);
+ void *q;
+
+ q = page_frag_memdup(NULL, p + off, copy,
+ sk->sk_allocation, ULONG_MAX);
+ kunmap_local(p);
+ if (!q)
+ return -ENOMEM;
+ page = virt_to_page(q);
+ off = offset_in_page(q);
+ put = true;
+ }
+
+ err = skb_append_pagefrags(skb, page, off, copy);
+ if (put)
+ put_page(page);
+ if (err < 0) {
+ iov_iter_revert(&msg->msg_iter, copy);
+ return err;
+ }
+
+ 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);
+ *pcopy = copy;
+ return 0;
+}
+
static int __ip_append_data(struct sock *sk,
struct flowi4 *fl4,
struct sk_buff_head *queue,
@@ -977,7 +1067,7 @@ static int __ip_append_data(struct sock *sk,
int err;
int offset = 0;
bool zc = false;
- unsigned int maxfraglen, fragheaderlen, maxnonfragsize, xlength;
+ unsigned int maxfraglen, fragheaderlen, maxnonfragsize, initial_length;
int csummode = CHECKSUM_NONE;
struct rtable *rt = (struct rtable *)cork->dst;
unsigned int wmem_alloc_delta = 0;
@@ -1017,7 +1107,7 @@ static int __ip_append_data(struct sock *sk,
(!exthdrlen || (rt->dst.dev->features & NETIF_F_HW_ESP_TX_CSUM)))
csummode = CHECKSUM_PARTIAL;

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

@@ -1053,7 +1143,7 @@ static int __ip_append_data(struct sock *sk,
return -EPERM;
if (!(rt->dst.dev->features & NETIF_F_SG))
return -EOPNOTSUPP;
- xlength = transhdrlen; /* We need an empty buffer to attach stuff to */
+ initial_length = transhdrlen; /* We need an empty buffer to attach stuff to */
}

cork->length += length;
@@ -1083,47 +1173,13 @@ static int __ip_append_data(struct sock *sk,
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;
+ err = __ip_splice_alloc(sk, &skb, fragheaderlen,
+ maxfraglen, hh_len);
+ if (err < 0)
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;
+ initial_length = length;

alloc_new_skb:
skb_prev = skb;
@@ -1136,7 +1192,7 @@ static int __ip_append_data(struct sock *sk,
* If remaining data exceeds the mtu,
* we know we need more fragment(s).
*/
- datalen = xlength + fraggap;
+ datalen = initial_length + fraggap;
if (datalen > mtu - fragheaderlen)
datalen = maxfraglen - fragheaderlen;
fraglen = datalen + fragheaderlen;
@@ -1150,7 +1206,7 @@ static int __ip_append_data(struct sock *sk,
* because we have no idea what fragment will be
* the last.
*/
- if (datalen == xlength + fraggap)
+ if (datalen == initial_length + fraggap)
alloc_extra += rt->dst.trailer_len;

if ((flags & MSG_MORE) &&
@@ -1258,48 +1314,9 @@ static int __ip_append_data(struct sock *sk,
goto error;
}
} else if (flags & MSG_SPLICE_PAGES) {
- struct msghdr *msg = from;
- struct page *page = NULL, **pages = &page;
- size_t off;
- bool put = false;
-
- copy = iov_iter_extract_pages(&msg->msg_iter, &pages,
- copy, 1, 0, &off);
- if (copy <= 0) {
- err = copy ?: -EIO;
- goto error;
- }
-
- if (!sendpage_ok(page)) {
- const void *p = kmap_local_page(page);
- void *q;
-
- q = page_frag_memdup(NULL, p + off, copy,
- sk->sk_allocation, ULONG_MAX);
- kunmap_local(p);
- if (!q) {
- err = copy ?: -ENOMEM;
- goto error;
- }
- page = virt_to_page(q);
- off = offset_in_page(q);
- put = true;
- }
-
- err = skb_append_pagefrags(skb, page, off, copy);
- if (put)
- put_page(page);
+ err = __ip_splice_pages(sk, skb, from, &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;