[PATCHv2,1/2] net: Allow ethtool to set interface in loopback mode.

This patch enables ethtool to set the loopback mode on a given interface.
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) ip -4 addr add 192.168.1.1/24 dev eth1
    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@google.com>
---
Changes since v1
 Added NETIF_F_LOOPBACK in loopback device's feature-set.

 drivers/net/loopback.c    |    3 ++-
 include/linux/netdevice.h |    3 ++-
 net/core/ethtool.c        |    2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

Please discard this, I do not wish to create a new thread for this.

Thanks,
--mahesh..

On Wed, May 4, 2011 at 6:26 PM, Mahesh Bandewar <maheshb@google.com> wrote:
> This patch enables ethtool to set the loopback mode on a given interface.
> 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) ip -4 addr add 192.168.1.1/24 dev eth1
>    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@google.com>
> ---
> Changes since v1
>  Added NETIF_F_LOOPBACK in loopback device's feature-set.
>
>  drivers/net/loopback.c    |    3 ++-
>  include/linux/netdevice.h |    3 ++-
>  net/core/ethtool.c        |    2 +-
>  3 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index d70fb76..4ce9e5f 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -174,7 +174,8 @@ static void loopback_setup(struct net_device *dev)
>                | NETIF_F_HIGHDMA
>                | NETIF_F_LLTX
>                | NETIF_F_NETNS_LOCAL
> -               | NETIF_F_VLAN_CHALLENGED;
> +               | NETIF_F_VLAN_CHALLENGED
> +               | NETIF_F_LOOPBACK;
>        dev->ethtool_ops        = &loopback_ethtool_ops;
>        dev->header_ops         = &eth_header_ops;
>        dev->netdev_ops         = &loopback_ops;
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index d5de66a..e7244ed 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1067,6 +1067,7 @@ struct net_device {
>  #define NETIF_F_RXHASH         (1 << 28) /* Receive hashing offload */
>  #define NETIF_F_RXCSUM         (1 << 29) /* Receive checksumming offload */
>  #define NETIF_F_NOCACHE_COPY   (1 << 30) /* Use no-cache copyfromuser */
> +#define NETIF_F_LOOPBACK       (1 << 31) /* Enable loopback */
>
>        /* Segmentation offload features */
>  #define NETIF_F_GSO_SHIFT      16
> @@ -1082,7 +1083,7 @@ struct net_device {
>        /* = all defined minus driver/device-class-related */
>  #define NETIF_F_NEVER_CHANGE   (NETIF_F_VLAN_CHALLENGED | \
>                                  NETIF_F_LLTX | NETIF_F_NETNS_LOCAL)
> -#define NETIF_F_ETHTOOL_BITS   (0x7f3fffff & ~NETIF_F_NEVER_CHANGE)
> +#define NETIF_F_ETHTOOL_BITS   (0xff3fffff & ~NETIF_F_NEVER_CHANGE)
>
>        /* List of features with software fallbacks. */
>  #define NETIF_F_GSO_SOFTWARE   (NETIF_F_TSO | NETIF_F_TSO_ECN | \
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index d8b1a8d..f26649d 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -362,7 +362,7 @@ static const char netdev_features_strings[ETHTOOL_DEV_FEATURE_WORDS * 32][ETH_GS
>        /* NETIF_F_RXHASH */          "rx-hashing",
>        /* NETIF_F_RXCSUM */          "rx-checksum",
>        /* NETIF_F_NOCACHE_COPY */    "tx-nocache-copy"
> -       "",
> +       /* NETIF_F_LOOPBACK */        "loopback",
>  };
>
>  static int __ethtool_get_sset_count(struct net_device *dev, int sset)
> --
> 1.7.3.1
>
>
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