[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 331d3efa82f..f927b6e8027 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);