net: splice: avoid high order page splitting

splice() can handle pages of any order, but network code tries hard to
split them in PAGE_SIZE units. Not quite successfully anyway, as
__splice_segment() assumed poff < PAGE_SIZE. This is true for
the skb->data part, not necessarily for the fragments.

This patch removes this logic to give the pages as they are in the skb.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -1706,27 +1706,15 @@ static bool spd_fill_page(struct splice_pipe_desc *spd,
 	return false;
 }
 
-static inline void __segment_seek(struct page **page, unsigned int *poff,
-				  unsigned int *plen, unsigned int off)
-{
-	unsigned long n;
-
-	*poff += off;
-	n = *poff / PAGE_SIZE;
-	if (n)
-		*page = nth_page(*page, n);
-
-	*poff = *poff % PAGE_SIZE;
-	*plen -= off;
-}
-
 static bool __splice_segment(struct page *page, unsigned int poff,
 			     unsigned int plen, unsigned int *off,
 			     unsigned int *len, struct sk_buff *skb,
 			     struct splice_pipe_desc *spd, bool linear,
 			     struct sock *sk,
 			     struct pipe_inode_info *pipe)
 {
+	unsigned int flen;
+
 	if (!*len)
 		return true;
 
@@ -1737,24 +1725,16 @@ static bool __splice_segment(struct page *page, unsigned int poff,
 	}
 
 	/* ignore any bits we already processed */
-	if (*off) {
-		__segment_seek(&page, &poff, &plen, *off);
-		*off = 0;
-	}
-
-	do {
-		unsigned int flen = min(*len, plen);
+	poff += *off;
+	plen -= *off;
+	*off = 0;
 
-		/* the linear region may spread across several pages  */
-		flen = min_t(unsigned int, flen, PAGE_SIZE - poff);
+	flen = min(*len, plen);
 
-		if (spd_fill_page(spd, pipe, page, &flen, poff, skb, linear, sk))
-			return true;
-
-		__segment_seek(&page, &poff, &plen, flen);
-		*len -= flen;
+	if (spd_fill_page(spd, pipe, page, &flen, poff, skb, linear, sk))
+		return true;
 
-	} while (*len && plen);
+	*len -= flen;
 
 	return false;
 }