[RFC][PATCH -mm take5 0/7] proposal for dynamic configurable netconsole

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

From: Keiichi KII <k-keiichi@bx.jp.nec.com>

The netconsole is a very useful module for collecting kernel message under
certain circumstances(e.g. disk logging fails, serial port is unavailable).

But current netconsole is not flexible. For example, if you want to change ip
address for logging agent, in the case of built-in netconsole, you can't change
config except for changing boot parameter and rebooting your system, or in the
case of module netconsole, you need to remove it and reload with different
parameters.

By adopting my patches, the current netconsole becomes a little complex.
But the kernel messages(especially panic messages) is significant information
 to solve bugs and troubles promptly and we have been losing serial console
port with PCs and Servers.

I think that we need the environment in which we can collect kernel messages
flexibly.

So, I propose the following extended features for netconsole.

1) support for multiple logging agents.
2) add interface to access each parameter of netconsole
   using sysfs.

[changes since take4]
-change kernel base from 2.6.21-rc6-mm1 to 2.6.22-rc4-mm2.
-update Documentation/networking/netconsole.txt
-fix Kconfig
-avoid forward-declared statics
-fix coding style
-use spin_lock_irqsave() and _restore()
-fix race condition(netconsole_event())
-remove extra lock(write in sysfs)
-change ioctl's location
-use kasprintf()
-error handling

Your comments are very welcome.

Signed-off-by: Keiichi KII <k-keiichi@bx.jp.nec.com>
Signed-off-by: Takayoshi Kochi <t-kochi@bq.jp.nec.com>
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