Re: [RFC][PATCH 2.6.19 2/6] support multiple logging agents

[Keiichi KII <k-keiichi@bx.jp.nec.com>]

>>  static struct netpoll np = {
>> >      .name = "netconsole",
>> >      .dev_name = "eth0",
>> > @@ -69,23 +84,91 @@ static struct netpoll np = {
>> >      .drop = netpoll_queue,
>> >  };
>
> Shouldn't this piece get dropped in this patch?
>

This piece isn't in -mm tree, but this piece is in 2.6.19.
Which version should I follow ?

>> -static int configured = 0;
>> +static int add_netcon_dev(const char* target_opt)
>> +{
>> +    static atomic_t netcon_dev_count = ATOMIC_INIT(0);
>
> Hiding this inside a function seems wrong. Why do we need a count? If
> we've already got a spinlock, why does it need to be atomic?
>

We don't have a spinlock for add_netcon_dev, because we don't need
to get a spinlock for add_netcon_dev except for list operation.
So, it must be atomic.

>>      local_irq_save(flags);
>> +    spin_lock(&netconsole_dev_list_lock);
>>      for(left = len; left; ) {
>>          frag = min(left, MAX_PRINT_CHUNK);
>> -        netpoll_send_udp(&np, msg, frag);
>> +        list_for_each_entry(dev, &active_netconsole_dev, list) {
>> +            spin_lock(&dev->netpoll_lock);
>> +            netpoll_send_udp(&dev->np, msg, frag);
>> +            spin_unlock(&dev->netpoll_lock);
>
> Why do we need a lock here? Why isn't the list lock sufficient? What
> happens if either lock is held when we get here?
>

The netpoll_lock is for each structure containing information related to netpoll
(remote IP address and port, local IP address and port and so on).
If we don't take a spinlock for each structure, the target IP address and port
number are subject to change on the way sending packets.

--
Keiichi KII
NEC Corporation OSS Promotion Center
E-mail: k-keiichi@bx.jp.nec.com
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