Re: [RFC][PATCH -mm take2 3/5] add interface for netconsole using sysfs

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

>> create a sysfs entry for netconsole in /sys/class/misc.
>> This entry has elements related to netconsole as follows.
>> You can change configuration of netconsole(writable attributes such as IP
>> address, port number and so on) and check current configuration of netconsole.
>>
>> -+- /sys/class/misc/
>>  |-+- netconsole/
>>    |-+- port1/
>>    | |--- id          [r--r--r--]  unique port id
>>    | |--- remove      [-w-------]  if you write something to "remove",
>>    | |                             this port is removed.
>>   
> IMHO this kind of "magic side effect" is a misuse of sysfs. and would
> make proper locking
> impossible. How do you deal with the dangling reference to the
> netconsole object?

I manage the reference by using a list.
If you write something to "remove", 
firstly the port entry is removed from sysfs and then
the reference is removed from the list and a resource of the port is freed.

> f= open (... netconsole/port1/remove")
> write(f, "", 1)
> sleep(2)
> write(f, "", 1) .... this probably would crash...
> 
> 
> Maybe having a state variable/sysfs file so you could setup the port and
> turn it on/off with write.

You are right.
When I tested above program, my machine crashed.

I'm going to rethink the interface for netconsole.

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