[patch] add kdump_after_notifier

[Takenori Nagano]

Vivek Goyal wrote:
 > So for the time being I think we can put RAS tools on die notifier list
> and if it runs into issues we can always think of creating a separate list.
> 
> Few things come to mind.
> 
> - Why there is a separate panic_notifier_list? Can't it be merged with
>   die_chain? die_val already got one of the event type as PANIC. If there
>   are no specific reasons then we should merge the two lists. Registering
>   RAS tools on a single list is easier.

I think it is difficult, because die_chain is defined by each architecture.

> - Modify Kdump to register on die_chain list. 
> - Modify Kdb to register on die_chain list.
> - Export all the registered members of die_chain through sysfs along with
>   their priorities. Priorities should be modifiable. Most likely one 
>   shall have to introduce additional field in struct notifier_block. This
>   field will be a string as an identifier of the user registerd. e.g
>   "Kdump", "Kdb" etc.
> 
> Now user will be able to view all the die_chain users through sysfs and
> be able to modify the order in which these should run by modifying their
> priority. Hence all the RAS tools can co-exist.

This is my image of your proposal.

- Print current order

# cat /sys/class/misc/debug/panic_notifier_list
priority   name
1          IPMI
2          watchdog
3          Kdb
4          Kdump

- change list order

# echo <before> <after> > /sys/class/debug/panic_notifier_list

- example

# cat /sys/class/misc/debug/panic_notifier_list
priority   name
1          IPMI
2          watchdog
3          Kdb
4          Kdump

# echo 4 1 > /sys/class/debug/panic_notifier_list
priority   name
1          Kdump
2          IPMI
3          watchdog
4          Kdb


Is my image almost same as your thought?

Thanks