6lowpan: add generic nhc layer interface

This patch adds a generic next header compression layer interface. There
exists various methods to do a header compression after 6LoWPAN header
to save payload. This introduce a generic nhc header which allow a
simple adding of a new header compression format instead of a static
implementation inside the 6LoWPAN header compression and uncompression
function.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Cc: Martin Townsend <mtownsend1973@gmail.com>
Reviewed-by: Stefan Schmidt <s.schmidt@samsung.com>
Acked-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 241 insertions, 0 deletions

diff --git a/net/6lowpan/nhc.c b/net/6lowpan/nhc.c
new file mode 100644
index 000000000000..fd20fc51a7c4
--- /dev/null
+++ b/net/6lowpan/nhc.c
@@ -0,0 +1,241 @@
+/*
+ *      6LoWPAN next header compression
+ *
+ *
+ *      Authors:
+ *      Alexander Aring         <aar@pengutronix.de>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/netdevice.h>
+
+#include <net/ipv6.h>
+
+#include "nhc.h"
+
+static struct rb_root rb_root = RB_ROOT;
+static struct lowpan_nhc *lowpan_nexthdr_nhcs[NEXTHDR_MAX];
+static DEFINE_SPINLOCK(lowpan_nhc_lock);
+
+static int lowpan_nhc_insert(struct lowpan_nhc *nhc)
+{
+        struct rb_node **new = &rb_root.rb_node, *parent = NULL;
+
+        /* Figure out where to put new node */
+        while (*new) {
+                struct lowpan_nhc *this = container_of(*new, struct lowpan_nhc,
+                                                       node);
+                int result, len_dif, len;
+
+                len_dif = nhc->idlen - this->idlen;
+
+                if (nhc->idlen < this->idlen)
+                        len = nhc->idlen;
+                else
+                        len = this->idlen;
+
+                result = memcmp(nhc->id, this->id, len);
+                if (!result)
+                        result = len_dif;
+
+                parent = *new;
+                if (result < 0)
+                        new = &((*new)->rb_left);
+                else if (result > 0)
+                        new = &((*new)->rb_right);
+                else
+                        return -EEXIST;
+        }
+
+        /* Add new node and rebalance tree. */
+        rb_link_node(&nhc->node, parent, new);
+        rb_insert_color(&nhc->node, &rb_root);
+
+        return 0;
+}
+
+static void lowpan_nhc_remove(struct lowpan_nhc *nhc)
+{
+        rb_erase(&nhc->node, &rb_root);
+}
+
+static struct lowpan_nhc *lowpan_nhc_by_nhcid(const struct sk_buff *skb)
+{
+        struct rb_node *node = rb_root.rb_node;
+        const u8 *nhcid_skb_ptr = skb->data;
+
+        while (node) {
+                struct lowpan_nhc *nhc = container_of(node, struct lowpan_nhc,
+                                                      node);
+                u8 nhcid_skb_ptr_masked[LOWPAN_NHC_MAX_ID_LEN];
+                int result, i;
+
+                if (nhcid_skb_ptr + nhc->idlen > skb->data + skb->len)
+                        return NULL;
+
+                /* copy and mask afterwards the nhid value from skb */
+                memcpy(nhcid_skb_ptr_masked, nhcid_skb_ptr, nhc->idlen);
+                for (i = 0; i < nhc->idlen; i++)
+                        nhcid_skb_ptr_masked[i] &= nhc->idmask[i];
+
+                result = memcmp(nhcid_skb_ptr_masked, nhc->id, nhc->idlen);
+                if (result < 0)
+                        node = node->rb_left;
+                else if (result > 0)
+                        node = node->rb_right;
+                else
+                        return nhc;
+        }
+
+        return NULL;
+}
+
+int lowpan_nhc_check_compression(struct sk_buff *skb,
+                                 const struct ipv6hdr *hdr, u8 **hc_ptr,
+                                 u8 *iphc0)
+{
+        struct lowpan_nhc *nhc;
+
+        spin_lock_bh(&lowpan_nhc_lock);
+
+        nhc = lowpan_nexthdr_nhcs[hdr->nexthdr];
+        if (nhc && nhc->compress)
+                *iphc0 |= LOWPAN_IPHC_NH_C;
+        else
+                lowpan_push_hc_data(hc_ptr, &hdr->nexthdr,
+                                    sizeof(hdr->nexthdr));
+
+        spin_unlock_bh(&lowpan_nhc_lock);
+
+        return 0;
+}
+
+int lowpan_nhc_do_compression(struct sk_buff *skb, const struct ipv6hdr *hdr,
+                              u8 **hc_ptr)
+{
+        int ret;
+        struct lowpan_nhc *nhc;
+
+        spin_lock_bh(&lowpan_nhc_lock);
+
+        nhc = lowpan_nexthdr_nhcs[hdr->nexthdr];
+        /* check if the nhc module was removed in unlocked part.
