[PATCH] Provide compatibility for older kernels in a separate file

Remove all Linux 2.6.21 compatibility from the driver - it shouldn't be
there for kernel submission.  Move all compatibility code to a separate
file compat.h.  Include it forcedly with the "-include" option.  Add
a makefile option to disable config.h inclusion.

Provide compatibility as far back as Linux 2.6.19 - it's not really hard
once the infrastructure is in place.

Signed-off-by: Pavel Roskin <proski@gnu.org>

3 files changed, 54 insertions, 33 deletions

diff --git a/Makefile b/Makefile
index 665906c..7cb3b48 100644
--- a/Makefile
+++ b/Makefile
@@ -39,6 +39,10 @@ SPECFILE = at76_usb.spec
 
 DISTFILES = $(SRCS) Makefile README COPYING CHANGELOG kernel_patch.diff
 
+ifndef NO_COMPAT_HEADERS
+EXTRA_CFLAGS += -include $(obj)/compat.h
+endif
+
 # get the version from at76_usb.h
 ifndef M
 VERSION = $(shell sed -n 's/^\#define.*DRIVER_VERSION.*"\(.*\)".*$$/\1/p' at76_usb.h)
diff --git a/at76_usb.c b/at76_usb.c
index d6a1e68..5039288 100644
--- a/at76_usb.c
+++ b/at76_usb.c
@@ -5455,13 +5455,9 @@ static void at76_ieee80211_to_eth(struct sk_buff *skb, int iw_mode)
 #endif /* IEEE_STANDARD */
 	}
 
-#ifdef SKB_WITH_OVERHEAD
 	skb_set_mac_header(skb, -(int)sizeof(struct ethhdr));
 	eth_hdr_p = (struct ethhdr *)skb_mac_header(skb);
-#else
-	eth_hdr_p = (struct ethhdr *)(skb->data - sizeof(struct ethhdr));
-	skb->mac.raw = (unsigned char *)eth_hdr_p;
-#endif
+
 	if (build_ethhdr) {
 		/* This needs to be done in this order (eth_hdr_p->h_dest may
 		 * overlap src_addr) */
@@ -5494,14 +5490,6 @@ static void at76_ieee80211_to_eth(struct sk_buff *skb, int iw_mode)
 }
 
 
-#ifndef SKB_WITH_OVERHEAD
-static inline void skb_reset_mac_header(struct sk_buff *skb)
-{
-	skb->mac.raw = skb->data;
-}
-#endif
-
-
 /* check for fragmented data in priv->rx_skb. If the packet was no fragment
    or it was the last of a fragment set a skb containing the whole packet
    is returned for further processing. Otherwise we get NULL and are
@@ -5543,17 +5531,10 @@ static struct sk_buff *at76_check_for_rx_frags(struct at76_priv *priv)
 		 hex2str(priv->obuf, data,
 		    min((int)(sizeof(priv->obuf) - 1) / 2, 32), '\0'));
 
-#ifdef SKB_WITH_OVERHEAD
-	at76_dbg(DBG_RX_FRAGS_SKB, "%s: incoming skb: head %p data %p "
-		 "tail %d end %d len %d",
-		 priv->netdev->name, skb->head, skb->data, skb->tail,
-		 skb->end, skb->len);
-#else
 	at76_dbg(DBG_RX_FRAGS_SKB, "%s: incoming skb: head %p data %p "
-		 "tail %p end %p len %d",
-		 priv->netdev->name, skb->head, skb->data, skb->tail,
-		 skb->end, skb->len);
-#endif
+		 "tail %p end %p len %d", priv->netdev->name, skb->head,
+		 skb->data, skb_tail_pointer(skb), skb_end_pointer(skb),
+		 skb->len);
 
 	if (data_len < 0) {
 		/* make sure data starts in the buffer */
@@ -5587,17 +5568,10 @@ static struct sk_buff *at76_check_for_rx_frags(struct at76_priv *priv)
 	/* remove FCS at end */
 	skb_trim(skb, length);
 
-#ifdef SKB_WITH_OVERHEAD
-	at76_dbg(DBG_RX_FRAGS_SKB, "%s: trimmed skb: head %p data %p tail %d "
-		 "end %d len %d data %p data_len %d",
-		 priv->netdev->name, skb->head, skb->data, skb->tail,
-		 skb->end, skb->len, data, data_len);
-#else
 	at76_dbg(DBG_RX_FRAGS_SKB, "%s: trimmed skb: head %p data %p tail %p "
-		 "end %p len %d data %p data_len %d",
-		 priv->netdev->name, skb->head, skb->data, skb->tail,
-		 skb->end, skb->len, data, data_len);
-#endif
+		 "end %p len %d data %p data_len %d", priv->netdev->name,
+		 skb->head, skb->data, skb_tail_pointer(skb),
+		 skb_end_pointer(skb), skb->len, data, data_len);
 
 	/* look if we've got a chain for the sender address.
 	   afterwards optr points to first free or the oldest entry,
diff --git a/compat.h b/compat.h
new file mode 100644
index 0000000..32a66c7
--- /dev/null
+++ b/compat.h
@@ -0,0 +1,43 @@
+/* Compatibility layer for older kernels */
+
+#include <linux/version.h>
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,22)
+#include <linux/skbuff.h>
+static inline unsigned char *skb_mac_header(const struct sk_buff *skb)
+{
+	return skb->mac.raw;
+}
+
+static inline void skb_reset_mac_header(struct sk_buff *skb)
+{
+	skb->mac.raw = skb->data;
+}
+
+static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
+{
+	skb->mac.raw = skb->data + offset;
+}
+
+static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
+{
+	return skb->end;
+}
+
+static inline unsigned char *skb_tail_pointer(const struct sk_buff *skb)
+{
+	return skb->tail;
+}
+#endif
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,20)
+#undef INIT_WORK
+#define INIT_WORK(_work, _func)						\
+	do {								\
+		INIT_LIST_HEAD(&(_work)->entry);			\
+		(_work)->pending = 0;					\
+		PREPARE_WORK((_work), (void (*)(void *))(_func),	\
+			     (void *)(_work));				\
+		init_timer(&(_work)->timer);				\
+	} while (0)
+#endif