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    Subject[PATCH -mm 5/9] netconsole: Introduce dev_status member
    From: Satyam Sharma <ssatyam@cse.iitk.ac.in>

    [5/9] netconsole: Introduce dev_status member

    Introduce a new member in netconsole_target that tracks the status (up or
    down) of the underlying interface network device that the specific logging
    target netpoll is attached to.

    We then join this up with the just-introduced net_device notifier, and
    introduce NETDEV_UP and NETDEV_DOWN notifications. By disabling the target
    when the corresponding local interface is down, we save the overhead of
    unnecessarily disabling interrupts and calling into the netpoll stack in
    console->write().

    Signed-off-by: Satyam Sharma <ssatyam@cse.iitk.ac.in>
    Cc: Keiichi Kii <k-keiichi@bx.jp.nec.com>
    Cc: Takayoshi Kochi <t-kochi@bq.jp.nec.com>

    ---

    drivers/net/netconsole.c | 42 +++++++++++++++++++++++++++++++-----------
    1 file changed, 31 insertions(+), 11 deletions(-)

    ---

    diff -ruNp a/drivers/net/netconsole.c b/drivers/net/netconsole.c
    --- a/drivers/net/netconsole.c 2007-07-03 22:05:51.000000000 +0530
    +++ b/drivers/net/netconsole.c 2007-07-04 03:04:45.000000000 +0530
    @@ -63,11 +63,23 @@ static int __init option_setup(char *opt
    __setup("netconsole=", option_setup);
    #endif

    +/*
    + * Why no net_dev_is_up() in netdevice.h? The kernel could lose a lot of
    + * weight if only netdevice.h had the good sense to export such a function.
    + * Oh well ...
    + */
    +static inline int net_dev_is_up(struct net_device *net_dev)
    +{
    + return ((net_dev->flags & IFF_UP) == IFF_UP);
    +}
    +
    /**
    * struct netconsole_target - Represents a configured netconsole target.
    + * @dev_status: Tracks whether the underlying interface is up or down.
    * @np: The netpoll structure for this target.
    */
    struct netconsole_target {
    + int dev_status;
    struct netpoll np;
    };

    @@ -89,11 +101,17 @@ static int netconsole_netdev_event(struc
    struct net_device *dev = ptr;
    struct netconsole_target *nt = &default_target;

    - if (!(event == NETDEV_CHANGEADDR || event == NETDEV_CHANGENAME))
    - goto done;
    + if (!(event == NETDEV_UP || event == NETDEV_DOWN ||
    + event == NETDEV_CHANGEADDR || event == NETDEV_CHANGENAME))
    + goto done;

    if (nt->np.dev == dev) {
    switch (event) {
    + case NETDEV_UP:
    + case NETDEV_DOWN:
    + nt->dev_status = net_dev_is_up(nt->np.dev);
    + break;
    +
    case NETDEV_CHANGEADDR:
    memcpy(nt->np.local_mac, dev->dev_addr, ETH_ALEN);
    break;
    @@ -118,16 +136,16 @@ static void write_msg(struct console *co
    unsigned long flags;
    struct netconsole_target *nt = &default_target;

    - local_irq_save(flags);
    -
    - for (left = len; left;) {
    - frag = min(left, MAX_PRINT_CHUNK);
    - netpoll_send_udp(&nt->np, msg, frag);
    - msg += frag;
    - left -= frag;
    + if (nt->dev_status) {
    + local_irq_save(flags);
    + for (left = len; left;) {
    + frag = min(left, MAX_PRINT_CHUNK);
    + netpoll_send_udp(&nt->np, msg, frag);
    + msg += frag;
    + left -= frag;
    + }
    + local_irq_restore(flags);
    }
    -
    - local_irq_restore(flags);
    }

    static struct console netconsole = {
    @@ -154,6 +172,8 @@ static int __init init_netconsole(void)
    if (err)
    goto out;

    + nt->dev_status = net_dev_is_up(nt->np.dev);
    +
    err = register_netdevice_notifier(&netconsole_netdev_notifier);
    if (err)
    return err;
    -
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