Is a driver allowed to modify dev->flags?

Is a driver allowed to modify dev->flags?

[Rask Ingemann Lambertsen]

Hi.

Is a network device driver allowed to modify dev->flags? For example:

if (dev->flags & IFF_ALLMULTI)
        dev->flags |= IFF_PROMISC;

I've found it to cause the IFF_PROMISC flag to stick when using "tcpdump -p", which to my surprice sets the IFF_ALLMULTI flag.

Regards,
Rask Ingemann Lambertsen

Re: Is a driver allowed to modify dev->flags?

[Ben Greear]

Rask Ingemann Lambertsen wrote:
> Hi.
> 
> Is a network device driver allowed to modify dev->flags? For example:
> 
> if (dev->flags & IFF_ALLMULTI)
>         dev->flags |= IFF_PROMISC;
> 
> I've found it to cause the IFF_PROMISC flag to stick when using "tcpdump -p", which to my surprice sets the IFF_ALLMULTI flag.
> 
> Regards,
> Rask Ingemann Lambertsen
> 
> 

You are supposed to increment the promisc requestors.  I think something like this:

dev_set_promiscuity(dev, 1);



-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
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Re: Is a driver allowed to modify dev->flags?

[Donald Becker]

On Tue, 1 Apr 2003, Rask Ingemann Lambertsen wrote:

> Is a network device driver allowed to modify dev->flags? For example:
> 
> if (dev->flags & IFF_ALLMULTI)
>         dev->flags |= IFF_PROMISC;

You must be looking at the atp.c driver, or a driver that cribbed from
it.  (Is anyone still running a parallel port Ethernet device?!)

Alan Cox added this code to atp.c because the chip doesn't have a
reasonable multicast filter.  The only way to receive all multicast
traffic was to turn on promiscuous mode.  But that caused a problem
with some parts of the protocol stack were passed traffic not intended
for the local host.

A better solution (which is usually easier to see later) is to have
the driver do the trivial final packet filtering itself.

> I've found it to cause the IFF_PROMISC flag to stick when using
> "tcpdump -p", which to my surprice sets the IFF_ALLMULTI flag. 

Which driver are you using?

-- 
Donald Becker				becker@scyld.com
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Re: Is a driver allowed to modify dev->flags?

[Rask Ingemann Lambertsen]

Donald Becker wrote:
> On Tue, 1 Apr 2003, Rask Ingemann Lambertsen wrote:
> 
> > Is a network device driver allowed to modify dev->flags? For example:
> >
> > if (dev->flags & IFF_ALLMULTI)
> >         dev->flags |= IFF_PROMISC;
> 
> You must be looking at the atp.c driver, or a driver that cribbed from
> it.  (Is anyone still running a parallel port Ethernet device?!)

No, but I've seen such code in other Ethernet drivers and adopted it for my NE3200 driver.

> > I've found it to cause the IFF_PROMISC flag to stick when using
> > "tcpdump -p", which to my surprice sets the IFF_ALLMULTI flag.
> 
> Which driver are you using?

My experimental NE3200 driver, linux 2.4.20 and tcpdump from Redhat 7.3.

Regards,
Rask Ingemann Lambertsen

Re: Is a driver allowed to modify dev->flags?

[Rask Ingemann Lambertsen]

I wrote: 

> Is a network device driver allowed to modify dev->flags? For example:
> 
> if (dev->flags & IFF_ALLMULTI)
>         dev->flags |= IFF_PROMISC;

Maybe the right question is: Is it necessary for the driver to set the IFF_PROMISC flag if the device enters promiscuous mode because it doesn't support all-multicast mode?

Regards,
Rask Ingemann Lambertsen