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Re: Deva interface

From: Bas Wijnen
Subject: Re: Deva interface
Date: Mon, 17 Jan 2005 10:13:27 +0100
User-agent: Mozilla Thunderbird 0.9 (X11/20041124)

Neal H. Walfield wrote:

*I tried to design some interfaces for deva.

deva should respond to at least these RPCs:


This is a good start.  We will also need a way to get some properties
of devices such as the preferred block size, the size of the device
(in the case of block devices) etc.  The list can always be extended
later depending on the actual needs (instead of perceived needs) of
the device drivers and the users.

I think the most important thing of the framework is to have clear definitions of "device class interfaces", a bit like usb device classes have them. The difference is that every device should fall into a class. An example: there should be a class "network device", for which an interface is defined. To write a driver for an ethernet card, or a modem, or a wifi card, it is then clear what interface to implement. Drivers may follow more than one interface (in fact, most devices will do that, I think). I mention in particular the modem, as I heard from some companies who were complaining about the way Linux handles them: in fact it doesn't at all, if you're lucky you get a serial port, with nowhere in the system a hint on how to set up exotic parameters. That sort of information should be usable by the client, either by making it available, or better yet, by providing an RPC to set it up.

There should be interface definitions for every possible device, of course, so every device driver writer knows what to implement, and every client knows what to interface. If someone wants to write a driver for a device which doesn't have an interface definition yet (because noone thought of such a device before), a new definition should be designed. Of course the interface definition database should be publicly readable in a logical place, probably somewhere on gnu.org.

I think this is the most important thing to get right. In the old days, you knew how to control a device, and an application had to be a device driver as well. This is still the case for "special" devices (such as spectrometers). In my opinion, programs should be able to use any device of some type, without needing any modification (or even a recompile) when a different device is used. This is of course the case for "normal" devices, such as hard drives and other "normal" drivers, such as filesystems. It should also be the case for the "special" devices and drivers.

Those were just some thoughts which I think are important to keep in mind while writing a ddf.


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