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    Subject[PATCH 4/4] netns: sysfs: add netns suffix to net devices sysfs entries
    Reminder: what we want is being able to create network interfaces with
    the same name in different network namespaces (eg. the loopback). The
    remaining issues are in sysfs.

    This patch dissociates network devices actual names (stored in struct
    net_device and seen by ifconfig/ip tools) and network device names
    stored in sysfs.

    When adding a network device in child net namespace (!init_net), when
    registering it in sysfs, a suffix unique to the current netns is
    appended to the actual device name. Currently this suffix is the netns
    ida ID in hexa form separated by a '@' char.

    In sysfs, we see all the network devices of all netns.

    # ll /sys/devices/virtual/net/
    ...
    drwxr-xr-x 4 root root 0 2008-10-13 14:08 lo
    drwxr-xr-x 4 root root 0 2008-10-13 16:31 lo@1
    ...
    drwxr-xr-x 4 root root 0 2008-10-13 16:31 lo@e5
    ...

    Then, in the child network namespace we can filter the contents of
    /sys/class/net with:

    * mount -t tmpfs /sys/class/net
    * and manually link the right devices from /sys/devices/virtual/net
    (ln -s ../../devices/virtual/net/lo@1 lo)

    Thus, /sys/class/net appears to be fine for the applications running
    in this namespace.

    FUSE can also be used to alter the view of /sys/class/net in the
    namespace.

    Issues:
    -------

    * The suffix

    We only have four characters left (BUS_ID_SIZE - IFNAMSIZ) to build the
    suffix: add a separator and encode the netns ID.
    By encoding the ID in hexa, it introduces a limit of 4095 (0xFFF)
    sub-network namespaces running at the same time.

    * This approach reduces isolation between network namespaces

    Everyone can see all the devices in each namespaces by exploring
    /sys/devices/../.. or /sys/class/net (if it's not re-mounted as tmpfs).

    * Does not work very well with CONFIG_SYSFS_DEPRECATED=y

    The filtering of /sys/class/net with CONFIG_SYSFS_DEPRECATED=y is more
    difficult to do because in this case /sys/class/net contains
    the actual directories (not symlinks).


    Signed-off-by: Benjamin Thery <benjamin.thery@bull.net>
    Tested-by: Serge Hallyn <serue@us.ibm.com>
    Acked-by: Serge Hallyn <serue@us.ibm.com>
    ---
    net/Kconfig | 2 +-
    net/core/dev.c | 4 +++-
    net/core/net-sysfs.c | 34 +++++++++++++++++++++++++++++++++-
    net/core/net-sysfs.h | 1 +
    4 files changed, 38 insertions(+), 3 deletions(-)

    Index: net-next-2.6/net/Kconfig
    ===================================================================
    --- net-next-2.6.orig/net/Kconfig
    +++ net-next-2.6/net/Kconfig
    @@ -27,7 +27,7 @@ menu "Networking options"
    config NET_NS
    bool "Network namespace support"
    default n
    - depends on EXPERIMENTAL && !SYSFS && NAMESPACES
    + depends on EXPERIMENTAL && NAMESPACES
    help
    Allow user space to create what appear to be multiple instances
    of the network stack.
    Index: net-next-2.6/net/core/dev.c
    ===================================================================
    --- net-next-2.6.orig/net/core/dev.c
    +++ net-next-2.6/net/core/dev.c
    @@ -894,6 +894,7 @@ int dev_alloc_name(struct net_device *de
    int dev_change_name(struct net_device *dev, const char *newname)
    {
    char oldname[IFNAMSIZ];
    + char devname[BUS_ID_SIZE];
    int err = 0;
    int ret;
    struct net *net;
    @@ -924,7 +925,8 @@ int dev_change_name(struct net_device *d
    strlcpy(dev->name, newname, IFNAMSIZ);

    rollback:
    - err = device_rename(&dev->dev, dev->name);
    + netdev_fill_bus_id_name(devname, dev);
    + err = device_rename(&dev->dev, devname);
    if (err) {
    memcpy(dev->name, oldname, IFNAMSIZ);
    return err;
    Index: net-next-2.6/net/core/net-sysfs.c
    ===================================================================
    --- net-next-2.6.orig/net/core/net-sysfs.c
    +++ net-next-2.6/net/core/net-sysfs.c
    @@ -468,6 +468,38 @@ static struct class net_class = {
    #endif
    };

    +/* Fill device bus_id name from net device name
    + * When registering a device for a child network namespace,
    + * a suffix is added to the name stored in "struct device"
    + * bus_id.
    + *
    + * devname size must be at least BUS_ID_SIZE
    + */
    +void netdev_fill_bus_id_name(char *devname, struct net_device *netdev)
    +{
    +#ifndef CONFIG_NET_NS
    + strlcpy(devname, netdev->name, BUS_ID_SIZE);
    +#else
    + struct net *net = dev_net(netdev);
    +
    + if (net_eq(net, &init_net))
    + strlcpy(devname, netdev->name, BUS_ID_SIZE);
    + else {
    + /*
    + * To allow registration of net devices with the same name in
    + * different namespaces, append the netns identifier to the
    + * device name in sysfs using the 4 bytes left in bus_id
    + * (BUS_ID_SIZE - IFNAMSIZ).
    + *
    + * devname is in the form: device_name@XXX
    + * the netns identifier is an integer < 4095, thus encodable
    + * in hexa in 3 characters ("FFF").
    + */
    + snprintf(devname, BUS_ID_SIZE, "%s@%x", netdev->name, net->id);
    + }
    +#endif
    +}
    +
    /* Delete sysfs entries but hold kobject reference until after all
    * netdev references are gone.
    */
    @@ -490,7 +522,7 @@ int netdev_register_kobject(struct net_d
    dev->groups = groups;

    BUILD_BUG_ON(BUS_ID_SIZE < IFNAMSIZ);
    - strlcpy(dev->bus_id, netdev->name, BUS_ID_SIZE);
    + netdev_fill_bus_id_name(dev->bus_id, netdev);

    #ifdef CONFIG_SYSFS
    *groups++ = &netstat_group;
    Index: net-next-2.6/net/core/net-sysfs.h
    ===================================================================
    --- net-next-2.6.orig/net/core/net-sysfs.h
    +++ net-next-2.6/net/core/net-sysfs.h
    @@ -5,4 +5,5 @@ int netdev_kobject_init(void);
    int netdev_register_kobject(struct net_device *);
    void netdev_unregister_kobject(struct net_device *);
    void netdev_initialize_kobject(struct net_device *);
    +void netdev_fill_bus_id_name(char *, struct net_device *);
    #endif
    --


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