[linux-dvb] [RFC PATCH] Choose dvb adapter number with a driver specific module option

Oliver Endriss o.endriss at gmx.de
Sun Aug 5 06:01:46 CEST 2007


Janne Grunau wrote:
> Hi,
> 
> Dynamic loading of modules by udev on startup (aka coldplugging) doesn't
> result in deterministic dvb adapter numbers.
> 
> V4L drivers have the {radio|vbi|video}_nr module options to allocate
> static minor numbers per driver.
> Attached patch adds a similiar mechanism to the dvb subsystem. To avoid
> problems with device unplugging and repluging each driver holds
> a DVB_MAX_ADAPTER long array of the preffered order of adapter numbers.
> options dvb-usb-dib0700 adapter_nr=7,6,5,4,3,2,1,0 would result in a
> reversed allocation of adapter numbers.
> With adapter_nr=2,5 it tries first to get adapter number 2 and 5. If both
> are already in use it will allocate the lowest free adapter number.
> 
> Besides following changes in dvb-core and dvb-usb core the patch adds to
> all drivers 
> ...

While I don't care much whether there is an option for this in the
driver, I'd like to point out that this is the wrong approach (imho).

Citing Greg Kroah-Hartman (udev-113/docs/udev_vs_devfs):
|    ...
|    2) udev does not care about the major/minor number schemes.  If the
|       kernel tomorrow switches to randomly assign major and minor numbers
|       to different devices, it would work just fine (this is exactly
|       what I am proposing to do in 2.7...)
|    3) This is the main reason udev is around.  It provides the ability
|       to name devices in a persistent manner.  More on that below.
|    ...

According to this, adding such an option is a step into the wrong
direction. The right way is to fix the udev scripts...

CU
Oliver

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