Re: shutdown node VS disconnect all hooks
From: Julian Elischer (julian_at_elischer.org)
Date: 05/28/04
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Date: Thu, 27 May 2004 16:33:28 -0700 (PDT) To: Gleb Smirnoff <glebius@cell.sick.ru>
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
>
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