Re: Permissions of usb hub and its children

[Fabian Steiner <fabian.steiner@gmail.com>]

Greg KH wrote:
> On Tue, Sep 05, 2006 at 11:50:03PM +0200, Fabian Steiner wrote:
>> Greg KH wrote:
>>> On Tue, Sep 05, 2006 at 11:52:54AM +0200, Fabian Steiner wrote:
>>>> Hello!
>>>>
>>>> I am trying to change the permissions of my usb hub with the follwing
>>>> udev rule:
>>>>
>>>> SUBSYSTEM="usb", DEVPATH="/devices/pci0000:00/0000:00:02.1/usb1/1-3",
>>>> OWNER="fabi", MODE="600
>>> What are you trying to change here?  The permissions of the usb hub in
>>> usbfs?
>> Yes, my intension was to assign proper permissions to the usb hub so
>> that all devices that are connected to that hub get the same permissions.
> 
> Ah, multi-user type setup?

Exactly :-) As there is no solution for this so far, we tried to do it
on our own, but as you can see we are not that successful since there
are quite a lot of different aspects to think of.

Our current solution is based on a simple python script which is
executed whenever a user logins (by using the PostLogin mechanism of
GDM). It then reads the environment variables $DISPLAY and $USER which
are set by GDM properly and tries to find out whether a usb hub was
assigned to that particular display. This is done manually by using a
config file.

If someone is interested, I will publish the script.


>> I am not quite sure whether this rule will fulfill all of my
>> requirements but so far it looks good. I.e. I don't know for sure
>> whether ENV{PHYSDEVPATH} is set for all devices and whether it contains
>> a sysfs address. Perhaps you could give me a hint :-)
> 
> Yes, that should work.  But remember, "usb1" the next time you boot
> might not be the same root hub you thought it was last time.  That all
> depends on PCI bus numbering (which can change, but rarely), and USB
> host controller driver loading order (which changes often due to the
> phase of the moon and such.)
> 
> So be careful about that.

Oh, I wasn't aware of that so far. I will probably have to rethink the
whole thing, I suppose ... Of course, the system should work under all
circumstances and not when the moon wants it to ;-)

> good luck,
> 
> greg k-h
> 

Thank you,
Fabian STeiner

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