[NET]: Share correct feature code between bridging and bonding

http://bugzilla.kernel.org/show_bug.cgi?id=8797 shows that the
bonding driver may produce bogus combinations of the checksum
flags and SG/TSO.

For example, if you bond devices with NETIF_F_HW_CSUM and
NETIF_F_IP_CSUM you'll end up with a bonding device that
has neither flag set.  If both have TSO then this produces
an illegal combination.

The bridge device on the other hand has the correct code to
deal with this.

In fact, the same code can be used for both.  So this patch
moves that logic into net/core/dev.c and uses it for both
bonding and bridging.

In the process I've made small adjustments such as only
setting GSO_ROBUST if at least one constituent device
supports it.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 39 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 6cc8a70350ac..a76021c71207 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3993,6 +3993,45 @@ static int __init netdev_dma_register(void)
 static int __init netdev_dma_register(void) { return -ENODEV; }
 #endif /* CONFIG_NET_DMA */
 
+/**
+ *      netdev_compute_feature - compute conjunction of two feature sets
+ *      @all: first feature set
+ *      @one: second feature set
+ *
+ *      Computes a new feature set after adding a device with feature set
+ *      @one to the master device with current feature set @all.  Returns
+ *      the new feature set.
+ */
+int netdev_compute_features(unsigned long all, unsigned long one)
+{
+        /* if device needs checksumming, downgrade to hw checksumming */
+        if (all & NETIF_F_NO_CSUM && !(one & NETIF_F_NO_CSUM))
+                all ^= NETIF_F_NO_CSUM | NETIF_F_HW_CSUM;
+
+        /* if device can't do all checksum, downgrade to ipv4/ipv6 */
+        if (all & NETIF_F_HW_CSUM && !(one & NETIF_F_HW_CSUM))
+                all ^= NETIF_F_HW_CSUM
+                        | NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM;
+
+        if (one & NETIF_F_GSO)
+                one |= NETIF_F_GSO_SOFTWARE;
+        one |= NETIF_F_GSO;
+
+        /* If even one device supports robust GSO, enable it for all. */
+        if (one & NETIF_F_GSO_ROBUST)
+                all |= NETIF_F_GSO_ROBUST;
+
+        all &= one | NETIF_F_LLTX;
+
+        if (!(all & NETIF_F_ALL_CSUM))
+                all &= ~NETIF_F_SG;
+        if (!(all & NETIF_F_SG))
+                all &= ~NETIF_F_GSO_MASK;
+
+        return all;
+}
+EXPORT_SYMBOL(netdev_compute_features);
+
 /*
  *      Initialize the DEV module. At boot time this walks the device list and
  *      unhooks any devices that fail to initialise (normally hardware not