Re: Using udev to collect device information

[Kay Sievers <kay.sievers@vrfy.org>]

On Mon, 2006-06-26 at 17:01 -0700, Greg KH wrote:
> On Mon, Jun 26, 2006 at 04:10:41PM -0700, Eric Munson wrote:
> > I am working on a project that maintains a list of active hardware on a
> >  machine and we want to make it hotplug "aware".  Making udev call our
> > process for adding or removing an entry to or from our list each time
> > hardware is added or removed seems easy enough, but I have several
> > questions:
> > 
> > 1.  Our system will be thread safe, but if we are calling the hotplug
> > updater each time a device is added or removed with the rules:
> > ACTION="add" RUN+="/usr/sbin/program"
> > and
> > ACTION="remove" RUN+="/usr/sbin/program"
> > Are we going to cause serious slow downs for the rest of the system if
> > we are flooded with adds/removes?  The program that we will be running
> > won't be terribly slow but it will include some disk IO.
> 
> It all depends on what your /usr/sbin/program does, we can't answer that
> for you.
> 
> > 2.  How can I pass information about the event, things like what device
> > is being added/removed into the program being called?  Does udev provide
> > any of this information during rule execution (I assume that udev has
> > it, I just need to know where to get it)?
> > 
> > Sorry if this is a gross abuse of udev, but we are looking to plug into
> > a "hotplug" like system without requiring our users to install the
> > linux-hotplug system so if there is a better way to accomplish the same
> > thing please let me know.
> 
> No, this is a fine way.  But why not just hook into HAL?  It already
> does all of this for you, and you can get it to send you DBUS messages
> for any new device in the system.

Right, HAL already keeps a nice list for most of the interesting things.
It also tells you for a lot of devices what you can do with the device.
You may want to look at it, if it matches your requirements. Just run
"lshal" on a recent system.

> Or, if you don't like how HAL works, you should at least look into how
> it ties into udev, as that sounds like the same exact way you want to do
> things.  But don't reinvent the wheel if you don't have to.

HAL tells udev to pass the complete events to an abstract namespace
socket (man 7 unix):
  RUN+="socket:/org/freedesktop/hal/udev_event"

On the socket, you get a message like this: <action>@<devpath>\0[<key>=<value>\0, ...]
  recv(3, "add@/class/input/input6/mouse2\0UDEV_LOG=3\0ACTION­d\0
  DEVPATH=/class/input/input6/mouse2\0SUBSYSTEM=input\0
  SEQNUM\x1518\0PHYSDEVPATH=/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0\0


Kay


Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
http://sel.as-us.falkag.net/sel?cmd=lnk&kid\x120709&bid&3057&dat\x121642
_______________________________________________
Linux-hotplug-devel mailing list  http://linux-hotplug.sourceforge.net
Linux-hotplug-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel