netdev - [PATCH] Net-ethtool : Allow ethtool to set interface in loopback mode.

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Date:	Tue, 30 Nov 2010 00:00:29 -0800
From:	Mahesh Bandewar <maheshb@...gle.com>
To:	David Miller <davem@...emloft.net>,
	linux-netdev <netdev@...r.kernel.org>
Subject: [PATCH] Net-ethtool : Allow ethtool to set interface in loopback mode.

This patch enables ethtool to set the loopback mode on a given
interface. This is the reworked version of earlier submit (which I
don't have reference to). By configuring the interface in loopback
mode in conjunction with a policy route / rule, a userland application
can stress the egress / ingress path exposing the flows of the change
in progress and potentially help developer(s) understand the impact of
those changes without even sending a packet out on the network.

Following set of commands illustrates one such example -
    a) ifconfig eth1 192.168.1.1
    b) ip -4 rule add from all iif eth1 lookup 250
    c) ip -4 route add local 0/0 dev lo proto kernel scope host table 250
    d) arp -Ds 192.168.1.100 eth1
    e) arp -Ds 192.168.1.200 eth1
    f) sysctl -w net.ipv4.ip_nonlocal_bind=1
    g) sysctl -w net.ipv4.conf.all.accept_local=1
    # Assuming that the machine has 8 cores
    h) taskset 000f netserver -L 192.168.1.200
    i) taskset 00f0 netperf -t TCP_CRR -L 192.168.1.100 -H 192.168.1.200 -l 30

Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
---
 include/linux/ethtool.h |    4 ++++
 net/core/ethtool.c      |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 0 deletions(-)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 6628a50..7523d45 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -678,6 +678,8 @@ struct ethtool_ops {
                                  struct ethtool_rxfh_indir *);
        int     (*set_rxfh_indir)(struct net_device *,
                                  const struct ethtool_rxfh_indir *);
+       int     (*get_loopback)(struct net_device *, u32 *);
+       int     (*set_loopback)(struct net_device *, u32);
 };
 #endif /* __KERNEL__ */

@@ -741,6 +743,8 @@ struct ethtool_ops {
 #define ETHTOOL_GSSET_INFO     0x00000037 /* Get string set info */
 #define ETHTOOL_GRXFHINDIR     0x00000038 /* Get RX flow hash indir'n table */
 #define ETHTOOL_SRXFHINDIR     0x00000039 /* Set RX flow hash indir'n table */
+#define ETHTOOL_SLOOPBACK      0x0000003a /* Enable / Disable Loopback */
+#define ETHTOOL_GLOOPBACK      0x0000003b /* Get Loopback status */

 /* compatibility with older code */
 #define SPARC_ETH_GSET         ETHTOOL_GSET
diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index 956a9f4..5c87c93 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1434,6 +1434,39 @@ static noinline_for_stack int ethtool_flash_device(struct
        return dev->ethtool_ops->flash_device(dev, &efl);
 }

+static int ethtool_set_loopback(struct net_device *dev, void __user *useraddr)
+{
+       struct ethtool_value edata;
+       const struct ethtool_ops *ops = dev->ethtool_ops;
+
+       if (!ops || !ops->set_loopback)
+               return -EOPNOTSUPP;
+
+       if (copy_from_user(&edata, useraddr, sizeof(edata)))
+               return -EFAULT;
+
+       return ops->set_loopback(dev, edata.data);
+}
+
+static int ethtool_get_loopback(struct net_device *dev, void __user *useraddr)
+{
+       struct ethtool_value edata;
+       const struct ethtool_ops *ops = dev->ethtool_ops;
+       int err;
+
+       if (!ops || !ops->get_loopback)
+               return -EOPNOTSUPP;
+
+       err = ops->get_loopback(dev, &edata.data);
+       if (err)
+               return (err);
+
+       if (copy_to_user(useraddr, &edata, sizeof(edata)))
+               return -EFAULT;
+
+       return 0;
+}
+
 /* The main entry point in this file.  Called from net/core/dev.c */

 int dev_ethtool(struct net *net, struct ifreq *ifr)
@@ -1678,6 +1711,12 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
        case ETHTOOL_SRXFHINDIR:
                rc = ethtool_set_rxfh_indir(dev, useraddr);
                break;
+       case ETHTOOL_SLOOPBACK:
+               rc = ethtool_set_loopback(dev, useraddr);
+               break;
+       case ETHTOOL_GLOOPBACK:
+               rc = ethtool_get_loopback(dev, useraddr);
+               break;
        default:
                rc = -EOPNOTSUPP;
        }
--
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