tun interface name conflicts with ppp driver

tun interface name conflicts with ppp driver

[Cedric Jehasse]

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Hi,

when a context is active, the interface name is typically ppp0. If you try
to run pppd for some other device/interface, the kernel ppp driver prints
an error because it can't register ppp0. It looks like it's assumed that
ppp* interface names are reserved for the ppp_driver.
Can the tun interface name be changed to eg. ofono0?

thanks,
Cedric

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Re: tun interface name conflicts with ppp driver

[Marcel Holtmann]

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Hi Cedric,

> when a context is active, the interface name is typically ppp0. If you try
> to run pppd for some other device/interface, the kernel ppp driver prints
> an error because it can't register ppp0. It looks like it's assumed that
> ppp* interface names are reserved for the ppp_driver.
> Can the tun interface name be changed to eg. ofono0?

actually we are using ppp%d syntax to assign the network interfaces. So
the kernel does the numbering. This is a bug in pppd and not ours.

Looking at the pppd code, it seems to hardcodes ppp0. So please complain
to them for assuming that a certain device name is owned by them.

Regards

Marcel

Re: tun interface name conflicts with ppp driver

[Cedric Jehasse]

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Hi Marcel,


> actually we are using ppp%d syntax to assign the network interfaces. So
> the kernel does the numbering. This is a bug in pppd and not ours.
>
> Looking at the pppd code, it seems to hardcodes ppp0. So please complain
> to them for assuming that a certain device name is owned by them.
>

pppd requests the ppp driver to create a network interface with the ioctl
 PPPIOCNEWUNIT. If the parameter passed to the ioctl is -1, the ppp driver
will allocate the unit itself. Because it's the first network interface
created by the ppp driver, and the ppp driver doesn't know about the tun
interface, it's choosing 0. Check ppp_create_interface() in ppp_generic.c
in the kernel to see how this is done.

So it seems the ppp driver reserves the ppp%d interface names.

Regards,
Cedric

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Re: tun interface name conflicts with ppp driver

[Marcel Holtmann]

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Hi Cedric,

> > actually we are using ppp%d syntax to assign the network interfaces. So
> > the kernel does the numbering. This is a bug in pppd and not ours.
> >
> > Looking at the pppd code, it seems to hardcodes ppp0. So please complain
> > to them for assuming that a certain device name is owned by them.
> >
> 
> pppd requests the ppp driver to create a network interface with the ioctl
>  PPPIOCNEWUNIT. If the parameter passed to the ioctl is -1, the ppp driver
> will allocate the unit itself. Because it's the first network interface
> created by the ppp driver, and the ppp driver doesn't know about the tun
> interface, it's choosing 0. Check ppp_create_interface() in ppp_generic.c
> in the kernel to see how this is done.
> 
> So it seems the ppp driver reserves the ppp%d interface names.

that is not how the kernel works. It is global and tun interface will
not interfere with ppp interface. In case ppp driver and pppd would do
it right, then there would be no conflict.

Regards

Marcel