Re: Hardware Abstraction Layer

[David Zeuthen <david@fubar.dk>]

On Tue, 2003-09-16 at 18:39, Greg KH wrote:
> On Sat, Sep 13, 2003 at 03:30:38PM +0200, David Zeuthen wrote:
> > Hi,
> > 
> > I'm currently working on a hardware abstraction layer, see
> > 
> >   http://pdx.freedesktop.org/~hal/
> > 
> > for use in desktop environments such as GNOME or KDE.  The HAL project
> > is in it's early stages - there is a draft spec planned and I got an
> > implementation running as well.
> 
> How does this differ from D-BUS?  Hm, in looking at your page, it says
> you are using D-BUS messages.  

I use D-BUS as the IPC mechanism between hotplug agents and applications
wanting to query a device database. In the middle there is a daemon. 

In a sense I want the entire HAL not to care about specific hardware
issues at all, but build on existing software like linux-hotplug ;-) 
(see my recent post to the xdg-list for detail)

> Oh, have you looked at udev too?  It will
> handle naming the devices for you in /dev.
> 

Excellent - will look into this later. Will this help me, e.g., getting
the information that my CF card reader is at /dev/sda1 when using the
kernel module usb-storage? Or have I misunderstood?

> > I want to hear how you think we can cooperate, by e.g. having
> > /sbin/hotplug send events to hald. Note that the HAL aims at a range of
> > UNIX-like systems, but I think we can handle that requirement... I use
> > GNU/Linux myself.
> 
> As was already posted, anyone can get /sbin/hotplug events by just
> dropping a link into the proper directory.  

Cool.

> Also, D-BUS messages will be
> created for all /sbin/hotplug events too.  You might want to work with
> that if it's easier for you.
> 

I'll be interested in this, definately. Are you using the service
org.freedesktop.DBus.Broadcast for this? 

I'll also need a unique ID of each device being hotplugged, and I have
some problems seeing this is even possible on some busses like USB. The
unique ID must be the same over plugs/unplugs.

Say, that I plug two identical cameras into the system with no
device-instance specific information. Corner case, but nasty one... 

In the event this is not possible the hotplug agent must somehow convey
this information so I can append a counter to make the ID unique in that
way.. 

Any suggestions / comments ?

> Hope this helps,
> 

Very much, Thanks,
David




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