Re: [ANNOUNCE] hotplug-ng 001 release

[Greg KH <gregkh@suse.de>]

On Fri, Feb 11, 2005 at 11:46:27PM +0300, Roman Kagan wrote:
> On Fri, Feb 11, 2005 at 11:36:27AM -0800, Greg KH wrote:
> > Do one thing, and do it well.
> > 
> > udev is for naming devices, not loading modules.
> 
> Well currently udev is doing a lot more: serializing, waiting for sysfs
> dir to appear, etc.  Not that I disagree with your first statement,
> though.
> 
> > Why, each type of autoload program needs to know how to handle the
> > different bus types.  So again, a single program doing a single thing
> > well.
> 
> udev already pokes enough in sysfs and has quite a lot of
> subsystem-specific knowledge, so adding module name generation is not
> too much of extra functionality.

If you look at the hotplug scripts, they really don't need to touch
sysfs at all.  (Note that the scsi one does, but I think we can fix the
scsi hotplug event to solve this issue...)

So module autoload has really nothing to do with sysfs.

Also, udev happens for the device _class_, not the device itself.
Modules bind to devices, device classes generate /dev nodes.  These
happen at two very different points in time (notibly the module events
need to happen before the device class ones are even able to be
generated.)  So udev has nothing to do with loading modules.

Also, for serialization, that's not needed for module loading as we
never unload modules automatically (that's impossible to do properly.)

> OTOH I'm fine with them being separate programs, provided they get the
> necessary info from sysfs so that they can be used for coldplugging too.
> This will require adding wait_for_sysfs logic to them, though.

coldplug can be a simple shell script, or eventually, something like
what udevstart is.  wait_for_sysfs stuff is not needed for that at all.

> [ BTW could you please remind the motivation for doing wait_for_sysfs
> instead of fixing the kernel to call out the hotplug usermode helper
> only after the correspoding sysfs directory has completed initializing? ]

How does the kernel know that the sysfs directory has completed
initializing?  :)

Note that Kay has proposed making the kobject registration a two step
process, generating the hotplug event later after the kobject has set up
sysfs "enough".  I'm reluctant to add that functionality as it make the
kernel more complex, and we've already solved the issue in userspace.

thanks,

greg k-h


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