+         * TODO: this is a workaround we should prevent unloading
+         * of nhc modules while unlocked part, this will always drop
+         * the lowpan packet but it's very unlikely.
+         *
+         * Solution isn't easy because we need to decide at
+         * lowpan_nhc_check_compression if we do a compression or not.
+         * Because the inline data which is added to skb, we can't move this
+         * handling.
+         */
+        if (unlikely(!nhc || !nhc->compress)) {
+                ret = -EINVAL;
+                goto out;
+        }
+
+        /* In the case of RAW sockets the transport header is not set by
+         * the ip6 stack so we must set it ourselves
+         */
+        if (skb->transport_header == skb->network_header)
+                skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+
+        ret = nhc->compress(skb, hc_ptr);
+        if (ret < 0)
+                goto out;
+
+        /* skip the transport header */
+        skb_pull(skb, nhc->nexthdrlen);
+
+out:
+        spin_unlock_bh(&lowpan_nhc_lock);
+
+        return ret;
+}
+
+int lowpan_nhc_do_uncompression(struct sk_buff *skb, struct net_device *dev,
+                                struct ipv6hdr *hdr)
+{
+        struct lowpan_nhc *nhc;
+        int ret;
+
+        spin_lock_bh(&lowpan_nhc_lock);
+
+        nhc = lowpan_nhc_by_nhcid(skb);
+        if (nhc) {
+                if (nhc->uncompress) {
+                        ret = nhc->uncompress(skb, sizeof(struct ipv6hdr) +
+                                              nhc->nexthdrlen);
+                        if (ret < 0) {
+                                spin_unlock_bh(&lowpan_nhc_lock);
+                                return ret;
+                        }
+                } else {
+                        spin_unlock_bh(&lowpan_nhc_lock);
+                        netdev_warn(dev, "received nhc id for %s which is not implemented.\n",
+                                    nhc->name);
+                        return -ENOTSUPP;
+                }
+        } else {
+                spin_unlock_bh(&lowpan_nhc_lock);
+                netdev_warn(dev, "received unknown nhc id which was not found.\n");
+                return -ENOENT;
+        }
+
+        hdr->nexthdr = nhc->nexthdr;
+        skb_reset_transport_header(skb);
+        raw_dump_table(__func__, "raw transport header dump",
+                       skb_transport_header(skb), nhc->nexthdrlen);
+
+        spin_unlock_bh(&lowpan_nhc_lock);
+
+        return 0;
+}
+
+int lowpan_nhc_add(struct lowpan_nhc *nhc)
+{
+        int ret;
+
+        if (!nhc->idlen || !nhc->idsetup)
+                return -EINVAL;
+
+        WARN_ONCE(nhc->idlen > LOWPAN_NHC_MAX_ID_LEN,
+                  "LOWPAN_NHC_MAX_ID_LEN should be updated to %zd.\n",
+                  nhc->idlen);
+
+        nhc->idsetup(nhc);
+
+        spin_lock_bh(&lowpan_nhc_lock);
+
+        if (lowpan_nexthdr_nhcs[nhc->nexthdr]) {
+                ret = -EEXIST;
+                goto out;
+        }
+
+        ret = lowpan_nhc_insert(nhc);
+        if (ret < 0)
+                goto out;
+
+        lowpan_nexthdr_nhcs[nhc->nexthdr] = nhc;
+out:
+        spin_unlock_bh(&lowpan_nhc_lock);
+        return ret;
+}
+EXPORT_SYMBOL(lowpan_nhc_add);
+
+void lowpan_nhc_del(struct lowpan_nhc *nhc)
+{
+        spin_lock_bh(&lowpan_nhc_lock);
+
+        lowpan_nhc_remove(nhc);
+        lowpan_nexthdr_nhcs[nhc->nexthdr] = NULL;
+
+        spin_unlock_bh(&lowpan_nhc_lock);
+
+        synchronize_net();
+}
+EXPORT_SYMBOL(lowpan_nhc_del);