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[lwip-devel] [bug #52770] mdns: move the announcements to a timer callba

From: Douglas
Subject: [lwip-devel] [bug #52770] mdns: move the announcements to a timer callback
Date: Wed, 3 Jan 2018 10:02:26 -0500 (EST)
User-agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0

Follow-up Comment #21, bug #52770 (project lwip):

> Douglas, any response to my comment #17?

> Again, we're not talking of the same thing. What I meant was that with the
current solution, you (Douglas, not "one") can implement the exact delay you

Telling people to not use LWIP_NETIF_EXT_STATUS_CALLBACK and schedule it all
themselves. Some things are hard to respond to delicately.

> What you proposed was to let everyone have an arbitrary delay of 50ms before
an announcement is sent. That might fit your needs. What if this is too long
or too short for the next user? To me, this looks like a solution to your
specific setup, not a generic fix.

The delay was not the key part of the change, it could be zero. Someone else
suggested it would be good to have a random delay, so I added support for
that. I added an option to control this too, so the timer was skipped and it
was sent immediately in the callers context.

> OK, got that. What I did not get yet is where do the multiple announcements
come from? Changing IPv4 address/netmask/gateway triple should only result in
one announcement. If it doesn't, let's fix this. Or is it something else
that's wrong for you?

The problem is not multiple announcements. It would not bother me if there
were a bunch of announcements when a change was make. There were some issues
with it announcing empty ip address but that was resolved. The point was that
they trigger an announcement in the context of the caller, and that that was a
burden on the callers stack. Look back to the original comment in the bug and
that should be clear see:

> The guts of the mdns code uses a significant amount of stack for a small
system. This makes it problematic calling into this code from the various
paths that trigger announcements. This patch has these code paths queue an
announcement that will be performed via a timer callback. 


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