net: add IFF_SKB_TX_SHARED flag to priv_flags

Pktgen attempts to transmit shared skbs to net devices, which can't be used by
some drivers as they keep state information in skbs.  This patch adds a flag
marking drivers as being able to handle shared skbs in their tx path.  Drivers
are defaulted to being unable to do so, but calling ether_setup enables this
flag, as 90% of the drivers calling ether_setup touch real hardware and can
handle shared skbs.  A subsequent patch will audit drivers to ensure that the
flag is set properly

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Jiri Pirko <jpirko@redhat.com>
CC: Robert Olsson <robert.olsson@its.uu.se>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Alexey Dobriyan <adobriyan@gmail.com>
CC: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if.h

@@ -76,6 +76,8 @@
 #define IFF_BRIDGE_PORT	0x4000		/* device used as bridge port */
 #define IFF_OVS_DATAPATH	0x8000	/* device used as Open vSwitch
 					 * datapath port */
+#define IFF_TX_SKB_SHARING	0x10000	/* The interface supports sharing
+					 * skbs on transmit */
 
 #define IF_GET_IFACE	0x0001		/* for querying only */
 #define IF_GET_PROTO	0x0002

net/core/pktgen.c

@@ -1070,7 +1070,9 @@ static ssize_t pktgen_if_write(struct file *file,
 		len = num_arg(&user_buffer[i], 10, &value);
 		if (len < 0)
 			return len;
-
+		if ((value > 0) &&
+		    (!(pkt_dev->odev->priv_flags & IFF_TX_SKB_SHARING)))
+			return -ENOTSUPP;
 		i += len;
 		pkt_dev->clone_skb = value;
 
@@ -3555,15 +3557,13 @@ static int pktgen_add_device(struct pktgen_thread *t, const char *ifname)
 	pkt_dev->min_pkt_size = ETH_ZLEN;
 	pkt_dev->max_pkt_size = ETH_ZLEN;
 	pkt_dev->nfrags = 0;
-	pkt_dev->clone_skb = pg_clone_skb_d;
 	pkt_dev->delay = pg_delay_d;
 	pkt_dev->count = pg_count_d;
 	pkt_dev->sofar = 0;
 	pkt_dev->udp_src_min = 9;	/* sink port */
 	pkt_dev->udp_src_max = 9;
 	pkt_dev->udp_dst_min = 9;
 	pkt_dev->udp_dst_max = 9;
-
 	pkt_dev->vlan_p = 0;
 	pkt_dev->vlan_cfi = 0;
 	pkt_dev->vlan_id = 0xffff;
@@ -3575,6 +3575,8 @@ static int pktgen_add_device(struct pktgen_thread *t, const char *ifname)
 	err = pktgen_setup_dev(pkt_dev, ifname);
 	if (err)
 		goto out1;
+	if (pkt_dev->odev->priv_flags & IFF_TX_SKB_SHARING)
+		pkt_dev->clone_skb = pg_clone_skb_d;
 
 	pkt_dev->entry = proc_create_data(ifname, 0600, pg_proc_dir,
 					  &pktgen_if_fops, pkt_dev);

net/ethernet/eth.c

@@ -340,6 +340,7 @@ void ether_setup(struct net_device *dev)
 	dev->addr_len		= ETH_ALEN;
 	dev->tx_queue_len	= 1000;	/* Ethernet wants good queues */
 	dev->flags		= IFF_BROADCAST|IFF_MULTICAST;
+	dev->priv_flags		= IFF_TX_SKB_SHARING;
 
 	memset(dev->broadcast, 0xFF, ETH_ALEN);