[PATCH v3 1/4] net: introduce helper sendpages_ok()

[Ofir Gal]

Network drivers are using sendpage_ok() to check the first page of an
iterator in order to disable MSG_SPLICE_PAGES. The iterator can
represent list of contiguous pages.

When MSG_SPLICE_PAGES is enabled skb_splice_from_iter() is being used,
it requires all pages in the iterator to be sendable. Therefore it needs
to check that each page is sendable.

The patch introduces a helper sendpages_ok(), it returns true if all the
contiguous pages are sendable.

Drivers who want to send contiguous pages with MSG_SPLICE_PAGES may use
this helper to check whether the page list is OK. If the helper does not
return true, the driver should remove MSG_SPLICE_PAGES flag.

Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Ofir Gal <ofir.gal at volumez.com>
---
 include/linux/net.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/linux/net.h b/include/linux/net.h
index 688320b79fcc..421a6b5b9ad1 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -322,6 +322,28 @@ static inline bool sendpage_ok(struct page *page)
 	return !PageSlab(page) && page_count(page) >= 1;
 }
 
+/*
+ * Check sendpage_ok on contiguous pages.
+ */
+static inline bool sendpages_ok(struct page *page, size_t len, size_t offset)
+{
+	struct page *p;
+	size_t count;
+
+	p = page + (offset >> PAGE_SHIFT);
+
+	count = 0;
+	while (count < len) {
+		if (!sendpage_ok(p))
+			return false;
+
+		p++;
+		count += PAGE_SIZE;
+	}
+
+	return true;
+}
+
 int kernel_sendmsg(struct socket *sock, struct msghdr *msg, struct kvec *vec,
 		   size_t num, size_t len);
 int kernel_sendmsg_locked(struct sock *sk, struct msghdr *msg,
-- 
2.45.1