[argyllcms] Re: Getting udev rules to work on Ubuntu 6.06

On Fri, 2006-11-24 at 12:05 +0000, Neil Woolford wrote:
> On Fri, 2006-11-24 at 12:47 +1100, Graeme Gill wrote:
> > Neil Woolford wrote:
> > 
> > > The key point is that the filename for the .rules file for the device
> > > must start with a number higher than 40.  This means that the mode
> > > setting in the udev rule will be processed after rather than before the
> > > system defaults in file 40-permissions.rules.  So 39-dtp94.rules will be
> > > overridden by the defaults, 41-dtp94.rules won't be.
> > 
> > Right. Most of the doco recommends the opposite, on the assumption
> > that the purpose of your new .rules file is to create a specific
> > device name. I would guess that your approach will only work if the
> > 40-permissions.rules creates a /dev entry for usb devices, in the
> > form that libusb is looking for (/dev/bus/usb/00M/00N). 

This appears to be handled in an earlier file, 20-names.rules, on Ubuntu
6.06.

> > My system for instance, has no such rule in the 40-permissions.rules file,
> > so I suspect your approach wouldn't work since there is nothing
> > to change the mode of. Perhaps you could identify the rule in
> > your 40-permissions.rules file that creates the /dev/bus/usb/*
> > 

The rule is a short section of code that I guess walks the tree of
potential devices;  I'm no programmer though...

> I'll have another look later in the day, but what appears to be
> happening in my (Ubuntu 6.06) 40-permissions.rules file is the setting
> of default permissions for (groups of) devices, rather than the creation
> of device entries themselves.
> 
> Later rules files apply over earlier ones so the default permission
> overrides the one set specifically for the device or vice versa
> depending on the lexical order of the filenames.
> 
> The files I'm looking at in .../udev/rules.d may of course be Ubuntu
> specific;  I noticed that one of the original posters was using Ubuntu
> as I currently am.  I've an experimental Mandriva setup on the laptop so
> I'll look at that too.

It does look horribly like there is a wide variation between
distributions in the implementation of udev rules;  certainly the rule
currently given in the installation instructions section of the
Argyllcms website works perfectly as 10-dtp94.rules on the Mandriva Free
2007 but not on Ubuntu 6.06.  (The contents of the ..../rules.d
directories are very different as well.)

To summarise my findings so far;  the installation instructions work
fine on Mandriva Free 2007:  Ubuntu 6.06 however requires a rule placed
after the default permissions file 40-permissions.rules and won't work
with both the use of = rather than == in the tests and the NAME
assignment at the end of the line.  So unfortunately there is a swamp
here because of variation in udev implementation and rule sets between
distributions.


Neil

PS  It is possible to set assignment to not be altered by following
rules by using := rather than = as the operator.  Perhaps something
like;

BUS=="usb", SYSFS{idVendor}=="0765", SYSFS{idProduct}=="d094",\
MODE:="666"

as 10-dtp94.rules might work on a larger range of distributions?  Or
would the removal of the kernel name section cause problems?  Feedback
from those with other systems please...

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