[NET]: Move generic skbuff stuff from XFRM code to generic code

Move generic skbuff stuff from XFRM code to generic code so that
AF_RXRPC can use it too.

The kdoc comments I've attached to the functions needs to be checked
by whoever wrote them as I had to make some guesses about the workings
of these functions.

Signed-off-By: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 188 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 331d3efa82fa..f927b6e8027e 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -55,6 +55,7 @@
 #include <linux/cache.h>
 #include <linux/rtnetlink.h>
 #include <linux/init.h>
+#include <linux/scatterlist.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
@@ -2002,6 +2003,190 @@ void __init skb_init(void)
 						NULL, NULL);
 }
 
+/**
+ *	skb_to_sgvec - Fill a scatter-gather list from a socket buffer
+ *	@skb: Socket buffer containing the buffers to be mapped
+ *	@sg: The scatter-gather list to map into
+ *	@offset: The offset into the buffer's contents to start mapping
+ *	@len: Length of buffer space to be mapped
+ *
+ *	Fill the specified scatter-gather list with mappings/pointers into a
+ *	region of the buffer space attached to a socket buffer.
+ */
+int
+skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
+{
+	int start = skb_headlen(skb);
+	int i, copy = start - offset;
+	int elt = 0;
+
+	if (copy > 0) {
+		if (copy > len)
+			copy = len;
+		sg[elt].page = virt_to_page(skb->data + offset);
+		sg[elt].offset = (unsigned long)(skb->data + offset) % PAGE_SIZE;
+		sg[elt].length = copy;
+		elt++;
+		if ((len -= copy) == 0)
+			return elt;
+		offset += copy;
+	}
+
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+		int end;
+
+		BUG_TRAP(start <= offset + len);
+
+		end = start + skb_shinfo(skb)->frags[i].size;
+		if ((copy = end - offset) > 0) {
+			skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+
+			if (copy > len)
+				copy = len;
+			sg[elt].page = frag->page;
+			sg[elt].offset = frag->page_offset+offset-start;
+			sg[elt].length = copy;
+			elt++;
+			if (!(len -= copy))
+				return elt;
+			offset += copy;
+		}
+		start = end;
+	}
+
+	if (skb_shinfo(skb)->frag_list) {
+		struct sk_buff *list = skb_shinfo(skb)->frag_list;
+
+		for (; list; list = list->next) {
+			int end;
+
+			BUG_TRAP(start <= offset + len);
+
+			end = start + list->len;
+			if ((copy = end - offset) > 0) {
+				if (copy > len)
+					copy = len;
+				elt += skb_to_sgvec(list, sg+elt, offset - start, copy);
+				if ((len -= copy) == 0)
+					return elt;
+				offset += copy;
+			}
+			start = end;
+		}
+	}
+	BUG_ON(len);
+	return elt;
+}
+
+/**
+ *	skb_cow_data - Check that a socket buffer's data buffers are writable
+ *	@skb: The socket buffer to check.
+ *	@tailbits: Amount of trailing space to be added
+ *	@trailer: Returned pointer to the skb where the @tailbits space begins
+ *
+ *	Make sure that the data buffers attached to a socket buffer are
+ *	writable. If they are not, private copies are made of the data buffers
+ *	and the socket buffer is set to use these instead.
+ *
+ *	If @tailbits is given, make sure that there is space to write @tailbits
+ *	bytes of data beyond current end of socket buffer.  @trailer will be
+ *	set to point to the skb in which this space begins.
+ *
+ *	The number of scatterlist elements required to completely map the
+ *	COW'd and extended socket buffer will be returned.
+ */
+int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer)
+{
+	int copyflag;
+	int elt;
+	struct sk_buff *skb1, **skb_p;
+
+	/* If skb is cloned or its head is paged, reallocate
+	 * head pulling out all the pages (pages are considered not writable
+	 * at the moment even if they are anonymous).
+	 */
+	if ((skb_cloned(skb) || skb_shinfo(skb)->nr_frags) &&
+	    __pskb_pull_tail(skb, skb_pagelen(skb)-skb_headlen(skb)) == NULL)
+		return -ENOMEM;
+
+	/* Easy case. Most of packets will go this way. */
+	if (!skb_shinfo(skb)->frag_list) {
+		/* A little of trouble, not enough of space for trailer.
+		 * This should not happen, when stack is tuned to generate
+		 * good frames. OK, on miss we reallocate and reserve even more
+		 * space, 128 bytes is fair. */
+
+		if (skb_tailroom(skb) < tailbits &&
+		    pskb_expand_head(skb, 0, tailbits-skb_tailroom(skb)+128, GFP_ATOMIC))
+			return -ENOMEM;
+
+		/* Voila! */
+		*trailer = skb;
+		return 1;
+	}
+
+	/* Misery. We are in troubles, going to mincer fragments... */
+
+	elt = 1;
+	skb_p = &skb_shinfo(skb)->frag_list;
+	copyflag = 0;
+
+	while ((skb1 = *skb_p) != NULL) {
+		int ntail = 0;
+
+		/* The fragment is partially pulled by someone,
+		 * this can happen on input. Copy it and everything
+		 * after it. */
+
+		if (skb_shared(skb1))
+			copyflag = 1;
+
+		/* If the skb is the last, worry about trailer. */
+
+		if (skb1->next == NULL && tailbits) {
+			if (skb_shinfo(skb1)->nr_frags ||
+			    skb_shinfo(skb1)->frag_list ||
+			    skb_tailroom(skb1) < tailbits)
+				ntail = tailbits + 128;
+		}
+
+		if (copyflag ||
+		    skb_cloned(skb1) ||
+		    ntail ||
+		    skb_shinfo(skb1)->nr_frags ||
+		    skb_shinfo(skb1)->frag_list) {
+			struct sk_buff *skb2;
+
+			/* Fuck, we are miserable poor guys... */
+			if (ntail == 0)
+				skb2 = skb_copy(skb1, GFP_ATOMIC);
+			else
+				skb2 = skb_copy_expand(skb1,
+						       skb_headroom(skb1),
+						       ntail,
+						       GFP_ATOMIC);
+			if (unlikely(skb2 == NULL))
+				return -ENOMEM;
+
+			if (skb1->sk)
+				skb_set_owner_w(skb2, skb1->sk);
+
+			/* Looking around. Are we still alive?
+			 * OK, link new skb, drop old one */
+
+			skb2->next = skb1->next;
+			*skb_p = skb2;
+			kfree_skb(skb1);
+			skb1 = skb2;
+		}
+		elt++;
+		*trailer = skb1;
+		skb_p = &skb1->next;
+	}
+
+	return elt;
+}
+
 EXPORT_SYMBOL(___pskb_trim);
 EXPORT_SYMBOL(__kfree_skb);
 EXPORT_SYMBOL(kfree_skb);
@@ -2036,3 +2221,6 @@ EXPORT_SYMBOL(skb_seq_read);
 EXPORT_SYMBOL(skb_abort_seq_read);
 EXPORT_SYMBOL(skb_find_text);
 EXPORT_SYMBOL(skb_append_datato_frags);
+
+EXPORT_SYMBOL_GPL(skb_to_sgvec);
+EXPORT_SYMBOL_GPL(skb_cow_data);