Date: Thu, 13 Jun 1996 10:29:53 -0600 From: Nate Williams <nate@sri.MT.net> To: Andrew McRae <amcrae@cisco.com> Cc: "Nate Williams" <nate@sneezy.sri.com>, hackers@freebsd.org Subject: Re: gated & pccard don't get along Message-ID: <199606131629.KAA19062@rocky.sri.MT.net> In-Reply-To: <199606131337.GAA21556@doberman.cisco.com> References: <199606131337.GAA21556@doberman.cisco.com>
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... > Having thought long and hard about this, I have come to the > conclusion that having hot-swappable resources and interfaces > is a great idea in theory, but the kernel (and parts of the user-land > and daemons) generally assumes that devices are not going to > appear and disappear at random intervals. It is pretty scary to > think of the changes required to really make the system understand > this concept fully. The net code is a good example; whilst the > insert/remove scripts can already do some of these things (like > add default routes etc.), we are really working with a bit > of glue around the edges, and not tackling some of the core > problems. Yet. :) This actually came up last night during one of the conversations Poul and I had after dinner. > One issue is the way various bits get informed about > changes [e.g a card being pulled]. The need is for programs > to be started or stopped, signals sent, kernel tables to be > modified, daemons to be informed [e.g gated] etc. I agree. The 'glue' in FreeBSD is pretty weak in this area. > Berny Goodheart and I were talking about this, and his > suggestion is to implement a registry scheme, I imagine with > a graph of dependancies and some IPC etc. Tandem (Berny's > employer) uses such a scheme to implement hot swap > in their high availability architecture. Having worked on such a scheme > myself, I appreciate the complexity. Unfortunately, you can't implement > just a *little* bit of the scheme. If you do *any* form of > hot swap, you have to go the whole hog. Cisco also support > hot-swap, and even when it's designed in from day one, it is > still a significant effort to make it work. While I agree in reality, in practice I think although we can't have 'the best' solution I think we can make the current glue a bit more useful, especially given the fact that we already pull in /etc/sysconfig which contains most of the 'customization' informtaion. > So I guess I am saying that the little bit of glue around > the edges is a pretty good scheme for FreeBSD, unless some > serious effort is undertaken. Thus I would consider pccard > to not really offer hot swap, but more of a `user friendly > hardware bus'. Having said that, I think the glue holds > together as much as can be expected :-) I hope we can make it stickier. :) Nate
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