shutdown node VS disconnect all hooks

[Julian Elischer]

On Fri, 28 May 2004, Gleb Smirnoff wrote:

>   Hi collegues,
> 
>   I'm again with the issue about node destruction process. If you
> already forgot the problem, I'll remind you: in RELENG_4 node cuts down
> all its hooks itself from shutdown method, while in HEAD it is done 
> in ng_rmnode() _before_ calling shutdown method. This breaks
> ng_tee behavior, and as I have noted, having hooks connected in
> shutdown method may be useful sometimes.
> 
>   OK, If we destroy node in such a sequence
> 
>   1. nodes shutdown method
>   2. ng_destroy_hook() on all hooks
>   3. ng_flush_input_queue()
> 
>   in some cases we may have node be lost when its shutdown method calls
> NG_NODE_UNREF. Ok, I have tried to put one more ref on node just before
> calling its shutdown method. Seems like it works! However we may catch
> panic in nodes which do not expect that ng_type_disconnect() may
> be called after ng_type_shutdown(). Since RELENG_4 the following nodes
> had been changed to don't expect this sequence:
> 
>   ng_socket
>   ng_atmllc
>   ng_bridge
>   ng_eiface
>   ng_etf
>   ng_ether
>   ng_frame_relay
>   ng_gif
>   ng_gif_demux
>   ng_iface
>   ng_l2tp
>   ng_lmi
>   ng_mppc
>   ng_one2many
>   ng_ppp
>   ng_pppoe
>   ng_pptpgre
>   ng_rfc1490
>   ng_source
>   ng_sppp
>   ng_tty
>   ng_vjc
>   ng_vlan
> 
> They all FREE priv in shutdown method, but use it in disconnect method.
> The problem can be solved by inserting ng_cutlinks() into beginning of 
> shutdown method for each of above nodes like it is done in RELENG_4.
> Ok, we need to edit more than 20 nodes to get back ng_tees behavior. I'm
> sure you don't like it :)

there are other reasons why this can not work.
That is why it was changed from 4.x.

> 
>   So, what about adding one more netgraph method into struct ng_type, say
> ng_preshutdown_t? This method is called first in ng_rmnode(), and then 
> current shutdown sequence is followed. We will set it to NULL in all existing
> nodes, and create a method in ng_tee, which calls ng_bypass(). Future
> implementations may use this method to send "goodbye" messages down hooks when
> shutting down.

That sounds like a much better solution. Node shutdown is done in 2
parts just as node connection is done in 2 parts.

>   And this will be a POLA-friendly solution - we will not lose functionality
> of RELENG_4 (which mpd relies on), and we will not break nodes which
> rely on current shutdown sequence.
> 
>   What's your opinion? If it is positive - I'll send patches.
> 

That is a very workable solution.

ng_warn_shutdown()
 ng_cutlinks()
ng_shutdown()

> -- 
> Totus tuus, Glebius.
> GLEBIUS-RIPN GLEB-RIPE
>