Re: udev enhancements

[Greg KH <greg@kroah.com>]

On Thu, Dec 16, 2004 at 10:27:59AM +0100, Hannes Reinecke wrote:
> Hi all,
> 
> I'm trying to figure out the best way to incorporating udev into some 
> system tools. Currently we're facing the following problem:
> 
> Any program dealing with device nodes (e.g. parted) need to figure out 
> some information about the device it handles:
> - partition naming: given a device name, generate the name of a
>   partition on that device.
> - number of partitions: each block device type has it's own maximal
>   number of partitions.
> 
> These information is mostly gathered from the device name. Of course, 
> you can't do that if you're using udev.
> So, to retain the existing functionality we would need to add two major 
> improvements to udev:
> 
> - Build udevinfo as library. This way any program can just link to this 
> library and retrieve any information from there instead of rely on some 
> build-in logic. That should actually be quite simple ...

Look at how HAL uses udevinfo to get this kind of information.  You
don't need to make udevinfo into a library to do this.  In fact, now
that the udev database is just a directory of files, you don't really
need udevinfo to get this yourself (just be careful if we change the
database format in the future...)

> - Add a 'dry-run' logic to udev/udevinfo: Given a devicename, how would 
> a partition on that device be named?

Look at udevtest, that provides a "dry-run" functionality.

> And it would also break the deadlock we're having now:
> Removable IDE devices _always_ do a re-read partition on _open_.
> So if we're using device_id to fetch information about a partition, 
> we're triggering hotplug events for each partition, which causes 
> device_id to re-run, which causes hotplug-events, which ...

Use {all_partitions} for such devices.  Linus has even argued that udev
itself should do this by default for these types of things just to make
it simpler.

thanks,

greg k-h


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